We present observations of the unusual optical transient SN 2010U, including spectra taken 1.03 days to 15.3 days after maximum light that identify it as a fast and luminous Fe II type nova. Our multi-band light curve traces the fast decline (t_2 = 3.5 days) from maximum light (M_V = -10.2 mag), placing SN 2010U in the top 0.5% of the most luminous novae ever observed. We find typical ejecta velocities of approximately 1100 km/s and that SN 2010U shares many spectral and photometric characteristics with two other fast and luminous Fe II type novae, including Nova LMC 1991 and M31N-2007-11d. For the extreme luminosity of this nova, the maximum magnitude vs. rate of decline relationship indicates a massive white dwarf progenitor with a low pre-outburst accretion rate. However, this prediction is in conflict with emerging theories of nova populations, which predict that luminous novae from massive white dwarfs should preferentially exhibit an alternate spectral type (He/N) near maximum light.
Galaxy clusters, the largest gravitationally bound objects in the Universe, are thought to grow by accreting mass from their surroundings through large-scale virial shocks. Due to electron acceleration in such a shock, it should appear as a gamma-ray, hard X-ray, and radio ring, elongated towards the large-scale filaments feeding the cluster, coincident with a cutoff in the thermal Sunyaev-Zel'dovich (SZ) signal. However, no such signature was found so far, and the very existence of cluster virial shocks has remained a theory. We report the discovery of a large, ~5 Mpc diameter gamma-ray ring around the Coma cluster, elongated towards the large scale filament connecting Coma and Abell 1367. The gamma-ray ring correlates both with a synchrotron signal and with the SZ cutoff. The gamma-ray, hard-X-ray, and radio signatures agree with analytic and numerical predictions, if the shock deposits a few percent of the thermal energy in relativistic electrons over a Hubble time, and ~1% of the energy in magnetic fields. The implied inverse-Compton and synchrotron cumulative emission from similar shocks dominates the diffuse extragalactic gamma-ray and low frequency radio backgrounds. Our results reveal the prolate structure of the hot gas in Coma, the feeding pattern of the cluster, and properties of the surrounding large scale voids and filaments. The anticipated detection of such shocks around other clusters would provide a powerful new cosmological probe.
(Abridged) Following on from a recently completed radial-velocity survey of the old (7 Gyr) open cluster NGC 188 in which we study in detail the solar-type hard binaries and blue stragglers of the cluster, here we investigate the dynamical evolution of NGC 188 through a sophisticated N-body model. We employ the observed binary properties of the young (150 Myr) open cluster M35, where possible, to guide our choices for parameters of the initial binary population. At 7 Gyr the main-sequence solar-type hard-binary population in the model matches that of NGC 188 in both binary frequency and distributions of orbital parameters. This agreement between the model and observations is in a large part due to the similarities between the NGC 188 and M35 solar-type binaries. Indeed, among the 7 Gyr main-sequence binaries in the model, only those with P>1000 days show potentially observable evidence for modifications by dynamical encounters. This emphasizes the importance of defining accurate initial conditions for star cluster models, which we propose is best accomplished through comparisons with observations of young open clusters like M35. Furthermore, this suggests that observations of the present-day binaries in even old open clusters can provide valuable information on their primordial binary populations. However, despite the model's successes at matching the true cluster, the model underproduces blue stragglers and produces an abundance of long-period circular main-sequence--white-dwarf binaries as compared to NGC 188. We conclude that improvements in the physics of mass transfer and common envelope may in fact solve both discrepancies with the observations. This project highlights the unique accessibility of open clusters to both comprehensive observational surveys and full-scale N-body simulations, and underscores the importance of open clusters to the study of star cluster dynamics.
The concentration-mass relation for dark matter-dominated halos is one of the essential results expected from a theory of structure formation. We present a simple prediction scheme, a cosmic emulator, for the c-M relation as a function of cosmological parameters for wCDM models. The emulator is constructed from 37 individual models, with three nested N-body gravity-only simulations carried out for each model. The mass range covered by the emulator is 2 x 10^{12} M_sun < M <10^{15} M_sun with a corresponding redshift range of z=0 -1. Over this range of mass and redshift, as well as the variation of cosmological parameters studied, the mean halo concentration varies from c ~ 2 to c ~ 8. The distribution of the concentration at fixed mass is Gaussian with a standard deviation of one-third of the mean value, almost independent of cosmology, mass, and redshift over the ranges probed by the simulations. We compare results from the emulator with previously derived heuristic analytic fits for the c-M relation, finding that they underestimate the halo concentration at high masses. Using the emulator to investigate the cosmology dependence of the c-M relation over the currently allowable range of values, we find -- not surprisingly -- that \sigma_8 and \omega_m influence it considerably, but also that the dark energy equation of state parameter, w, has a substantial effect. In general, the concentration of lower-mass halos is more sensitive to changes in cosmological parameters as compared to cluster mass halos.
We present the first 3D simulations to include the effects of dark matter annihilation feedback during the collapse of primordial mini-halos. We begin our simulations from cosmological initial conditions and account for dark matter annihilation in our treatment of the chemical and thermal evolution of the gas. The dark matter is modelled using an analytical density profile that responds to changes in the peak gas density. We find that the gas can collapse to high densities despite the additional energy input from the dark matter. No objects supported purely by dark matter annihilation heating are formed in our simulations. However, we find that the dark matter annihilation heating has a large effect on the evolution of the gas following the formation of the first protostar. Previous simulations without dark matter annihilation found that protostellar discs around Population III stars rapidly fragmented, forming multiple protostars that underwent mergers or ejections. When dark matter annihilation is included, however, these discs become stable to radii of 1000 AU or more. In the cases where fragmentation does occur, it is a wide binary that is formed.
Many helioseismic measurements suffer from substantial systematic errors. A particularly frustrating one is that time-distance measurements suffer from a large center to limb effect which looks very similar to the finite light travel time, except that the magnitude depends on the observable used and can have the opposite sign Zhao et al. (2012). This has frustrated attempts to determine the deep meridional flow in the solar convection zone, with Zhao et al. (2012) applying an ad hoc correction with little physical basis to correct the data. In this letter we propose that part of this effect can be explained by the highly asymmetrical nature of the solar granulation which results in what appears to the oscillation modes as a net radial flow, thereby imparting a phase shift on the modes as a function of observing height and thus heliocentric angle.
We describe the La Silla-QUEST (LSQ) Variability Survey. LSQ is a dedicated wide-field synoptic survey in the Southern Hemisphere, focussing on the discovery and study of transients ranging from low redshift (z < 0.1) SN Ia, Tidal Disruption events, RR Lyr{\ae} variables, CVs, Quasars, TNOs and others. The survey utilizes the 1.0-m Schmidt Telescope of the European Southern Observatory at La Silla, Chile, with the large-area QUEST camera, a mosaic of 112 CCDs with field of view of 9.6 square degrees. The LSQ Survey was commissioned in 2009, and is now regularly covering ~1000 square deg per night with a repeat cadence of hours to days. The data are currently processed on a daily basis. We present here a first look at the photometric capabilities of LSQ and we discuss some of the most interesting recent transient detections.
Bent-double radio sources have been used as a probe to measure the density of intergalactic gas in galaxy groups. We carry out a series of high-resolution, 3D simulations of AGN jets moving through an external medium with a constant density in order to develop a general formula for the radius of curvature of the jets, and to determine how accurately the density of the intra-group medium (IGM) can be measured. Our simulations produce curved jets ending in bright radio lobes with an extended trail of low surface brightness radio emission. The radius of curvature of the jets varies with time by only about 25%. The radio trail seen in our simulations is typically not detected in known sources, but may be detectable in lower resolution radio observations. The length of this tail can be used to determine the age of the AGN. We also use our simulation data to derive a formula for the kinetic luminosity of observed jets in terms of the radius of curvature and jet pressure. In characterizing how well observations can measure the IGM density, we find that the limited resolution of typical radio observations leads to a systematic under-estimate of the density of about 50%. The unknown angles between the observer and the direction of jet propagation and direction of AGN motion through the IGM leads to an uncertainty of about 50% in estimates of the IGM density. Previous conclusions drawn using these sources, indicating that galaxy groups contain significant reservoirs of baryons in their IGM, are still valid when considering this level of uncertainty. In addition, we model the X-ray emission expected from bent-double radio sources. We find that known sources in reasonably dense environments should be detectable in ~100 ks Chandra observations. X-ray observations of these sources would place constraints on the IGM density and AGN velocity that are complementary to radio observations.
As the 50th anniversary of the Cerro Tololo Inter-American Observatory (CTIO) draws near, the author was surprised to learn that the published latitude and longitude for CTIO in the Astronomical Almanac and iraf observatory database appears to differ from modern GPS-measured geodetic positions by nearly a kilometer. Surely, the position for CTIO could not be in error after five decades? The source of the discrepancy appears to be due to the ~30" difference between the astronomical and geodetic positions -- a systematic effect due to vertical deflection first reported by Harrington, Mintz Blanco, & Blanco (1972). Since the astronomical position is not necessarily the desired quantity for some calculations, and since the number of facilities on Cerro Tololo and neighboring Cerro Pachon has grown considerably over the years, I decided to measure accurate geodetic positions for all of the observatories and some select landmarks on the two peaks using GPS and Google Earth. Both sets of measurements were inter-compared, and externally compared to a high accuracy geodetic position for a NASA Space Geodesy Program survey monument on Tololo. I conclude that Google Earth can currently be used to determine absolute geodetic positions (i.e. compared to GPS) accurate to roughly +-0.15" (+-5 m) in latitude and longitude without correction, or approximately +-0".10 (+-3 m) with correction. I tabulate final geodetic and geocentric positions on the WGS-84 coordinate system for all astronomical observatories on Cerro Tololo and Cerro Pachon with accuracy +-0".1 (+-3 m). One surprise is that an oft-cited position for LSST is in error by 9.4 km and the quoted elevation is in error by 500 m.
In certain mass ranges, massive stars can undergo a violent pulsation triggered by the electron/positron pair instability that ejects matter, but does not totally disrupt the star. After one or more of these pulsations, such stars are expected to undergo core-collapse to trigger a supernova explosion. The mass range susceptible to this pulsational phenomena may be as low as 50-70 Msun if the progenitor is of very low metallicity and rotating sufficiently rapidly to undergo nearly homogeneous evolution. The mass, dynamics, and composition of the matter ejected in the pulsation are important aspects to determine the subsequent observational characteristics of the explosion. We examine the dynamics of a sample of stellar models and rotation rates and discuss the implications for the first stars, for LBV-like phenomena, and for superluminous supernovae. We find that the shells ejected by pulsational pair-instability events with rapidly rotating progenitors (>30% the critical value) are hydrogen-poor and helium and oxygen-rich.
We investigate the obliquity and spin period of Earth-Moon like systems after 4.5 Gyr of tidal evolution with various satellite masses and initial planetary obliquity and discuss their relations to the habitability of the planet. We find three possible outcomes: either i) the system is still evolving, ii) the system is double synchronous or iii) the satellite has collided with the planet. The transition between case i) and ii) is abrupt and occurs at slightly larger satellite mass ($m_s \sim 0.02m_p$) than the lunar mass. We suggest that cases ii) and iii) are less habitable than case i). Using results from models of giant impacts and satellite accretion, we found that the systems that mimic our own with rotation period $12 < P_p < 48$ h and current planetary obliquity $\varepsilon_p < 40^\circ$ or $\varepsilon_p > 140^\circ$ only represent 14% of the possible outcomes. Elser et al. (2011) conclude that the probability of a terrestrial planet having a heavy satellite is 13%. Combining these results suggests that the probability of ending up with a system such as our own is of the order of 2%.
In the era of precision cosmology the Virgo cluster takes on a new role in the cosmic distance scale. Its traditional role of testing the consistency of secondary distance indicators is replaced by an ensemble of distance measurements within the Local Supercluster united by a velocity field model obtained from redshift survey based reconstruction. WMAP leads us to see the Hubble Constant as one of six parameters in a standard model of cosmology with considerable covariance between parameters. Independent experiments, such as WMAP and the HST Key Project (and their successors) constrain these parameters.
Polycyclic Aromatic Hydrocarbon (PAH) emission features dominate the mid-infrared spectra of star-forming galaxies and can be useful to calibrate star formation rates and diagnose ionized states of grains. However, the PAH 3.3 micron feature has not been studied as much as other PAH features since it is weaker than others and resides outside of Spitzer capability. In order to detect and calibrate the 3.3 micron PAH emission and investigate its potential as a star formation rate indicator, we carried out an AKARI mission program, AKARI mJy Unbiased Survey of Extragalactic Survey (AMUSES) and compare its sample with various literature samples. We obtained 2 ~5 micron low resolution spectra of 20 flux-limited galaxies with mixed SED classes, which yields the detection of the 3.3 micron PAH emission from three out of 20 galaxies. For the combined sample of AMUSES and literature samples, the 3.3 micron PAH luminosities correlate with the infrared luminosities of star-forming galaxies, albeit with a large scatter (1.5 dex). The correlation appears to break down at the domain of ultra-luminous infrared galaxies (ULIRGs), and the power of the 3.3 micron PAH luminosity as a proxy for the infrared luminosity is hampered at log[L(PAH3.3)/(erg/sec)] > -42.0. Possible origins for this deviation in the correlation are discussed, including contribution from AGN and strongly obscured YSOs, and the destruction of PAH molecules in ULIRGs.
We investigate the dust velocity and spatial distribution in an eccentric protoplanetary disk under the secular gravitational perturbation of an embedded planet of about 5 Jupiter masses. We first employ the FARGO code to obtain the two-dimensional density and velocity profiles of the eccentric gas disk exterior to the gap opened up by the embedded planet in the quasi-steady state. We then apply the secular perturbation theory and incorporate the gas drag to estimate the dust velocity and density on the secular timescale. The dust-to-gas ratio of the unperturbed disk is simply assumed to be 0.01. In our fiducial disk model with the planet at 5 AU, we find that 0.01 cm- to 1 m-sized dust particles are well coupled to the gas. Consequently, the particles behave similarly to the gas and exhibit asymmetric dynamics as a result of eccentric orbits. The dust surface density is enhanced around the apocenter of the disk. However, for the case of a low-density gaseous disk (termed "transition disk" henceforth in this work) harboring the planet at 100 AU, the azimuthal distributions of dust of various sizes can deviate significantly. Overall, the asymmetric structure exhibits a phase correlation between the gas velocity fields and dust density distribution. Therefore, our study potentially provides a reality check as to whether an asymmetric disk gap detected at sub-millimeter and centimeter wavelengths is a signpost of a massive gas giant planet.
We apply the Wiener Hermite (WH) expansion to the non-linear evolution of Large-Scale Structure, and obtain an approximate expression for the matter power spectrum in full order of the expansion. This method allows us to expand any random function in terms of an orthonormal bases in space of random functions in such a way that the first order of the expansion expresses the Gaussian distribution, and others are the deviation from the Gaussianity. It is proved that the Wiener Hermite expansion is mathematically equivalent with the $\Gamma$-expansion approach in the Renormalized Perturbation Theory (RPT). While an exponential behavior in the high-$k$ limit has been proved for the mass density and velocity fluctuations of Dark Matter in the RPT, we reprove the behavior in the context of the Wiener Hermite expansion using the result of Standard Perturbation Theory (SPT). We propose a new approximate expression for the matter power spectrum which interpolates the low-$k$ expression corresponding to 1-loop level in SPT and the high-$k$ expression obtained by taking a high-$k$ limit of the WH expansion. The validity of our prescription is specifically verified by comparing with the 2-loop solutions of the SPT. The proposed power spectrum agrees with the result of $N$-body simulation with the accuracy better than 1% or 2% in a range of the BAO scales, where the wave number is about $k= 0.2 \sim 0.4$ $h{\rm Mpc^{-1}}$ at $z=0.5-3.0$. This accuracy is comparable to or slightly less than the ones in the Closure Theory whose the fractional difference from N body result is within 1%. A merit of our method is that the computational time is very short because only single and double integrals are involved in our solution.
The equation of state (EoS) of the outer crust of a cold non-accreting magnetar has been determined using the model of Lai and Shapiro (1991). For this purpose, we have made use of the latest experimental atomic mass data complemented with a Hartree-Fock-Bogoliubov (HFB) mass model. Magnetar crusts are found to be significantly different from the crusts of ordinary neutron stars.
Context. Kepler-17 is a G2V sun-like star accompanied by a transiting planet with a mass of ~2.5 Jupiter masses and an orbital period of 1.486 d, recently discovered by the Kepler space telescope. This star is highly interesting as a young solar analogue. Aims. We used about 500 days of high-precision, high-duty-cycle optical photometry collected by Kepler to study the rotation of the star and the evolution of its photospheric active regions. Methods. We applied a maximum-entropy light curve inversion technique to model the flux rotational modulation induced by active regions that consist of dark spots and bright solar-like faculae with a fixed area ratio. Their configuration was varied after a fixed time interval to take their evolution into account. Active regions were used as tracers to study stellar differential rotation, and planetary occultations were used to constrain the latitude of some spots. Results. Our modelling approach reproduces the light variations of Kepler-17 with a standard deviation of the residuals comparable with the precision of Kepler photometry. We find several active longitudes where individual active regions appear, evolve, and decay with lifetimes comparable to those observed in the Sun, although the star has a spotted area ~10-15 times larger than the Sun at the maximum of the 11-yr cycle. Kepler-17 shows a solar-like latitudinal differential rotation, but the fast spot evolution prevents a precise determination of its amplitude. Moveover, the star shows a cyclic variation of the starspot area with a period of 47.1 \pm 4.5 d, particularly evident during the last 200 days of the observations, similar to the solar Rieger cycles. Possible effects of the close-in massive planet on stellar photospheric activity cannot be excluded, but require a long-term monitoring to be unambiguously detected.
We analysed the optical and radio properties of lobe-dominated giant-sized (> 0.72 Mpc) radio quasars and compared the results with those derived for a sample of smaller radio sources to determine whether the large size of some extragalactic radio sources is related to the properties of their nuclei. We compiled the largest (to date) sample of giant radio quasars, including 24 new and 21 previously-known objects, and calculated a number of important parameters of their nuclei such as the black hole mass and the accretion rate. We conclude that giant radio quasars have properties similar to those of smaller size and that giant quasars do not have more powerful central engines than other radio quasars. The results obtained are consistent with evolutionary models of extragalactic radio sources which predict that giant radio quasars could be more evolved (aged) sources compared to smaller radio quasars. In addition we found out that the environment may play only a minor role in formation of large-scale radio structures.
We explore the possibility of detecting Super Earths via transit timing variations with the satellite CoRoT.
In recent years, the fullerene species C60 (and to a lesser extent also C70) has been reported in the mid-IR spectra of various astronomical objects. Cosmic fullerenes form in the circumstellar material of evolved stars, and survive in the interstellar medium (ISM). It is not entirely clear how they form or what their excitation mechanism is.
The magnetorotational instability (MRI) has been suggested to have an important role on the dynamics of accretion disks. We investigate MRI as an alternative way for guiding the plasma from the disk to the funnel flow at the disk-magnetosphere boundary of classical T Tauri stars (CTTSs) by considering the diamagnetic effects. We solve the magnetohydrodynamic equations by including the effect of both the magnetic field gradient and the perpendicular (to the field) velocity gradient produced by the magnetization current at the disk-magnetosphere boundary for the first time. Diamagnetic current modified MRI produces a non-propagating mode which may lift the plasma from the disk towards the vertical magnetic field lines. Our model also shows that the diamagnetic effects play an important role in triggering the MRI. The instability becomes more powerful with the inclusion of the gradient in the magnetic field and the perpendicular velocity.
SUPERBOX-10 is the successor of SUPERBOX, a particle-mesh code where additional grids and sub-grids are applied to regions of high particle density. Previous limitations have been solved. For instance, the vertical resolution is improved considerably when flattened grids are used. Since the computationally most intensive part is the Fast Fourier Transform, we introduce a parallelised version using the library FFTW, resulting in a speed-up of a few. The new features are tested using a galaxy model consisting of an exponential disc, a bulge and a dark matter halo. We demonstrate that the use of flattened grids efficiently reduces numerical heating. We simulate the merging of disc-bulge-halo galaxies with small spherical satellites. As a result, satellites on orbits with both low eccentricity and inclination heat the disc most efficiently. Moreover, we find that most of the satellite's energy and angular momentum is transfered to the halo.
A study of the response in energy of the radio-detection method of air showers initiated by ultra-high-energy cosmic rays is presented. Data analysis of the CODALEMA experiment shows that a strong correlation can be demonstrated between the primary energy of the cosmic ray and the electric field amplitude estimated at the heart of the radio signal. Its sensitivity to the characteristics of shower suggests that energy resolution of less than 20% can be achieved. It suggests also that, not only the Lorentz force, but also another contribution proportional to all charged particles generated in the development of the shower, could play a significant role in the amplitude of the electric field peak measured by the antennas (as coherence or the charge excess).
We study the gravitational effect of non-self-annihilating dark matter on compact stellar objects. The self-interaction of condensate dark matter can give high accretion rate of dark matter onto stars. Phase transition to condensation state takes place when the dark matter density exceeds the critical value. A compact degenerate dark matter core is developed and alter the structure and stability of the stellar objects. Condensate dark matter admixed neutron stars is studied through the two-fuid TOV equation. The existence of condensate dark matter deforms the mass-radius relation of neutron stars and lower their maximum baryonic masses and radii. The possible effects on the Gamma-ray Burst rate in high redshift are discussed.
We study the relations between the multimodality of galaxy clusters drawn from the SDSS DR8 and the environment where they reside. We find that multimodal clusters reside in higher density environment than unimodal clusters. We determine morphological types of superclusters and show that clusters in superclusters of spider morphology have higher probabilities to have substructure and larger peculiar velocities of their main galaxies than clusters in superclusters of filament morphology. Our study shows the importance of the role of superclusters as high density environment which affects the properties of galaxy systems in them.
We present an inflationary model preceded by a bounce in a metric theory a l\'{a} $f(R)$ where $R$ is the scalar curvature of the space-time. The model is asymptotically de Sitter such that the gravitational action tends asymptotically to a Hilbert-Einstein action, therefore modified gravity affects only the early stages of the universe. We then analyse the spectrum of the gravitational waves through the method of the Bogoliubov coefficients by two means: taking into account the gravitational perturbations due to the modified gravitational action in the $f(R)$ setup and by simply considering those perturbations inherent to the standard Hilbert-Einstein action. We show that there are distinctive (oscillatory) signals on the spectrum for very low frequencies; i.e. corresponding to modes that are currently entering the horizon.
By way of expressing the Hubble expansion rate for the general Lema\^{i}tre-Tolman-Bondi (LTB) metric as a function of cosmic time, we test the scale on which the Copernican Principle holds in the context of a void model. By performing parameter estimation on the CGBH void model, we show the Hubble parameter data favors a void with characteristic radius of $2 \sim 3$ Gpc. This brings the void model closer, but not yet enough, to harmony with observational indications given by the background kinetic Sunyaev-Zel'dovich effect and the normalization of near-infrared galaxy luminosity function. However, the test of such void models may ultimately lie in the future detection of the discrepancy between longitudinal and transverse expansion rates, a touchstone of inhomogeneous models. With the proliferation of observational Hubble parameter data and future large-scale structure observation, a definitive test could be performed on the question of cosmic homogeneity.
During the last decade, hundreds of young massive cluster candidates have been detected in the disk of the Milky Way. We investigate one of these candidates, Mercer 81, which was discovered through a systematic search for stellar overdensities, with follow-up NICMOS/HST infrared narrow-band photometry to find emission-line stars and confirm it as a massive cluster. Surprisingly, the brightest stars turned out to be a chance alignment of foreground stars, while a real massive cluster was found among some fainter stars in the field. From a first spectroscopic study of four emission-line stars (ISAAC/VLT), it follows that Mercer 81 is a very massive young cluster, placed at the far end of the Galactic bar. Additionally, in this work we present some unpublished spectra from a follow-up observation program which confirm that the cluster hosts several Nitrogen-rich Wolf-Rayet stars (WN) and blue supergiants.
We observed the Crab pulsar in October 2008 at the Copernico Telescope in Asiago - Cima Ekar with the optical photon counter Aqueye (the Asiago Quantum Eye) which has the best temporal resolution and accuracy ever achieved in the optical domain (hundreds of picoseconds). Our goal was to perform a detailed analysis of the optical period and phase drift of the main peak of the Crab pulsar and compare it with the Jodrell Bank ephemerides. We determined the position of the main peak using the steepest zero of the cross-correlation function between the pulsar signal and an accurate optical template. The pulsar rotational period and period derivative have been measured with great accuracy using observations covering only a 2 day time interval. The error on the period is 1.7 ps, limited only by the statistical uncertainty. Both the rotational frequency and its first derivative are in agreement with those from the Jodrell Bank radio ephemerides archive. We also found evidence of the optical peak leading the radio one by ~230 microseconds. The distribution of phase-residuals of the whole dataset is slightly wider than that of a synthetic signal generated as a sequence of pulses distributed in time with the probability proportional to the pulse shape, such as the average count rate and background level are those of the Crab pulsar observed with Aqueye. The counting statistics and quality of the data allowed us to determine the pulsar period and period derivative with great accuracy in 2 days only. The time of arrival of the optical peak of the Crab pulsar leads the radio one in agreement with what recently reported in the literature. The distribution of the phase residuals can be approximated with a Gaussian and is consistent with being completely caused by photon noise (for the best data sets).
Atomic cooling haloes with T_vir > 10^4 K are the most plausible sites for the formation of the first galaxies. In this article, we aim to study the implications of gravity driven turbulence in protogalactic haloes. By varying the resolution per Jeans length, we explore whether the turbulent cascade is resolved well enough to obtain converged results. We have performed high resolution cosmological simulations using the adaptive mesh refinement code Enzo including a subgrid-scale turbulence model to study the role of unresolved turbulence. We compared the results of three different Jeans resolutions from 16 to 64 cells. While radially averaged profiles roughly agree at different resolutions, differences in the morphology reveal that even the highest resolution employed provides no convergence. Moreover, taking into account unresolved turbulence significantly influences the morphology of a halo. We have quantified the properties of the high-density clumps in the halo. These clumps are gravitationally unbound with temperature above 6000 K and densities of the order of 10^-12 gcm^-3. In general, the clumps with SGS turbulence are denser and more massive compared with their counterparts in the standard simulation setup that ignores unresolved turbulence.
The IceCube Observatory at the South Pole is composed of a cubic kilometer scale neutrino telescope buried beneath the icecap and a square-kilometer surface water Cherenkov tank detector array known as IceTop. The combination of the surface array with the in-ice detector allows the dominantly electromagnetic signal of air showers at the surface and their high-energy muon signal in the ice to be measured in coincidence. This ratio is known to carry information about the nuclear composition of the primary cosmic rays. This paper reviews the recent results from cosmic-ray measurements performed with IceTop/IceCube: energy spectrum, mass composition, anisotropy, search for PeV gamma sources, detection of high energy muons to probe the initial stages of the air shower development, and study of transient events using IceTop in scaler mode.
In the advent of new large galaxy surveys, which will produce enormous datasets with hundreds of millions of objects, new computational techniques are necessary in order to extract from them any two-point statistic, the computational time of which grows with the square of the number of objects to be correlated. Fortunately technology now provides multiple means to massively parallelize this problem. Here we present a free-source code specifically designed for this kind of calculations. Two implementations are provided: one for execution on shared-memory machines using OpenMP and one that runs on graphical processing units (GPUs) using CUDA. The code is available at this http URL
Aims: Accurate astrometry is required to reliably cross-match 20th-century catalogues against 21st-century surveys. The present work aims to provide such astrometry for the 625 entries of the Bohannan & Epps (BE74) catalogue of H$\alpha$ emission-line stars. Methods: BE74 targets have been individually identified in digital images and, in most cases, unambiguously matched to entries in the UCAC4 astrometric catalogue. Results: Sub-arcsecond astrometry is now available for almost all BE74 stars. Several identification errors in the literature illustrate the perils of relying solely on positional coincidences using poorer-quality astrometry.
In 1983 to 84, we proposed a new method in which all stochastic processes concerned are exactly taken into account as for range fluctuation of high energy muons, without introducing any approximation which may distort fluctuation effect. Now, we call it tentatively Time Sequential Procedure. In 1991, Lipari and Stanev proposed another method for the same problem. They divided the problem into two part, soft part and hard part, and applied Monte Carlo technique to the latter part. Here, we call their method tentatively $V_{cut}$ Procedure. It is well known that the procedure has been widely utilized in the analysis of high energy muon events in KM3 detectors. In the present paper, we examine the limit for applicability to $V_{cut}$ Procedure for the range fluctuation, comparing with Time Sequential Procedure. It is concluded that $V_{cut}$ Procedure give not so different values from Time Sequential Procedure on the survival probability for high energy muons, but it connotes critical problems related to energy measurements on high energy muon events due to Cherenkov light signals, owing to the inconsistency of the procedure involved. Thus, we try to the revival of Time Sequential Procedure for the establishment of more reliable theory for the observation of Cherenkov light whose origins are high and extremely high energy muons.
We present results from the first self-consistent multi-fluid simulations of chromospheric magnetic reconnection in a weakly ionized reacting plasma. We simulate two dimensional magnetic reconnection in a Harris current sheet with a numerical model which includes ion-neutral scattering collisions, ionization, recombination, optically thin radiative loss, collisional heating, and thermal conduction. In the resulting tearing mode reconnection the neutral and ion fluids become decoupled upstream from the reconnection site, creating an excess of ions in the reconnection region and therefore an ionization imbalance. Ion recombination in the reconnection region, combined with Alfv\'{e}nic outflows, quickly removes ions from the reconnection site, leading to a fast reconnection rate independent of Lundquist number. In addition to allowing fast reconnection, we find that these non-equilibria partial ionization effects lead to the onset of the nonlinear secondary tearing instability at lower values of the Lundquist number than has been found in fully ionized plasmas.These simulations provide evidence that magnetic reconnection in the chromosphere could be responsible for jet-like transient phenomena such as spicules and chromospheric jets.
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We use maximum entropy arguments to derive the phase space distribution of a
virialized dark matter halo. Our distribution function gives an improved
representation of the end product of violent relaxation. This is achieved by
incorporating physically motivated dynamical constraints (specifically on
orbital actions) which prevent arbitrary redistribution of energy.
We compare the predictions with three high-resolution dark matter simulations
of widely varying mass. The numerical distribution function is accurately
predicted by our argument, producing an excellent match for the vast majority
of particles.
The remaining particles constitute the central cusp of the halo (<4% of the
dark matter). They can be accounted for within the presented framework once the
short dynamical timescales of the centre are taken into account.
We present TA-DA, a new software aimed at greatly simplify and improve the analysis of stellar photometric data in comparison with theoretical models, and allow the derivation of stellar parameters from multi-band photometry. Its flexibility allows one to address a number of such problems: from the interpolation of stellar models, or sets of stellar physical parameters in general, to the computation of synthetic photometry in arbitrary filters or units; from the analysis of observed color-magnitude diagrams, to a Bayesian derivation of stellar parameters (and extinction) based on multi-band data. TA-DA is available as a pre-compiled IDL widget-based application; its graphical user interface makes it considerably user-friendly. In this paper we describe the software and its functionalities.
We compute the scale dependence of fNL for multi-field inflation model, allowing for an arbitrary field space metric. We show that, in addition to multi-field effects and self interactions, the curved field space metric provides another source of scale dependence, which arises from the field-space Riemann curvature tensor and its derivatives. The scale dependence may be detectable within the near future if the amplitude of fNL is not too far from the current observational bounds.
We investigate the effects of stellar limb-darkening and photospheric perturbations for the onset of wind structure arising from the strong, intrinsic line-deshadowing instability (LDI) of a line-driven stellar wind. A linear perturbation analysis shows that including limb-darkening reduces the stabilizing effect of the diffuse radiation, leading to a net instability growth rate even at the wind base. Numerical radiation-hydrodynamics simulations of the non-linear evolution of this instability then show that, in comparison with previous models assuming a uniformly bright star without base perturbations, wind structure now develops much closer ($r \la 1.1 R_\star$) to the photosphere. This is in much better agreement with observations of O-type stars, which typically indicate the presence of strong clumping quite near the wind base.
A number of ultra-cool dwarfs emit circularly polarised radio waves generated by the electron cyclotron maser instability. In the solar system such radio is emitted from regions of strong auroral magnetic field-aligned currents. We thus apply ideas developed for Jupiter's magnetosphere, being a well-studied rotationally-dominated analogue in our solar system, to the case of fast-rotating UCDs. We explain the properties of the radio emission from UCDs by showing that it would arise from the electric currents resulting from an angular velocity shear in the fast-rotating magnetic field and plasma, i.e. by an extremely powerful analogue of the process which causes Jupiter's auroras. Such a velocity gradient indicates that these bodies interact significantly with their space environment, resulting in intense auroral emissions. These results strongly suggest that auroras occur on bodies outside our solar system.
We discuss how different cosmological models of the Universe affect the probability that a background source has multiple images related by an angular distance $\theta_E$ of the line of sight, \textit{i. e.}, the optical depth of gravitational lensing. We examine some cosmological models for different values of the density parameter $\Omega_i$: i) the cold dark matter model, ii) the $\Lambda$CDM model, iii) the Bose-Einstein condensate dark matter model, iv) the Chaplygin gas model, v) the viscous fluid cosmological model and vi) the holographic dark energy model. We note that the dependence of the energy-matter content of the universe profoundly alters the frequency of multiple quasar image.
In this paper, we investigate the gamma ray signal produced from dark matter collisions with high energy cosmic protons. Notably, we extend past results by including important hadronization effects. We find that showering and hadronization, especially from proton remnants that do not participate in hard scattering, produce a large rate of photons in the forward direction that significantly change the photon energy and angular distribution compared to previous results which used only parton level calculations. Due to this enhancement, the gamma ray signal from the nearby active galactic nuclei Centaurus A is be potentially testable in future Fermi-LAT and HESS measurements, for a dark matter mass and coupling consistent with current XENON100 bounds.
A fast transition between a standard matter-like era and a late $\Lambda$CDM-like epoch (or more in general, a CDM+DE era), generated by a single Unified Dark Matter component, can provide a new interesting paradigm in the context of general relativity, alternative to $\Lambda$CDM itself or other forms of DE or modified gravity theories invoked to explain the observed acceleration of the Universe. UDM models with a fast transition have interesting features, leading to measurable predictions, thus they should be clearly distinguishable from $\Lambda$CDM (and alternatives) through observations. Here we look at different ways of prescribing phenomenological UDM models with fast transition, then focusing on a particularly simple model. We analyse the viability of this model by studying features of the background model and properties of the adiabatic UDM perturbations, which depend on the effective speed of sound and the functional form of the Jeans scale. As a result, theoretical constraints on the parameters of the models are found that allow for a behaviour compatible with observations.
Unlike at lower redshift, where there is a 40% detection rate, surveys for 21-cm absorption arising within the hosts of z > 1 radio galaxies and quasars have been remarkably unsuccessful. Curran et al.(2008) suggest that this is due to the high redshift selection biasing towards the most optically bright objects (those most luminous in the ultra-violetin the rest-frame), where the gas is ionised by the active galactic nucleus. They therefore argue that there must be a population of fainter objects in which the hydrogen is not ionised and which exhibit a similar detection rate as at lower redshifts. In order to find this "missing" gas at high redshift, we have therefore undertaken a survey of z > 2 radio sources, selected by optical faintness. Despite having optical magnitudes which indicate that the targets have ultra-violet luminosities below the threshold where all of the gas is ionised, there were no detections in any of the eight sources for which useable data were obtained. Upon an analysis of the spectral energy distributions, ionising photon rates can only be determined for three of these, all of which suggest that the objects are above the highest luminosity of a current 21-cm detection. The possibility that the other five could be located at lower photon rates cannot be ruled out, although zero detections out of five is not statistically significant. Another possible cause of the non-detections is that our selection biases the sample towards sources which are very steep in the radio band, with a mean spectral index of = -1.0, cf. -0.3 for both the 21-cm detections and UV luminous non-detections. This adds the further possibility that the sources have very extended emission, which would have the effect of reducing the coverage by the putative absorbing gas, thus decreasing the sensitivity of the observation.
We describe a method to measure the M-sigma relation in the non-local universe using dust-obscured QSOs. We present results from a pilot sample of nine 2MASS red QSOs with redshifts 0.14<z<0.37. We find that there is an offset (0.8 dex, on average) between the position of our objects and the local relation for AGN, in the sense that the majority of red QSO hosts have lower velocity dispersions and/or more massive BHs than local galaxies. These results are in agreement with recent studies of AGN at similar and higher redshifts. This could indicate an unusually rapid growth in the host galaxies since z~0.2, if these objects were to land in the local relation at present time. However, the z>0.1 AGN (including our sample and those of previous studies) have significantly higher BH mass than those of local AGN, so a direct comparison is not straightforward. Further, using several samples of local and higher-z AGN, we find a striking trend of an increasing offset with respect to the local M-sigma relation as a function of AGN luminosity, with virtually all objects with log(L_5100/erg s^-1) > 43.6 falling above the relation. Given the relatively small number of AGN at z>0.1 for which there are direct measurements of stellar velocity dispersions, it is impossible at present to determine whether there truly is evolution in M-sigma with redshift. Larger, carefully selected samples of AGN are necessary to disentangle the dependence of M-sigma on mass, luminosity, accretion rates, and redshift.
The origin of hard X-ray (HXR) excess emission from clusters of galaxies is still an enigma, whose nature is debated. One of the possible mechanism to produce this emission is the bremsstrahlung model. However, previous analytical and numerical calculations showed that in this case the intracluster plasma had to be overheated very fast because suprathermal electrons emitting the HXR excess lose their energy mainly by Coulomb losses, i.e., they heat the background plasma. It was concluded also from these investigations that it is problematic to produce emitting electrons from a background plasma by stochastic (Fermi) acceleration because the energy supplied by external sources in the form of Fermi acceleration is quickly absorbed by the background plasma. In other words the Fermi acceleration is ineffective for particle acceleration. We revisited this problem and found that at some parameter of acceleration the rate of plasma heating is rather low and the acceleration tails of non-thermal particles can be generated and exist for a long time while the plasma temperature is almost constant. We showed also that for some regime of acceleration the plasma cools down instead of being heated up, even though external sources (in the form of external acceleration) supply energy to the system. The reason is that the acceleration withdraws effectively high energy particles from the thermal pool (analogue of Maxwell demon).
In previous articles, we described how electromagnetic waves emitted from objects in the sky are collected by the ALMA antennas (Anatomy of ALMA), and how they are combined in order to produce images. Before these images can be processed, they are picked up by the antennas and concentrated by the large main mirror and a smaller secondary mirror in the so called focal point of each antenna. In order to process the data they must be first converted to electromagnetic waves of a lower frequency and amplified. This is the role of the ALMA receivers. In principle they work like a normal AM receiver, but at much higher frequencies. Here we describe how they work and what makes them special.
Here we will discuss which calibrations are needed, how to perform them and how the calibration affect ALMA observations. This first part concentrates on aspects related to a single antenna, namely antenna pointing (including the antenna metrology), focusing, and the amplitude calibration, we also mention the bandpass calibration for single measurements.
In this paper, we investigate the link between the hypervelocity stars (HVSs) discovered in the Galactic halo and the S-stars moving in the Galactic center (GC), under the hypothesis that they are both the products of the tidal breakup of the same population of stellar binaries by the central massive black hole (MBH). By adopting several hypothetical models for binaries to be injected into the vicinity of the MBH and doing numerical simulations, we realize the tidal breakup processes of the binaries and their follow-up evolution. We find that many statistical properties of the detected HVSs and S-stars can be reproduced under some binary injecting models, and their number ratio can be re-produced if the stellar initial mass function is top-heavy (e.g., with slope ~-1.6). The total number of the captured companions is ~50 that have masses in the range ~3-7Msun and semimajor axes <~4000 AU and survive to the present within their main-sequence lifetime. The innermost one is expected to have a semimajor axis ~300-1500 AU and a pericenter distance ~10-200 AU, with a significant probability of being closer to the MBH than S2. Future detection of such a closer star would offer an important test to general relativity. The majority of the surviving ejected companions of the S-stars are expected to be located at Galactocentric distances <~20 kpc, and have heliocentric radial velocities ~-500-1500 km/s and proper motions up to ~5-20 mas/yr. Future detection of these HVSs may provide evidence for the tidal-breakup formation mechanism of the S-stars.
D-H type II radio bursts are widely thought to be caused by the coronal mass ejections (CMEs). However, it is still unclear where the exact source of the type IIs on the shock surface is. We identify the source regions of the decameter-hectometric (D--H) type IIs based on imaging observations from SOHO/LASCO and the radio dynamic spectrum from Wind/Waves. The analysis of two well-observed events suggests that the sources of these two events are located in the interaction regions between shocks and streamers, and that the shocks are enhanced significantly in these regions.
This paper gives an brief overview of the structure of hypothetical strange quarks stars (quark stars, for short), which are made of absolutely stable 3-flavor strange quark matter. Such objects can be either bare or enveloped in thin nuclear crusts, which consist of heavy ions immersed in an electron gas. In contrast to neutron stars, the structure of quark stars is determined by two (rather than one) parameters, the central star density and the density at the base of the crust. If bare, quark stars possess ultra-high electric fields on the order of 10^{18} to 10^{19} V/cm. These features render the properties of quark stars more multifaceted than those of neutron stars and may allow one to observationally distinguish quark stars from neutron stars.
Several mechanisms of bar formation in stellar galactic disks are considered, including Toomre swing amplification and normal mode approach. On example of the well-known model of Kuzmin--Toomre using N-body simulations it was shown that the stellar bar is developed as a result of the evolution of an unstable normal mode. The pattern speed and the growth rate found agree well with linear perturbation theory. Nonlinear evolution of the bar is followed. Role of the growing transient spirals in bar formation is discussed.
We aim at resolving the circumstellar environment around ?beta Pic in the near-infrared in order to study the inner planetary system (< 200 mas, i.e., ~4 AU). Precise interferometric fringe visibility measurements were obtained over seven spectral channels dispersed across the H band with the four-telescope VLTI/PIONIER interferometer. Thorough analysis of interferometric data was performed to measure the stellar angular diameter and to search for circumstellar material. We detected near-infrared circumstellar emission around beta ?Pic that accounts for 1.37% +/- 0.16% of the near-infrared stellar flux and that is located within the field-of-view of PIONIER (i.e., ~200 mas in radius). The flux ratio between this excess and the photosphere emission is shown to be stable over a period of 1 year and to vary only weakly across the H band, suggesting that the source is either very hot (> 1500 K) or dominated by the scattering of the stellar flux. In addition, we derive the limb-darkened angular diameter of beta Pic with an unprecedented accuracy (theta_LD= 0.736 +/- 0.019 mas). Conclusions. The presence of a small H-band excess originating in the vicinity of beta Pic is revealed for the first time thanks to the high-precision visibilities enabled by VLTI/PIONIER. This excess emission is likely due to the scattering of stellar light by circumstellar dust and/or the thermal emission from a yet unknown population of hot dust, although hot gas emitting in the continuum cannot be firmly excluded.
Chemical compositions are determined based on high-resolution spectroscopy for 137 candidate extremely metal-poor (EMP) stars selected from the Sloan Digital Sky Survey (SDSS) and its first stellar extension, the Sloan Extension for Galactic Understanding and Exploration (SEGUE). High-resolution spectra with moderate signal-to-noise (S/N) ratios were obtained with the High Dispersion Spectrograph of the Subaru Telescope. Most of the sample (approximately 80%) are main-sequence turn-off stars, including dwarfs and subgiants. Four cool main-sequence stars, the most metal-deficient such stars known, are included in the remaining sample. Good agreement is found between effective temperatures estimated by the SEGUE stellar parameter pipeline, based on the SDSS/SEGUE medium-resolution spectra, and those estimated from the broadband $(V-K)_0$ and $(g-r)_0$ colors. Our abundance measurements reveal that 70 stars in our sample have [Fe/H] $ < -3$, adding a significant number of EMP stars to the currently known sample. Our analyses determine the abundances of eight elements (C, Na, Mg, Ca, Ti, Cr, Sr, and Ba) in addition to Fe. The fraction of carbon-enhanced metal-poor stars ([C/Fe]$> +0.7$) among the 25 giants in our sample is as high as 36%, while only a lower limit on the fraction (9%) is estimated for turn-off stars. This paper is the first of a series of papers based on these observational results. The following papers in this series will discuss the higher-resolution and higher-S/N observations of a subset of this sample, the metallicity distribution function, binarity, and correlations between the chemical composition and kinematics of extremely metal-poor stars.
Type Ia supernovae are thought to occur as a white dwarf made of carbon and oxygen accretes sufficient mass to trigger a thermonuclear explosion$^{1}$. The accretion could occur slowly from an unevolved (main-sequence) or evolved (subgiant or giant) star$^{2,3}$, that being dubbed the single-degenerate channel, or rapidly as it breaks up a smaller orbiting white dwarf (the double- degenerate channel)$^{3,4}$. Obviously, a companion will survive the explosion only in the single-degenerate channel$^{5}$. Both channels might contribute to the production of type Ia supernovae$^{6,7}$ but their relative proportions still remain a fundamental puzzle in astronomy. Previous searches for remnant companions have revealed one possible case for SN 1572$^{8,9}$, though that has been criticized$^{10}$. More recently, observations have restricted surviving companions to be small, main-sequence stars$^{11,12,13}$, ruling out giant companions, though still allowing the single-degenerate channel. Here we report the result of a search for surviving companions to the progenitor of SN 1006$^{14}$. None of the stars within 4' of the apparent site of the explosion is associated with the supernova remnant, so we can firmly exclude all giant and subgiant companions to the progenitor. Combined with the previous results, less than 20 per cent of type Iae occur through the single degenerate channel.
We have performed the Fourier decomposition analysis of 8- and 13-year V-band light curves of a carefully selected sample of 454 fundamental-mode RR Lyrae variables (RRab type), detected in a 14 square degree area of the Small Magellanic Cloud (SMC) and listed in the Optical Gravitational Lensing Experiment, phase III, Catalogue of Variable Stars. The Fourier decomposition parameters were used to derive metal abundances and distance moduli, following the methodology described by Kapakos, Hatzidimitriou & Soszy\'nski. The average metal abundance of the RRab stars on the new scale of Carretta et al. was found to be <[Fe/H]C09> = -1.69pm0.41 dex (std, with a standard error of 0.02 dex). A tentative metallicity gradient of -0.013pm0.007 dex/kpc was detected, with increasing metal abundance towards the dynamical center of the SMC, but selection effects are also discussed. The distance modulus of the SMC was re-estimated and was found to be <\mu> = 19.13pm0.19 (std) in a distance scale where the distance modulus of the Large Magellanic Cloud (LMC) is \mu_LMC = 18.52pm0.06(std). The average 1-sigma line-of-sight depth was found to be sigma_int = 5.3pm0.4 kpc (std), while spatial variations of the depth were detected. The SMC was found to be deeper in the north-eastern region, while metal richer and metal poorer objects in the sample seem to belong to different dynamical structures. The former have smaller scale height and may constitute a thick disk, its width being 10.40pm0.02 kpc, and a bulge whose size (radius) is estimated to be 2.09pm0.81 kpc. The latter seem to belong to a halo structure with a maximum depth along the line of sight extending over 16 kpc in the SMC central region and falling to 12 kpc in the outer regions.
The predicted orbital period histogram of an sdB population is bimodal with a peak at short (< 10 days) and long (> 250 days) periods. Observationally, there are many short-period sdB systems known, but only very few long-period sdB binaries are identified. As these predictions are based on poorly understood binary interaction processes, it is of prime importance to confront the predictions to observational data. In this contribution we aim to determine the absolute dimensions of the long-period sdB+MS binary system PG1104+243. High-resolution spectroscopy time-series were obtained with HERMES at the Mercator telescope at La Palma, and analyzed to obtain radial velocities of both components. Photometry from the literature was used to construct the spectral energy distribution (SED) of the binary. Atmosphere models were used to fit this SED and determine the surface gravity and temperature of both components. The gravitational redshift provided an independent confirmation of the surface gravity of the sdB component. An orbital period of 753 +- 3 d and a mass ratio of q = 0.637 +- 0.015 were found from the RV-curves. The sdB component has an effective temperature of Teff = 33500 +- 1200 K and a surface gravity of logg = 5.84 +- 0.08 dex, while the cool companion is found to be a G-type star with Teff = 5930 +- 160 K and logg = 4.29 +- 0.05 dex. Assuming a canonical mass of Msdb = 0.47 Msun, the MS component has a mass of 0.74 +- 0.07 Msun, and its Teff corresponds to what is expected for a terminal age main-sequence star with sub-solar metalicity. PG1104+243 is the first long-period sdB binary in which accurate physical parameters of both components could be determined, and the first sdB binary in which the gravitational redshift is measured. Furthermore, PG1104+243 is the first sdB+MS system that shows consistent evidence for being formed through stable Roche-lobe overflow.
We present the results from the first public blind PSF reconstruction challenge, the GRavitational lEnsing Accuracy Testing 2010 (GREAT10) Star Challenge. Reconstruction of a spatially varying PSF, sparsely sampled by stars, at non-star positions is a critical part in the image analysis for weak lensing where inaccuracies in the modelled ellipticity and size-squared can impact the ability to measure the shapes of galaxies. This is of importance because weak lensing is a particularly sensitive probe of dark energy, and can be used to map the mass distribution of large scale structure. Participants in the challenge were presented with 27,500 stars over 1300 images subdivided into 26 sets, where in each set a category change was made in the type or spatial variation of the PSF. Thirty submissions were made by 9 teams. The best methods reconstructed the PSF with an accuracy of ~0.00025 in ellipticity and ~0.00074 in size squared. For a fixed pixel scale narrower PSFs were found to be more difficult to model than larger PSFs, and the PSF reconstruction was severely degraded with the inclusion of an atmospheric turbulence model (although this result is likely to be a strong function of the amplitude of the turbulence power spectrum).
The rotation dynamics of spiral galaxies is modeled using a sum of two mass distributions: a spherical bulge and a thin disk. The density functions representing these mass distributions are calculated from the total angular momentum of the galaxy and known rotation curves. When both bulge and disk density functions are assumed to be smooth and are given a value of zero beyond the edge of the galaxy, a unique solution is obtained. Moreover, the calculated density functions show that constant rotation curves are obtained from a nearly exponential luminosity profile with a dark matter distribution which follows that of the light emitting matter, without the need for modified Newtonian dynamics. Experimental detection of molecular hydrogen in spiral galaxies confirms the presence of a baryonic massive component consistent with the results obtained with this model. It is proposed that dark matter does not have to be exotic non-baryonic matter. Instead, it can be made of molecular hydrogen and condensed matter.
This paper describes the data preprocessing and reduction methods together with SLODAR analysis and wind profiling techniques for GeMS: the Gemini MCAO System. The wavefront gradient measurements of the five GeMS's Shack-Hartmann sensors, each one pointing to a laser guide star, are combined with the DM commands sent to three deformable mirrors optically conjugated at 0, 4.5 and 9 km in order to reconstruct pseudo-open loop slopes. These pseudo-open loop slopes are then used to reconstruct atmospheric turbulence profiles, based on the SLODAR and wind-profiling methods. We introduce the SLODAR method, and how it has been adapted to work in a close-loop, multi Laser Guide Star system. We show that our method allows characterizing the turbulence of up to 16 layers for altitudes spanning from 0 to 19 km. The data preprocessing and reduction methods are described, and results obtained from observations made in 2011 are presented. The wind profiling analysis is shown to be a powerful technique not only for characterizing the turbulence intensity, wind direction and speed, but also as it can provide a verification tool for SLODAR results. Finally, problems such as fratricide effect in multiple laser system due to Rayleigh scattering, centroid gain variations, and limitations of the method are also addressed.
We study the magnetic properties of small-scale transients in coronal hole. We found all brightening events are associated with bipolar regions and caused by magnetic flux emergence followed by cancellation with the pre-existing and newly emerging magnetic flux. In the coronal hole, 19 of 22 events have a single stable polarity which does not change its position in time. In eleven cases this is the dominant polarity. The dominant flux of the coronal hole form the largest concentration of magnetic flux in terms of size while the opposite polarity is distributed in small concentrations. In the coronal hole the number of magnetic elements of the dominant polarity is four times higher than the non-dominant one. The supergranulation configuration appears to preserve its general shape during approximately nine hours of observations although the large concentrations in the network did evolve and were slightly displaced, and their strength either increased or decreased. The emission fluctuations seen in the X-ray bright points are associated with reoccurring magnetic cancellation in the footpoints. Unique observations of an X-ray jet reveal similar magnetic behaviour in the footpoints, i.e. cancellation of the opposite polarity magnetic flux. We found that the magnetic flux cancellation rate during the jet is much higher than in bright points. Not all magnetic cancellations result in an X-ray enhancement, suggesting that there is a threshold of the amount of magnetic flux involved in a cancellation above which brightening would occur at X-ray temperatures. Our study demonstrates that the magnetic flux in coronal holes is continuously recycled through magnetic reconnection which is responsible for the formation of numerous small-scale transient events. The open magnetic flux forming the coronal-hole phenomenon is largely involved in these transient features.
We performed a Chandra X-ray study of three giant H II regions (GHRs), NGC 5461, NGC 5462, and NGC 5471, in the spiral galaxy M101. The X-ray spectra of the three GHRs all contain a prominent thermal component with a temperature of ~0.2 keV. In NGC 5461, the spatial distribution of the soft (< 1.5 keV) X-ray emission is generally in agreement with the extent of H1105, the most luminous H II region therein, but extends beyond its southern boundary, which could be attributed to outflows from the star cloud between H1105 and H1098. In NGC 5462, the X-ray emission is displaced from the H II regions and a ridge of blue stars; the H-alpha filaments extending from the ridge of star cloud to the diffuse X-rays suggest that hot gas outflows have occurred. The X-rays from NGC 5471 are concentrated at the B-knot, a "hypernova remnant" candidate. Assuming a Sedov-Taylor evolution, the derived explosion energy, on the order of 10^52 ergs, is consistent with a hypernova origin. In addition, a bright source in the field of NGC 5462 has been identified as a background AGN, instead of a black hole X-ray binary in M101.
In this paper, we study the degeneracies among several cosmological parameters in detail and discuss their impacts on the determinations of these parameters from the current and future observations. By combining the latest data sets, including type-Ia supernovae "Union2.1" compilation, WMAP seven-year data and the baryon acoustic oscillations from the SDSS Data Release Seven, we perform a global analysis to determine the cosmological parameters, such as the equation of state of dark energy w, the curvature of the universe \Omega_k, the total neutrino mass \sum{m_\nu}, and the parameters associated with the power spectrum of primordial fluctuations (n_s, \alpha_s and r). We pay particular attention on the degeneracies among these parameters and the influences on their constraints, by with or without including these degeneracies, respectively. We find that $w$ and \Omega_k or \sum{m_\nu} are strongly correlated. Including the degeneracies will significantly weaken the constraints. Furthermore, we study the capabilities of future observations and find these degeneracies can be broken very well. Consequently, the constraints of cosmological parameters can be improved dramatically.
The flux variability of blazars at very high energies remains of puzzling origin. Flux variations at time-scales down to the minute suggest that variability originates from the jet, where a relativistic boost can shorten the observed time-scale, while the linear relation between the flux and its RMS or the skewness of the flux distribution suggest that the variability stems from multiplicative processes, associated in some models with the accretion disk. We study the RMS-flux relation and emphasize its link with Pareto distributions, characterized by a power-law probability density function. Such distributions are naturally generated within a minijets-in-a-jet statistical model, in which boosted emitting regions are isotropically oriented within the bulk relativistic flow of a jet. We prove that, within this model, the flux of a single minijet is proportional to its RMS. This relation still holds when considering a large number of emitting regions, for which the distribution of the total flux is skewed and could be interpreted as being log-normal. The minijets-in-a-jet statistical model reconciles the fast variations and the statistical properties of the flux of blazars at very high energies.
Current generation neutrino telescopes cover an energy range from about 10 GeV to beyond $10^9$ GeV. IceCube sets the scale for future experiments to make improvements. Strategies for future upgrades will be discussed in three energy ranges. At the low-energy end, an infill detector to IceCube's DeepCore would add sensitivity in the energy range from a few to a few tens of GeV with the primary goal of measuring the neutrino mass hierarchy. In the central energy range of classical optical neutrino telescopes, next generation detectors are being pursued in the Mediterranean and at Lake Baikal. The KM3NeT detector in its full scale would establish a substantial increase in sensitivity over IceCube. At the highest energies, radio detectors in ice are among the most promising and pursued technologies to increase exposure at $10^9$ GeV by more than an order of magnitude compared to IceCube.
Gas outflows appear to be a phenomenon shared by the vast majority of quasars. Observations indicate that there is wide range in outflow prominence. In this paper we review how the 4D eigenvector 1 scheme helps to organize observed properties and lead to meaningful constraints on the outflow physical and dynamical processes.
The onset of massive star formation is not well understood because of observational and theoretical difficulties. To find the dense and cold clumps where massive star formation can take place, we compiled a sample of high infrared extinction clouds, which were observed previously by us in the 1.2 mm continuum emission and ammonia. We try to understand the star-formation stages of the clumps in these high extinction clouds by studying the infall and outflow properties, the presence of a young stellar object (YSO), and the level of the CO depletion through a molecular line survey with the IRAM 30m and APEX 12m telescopes. Moreover, we want to know if the cloud morphology, quantified through the column density contrast between the clump and the clouds, has an impact on the star formation occurring inside it. We find that the HCO+(1-0) line is the most sensitive for detecting infalling motions. SiO, an outflow tracer, was mostly detected toward sources with infall, indicating that infall is accompanied by collimated outflows. The presence of YSOs within a clump depends mostly on its column density; no signs of YSOs were found below 4E22 cm-2. Star formation is on the verge of beginning in clouds that have a low column density contrast; infall is not yet present in the majority of the clumps. The first signs of ongoing star formation are broadly observed in clouds where the column density contrast between the clump and the cloud is higher than two; most clumps show infall and outflow. Finally, the most evolved clumps are in clouds that have a column density contrast higher than three; almost all clumps have a YSO, and in many clumps, the infall has already halted. Hence, the cloud morphology, based on the column density contrast between the cloud and the clumps, seems to have a direct connection with the evolutionary stage of the objects forming inside.
The iron line at 6.4 keV provides a valuable spectral diagnostic in several fields of X-ray astronomy. It often results from the reprocessing of external X-rays by a neutral or low-ionized medium, but it can also be excited by impacts of low-energy cosmic rays. This paper aims to provide signatures allowing identification of radiation from low-energy cosmic rays in X-ray spectra showing the 6.4 keV line. We study in detail the production of nonthermal line and continuum X-rays by interaction of accelerated electrons and ions with a neutral ambient gas. Corresponding models are then applied to XMM-Newton observations of the X-ray emission emanating from the Arches cluster region near the Galactic center. Bright 6.4 keV line structures are observed around the Arches cluster. This emission is very likely produced by cosmic rays. We find that it can result from the bombardment of molecular gas by energetic ions, but probably not by accelerated electrons. Using a model of X-ray production by cosmic-ray ions, we obtain a best-fit metallicity of the ambient medium of 1.7 plus-minus 0.2 times the solar metallicity. A large flux of low-energy cosmic ray ions could be produced in the ongoing supersonic collision between the star cluster and an adjacent molecular cloud. We find that a particle acceleration efficiency in the resulting shock system of a few percent would give enough power in the cosmic rays to explain the luminosity of the nonthermal X-ray emission. Depending on the unknown shape of the kinetic energy distribution of the fast ions above 1 GeV per nucleon, the Arches cluster region may be a source of high-energy gamma-rays detectable with the Fermi Gamma-ray Space Telescope. At present, the X-ray emission prominent in the 6.4 keV Fe line emanating from the Arches cluster region probably offers the best available signature for a source of low-energy hadronic cosmic rays in the Galaxy.
This is a summary of my lectures during the 2011 IAC Winter School in Puerto de la Cruz. I give an introduction to the field of stellar populations in galaxies, and highlight some new results. Since the title of the Winter School was {\it Secular Evolution of Galaxies} I mostly concentrate on nearby galaxies, which are best suited to study this theme. Of course, the understanding of stellar populations is intimately connected to understanding the formation and evolution of galaxies, one of the great outstanding problems of astronomy. We are currently in a situation where very large observational advances have been made in recent years. Galaxies have been detected up to a redshift of 10. A huge effort has to be made so that stellar population theory can catch up with observations. Since most galaxies are far away, information about them has to come from stellar population synthesis of integrated light. Here I will discuss how stellar evolution theory, together with observations in our Milky Way and Local Group, are used as building blocks to analyze these integrated stellar populations.
In this paper we use radio polarimetric observations of the jet of the nearby bright quasar 3C\,345 to estimate the fluid velocity on kiloparsec scales. The jet is highly polarized, and surprisingly, the electric vector position angles in the jet are ``twisted'' with respect to the jet axis. Simple models of magnetized jets are investigated in order to study various possible origins of the electric vector distribution. In a cylindrically-symmetric transparent jet a helical magnetic field will appear either transverse or longitudinal due to partial cancellations of Stokes parameters between the front and back of the jet. Synchrotron opacity can break the symmetry, but it leads to fractional polarization less than that observed, and to strong frequency dependence that is not seen. Modeling shows that differential Doppler boosting in a diverging jet can break the symmetry, allowing a helical magnetic field to produce a twisted electric vector pattern. Constraints on the jet inclination, magnetic field properties, intrinsic opening angle, and fluid velocities are obtained, and show that highly relativistic speeds ($\beta \ga 0.95$) are required. This is consistent with the observed jet opening angle, with the absence of a counter-jet, with the polarization of the knots at the end of the jet, and with some inverse-Compton models for the X-ray emission from the 3C\,345 jet. This model can also apply on parsec scales and may help explain those sources where the electric vector position angles in the jet are neither parallel nor transverse to the jet axis.
This paper presents cosmological results from the final data release of the WiggleZ Dark Energy Survey. We perform full analyses of different cosmological models using the WiggleZ power spectra measured at z=0.22, 0.41, 0.60, and 0.78, combined with other cosmological datasets. The limiting factor in this analysis is the theoretical modelling of the galaxy power spectrum, including non-linearities, galaxy bias, and redshift-space distortions. In this paper we assess several different methods for modelling the theoretical power spectrum, testing them against the Gigaparsec WiggleZ simulations (GiggleZ). We fit for a base set of 6 cosmological parameters, {Omega_b h^2, Omega_CDM h^2, H_0, tau, A_s, n_s}, and 5 supplementary parameters {n_run, r, w, Omega_k, sum m_nu}. In combination with the Cosmic Microwave Background (CMB), our results are consistent with the LambdaCDM concordance cosmology, with a measurement of the matter density of Omega_m =0.29 +/- 0.016 and amplitude of fluctuations sigma_8 = 0.825 +/- 0.017. Using WiggleZ data with CMB and other distance and matter power spectra data, we find no evidence for any of the extension parameters being inconsistent with their LambdaCDM model values. The power spectra data and theoretical modelling tools are available for use as a module for CosmoMC, which we here make publicly available at this http URL We also release the data and random catalogues used to construct the baryon acoustic oscillation correlation function.
Recent indications from both particle physics and cosmology suggest the existence of more than three neutrino species. In cosmological analyses the effects of neutrino mass and number of species can in principle be disentangled for fixed cosmological parameters. However, since we do not have perfect measurements of the standard Lambda Cold Dark Matter model parameters some correlation remains between the neutrino mass and number of species, and both parameters should be included in the analysis. Combining the newest observations of several cosmological probes (cosmic microwave background, large scale structure, expansion rate) we obtain N_eff=3.58(+0.15/-0.16 at 68% CL) (+0.55/-0.53 at 95% CL) and a sum of neutrino masses of less than 0.60 eV (95 CL), which are currently the strongest constraints on N_eff and M_nu from an analysis including both parameters. The preference for N_eff >3 is now at a 2sigma level.
Using several cosmological observations, i.e. the cosmic microwave background anisotropies (WMAP), the weak gravitational lensing (CFHTLS), the measurements of baryon acoustic oscillations (SDSS+WiggleZ), the most recent observational Hubble parameter data, the Union2.1 compilation of type Ia supernovae, and the HST prior, we impose constraints on the sum of neutrino masses ($\mnu$), the effective number of neutrino species ($\neff$) and dark energy equation of state ($w$), individually and collectively. We find that a tight upper limit on $\mnu$ can be extracted from the full data combination, if $\neff$ and $w$ are fixed. However this upper bound is severely weakened if $\neff$ and $w$ are allowed to vary. This result naturally raises questions on the robustness of previous strict upper bounds on $\mnu$, ever reported in the literature. The best-fit values from our most generalized constraint read $\mnu=0.556^{+0.231}_{-0.288}\rm eV$, $\neff=3.839\pm0.452$, and $w=-1.058\pm0.088$ at 68% confidence level, which shows a firm lower limit on total neutrino mass, favors an extra light degree of freedom, and supports the cosmological constant model. The constraining ability of current weak lensing data is indeed helpful when $w=-1$ yet is of little help once $w$ is freed. The dataset of Hubble parameter gains numerous advantages over supernovae, when $w$ is fixed, particularly its illuminating power in constraining $\neff$. As long as $w$ is included as a free parameter, it is still the standardizable candles of type Ia supernovae that play the most dominant role in the parameter constraints.
The scientific output of Parkes over its fifty year history is briefly reviewed on a year-by-year basis, and placed in context with other national and international events of the time.
The details of the physical process through which high-mass stars form remains nearly as much of a mystery now as it was when the Parkes radio telescope commenced operation. The energy output from high-mass stars influence, or directly drive many important processes in the evolution of galaxies and so understanding in detail when and how they form is important for a broad range of fields of astrophysics. Interstellar masers are one of the most readily observed signposts of regions where young high-mass stars have formed. We have recently made great progress towards using the different maser species and transitions to construct a maser-based evolutionary timeline for high-mass star formation. Here we give an overview of this work, highlighting the particular contribution that past and on-going observations with the Parkes 64m radio telescope have made to this area.
We present a regular cubic lattice solution to Einstein field equations that is exact at second order in a small parameter. We show that this solution is kinematically equivalent to the Friedmann-Lema\^itre-Robertson-Walker (FLRW) solution with the same averaged energy density. This allows us to discuss the fitting problem in that framework: are observables along the past lightcone of observers equivalent to those in the analogue FLRW model obtained by smoothing spatially the distribution of matter? We find a criterion on the compacity of the objects that must be satisfied in order for the answer to this question to be positive and given by perturbative arguments. If this criterion is not met, the answer to this question must be addressed fully non perturbatively along the past lightcone, even though the spacetime geometry can be described perturbatively.
In this paper we consider scalar-tensor theories, allowing for both conformal and disformal couplings to a fluid with a generic equation of state. We derive the effective coupling for both background cosmology and for perturbations in that fluid. As an application we consider the scalar degree of freedom to be coupled to baryons and study the dynamics of the tightly coupled photon-baryon fluid in the early universe. We derive an expression for the effective speed of sound, which differs from its value in General Relativity. We apply our findings to the \mu-distortion of the cosmic microwave background radiation, which depends on the effective sound-speed of the photon-baryon fluid, and show that the predictions differ from General Relativity. Thus, the \mu-distortion provides further information about gravity in the very early universe well before decoupling.
There are very few reports of flare signatures in the solar irradiance at H i Lyman {\alpha} at 121.5 nm, i.e. the strongest line of the solar spectrum. The LYRA radiometer onboard PROBA2 has observed several flares for which unambiguous signatures have been found in its Lyman-{\alpha} channel. Here we present a brief overview of these observations followed by a detailed study of one of them, the M2 flare that occurred on 8 February 2010. For this flare, the flux in the LYRA Lyman-{\alpha} channel increased by 0.6%, which represents about twice the energy radiated in the GOES soft X-ray channel and is comparable with the energy radiated in the He ii line at 30.4 nm. The Lyman-{\alpha} emission represents only a minor part of the total radiated energy of this flare, for which a white-light continuum was detected. Additionally, we found that the Lyman-{\alpha} flare profile follows the gradual phase but peaks before other wavelengths. This M2 flare was very localized and has a very brief impulsive phase, but more statistics are needed to determine if these factors influence the presence of a Lyman-{\alpha} flare signal strong enough to appear in the solar irradiance.
The Large Yield Radiometer (LYRA) is a radiometer that has monitored the solar irradiance at high cadence and in four pass bands since January 2010. Both the instrument and its space- craft, PROBA2 (Project for On-Board Autonomy), have several innovative features for space instrumentation, which makes the data reduction necessary to retrieve the long term variations of solar irradiance more complex than for a fully optimized solar physics mission. In this paper, we describe how we compute the long term time series of the two extreme ultraviolet irradiance channels of LYRA, and compare the results with SDO/EVE. We find that the solar EUV irradi- ance has increased by a factor 2 since the last solar minimum (between solar cycles 23 and 24), which agrees reasonably well with the EVE observations.
By investigating the correlations between dust column density as inferred from infrared data and the observed colours of celestial objects at cosmological distances with small colour dispersion, we constrain the properties of Milky Way dust. Results derived using colours of quasars, brightest central galaxies and large red galaxies are broadly consistent, indicating a proportionality constant between the reddening E(B-V)=A_B-A_V and the dust column density D^T (given in units of MJy/sr) of p=E(B-V)/D^T=0.02 and a reddening parameter R_V=A_V/E(B-V)=3 with fractional uncertainties of the order 10%. The data does not provide any evidence for spatial variations in the dust properties, except for a possible hint of scatter in the dust extinction properties at the longest optical wavelengths.
We consider a model of preheating where the coupling of the inflaton to the preheat field is modulated by an additional scalar field which is light during inflation. We establish that such a model produces the observed curvature perturbation analogously to the modulated reheating scenario. The contribution of modulated preheating to the power spectrum and to non-Gaussianity can however be significantly larger compared to modulated perturbative reheating. We also consider the implications of the current constraints on isocurvature perturbations in case where the modulating field is responsible for cold dark matter. We find that existing bounds on CDM isocurvature perturbations imply that modulated preheating is unlikely to give a dominant contribution to the curvature perturbation and that the same bounds suggest important constraints on non-Gaussianity and the amount of primordial gravitational waves.
We present forecasts for the accuracy of determining the parameters of a minimal cosmological model and the total neutrino mass based on combined mock data for a future Euclid-like galaxy survey and Planck. We consider two different galaxy surveys: a spectroscopic redshift survey and a cosmic shear survey. We make use of the Monte Carlo Markov Chains (MCMC) technique and assume two sets of theoretical errors. The first error is meant to account for uncertainties in the modelling of the effect of neutrinos on the non-linear galaxy power spectrum and we assume this error to be fully correlated in Fourier space. The second error is meant to parametrize the overall residual uncertainties in modelling the non-linear galaxy power spectrum at small scales, and is conservatively assumed to be uncorrelated and to increase with the ratio of a given scale to the scale of non-linearity. It hence increases with wavenumber and decreases with redshift. With these two assumptions for the errors and assuming further conservatively that the uncorrelated error rises above 2% at k = 0.4 h/Mpc and z = 0.5, we find that a future Euclid-like cosmic shear/galaxy survey achieves a 1-sigma error on Mnu close to 32 meV/25 meV, sufficient for detecting the total neutrino mass with good significance. If the residual uncorrelated errors indeed rises rapidly towards smaller scales in the non-linear regime as we have assumed here then the data on non-linear scales does not increase the sensitivity to the total neutrino mass. Assuming instead a ten times smaller theoretical error with the same scale dependence, the error on the total neutrino mass decreases moderately from sigma(Mnu) = 18 meV to 14 meV when mildly non-linear scales with 0.1 h/Mpc < k < 0.6 h/Mpc are included in the analysis of the galaxy survey data.
Until recently our knowledge of the Galactic Bulge stellar populations was based on the study of a few low extinction windows. Large photometric and spectroscopic surveys are now underway to map large areas of the bulge. They probe several complex structures which are still to be fully characterized as well as their links with the inner disc, the thick disc and the inner halo. I will review our current, rapidly increasing, knowledge of the bulge stellar populations and the new insight expected towards the Gaia era to disentangle the formation history of the Galactic inner regions.
A framework is presented for a statistical theory of neutron star glitches, motivated by the results emerging from recent Gross-Pitaevskii simulations of pinned, decelerating quantum condensates. It is shown that the observed glitch size distributions cannot be reproduced if superfluid vortices unpin independently via a Poisson process; the central limit theorem yields a narrow Gaussian for the size distribution, instead of the broad, power-law tail observed. This conclusion is not altered fundamentally when a range of pinning potentials is included, which leads to excavation of the potential distribution of occupied sites, vortex accumulation at strong pinning sites, and hence the occasional, abnormally large glitch. Knock-on processes are therefore needed to make the unpinning rate of a vortex conditional on the pinning state of its near and/or remote neighbours, so that the Gaussian size distributions resulting generically from the central limit theorem are avoided. At least two knock-on processes, nearest- neighbour proximity knock-on and remote acoustic knock-on, are clearly evident in the Gross-Pitaevskii simulation output. It is shown that scale-invariant (i.e. power-law) vortex avalanches occur when knock-on is included, provided that two specific relations hold between the temperature and spin-down torque. This fine tuning is unlikely in an astronomical setting, leaving the overall problem partly unsolved. A state-dependent Poisson formalism is presented which will form the basis of future studies in this area.
While the sources of X-ray and radio emission in the different states of low-mass X-ray binaries are relatively well understood, the origin of the near-infrared (NIR) and optical emission is more often debated. It is likely that the NIR/optical flux originates from an amalgam of different emission regions, because it occurs at the intersecting wavelengths of multiple processes. We aim to identify the NIR/optical emission region(s) of one such low-mass X-ray binary and black hole candidate, XTE J1650-500, via photometric, timing, and spectral analyses. We present unique NIR/optical images and spectra, obtained with the ESO-New Technology Telescope, during the peak of the 2001 outburst of XTE J1650-500. The data suggest that the NIR/optical flux is due to a combination of emission mechanisms including a significant contribution from X-ray reprocessing and, at early times in the hard state, a relativistic jet that is NIR/radio dim compared to similar sources.The jet of XTE J1650-500 is relatively weak compared to that of other black hole low-mass X-ray binaries, possibly because we observe as it is being "turned off" or quenched at the state transition. While there are several outliers to the radio--X-ray correlation of the hard state of low-mass X-ray binaries, XTE J1650-500 is the first example of an outlier to the NIR/optical--X-ray correlation.
We present the results of 12CO(J = 1-0) mapping observations toward four interacting galaxies in early and mid stages of the interaction to understand the behavior of molecular gas in galaxy-galaxy interaction. The observations were carried out using the 45-m telescope at Nobeyama Radio Observatory (NRO). We compared our CO total flux to those previously obtained with single-dish observations and found that there are no discrepancy between them. Applying a typical CO-H2 conversion factor, all constituent galaxies have molecular gas mass more than 10^9 M_sun. Comparisons to HI, Ks and tracers of SF such as Halpha, FUV, 8 um and 24 um revealed that the distribution of molecular gas in interacting galaxies in the early stage of the interaction differs from atomic gas, stars and star-forming regions. These differences are not explained without the result of the interaction. Central concentration of molecular gas of interacting galaxies in the early stage of the interaction is lower than that of isolated galaxies, which suggests molecular gas is distributed off-centre and/or extends in the beginning of the interaction.
The spin state of small asteroids can change on a long timescale by the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect, the net torque that arises from anisotropically scattered sunlight and proper thermal radiation from an irregularly-shaped asteroid. The secular change in the rotation period caused by the YORP effect can be detected by analysis of asteroid photometric lightcurves. We analyzed photometric lightcurves of near-Earth asteroids (1865) Cerberus, (2100) Ra-Shalom, and (3103) Eger with the aim to detect possible deviations from the constant rotation caused by the YORP effect. We carried out new photometric observations of the three asteroids, combined the new lightcurves with archived data, and used the lightcurve inversion method to model the asteroid shape, pole direction, and rotation rate. The YORP effect was modeled as a linear change in the rotation rate in time d\omega /dt. Values of d\omega/ dt derived from observations were compared with the values predicted by theory. We derived physical models for all three asteroids. We had to model Eger as a nonconvex body because the convex model failed to fit the lightcurves observed at high phase angles. We probably detected the acceleration of the rotation rate of Eger d\omega / dt = (1.4 +/- 0.6) x 10^{-8} rad/d (3\sigma error), which corresponds to a decrease in the rotation period by 4.2 ms/yr. The photometry of Cerberus and Ra-Shalom was consistent with a constant-period model, and no secular change in the spin rate was detected. We could only constrain maximum values of |d\omega / dt| < 8 x 10^{-9} rad/d for Cerberus, and |d\omega / dt| < 3 x 10^{-8} rad/d for Ra-Shalom.
Relativistic jets in AGN in general, and in blazars in particular, are the most energetic and among the most powerful astrophysical objects known so far. Their relativistic nature provides them with the ability to emit profusely at all spectral ranges from radio wavelengths to gamma-rays, as well as to vary extremely at time scales from hours to years. Since the birth of gamma-ray astronomy, locating the origin of gamma-ray emission has been a fundamental problem for the knowledge of the emission processes involved. Deep and densely time sampled monitoring programs with the Fermi Gamma-ray Space Telescope and other facilities at most of the available spectral ranges (including millimeter interferometric imaging and polarization measurements wherever possible) are starting to shed light for the case of blazars. After a short review of the status of the problem, we summarize two of our latest results -obtained from the comprehensive monitoring data compiled by the Boston University Blazar monitoring program - that locate the GeV flaring emission of the BL Lac objects AO 0235+164 and OJ287 within the jets of these blazars, at >12 parsecs from the central AGN engine.
We analyze whether there is any residual foreground contamination in the cleaned WMAP 7 years data for the differential assemblies, Q, V and W. We calculate the correlation between the foreground map, from which long wavelength correlations have been subtracted, and the foreground reduced map for each differential assembly after applying the Galaxy and point sources masks. We find positive correlations for all the differential assemblies, with high statistical significance. For Q and V, we find that a large fraction of the contamination comes from pixels where the foreground maps have positive values larger than three times the rms values. These findings imply the presence of residual contamination from Galactic emissions and unresolved point sources. We redo the analysis after masking the extended point sources cataloque of Scodeller et al. [7] and find a drop in the correlation and corresponding significance values. To quantify the effect of the residual contamination on the search for primordial non-Gaussianity in the CMB we add estimated contaminant fraction to simulated Gaussian CMB maps and calculate the characteristic non-Gaussian deviation shapes of Minkowski Functionals that arise due to the contamination. We find remarkable agreement of these deviation shapes with those measured from WMAP data, which imply that a major fraction of the observed non-Gaussian deviation comes from residual foreground contamination. We also compute non-Gaussian deviations of Minkowski Functionals after applying the point sources mask of Scodeller et al. and find a decrease in the overall amplitudes of the deviations which is consistent with a decrease in the level of contamination.
Seven of ten candidate H-alpha emission-line stars found in an objective grism survey of a 1 square degree region in MBM 18, were observed spectroscopically. Four of these have weak H-alpha emission, and 6 out of 7 have spectral types M1-M4V. One star is of type F7-G1V, and has H-alpha in absorption. The spectra of three of the M-stars may show an absorption line of LiI, although none of these is an unambiguous detection. For the six M-stars a good fit is obtained with pre-main-sequence isochrones indicating ages between 7.5 and 15Myr. The molecular cloud mass, derived from the integrated 12CO(1-0) emission, is 160Mo (for a distance of 120pc), much smaller than the virial mass (10^3Mo), and the cloud is not gravitationally bound. Nor are the individual clumps we identified through a clump-finding routine. Considering the relative weakness or absence of the H-alpha emission, the absence of other emission lines, and the lack of clear LiI absorption, the targets are not T Tauri stars. With ages between 7.5 and 15Myr they are old enough to explain the lack of lithium in their spectra. Based on the derived distances (60-250pc), some of the stars may lie inside the molecular cloud (120-150pc). From the fact that the cloud as a whole, as well as the individual clumps, are not gravitationally bound, in combination with the ages of the stars we conclude that it is not likely that (these) stars were formed in MBM 18.
The Richardson-Lucy method is the most popular deconvolution method in astronomy because it preserves the number of counts and the non-negativity of the original object. Regularization is, in general, obtained by an early stopping of Richardson-Lucy iterations. In the case of point-wise objects such as binaries or open star clusters, iterations can be pushed to convergence. However, it is well-known that Richardson-Lucy is an inefficient method. In most cases, acceptable solutions are obtained at the cost of hundreds or thousands of iterations. A general optimization method, referred to as the scaled gradient projection method, has been proposed for the constrained minimization of continuously differentiable convex functions. It is applicable to the non-negative minimization of the Kullback-Leibler divergence. If the scaling suggested by Richardson-Lucy is used in this method, then it provides a considerable increase in the efficiency of Richardson-Lucy. Therefore the aim of this paper is to apply the scaled gradient projection method to a number of imaging problems in astronomy such as single image deconvolution, multiple image deconvolution, and boundary effect correction. The corresponding algorithms are derived and implemented in interactive data language. To attempt to achieve a further increase in efficiency, we also consider an implementation on graphic processing units. The proposed algorithms are tested on simulated images. The acceleration of scaled gradient projection methods achieved with respect to the corresponding Richardson-Lucy methods strongly depends on both the problem and the specific object to be reconstructed, and in our simulations the improvement achieved ranges from about a factor of 4 to more than 30. Moreover, significant accelerations of up to two orders of magnitude have been observed between the serial and parallel implementations of the algorithms.
The theory of massive star formation currently suffers from a scarce observational base of massive young stellar objects to compare with. In this paper, we present OVRO CO(1-0), 13CO(1-0), C18O(1-0), and 2.6 mm continuum images of the infrared source IRAS 19520+2759 together with complementary single-dish observations of CS(1-0), obtained with the 34m antenna DSS-54 at the Madrid Deep Space Communications Complex, as well as archive images at different wavelengths. As a result from our work, IRAS 19520+2759, with a controversial nature in the past, is firmly established as a massive young stellar object associated with a strong and compact millimetre source and driving a collimated outflow. In addition, a second fainter millimetre source is discovered about 4 arcsec to the south, which is also driving an outflow. Furthermore, the two millimetre sources are associated with C18O clumps elongated perpendicularly to the outflows, which may be related to rotating toroids. The masses of gas and dust of the millimetre sources are estimated to be around 100 and 50 Msun. MM1, the dominant source at all wavelengths, with a total luminosity of (1-2)x10^5 Lsun at 9 kpc, is however not associated with 6 cm emission down to a rms noise level of 0.1 mJy. We propose that IRAS 19520+2759 could be an example of the recent theoretical prediction of `bloated' or `swollen' star, i.e., a massive young stellar object whose radius has increased due to effects of accretion at a high-mass accretion rate.
BL Lacertae is the prototype of the BL Lac class of active galactic nuclei, exhibiting intensive activity on parsec (pc) scales, such as intense core variability and multiple ejections of jet components. In particular, in previous works the existence of precession motions in the pc-scale jet of BL Lacertae has been suggested. In this work we revisit this issue, investigating temporal changes of the observed right ascension and declination offsets of the jet knots in terms of our relativistic jet-precession model. The seven free parameters of our precession model were optimized via a heuristic cross-entropy method, comparing the projected precession helix with the positions of the jet components on the plane of the sky and imposing constraints on their maximum and minimum superluminal velocities. Our optimized best model is compatible with a jet having a bulk velocity of 0.9824c, which is precessing with a period of about 12.1 yr in the observer's reference frame and changing its orientation in relation to the line of sight between 4 and 5 degrees, approximately. Assuming that the jet precession has its origin in a supermassive binary black hole system, we show that the 2.3-yr periodic variation in the structural position angle of the very-long-baseline interferometry (VLBI) core of BL Lacertae reported by Stirling et al. is compatible with a nutation phenomenon if the secondary black hole has a mass higher than about six times that of the primary black hole.
We are conducting a study on the imprint of the ISM on optical spectra based on two types of ongoing spectroscopic massive-star surveys: on the one hand, intermediate-resolution (R = 2500) green-blue spectra for ~3000 stars obtained with the Galactic O Star Spectroscopic Survey (GOSSS). On the other hand, high-resolution (R = 23 000 - 65 000) optical spectra for 600 stars obtained from three different surveys, OWN, IACOB, and NoMaDS. The R = 2500 data allows us to reach a larger sample with an average larger extinction while the R = 23 000 - 65 000 sample provides access to more diffuse interstellar bands (DIBs) and allows for the resolution in velocity of some ISM features. For each spectrum we are measuring the equivalent widths, FWHMs, and central wavelengths of 10-40 DIBs and interstellar lines (e.g. Ca II H+K, Na I D1+D2) and, in the case of GOSSS, the existence of an H II region around the star. We have also derived from auxiliary data or compiled from the literature values for the reddening, extinction law, H I column density, parallax, and H alpha emission. All of this constitutes the most complete collection ever of optical information on the ISM within 3 kpc of the Sun. We are analyzing the correlations between all of the collected quantities to discriminate between different possible origins of the DIBs.
The Differential Emission Measure (DEM) analysis is one of the most used
diagnostic tools for solar and stellar coronae. Being an inverse problem, it
has limitations due to the presence of random and systematic errors. We present
in theses series of papers an analysis of the robustness of the inversion in
the case of AIA/SDO observations. We completely characterize the DEM inversion
and its statistical properties, providing all the solutions consistent with the
data along with their associated probabilities, and a test of the suitability
of the assumed DEM model.
While Paper I focused on isothermal conditions, we now consider multi-thermal
plasmas and investigate both isothermal and multithermal solutions. We
demonstrate how the ambiguity between noises and multi-thermality fundamentally
limits the temperature resolution of the inversion. We show that if the
observed plasma is multi-thermal, isothermal solutions tend to cluster on a
constant temperature whatever the number of passbands or spectral lines. The
multi-thermal solutions are also found to be biased toward near isothermal
solutions around 1 MK. This is true even if the residuals support the chosen
DEM model, possibly leading to erroneous conclusions on the observed plasma. We
propose tools to identify and quantify the possible degeneracy of solutions,
thus helping the interpretation of DEM inversion.
DEM analysis is a major diagnostic tool for stellar atmospheres. But both its
derivation and its interpretation are notably difficult because of random and
systematic errors, and the inverse nature of the problem. We use simulations
with simple thermal distributions to investigate the inversion properties of
SDO/AIA observations of the solar corona. This allows a systematic exploration
of the parameter space and using a statistical approach, the respective
probabilities of all the DEMs compatible with the uncertainties can be
computed. Following this methodology, several important properties of the DEM
inversion, including new limitations, can be derived and presented in a very
synthetic fashion.
In this first paper, we describe the formalism and we focus on isothermal
plasmas, as building blocks to understand the more complex DEMs studied in the
second paper. The behavior of the inversion of AIA data being thus quantified,
and we provide new tools to properly interpret the DEM. We quantify the
improvement of the isothermal inversion with 6 AIA bands compared to previous
EUV imagers. The maximum temperature resolution of AIA is found to be 0.03 log
Te, and we derive a rigorous test to quantify the compatibility of observations
with the isothermal hypothesis. However we demonstrate limitations in the
ability of AIA alone to distinguish different physical conditions.
The majority of stars reside in multiple systems, especially binaries. The formation and early evolution of binaries is a longstanding problem in star formation that is not fully understood. In particular, how the magnetic field observed in star-forming cores shapes the binary characteristics remains relatively unexplored. We demonstrate numerically, using the ENZO-MHD code, that a magnetic field of the observed strength can drastically change two of the basic quantities of a binary system: the orbital separation and mass ratio of the two components. Our calculations focus on the protostellar mass accretion phase, after a pair of stellar 'seeds' have already formed. We find that, in dense cores magnetized to a realistic level, the angular momentum of the gas accreted by the protobinary is greatly reduced by magnetic braking. Accretion of strongly braked material shrinks the protobinary separation by a large factor compared to the non-magnetic case. The magnetic braking also changes the evolution of the mass ratio of unequal-mass protobinaries by producing gas of low specific angular momentum that accretes preferentially onto the primary rather than the secondary. This is in contrast with the preferential mass accretion onto the secondary previously found for protobinaries accreting from an unmagnetized envelope, which tends to drive the mass ratio towards unity. In addition, the magnetic field greatly modifies the morphology and dynamics of the protobinary accretion flow. It suppresses the circumstellar and circumbinary disks that feed the protobinary in the non-magnetic case; the binary is fed instead by a fast collapsing pseudodisk whose rotation is strongly braked. The magnetic braking-driven inward migration of binaries from their birth locations may be constrained by high-resolution observations of the orbital distribution of deeply embedded protobinaries, especially with ALMA.
We use analytical examples and asymptotic forms to examine the mathematical structure and physical meaning of the seismic cross correlation measurement. We show that in general, cross correlations are not Green's functions of medium, and may be very different depending on the source distribution. The modeling of noise sources using spatial distributions as opposed to discrete collections of sources is emphasized. When stations are illuminated by spatially complex source distributions, cross correlations show arrivals at a variety of time lags, from zero to the maximum surface-wave arrival time. Here, we demonstrate the possibility of inverting for the source distribution using the energy of the full cross-correlation waveform. The interplay between the source distribution and wave attenuation in determining the functional dependence of cross correlation energies on station-pair distance is quantified. Without question, energies contain information about wave attenuation. However, the accurate interpretation of such measurements is tightly connected to the knowledge of the source distribution.
The dust cannot survive closer to the star from the point where a grain reaches a temperature equal to the sublimation temperature. The boundary between a dust-free and a dusty region defines the sublimation wall. In the literature two models for the structure of the wall are used: a wall with a fixed sublimation temperature and a wall with a density-dependent sublimation temperature. In the former, the wall is vertical and in the latter, the wall is curved. We find important differences between these models SEDs in the wavelength range from 3 to 8\mu m, being the emission of the former larger than that of the latter model. We quantify the differences in IRAC colors when these models are used to explain the observations. In the IRAC color-color diagram ([3.6]-[4.5] vs. [5.8]-[8.0]), the models are located in specific regions, either depending on the inclination, the mass accretion rate, or which model is used.
The velocity distribution function (VDF) of the hypothetical Weakly Interacting Massive Particles (WIMPs), currently the most favored candidate for the Dark Matter (DM) in the Galaxy, is determined directly from the rotation curve data of the Galaxy assuming isotropic VDF. This is done by "inverting" --- using Eddington's method --- the Navarro-Frenk-White universal density profile of the DM halo of the Galaxy, the parameters of which are determined, by using Markov Chain Monte Carlo (MCMC) technique, from a recently compiled set of observational data on the Galaxy's rotation curve extended to distances well beyond the visible edge of the disk of the Galaxy. The derived most-likely local isotropic VDF strongly differs from the Maxwellian form assumed in the "Standard Halo Model" (SHM) customarily used in the analysis of the results of WIMP direct-detection experiments. A parametrized (non-Maxwellian) form of the derived most-likely local VDF is given. The astrophysical "g-factor" that determines the effect of the WIMP VDF on the expected event rate in a direct-detection experiment can be lower for the most-likely VDF than that for the closest Maxwellian VDF by as much two orders of magnitude at the lowest WIMP mass threshold of a typical experiment.
We present three newly discovered sub-Jupiter mass planets from the SuperWASP survey: WASP-54b is a heavily bloated planet of mass 0.636$^{+0.025}_{-0.024}$ \mj and radius 1.653$^{+0.090}_{-0.083}$ \rj. It orbits a F9 star, evolving off the main sequence, every 3.69 days. Our MCMC fit of the system yields a slightly eccentric orbit ($e=0.067^{+0.033}_{-0.025}$) for WASP-54b. We investigated further the veracity of our detection of the eccentric orbit for WASP-54b, and we find that it could be real. However, given the brightness of WASP-54 V=10.42 magnitudes, we encourage observations of a secondary eclipse to draw robust conclusions on both the orbital eccentricity and the thermal structure of the planet. WASP-56b and WASP-57b have masses of 0.571$^{+0.034}_{-0.035}$ \mj and $0.672^{+0.049}_{-0.046}$ \mj, respectively; and radii of $1.092^{+0.035}_{-0.033}$ \rj for WASP-56b and $0.916^{+0.017}_{-0.014}$ \rj for WASP-57b. They orbit main sequence stars of spectral type G6 every 4.67 and 2.84 days, respectively. WASP-56b and WASP-57b show no radius anomaly and a high density possibly implying a large core of heavy elements; possibly as high as $\sim$50 M$_{\oplus}$ in the case of WASP-57b. However, the composition of the deep interior of exoplanets remain still undetermined. Thus, more exoplanet discoveries such as the ones presented in this paper, are needed to understand and constrain giant planets' physical properties.
Vorticity is ubiquitous in nature however, to date, studies of vorticity in cosmology and the early universe have been quite rare. In this paper, based on a talk in session CM1 of the 13th Marcel Grossmann Meeting, we consider vorticity generation from scalar cosmological perturbations of a perfect fluid system. We show that, at second order in perturbation theory, vorticity is sourced by a coupling between energy density and entropy gradients, thus extending a well-known feature of classical fluid dynamics to a relativistic cosmological framework. This induced vorticity, sourced by isocurvature perturbations, may prove useful in the future as an additional discriminator between inflationary models.
We present an analytical model of the relation between the surface density of gas and star formation rate in galaxies and clouds, as a function of the presence of supersonic turbulence and the associated structure of the interstellar medium. The model predicts a power-law relation of index 3/2, flattened under the effects of stellar feedback at high densities or in very turbulent media, and a break at low surface densities when ISM turbulence becomes too weak to induce strong compression. This model explains the diversity of star formation laws and thresholds observed in nearby spirals and their resolved regions, the Small Magellanic Cloud, high-redshift disks and starbursting mergers, as well as Galactic molecular clouds. While other models have proposed interstellar dust content and molecule formation to be key ingredients to the observed variations of the star formation efficiency, we demonstrate instead that these variations can be explained by interstellar medium turbulence and structure in various types of galaxies.
LOFT, the large observatory for X-ray timing, was selected by the European Space Agency (ESA) in February 2011 as one of four medium size mission concepts for the Cosmic Vision program that will compete for a launch opportunity in the early 2020s. LOFT will carry out high-time resolution (10 {\mu}s) and spectroscopic observations (<260 eV) of compact objects in the X-ray band (2-80 keV), with unprecedented throughput, thanks to its 10 m^2 effective area. LOFT will address the fundamental questions of the Cosmic Vision Theme "Matter under extreme conditions": What is the fundamental equation of state of a compact object? Does matter orbiting close to the event horizon follow the predictions of general relativity?
The infrared (IR) emission of M_* galaxies (10^{10.4} < M_{star} < 10^{11.0} M_\sun) in galaxy pairs, derived using data obtained in Herschel (PEP/HerMES) and Spitzer (S-COSMOS) surveys, is compared to that of single disk galaxies in well matched control samples to study the cosmic evolution of the star-formation enhancement induced by galaxy-galaxy interaction. Both the mean IR SED and mean IR luminosity of star-forming galaxies (SFGs) in SFG+SFG (S+S) pairs in the redshift bin of 0.6 < z < 1 are consistent with no star-formation enhancement. SFGs in S+S pairs in a lower redshift bin of 0.2 < z < 0.6 show marginal evidence for a weak star-formation enhancement. Together with the significant and strong sSFR enhancement shown by SFGs in a local sample of S+S pairs (obtained using previously published Spitzer observations), our results reveal a trend for the star-formation enhancement in S+S pairs to decrease with increasing redshift. Between z=0 and z=1, this decline of interaction-induced star-formation enhancement occurs in parallel with the dramatic increase (by a factor of ~10) of the sSFR of single SFGs, both can be explained by the higher gas fraction in higher z disks. SFGs in mixed pairs (S+E pairs) do not show any significant star-formation enhancement at any redshift. The difference between SFGs in S+S pairs and in S+E pairs suggests a modulation of the sSFR by the inter-galactic medium IGM in the dark matter halos (DMH) hosting these pairs.
We demonstrate that accurate and precise cosmological information can be extracted from the cell count analysis of the 3D spatial clustering of galaxies once the second-order ratio between one- and two-point moments of the smoothed galaxy density distribution is analyzed. This probe does not require the calibration of any standard rod, the knowledge of the galaxy bias nor the modeling of galaxy redshift distortions. Using the spectroscopic Sloan Digital Sky Survey (SDSS) data release 7 (DR7) galaxy sample, no cosmic microwave background (CMB) information, weak (flat) priors on the value of the curvature of the universe (Omega_k) and the constant value of the dark energy equation of state (w), we estimate the abundance of matter (Omega_m) with a relative error of 11% (at 68% c.l.). The method may be instrumental in searching for evidences of new physics beyond the standard model of cosmology and in planning future missions such as BigBOSS or EUCLID.
Observable consequences of the hypothesis that the observed universe is a numerical simulation performed on a cubic space-time lattice or grid are explored. The simulation scenario is first motivated by extrapolating current trends in computational resource requirements for lattice QCD into the future. Using the historical development of lattice gauge theory technology as a guide, we assume that our universe is an early numerical simulation with unimproved Wilson fermion discretization and investigate potentially-observable consequences. Among the observables that are considered are the muon g-2 and the current differences between determinations of alpha, but the most stringent bound on the inverse lattice spacing of the universe, b^(-1) >~ 10^(11) GeV, is derived from the high-energy cut off of the cosmic ray spectrum. The numerical simulation scenario could reveal itself in the distributions of the highest energy cosmic rays exhibiting a degree of rotational symmetry breaking that reflects the structure of the underlying lattice.
We study the multifield inflationary models where the cosmological perturbation is sourced by light scalar fields other than the inflaton. We exploit the operator product expansion and partly the symmetries present during the de Sitter epoch to characterize the non-Gaussian four-point correlator in the squeezed limit. We point out that the contribution to it from the intrinsic non-Gaussianity of the light fields at horizon crossing can be larger than the usually studied contribution arising on superhorizon scales and it comes with a different shape. Our findings indicate that particular attention needs to be taken when studying the effects of the primordial NG on real observables, such as the clustering of dark matter halos.
If two particles collide near the black hole horizon, the energy in the centre of mass (CM) frame can grow indefinitely (the so-called the BSW effect). This requires fine-tuning the parameters (the energy, angular momentum or electric charge) of one particle. We show that the CM energy can be unbound also for collisions in the space-time of quasiblack holes - QBHs (the objects on the threshold of forming the horizon which do not collapse). It does not require special fine-tuning of parameters and occurs when any particle inside a QBH having a finite energy collides with the particle that entered a QBH from the outside region.
We studied the Fermi and Gamow-Teller responses of cold symmetric nuclear matter within a unified dynamical model, suitable to account for both short- and long-range correlation effects. The formalism of correlated basis functions has been used to construct two-body effective interactions and one-body effective weak operators. The inclusion of the three-body cluster term allowed for incorporating in the effective interaction a realistic model of three- nucleon forces, namely the UIX potential. Moreover, the sizable unphysical dependence of the effective weak operator is removed once the three-body cluster term is taken into account.
Continuous sequences of asymptotically flat solutions to the Einstein-Maxwell equations describing regular equilibrium configurations of ordinary matter can reach a black hole limit. For a distant observer, the spacetime becomes more and more indistinguishable from the metric of an extreme Kerr-Newman black hole outside the horizon when approaching the limit. From an internal perspective, a still regular but non-asymptotically flat spacetime with the extreme Kerr-Newman near-horizon geometry at spatial infinity forms at the limit. Interesting special cases are sequences of Papapetrou-Majumdar distributions of electrically counterpoised dust leading to extreme Reissner-Nordstrom black holes and sequences of rotating uncharged fluid bodies leading to extreme Kerr black holes.
Compact objects, like neutron stars and white dwarfs, may accrete dark matter, and then be sensitive probes of its presence. These compact stars with a dark matter component can be modeled by a perfect fluid minimally coupled to a complex scalar field (representing a bosonic dark matter component), resulting in objects known as fermion-boson stars. We have performed the dynamical evolution of these stars in order to analyze their stability, and to study their spectrum of normal modes, which may reveal the amount of dark matter in the system. Their stability analysis shows a structure similar to that of an isolated (fermion or boson) star, with equilibrium configurations either laying on the stable or on the unstable branch. The analysis of the spectrum of normal modes indicates the presence of new oscillation modes in the fermionic part of the star, which result from the coupling to the bosonic component through the gravity.
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We investigate the shape of the extinction law in two 1-degree square fields of the Perseus Molecular Cloud complex. We combine deep red-optical (r, i, and z-band) observations obtained using Megacam on the MMT with UKIDSS near-infrared (J, H, and K-band) data to measure the colours of background stars. We develop a new hierarchical Bayesian statistical model, including measurement error, intrinsic colour variation, spectral type, and dust reddening, to simultaneously infer parameters for individual stars and characteristics of the population. We implement an efficient MCMC algorithm utilising generalised Gibbs sampling to compute coherent probabilistic inferences. We find a strong correlation between the extinction (Av) and the slope of the extinction law (parameterized by Rv). Because the majority of the extinction toward our stars comes from the Perseus molecular cloud, we interpret this correlation as evidence of grain growth at moderate optical depths. The extinction law changes from the diffuse value of Rv = 3 to the dense cloud value of Rv = 5 as the column density rises from Av = 2 mags to Av = 10 mags. This relationship is similar for the two regions in our study, despite their different physical conditions, suggesting that dust grain growth is a fairly universal process.
Dark matter haloes from cosmological N-body simulations typically have triaxial shapes and anisotropic velocity distributions. Recently it has been shown that the velocity anisotropy, beta, of cosmological haloes and major merger remnants depends on direction in such a way that beta is largest along the major axis and smallest along the minor axis. In this work we use a wide range of non-cosmological N-body simulations to examine halo shapes and direction-dependence of velocity anisotropy profiles. For each of our simulated haloes we define 48 cones pointing in different directions, and from the particles inside each cone we compute velocity anisotropy profiles. We find that elongated haloes can have very distinct velocity anisotropies. We group the behaviour of haloes into three different categories, that range from spherically symmetric profiles to a much more complex behaviour, where significant differences are found for beta along the major and minor axes. We encourage future studies of velocity anisotropies in haloes from cosmological simulations to calculate beta-profiles in cones, since it reveals information, which is hidden from a spherically averaged profile. Finally, we show that spherically averaged profiles often obey a linear relation between beta and the logarithmic density slope in the inner parts of haloes, but this relation is not necessarily obeyed, when properties are calculated in cones.
We investigate the contribution of star-forming galaxies to the ionizing background at z~3, building on previous work based on narrowband (NB3640) imaging in the SSA22a field. We use new Keck/LRIS spectra of Lyman break galaxies (LBGs) and narrowband-selected Lya emitters (LAEs) to measure redshifts for 16 LBGs and 87 LAEs at z>3.055, such that our NB3640 imaging probes the Lyman-continuum (LyC) region. When we include the existing set of spectroscopically-confirmed LBGs, our total sample with z>3.055 consists of 41 LBGs and 91 LAEs, of which nine LBGs and 20 LAEs are detected in our NB3640 image. With our combined imaging and spectroscopic data sets, we critically investigate the origin of NB3640 emission for detected LBGs and LAEs. We remove from our samples 3 LBGs and 3 LAEs with spectroscopic evidence of contamination of their NB3640 flux by foreground galaxies, and statistically model the effects of additional, unidentified foreground contaminants. The resulting contamination and LyC-detection rates, respectively, are 62 +/-13% and 8 +/-3% for our LBG sample, and 47 +/-10% and 12 +/-2% for our LAE sample. The corresponding ratios of non-ionizing UV to LyC flux-density, corrected for intergalactic medium (IGM) attenuation, are 18.0 +34.8/-7.4 for LBGs, and 3.7 +2.5/-1.1 for LAEs. We use these ratios to estimate the total contribution of star-forming galaxies to the ionizing background and the hydrogen photoionization rate in the IGM, finding values larger than, but consistent with, those measured in the Lya forest. Finally, the measured UV to LyC flux-density ratios imply model-dependent LyC escape fractions of f_{esc}^{LyC} ~ 5-7% for our LBG sample and f_{esc}^{LyC} ~ 10-30% for our fainter LAE sample.
Pulsar timing arrays (PTAs) might detect gravitational waves (GWs) from massive black hole (MBH) binaries within this decade. The signal is expected to be an incoherent superposition of several nearly-monochromatic waves of different strength. The brightest sources might be individually resolved, and the overall deconvolved, at least partially, in its individual components. In this paper we extend the maximum-likelihood based method developed in Babak & Sesana 2012, to search for individual MBH binaries in PTA data. We model the signal as a collection of circular monochromatic binaries, each characterized by three free parameters: two angles defining the sky location, and the frequency. We marginalize over all other source parameters and we apply an efficient multi-search genetic algorithm to maximize the likelihood function and look for sources in synthetic datasets. On datasets characterized by white Gaussian noise plus few injected sources with signal-to-noise ratio (SNR) in the range 10-60, our search algorithm performs well, recovering all the injections with no false positives. Individual source SNRs are estimated within few % of the injected values, sky locations are recovered within few degrees, and frequencies are determined with sub-Fourier bin precision.
We present velocity-resolved reverberation results for five active galactic nuclei. We recovered velocity-delay maps using the maximum-entropy method for four objects: Mrk 335, Mrk 1501, 3C120, and PG2130+099. For the fifth, Mrk 6, we were only able to measure mean time delays in different velocity bins of the H\beta\ emission line, but see tentative evidence of combined virial motion and infalling gas. The four velocity-delay maps show unique dynamical signatures for each object. For 3C120, the Balmer lines show kinematic signatures consistent with both an inclined disk and infalling gas, but the HeII 4686 emission line is suggestive only of inflow. The Balmer lines in Mrk 335, Mrk 1501, and PG 2130+099 show signs of infalling gas, but the HeII emission in Mrk 335 is consistent with an inclined disk. The maps for 3C120 and Mrk 335 are two of the most clearly defined velocity-delay maps to date. These maps constitute a large increase in the number of objects for which we have resolved velocity-delay maps and provide evidence supporting the reliability of reverberation-based black hole mass measurements.
We present the results of our systematic search for extended emission components following initial short gamma-ray burst (GRB) spikes, using Burst and Transient Source Experiment (BATSE) observations. We performed the extended emission search for both short- and long-duration GRBs to unveil the BATSE population of new hybrid class of GRBs similar to GRB 060614. For the identified bursts, we investigate temporal and spectral characteristics of their initial spikes as well as their extended emission. Our results reveal that the fraction of GRBs with extended emission is ~7% of the total number of our BATSE sample. We find that the spectrum of the extended emission is, in general, softer than that of the initial spike, which is in accord with what has been observed in the prototypical bursts, GRB 060614. We also find that the energy fluence of the extended emission varies on a broad range from 0.1 to 40 times of the fluence of the initial spike. We discuss our results in the context of existing physical models, in particular within the two-component jet model.
Recent measurements by the ARCADE2 experiment unambiguously show an excess in the isotropic radio background at frequencies below the GHz scale. We argue that this excess may be a natural consequence of the interaction of visible and dark matter in the early universe if the dark matter consists of heavy nuggets of quark matter. Explanation of the observed radio band excess requires the introduction of no new parameters, rather we exploit the same dark matter model and identical normalization parameters to those previously used to explain other excesses of diffuse emission from the centre of our galaxy. These previously observed excesses include the WMAP Haze of GHz radiation, keV X -ray emission and MeV gamma-ray radiation.
This paper describes a new catalog that supplements the existing DEEP2 Galaxy Redshift Survey photometric and spectroscopic catalogs with ugriz photometry from two other surveys; the Canada-France-Hawaii Legacy Survey (CFHTLS) and the Sloan Digital Sky Survey (SDSS). Each catalog is cross-matched by position on the sky in order to assign ugriz photometry to objects in the DEEP2 catalogs. We have recalibrated the CFHTLS photometry where it overlaps DEEP2 in order to provide a more uniform dataset. We have also used this improved photometry to predict DEEP2 BRI photometry in regions where only poorer measurements were available previously. In addition, we have included improved astrometry tied to SDSS rather than USNO-A2.0 for all DEEP2 objects. In total this catalog contains ~27,000 objects with full ugriz photometry as well as robust spectroscopic redshift measurements, 64% of which have r > 23. By combining the secure and accurate redshifts of the DEEP2 Galaxy Redshift Survey with ugriz photometry, we have created a catalog that can be used as an excellent testbed for future photo-z studies, including tests of algorithms for surveys such as LSST and DES.
This work describes a new instrument optimized for a detection of the neutral hydrogen 21cm power spectrum between redshifts of 0.5-1.5: the Baryon Acoustic Oscillation Broadband and Broad-beam (BAOBAB) Array. BAOBAB will build on the efforts of a first generation of 21cm experiments which are targeting a detection of the signal from the Epoch of Reionization at z ~ 10. At z ~ 1, the emission from neutral hydrogen in self-shielded overdense halos also presents an accessible signal, since the dominant, synchrotron foreground emission is considerably fainter than at redshift 10. The principle science driver for these observations are Baryon Acoustic Oscillations in the matter power spectrum which have the potential to act as a standard ruler and constrain the nature of dark energy. BAOBAB will fully correlate dual-polarization antenna tiles over the 600-900MHz band with a frequency resolution of 300 kHz and a system temperature of 50K. The number of antennas will grow in staged deployments, and reconfigurations of the array will allow for both traditional imaging and high power spectrum sensitivity operations. We present calculations of the power spectrum sensitivity for various array sizes, with a 35-element array measuring the cosmic neutral hydrogen fraction as a function of redshift, and a 132-element system detecting the BAO features in the power spectrum, yielding a 1.8% error on the z ~ 1 distance scale, and, in turn, significant improvements to constraints on the dark energy equation of state over an unprecedented range of redshifts from ~0.5-1.5.
The Planck-ATCA Co-eval Observations (PACO) have provided multi-frequency (5-40 GHz) flux density measurements of complete samples of Australia Telescope 20 GHz (AT20G) radio sources at frequencies below and overlapping with Planck frequency bands, almost simultaneously with Planck observations. In this work we analyse the data in total intensity for the spectrally-selected PACO sample, a complete sample of 69 sources brighter than 200 mJy at 20 GHz selected from the AT20G survey catalogue to be inverted or upturning between 5 and 20 GHz. We study the spectral behaviour and variability of the sample. We use the variability between AT20G (2004-2007) and PACO (2009-2010) epochs to discriminate between candidate High Frequency Peakers (HFPs) and candidate blazars. The HFPs picked up by our selection criteria have spectral peaks > 10 GHz in the observer frame and turn out to be rare (<0.5% of the S >200 mJy sources), consistent with the short duration of this phase implied by the `youth' scenario. Most (~ 89 %) of blazar candidates have remarkably smooth spectra, well described by a double power-law, suggesting that the emission in the PACO frequency range is dominated by a single emitting region. Sources with peaked PACO spectra show a decrease of the peak frequency with time at a mean rate of -3 +- 2 GHz/yr on an average timescale of \tau = 2.1 +- 0.5 yr. The 5-20 GHz spectral indices show a systematic decrease from AT20G to PACO observations. At higher frequencies spectral indices steepen: the median \alpha 30-40 GHz is steeper than the median \alpha 5-20 GHz by \delta\alpha = 0.6. Taking further into account the WISE data we find that the SEDs, \nu S(\nu), of most of our blazars peak at \nu_p <10^5 GHz; the median peak wavelength is \lambda_p ~93 \mu m. Only 6 have \nu_p>10^5 GHz.
We report the result of a new Chandra observation of the black hole X-ray transient H 1705-250 in quiescence. H 1705-250 was barely detected in the new 50 ks Chandra observation. With 5 detected counts, we estimate the source quiescent luminosity to be Lx~9.1e30 erg/s in the 0.5-10 keV band (adopting a distance of 8.6 kpc). This value is in line with the quiescent luminosities found among other black hole X-ray binaries with similar orbital periods. By using images taken with the Faulkes Telescope North, we derive a refined position of H 1705-250. We also present the long-term lightcurve of the optical counterpart from 2006 to 2012, and show evidence for variability in quiescence.
We produce catalogues of voids for SDSS DR7 redshift survey and for a Millennium I simulation mock data. The mock catalog is constructed such that it closely represents SDSS DR7 survey. We carry a parallel analysis of the two catalogues and find that in both the observation and the simulation, voids tend to be equally spherical. The total volume occupied by the voids and their total number are slightly larger in the simulation than in the observation. We find that large voids are less abundant in the simulation and the total luminosity of the galaxies contained in a void with a given radius is on average higher than observed by SDSS DR7 survey. We expect these discrepancies to be, in fact, even more important than found here since the present value of $\sigma_8$ given by WMAP7 is lower than the value of 0.9 used in the Millennium I simulation. The reason why the simulation fails to produce enough of the large and dark voids could be due to the failure of certain semi-analytic models of galaxy formation in reducing the small-scale power of $\Lambda$CDM and in producing sufficient power on large scales.
Since it was theorized by Kerr in 1963, determining the spin of black holes from observed data was paid very little attention until few years back. The main reasons behind this were the unavailability of adequate data and the lack of appropriate techniques. In this article, we explore determining/predicting the spin of several black holes in X-ray binaries and in the center of galaxies, using X-ray and gamma-ray satellite data. For X-ray binaries, in order to explain observed quasi-periodic oscillations, our model predicts the spin parameter of underlying black holes. On the other hand, the nature of spin parameters of black holes in BL Lacs and Flat Spectrum Radio Quasars is predicted by studying the total luminosities of systems based on Fermi gamma-ray data. All sources considered here exhibit characteristics of spinning black holes, which verifies natural existence of the Kerr metric.
We present an extensive, long-slit, high-resolution coverage of the complex planetary nebula (PN), NGC 7026. We acquired ten spectra using the Manchester Echelle Spectrometer at San Pedro Martir Observatory in Baja California, Mexico, and each shows exquisite detail, revealing the intricate structure of this object. Incorporating these spectra into the 3-dimensional visualization and kinematic program, SHAPE, and using HST images of NGC 7026, we have produced a detailed structural and kinematic model of this PN. NGC 7026 exhibits remarkable symmetry consisting of three lobe-pairs and four sets of knots, all symmetrical about the nucleus and displaying a conical outflow. Comparing the 3-D structure of this nebula to recent, XMM-Newton X-ray observations, we investigate the extended X-ray emission in relation to the nebular structure. We find that the X-ray emission, while confined to the closed, northern lobes of this PN, shows an abrupt termination in the middle of the SE lobe, which our long slit data shows to be open. This is where the shocked, fast wind seems to be escaping the interior of the nebula and the X-ray emission rapidly cools in this region.
The upcoming new generation of spectroscopic galaxy redshift surveys will provide large samples of cosmic voids, the distinct, large underdense structures in the universe. Combining these with future galaxy imaging surveys, we study the prospects of probing the underlying matter distribution in and around cosmic voids via the weak gravitational lensing effects of stacked voids, utilizing both shear and magnification information. The statistical precision is greatly improved by stacking together a large number of voids along different lines of sight, even when taking into account the impact of inherent miscentering and projection effects. We show that Dark Energy Task Force Stage IV surveys, such as the Euclid satellite and the Large Synoptic Survey Telescope, should be able to detect the void lensing signal with sufficient precision from stacking abundant medium-sized voids, thus providing direct constraints on the matter density profile of voids independent of assumptions on galaxy bias.
Precisely measured astrometric parameters are integral to successful pulsar timing campaigns. They are commonly measured by fitting the astrometric parameters of a deterministic timing model to a series of pulse times of arrival (TOAs). TOAs measured to microsecond precision over several-year spans can in this way provide astrometric parameters precise to sub-milliarcsecond levels. However, pulsars do not pulsate in a deterministic fashion. Many display significant amounts of red spin noise. Furthermore, a stochastic background of gravitational waves can lead to red noise-like structure in TOAs. We investigate how noise of different spectral types is absorbed by timing models and leads to significant estimation errors in the astrometric parameters. Independent of timing, very long baseline interferometry (VLBI) is capable of providing sub-milliarcsecond astrometric parameters for pulsars. We find that incorporating VLBI astrometric measurements into the timing models of pulsars for which only a couple of years of timing data exist will lead to more realistic assessments of red spin noise, yield more accurate astrometric parameters, and could enhance the amplitude of certain gravitational wave signatures in post-fit timing residuals by factors of 20 or more.
This chapter reviews various methods of detecting planetary companions to stars from an observational perspective, focusing on radial velocities, astrometry, direct imaging, transits, and gravitational microlensing. For each method, this chapter first derives or summarizes the basic observable phenomena that are used to infer the ex- istence of planetary companions, as well as the physical properties of the planets and host stars that can be derived from the measurement of these signals. This chapter then outlines the general experimental requirements to robustly detect the signals us- ing each method, by comparing their magnitude to the typical sources of measurement uncertainty. This chapter goes on to compare the various methods to each other by outlining the regions of planet and host star parameter space where each method is most sensitive, stressing the complementarity of the ensemble of the methods at our disposal. Finally, there is a brief review of the history of the young exoplanet field, from the first detections to current state-of-the-art surveys for rocky worlds.
We investigate how explosions of aspherical supernovae (A-SNe) can influence star formation histories and chemical evolution of dwarf galaxies by using a new chemodynamical model. We mainly present the numerical results of two comparative models so that the A-SN feedback effects on galaxies can be more clearly seen. SNe originating from stars with masses larger than 30M_sun are A-SNe in the "ASN" model whereas all SNe are spherical ones (S-SNe) in the "SSN" model. Each S-SN and A-SN are assumed to release feedback energy of 10^{51} erg and 10^{52} erg, respectively, and chemical yields and feedback energy of A-SN ejecta depend on angles between the axis of symmetry and the ejection directions. We find that star formation can become at least by a factor of ~3 lower in the ASN model in comparison with the SSN one owing to the more energetic feedback of A-SNe. As a result of this, chemical evolution can proceed very slowly in the ASN model. A-SN feedback effects can play a significant role in the formation of giant gaseous holes and energetic gaseous outflow and unique chemical abundances (e.g., high [Mg/Ca]). Based on these results, we provide a number of implications of the A-SN feedback effects on galaxy formation and evolution.
We investigate the molecular evolution and D/H abundance ratios that develop as star formation proceeds from a dense-cloud core to a protostellar core, by solving a gas-grain reaction network applied to a 1-D radiative hydrodynamic model with infalling fluid parcels. Spatial distributions of gas and ice-mantle species are calculated at the first-core stage, and at times after the birth of a protostar. Gas-phase methanol and methane are more abundant than CO at radii $r\lesssim 100$ AU in the first-core stage, but gradually decrease with time, while abundances of larger organic species increase. The warm-up phase, when complex organic molecules are efficiently formed, is longer-lived for those fluid parcels in-falling at later stages. The formation of unsaturated carbon chains (warm carbon-chain chemistry) is also more effective in later stages; C$^+$, which reacts with CH$_4$ to form carbon chains, increases in abundance as the envelope density decreases. The large organic molecules and carbon chains are strongly deuterated, mainly due to high D/H ratios in the parent molecules, determined in the cold phase. We also extend our model to simulate simply the chemistry in circumstellar disks, by suspending the 1-D infall of a fluid parcel at constant disk radii. The species CH$_3$OCH$_3$ and HCOOCH$_3$ increase in abundance in $10^4-10^5$ yr at the fixed warm temperature; both also have high D/H ratios.
With galaxy groups constructed from the Sloan Digital Sky Survey (SDSS), we analyze the expected galaxy-galaxy lensing signals around satellite galaxies residing in different host haloes and located at different halo-centric distances. We use Markov Chain Monte Carlo (MCMC) method to explore the potential constraints on the mass and density profile of subhaloes associated with satellite galaxies from SDSS-like surveys and surveys similar to the Large Synoptic Survey Telescope (LSST). Our results show that for SDSS-like surveys, we can only set a loose constraint on the mean mass of subhaloes. With LSST-like surveys, however, both the mean mass and the density profile of subhaloes can be well constrained.
We constrain the dominant optical selection effects biasing the Gamma-Ray Burst (GRB) redshift distribution using Swift triggered redshifts acquired from the optical afterglow (OA). Models for the Malmquist, redshift desert, and dust extinction biases are used to show how the "true" GRB redshift distribution is distorted to its presently observed biased distribution. We find that that the statistically optimal model shows that GRB host galaxy dust extinction could account for up to 17% of missing redshifts, but the bias is negligible at very high-$z$. The redshift desert, and optically faint bursts missed because they are at high-$z$, reduce the overall fraction of redshifts by only 4% and \sim2% respectively. Significant sources of bias for the very high-$z$ sample include the limiting sensitivity of the telescopes, the time to acquire spectroscopic/photometric redshifts, and Lyman-$\alpha$ dropout. The statistically optimal model requires an increasing mean optical afterglow luminosity with redshift. This could be explained by a decrease in dust obscuration in GRB hosts at high-$z$. Alternatively, the optimal model can also be obtained without optical afterglow brightness evolution, but requires a source rate evolution four times higher than the star formation rate at $z=10$ compared to z=0. We find it is not necessary to invoke high-energy GRB luminosity evolution with redshift to account for the observed GRB rate excess at high-$z$.
We analytically derive a more accurate formula for the power spectrum of the biased objects with the primordial non-Gaussianity parameterized not only by the non-linearity parameter fNL, but also by gNL and tauNL which characterize the trispectrum of the primordial curvature perturbations. We adopt the integrated perturbation theory which was constructed in Matsubara (2011). We discuss an inequality between fNL and tauNL in the context of the scale-dependent bias, by introducing a stochasticity parameter. We also mention higher order loop corrections into the scale-dependency of the bias parameter.
We introduce the GENJI program (Gamma-ray Emitting Notable AGN Monitoring by Japanese VLBI), which is a monitoring program of gamma-ray bright AGNs with the VERA array (VLBI Exploration of Radio Astrometry). The GENJI programme aims a dense monitoring at 22 GHz towards the $\gamma$-ray emitting active galactic nuclei (AGNs) to investigate the radio time variation of the core and possible ejection of new radio component, motion of jets, and their relation with the emission at other wavelengths especially in $\gamma$-rays. Currently we are monitoring 8 $\gamma$-ray-emitting notable AGNs (DA 55, 3C 84, M 87, PKS 1510-089, DA 406, NRAO 530, BL Lac, 3C 454.3) about once every two weeks. This programme is promising to trace the trend of radio time variation on shorter timescale than conventional VLBI monitoring programme and to provide complimentary data with them (e.g., MOJAVE, Boston University Blazar Project). In particular, we successfully coordinated quick follow-up observations after the GeV $\gamma$-ray flare in NRAO 530 and 3C 454.3 reported by the Fermi Gamma-ray Space Telescope. Here we present the initial results of morphology and light curves for the first 7-month operation.
The Interferometric studies of novae in the optical and near-infrared is a nascent but fast emerging field which has begun to provide new and invaluable insights into the nova phenomenon. This is particularly so in the early stages of the eruption when all the relevant physical phenomena are on the scale of milli-arcseconds and thus are amenable to be studied only by interferometric techniques. In this review the instruments and arrays involved in this domain of work are briefly described, followed by a description of the major results obtained so far. A discussion is made of the physical aspects, where the application of interferometric techniques, can bring the most valuable information. Finally, prospects for the near future are discussed.
We study how the magnetorotational instability (MRI) in protoplanetary disks
is affected by the electric discharge caused by the electric field in the
resistive MHD. We have performed three-dimensional shearing box simulations
with various values of plasma beta and electrical breakdown models. We find the
self-sustainment of the MRI in spite of the high resistivity. The instability
gives rise to the large electric field that causes the electrical breakdown,
and the breakdown maintains the high ionization degree required for the
instability.
The condition for this self-sustained MRI is set by the balance between the
energy supply from the shearing motion and the energy consumed by the Ohmic
dissipation. We apply the condition to various disk models and study where the
active, self-sustained, and dead zones of MRI are. In the fiducial minimum-mass
solar nebula (MMSN) model, the newly-found sustained zone occupies only the
limited volume of the disk. In the late-phase gas-depleted disk models,
however, the sustained zone occupies larger volume of the disk.
The morphologic properties of the magnetic networks during Carrington Rotations (CR) 1955 to 2091 (from 1999 to 2010) have been analyzed by applying the watershed algorithm to magnetograms observed by the Michelson Doppler Interferometer (MDI) on board the Solar and Heliospheric Observatory (SOHO) spacecraft. We find that the average area of magnetic cells on the solar surface at lower latitudes (within +-50 degree) are smaller than those at higher latitudes (beyond +-50 degree). Statistical analysis of these data indicates that the magnetic networks are of fractal in nature, and the average fractal dimension is D_f = 1.253+-0.011. We also find that both the fractal dimension and the size of the magnetic networks are anti-correlated with the sunspot area. This is perhaps because a strong magnetic field can suppress spatially modulated oscillation, compress the boundaries of network cells, leading to smoother cell boundaries. The fractal dimension of the cell deviates that predicted from an isobar of Kolmogorov homogeneous turbulence.
Although cosmological observations suggest that the fluctuations of seed fields are almost Gaussian, the possibility of a small deviation of their fields from Gaussianity is widely discussed. Theoretically, there exist numerous inflationary scenarios which predict large and characteristic non-Gaussianities in the primordial perturbations. These model-dependent non-Gaussianities act as sources of the Cosmic Microwave Background (CMB) bispectrum; therefore, the analysis of the CMB bispectrum is very important and attractive in order to clarify the nature of the early Universe. Currently, the impacts of the primordial non-Gaussianities in the scalar perturbations, where the rotational and parity invariances are kept, on the CMB bispectrum have been well-studied. However, for a complex treatment, the CMB bispectra generated from the non-Gaussianities, which originate from the vector- and tensor-mode perturbations and include the violation of the rotational or parity invariance, have never been considered in spite of the importance of this information. On the basis of our current studies, this thesis provides the general formalism for the CMB bispectrum sourced by the non-Gaussianities not only in the scalar-mode perturbations but also in the vector- and tensor-mode perturbations. Applying this formalism, we calculate the CMB bispectrum from two scalars and a graviton correlation and that from primordial magnetic fields, and we then outline new constraints on these amplitudes. Furthermore, this formalism can be easily extended to the cases where the rotational or parity invariance is broken. We also compute the CMB bispectra from the non-Gaussianities of the curvature perturbations with a preferred direction and the graviton non-Gaussianities induced by the parity-violating Weyl cubic terms. We also present some unique impacts to the violation of these invariances on the CMB bispectrum.
We present here a new spectral energy distribution (SED) fitting approach that we adopt to select radio-excess sources amongst distant star-forming galaxies in the GOODS-Herschel (North) field and to reveal the presence of hidden, highly obscured AGN. Through extensive SED analysis of 458 galaxies with radio 1.4 GHz and mid-IR 24 um detections using some of the deepest Chandra X-ray, Spitzer and Herschel infrared, and VLA radio data available to date, we have robustly identified a sample of 51 radio-excess AGN (~1300 deg^-2) out to redshift z~3. These radio-excess AGN have a significantly lower far-IR/radio ratio (q<1.68) than the typical relation observed for star-forming galaxies (q~2.2). We find that ~45% of these radio-excess sources have a dominant AGN component in the mid-IR band, while for the remainders the excess radio emission is the only indicator of AGN activity. The fraction of radio-excess AGN increases with X-ray luminosity reaching ~60% at Lx~10^44-10^45 erg/s, making these sources an important part of the total AGN population. However, almost half (24/51) of these radio-excess AGN are not detected in the deep Chandra X-ray data, suggesting that some of these sources might be heavily obscured. We also find that the specific star formation rates (sSFRs) of the radio-excess AGN are on average lower that those observed for X-ray selected AGN hosts, indicating that our sources are forming stars more slowly than typical AGN hosts, and possibly their star formation is progressively quenching.
Using Science Verification data from the Atacama Large
Millimeter/Submillimeter Array (ALMA), we have identified and imaged five
rotational transitions (J=5-4 and J=6-5) of the three silicon monoxide
isotopologues 28SiO v=0, 1, 2 and 29SiO v=0 and 28Si18O v=0 in the frequency
range from 214 to 246 GHz towards the Orion BN/KL region. The emission of the
ground-state 28SiO, 29SiO and 28Si18O shows an extended bipolar shape in the
northeast-southwest direction at the position of Radio Source I, indicating
that these isotopologues trace an outflow (~18 km/s, P.A. ~50deg, ~5000 AU in
diameter) that is driven by this embedded high-mass young stellar object (YSO).
Whereas on small scales (10-1000 AU) the outflow from Source I has a
well-ordered spatial and velocity structure, as probed by Very Long Baseline
Interferometry (VLBI) imaging of SiO masers, the large scales (500-5000 AU)
probed by thermal SiO with ALMA reveal a complex structure and velocity field,
most likely related to the effects of the environment of the BN/KL region on
the outflow emanating from Source I.
The emission of the vibrationally-excited species peaks at the position of
Source I. This emission is compact and not resolved at an angular resolution of
~1.5" (~600 AU at a distance of 420 pc). 2-D Gaussian fitting to individual
velocity channels locates emission peaks within radii of 100 AU, i.e. they
trace the innermost part of the outflow. A narrow spectral profile and spatial
distribution of the v=1 J=5-4 line similar to the masing v=1 J=1-0 transition,
provide evidence for the most highly rotationally excited (frequency > 200 GHz)
SiO maser emission associated with Source I known to date. The maser emission
will enable studies of the Source I disk-outflow interface with future ALMA
longest baselines.
We describe a new methodology to analyze the reionization process in numerical simulations: The evo- lution of the reionization is investigated by focusing on the merger histories of individual HII regions. From the merger tree of ionized patches, one can track the individual evolution of the regions such as e.g. their size, or investigate the properties of the percolation process by looking at the formation rate, the frequency of mergers and the number of individual HII regions involved in the mergers. By applying this technique to cosmological simulations with radiative transfer, we show how this methodology is a good candidate to quantify the impact of the star formation adopted on the history of the reionization. As an application we show how different models of sources result in different evolutions and geometry of the reionization even though they produce e.g. similar ionized fraction or optical depth.
The line profile asymmetry defining the Evershed effect in sunspot penumbrae, disappears abruptly at the outer sunspot boundary over a horizontal distance of less than 500 km immediately at the outermost ends of the dark penumbral continuum structures ('filaments'). This is indicated from the non-magnetic lines Ni I 5435.9 (g=0.5) and Fe I 5434.5 (g=0), which loose their profile asymmetries at the same spatial location although formed at a vertical height distance of 300 km. The widely accepted 'canopy' picture conflicts with this finding which, in contrary, suggests that the gas motion associated with the Evershed effect disappears together with the continuum intensity drop at the outer sunspot (penumbral) border. Corresponding downflows must then be smaller than the spatial resolution presently achieved (i.e., <0.5 arcsec) and located at the immediate outer sunspot border. It is suggested that this location marks the sharp threshold of the equipartition between kinetic and magnetic energy density at the outer penumbral boundary.
The Fermi Gamma-ray Space Telescope (formerly known as Gamma-ray Large Area Space Telescope, GLAST) was successfully launched on June 11 2008. Its main instrument is the Large Area Telescope (LAT), which detects gamma rays from 20 MeV to more than 300 GeV. It is a pair-conversion telescope with 16 identical towers (tracker and calorimeter), covered by an anti-coincidence detector to reject charged particles. The calorimeter is a hodoscopic array of CsI(Tl) crystals, arranged in 8 alternating orthogonal layers, with a total thickness of 8.6 radiation lengths. In this paper we will present the performance of the LAT, with special attention to the calorimeter, which provides a good energy measurement up to 3 TeV. We will also review some of its scientific results after 4 years of operation, focusing on measurements which extend up to very high energy, such as the spectrum of the extragalactic diffuse emission, the spectrum of cosmic electrons and the positron fraction.
We propose a two parameter generalization for the dark energy equation of state (EOS) for thawing dark energy models, which includes PNGB, CPL and algerbraic thawing models as limiting cases; and confront our model with latest Supernova Type Ia (SNe Ia) Data from Union 2.1 compilation, latest Observational Hubble Data (OHD), Cosmic Microwave Background (CMB) Data from 7 year WMAP results and latest Baryon Acoustic Oscillation Data from SDSS Data Release 9 to constrain our parameter space. The analysis reveals that thawing dark energy EOS is not unique from the observational point of view so far as the standard parameters (dark energy EOS, present value of matter density parameter and Hubble parameter) are concerned. In other words, different thawing dark energy models are not distinguishable from each other with the help of best-fit values of matter density parameter at present epoch, linear growth of matter perturbation and the average deceleration parameter. But tuning the model parameters does leave its impact on the variation of dark energy EOS as well as the model-independent parameters like the statefinder pair and $Om3$ parameters. We are thus led to the conclusion that unlike the standard parameters, the model-independent parameters and the variation of EOS serve as model discriminators for different thawing dark energy models.
We present CH and CN index analysis and C and N abundance calculations based on the low-resolution blue spectra of red giant branch (RGB) stars in the Galactic globular cluster NGC 7089 (M 2). Our main goal is to investigate the C-N anticorrelation for this intermediate metallicity cluster. The data were collected with DOLORES, the multiobject, low-resolution facility at the Telescopio Nazionale Galileo. Spectroscopic data were coupled with UV photometry obtained during the spectroscopic run. We found a considerable star-to-star variation in both A(C) and A(N) at all luminosities for our sample of 35 targets. These abundances appear to be anticorrelated, with a hint of bimodality in the C content for stars with luminosities below the RBG bump (V~15.7), while the range of variations in N abundances is very large and spans almost ~ 2 dex. We find additional C depletion as the stars evolve off the RGB bump, in fairly good agreement with theoretical predictions for metal-poor stars in the course of normal stellar evolution. We isolated two groups with N-rich and N-poor stars and found that N abundance variations correlate with the (U-V) color in the DOLORES color-magnitude diagram (CMD). The V, (U-V) CMD for this cluster shows an additional RGB sequence, located at the red of the main RGB and amounting to a small fraction of the total giant population. We identified two CH stars detected in previous studies in our U, V images. These stars, which are both cluster members, fall on this redder sequence, suggesting that the anomalous RGB should have a peculiar chemical pattern. Unfortunately, no additional spectra were obtained for stars in this previously unknown RGB branch.
We study a large sample of narrow-line radio galaxies (NLRGs) with extended radio structures. Using 1.4 GHz radio luminosities, $L_{1.4}$, narrow optical emission line luminosities, $L_{\oiii}$ and $L_{H_{\alpha}}$, as well as black hole masses $M_{BH}$ derived from stellar velocity dispersions measured from the optical spectra obtained with the Sloan Digital Sky Survey, we find that: (i) NLRGs cover about 4 decades of the Eddington ratio, $\lambda \equiv L_{bol}/L_{Edd} \propto L_{line}/M_{BH}$; (ii) $L_{1.4}/M_{BH}$ strongly correlates with $\lambda$; (iii) radio-loudness, ${\cal R} \equiv L_{1.4}/L_{line}$, strongly anti-correlates with $\lambda$. A very broad range of the Eddington ratio indicates that the parent population of NLRGs includes both radio-loud quasars (RLQs) and broad-line radio galaxies (BLRGs). The correlations they obey and their high jet production efficiencies favor a jet production model which involves the so-called 'magnetically choked' accretion scenario. In this model, production of the jet is dominated by the Blandford-Znajek mechanism, and the magnetic fields in the vicinity of the central black hole are confined by the ram pressure of the accretion flow. Since large net magnetic flux accumulated in central regions of the accretion flow required by the model can take place only via geometrically thick accretion, we speculate that the massive, 'cold' accretion events associated with luminous emission-line AGN can be accompanied by an efficient jet production only if preceded by a hot, very sub-Eddington accretion phase.
We report the design and development of a self-contained multi-band receiver (MBR) system, intended for use with a single large aperture to facilitate sensitive & high time-resolution observations simultaneously in 10 discrete frequency bands sampling a wide spectral span (100-1500 MHz) in a nearly log-periodic fashion. The development of this system was primarily motivated by need for tomographic studies of pulsar polar emission regions. Although the system design is optimized for the primary goal, it is also suited for several other interesting astronomical investigations. The system consists of a dual-polarization multi-band feed (with discrete responses corresponding to the 10 bands pre-selected as relatively RFI-free), a common wide-band RF front-end, and independent back-end receiver chains for the 10 individual sub-bands. The raw voltage time-sequences corresponding to 16 MHz bandwidth each for the two linear polarization channels and the 10 bands, are recorded at the Nyquist rate simultaneously. We present the preliminary results from the tests and pulsar observations carried out with the Green Bank Telescope using this receiver. The system performance implied by these results, and possible improvements are also briefly discussed.
With the ever increasing size and complexity of fully self-consistent simulations of galaxy formation within the framework of the cosmic web, the demands upon object finders for these simulations has simultaneously grown. To this extent we initiated the Halo Finder Comparison Project that gathered together all the experts in the field and has so far led to two comparison papers, one for dark matter field haloes (Knebe et al. 2011), and one for dark matter subhaloes (Onions et al. 2012). However, as state-of-the-art simulation codes are perfectly capable of not only following the formation and evolution of dark matter but also account for baryonic physics (e.g. hydrodynamics, star formation, feedback) object finders should also be capable of taking these additional processes into consideration. Here we report on a comparison of codes as applied to the Constrained Local UniversE Simulation (CLUES) of the formation of the Local Group which incorporates much of the physics relevant for galaxy formation. We compare both the properties of the three main galaxies in the simulation (representing the MW, M31, and M33) as well as their satellite populations for a variety of halo finders ranging from phase-space to velocity-space to spherical overdensity based codes, including also a mere baryonic object finder. We obtain agreement amongst codes comparable to (if not better than) our previous comparisons, at least for the total, dark, and stellar components of the objects. However, the diffuse gas content of the haloes shows great disparity, especially for low-mass satellite galaxies. This is primarily due to differences in the treatment of the thermal energy during the unbinding procedure. We acknowledge that the handling of gas in halo finders is something that needs to be dealt with carefully, and the precise treatment may depend sensitively upon the scientific problem being studied.
We propose a simplified picture of low mass X-ray binaries containing a neutron star (NS-LMXBs) based on data obtained from AqlX-1 and 4U1608-52 which often produce outbursts. In this picture we propose at least three states and three state transitions; i.e., the states: (1) soft state, (2) hard-high state, and (3) hard-low state, and the state transitions: (i) hard-high state to soft state, (ii) soft state to hard-high state, and (iii) hard-high state to hard-low state or vice versa. Gases from the accretion disc of an NS-LMXB penetrate almost the entire magnetic field and accrete onto the neutron star in cases (1) and (2), whereas in case (3) some gases accrete around the magnetic poles in a manner resembling the behavior of an X-ray pulsar, and considerable gas is dispersed or ejected by the propeller effect. Transition (iii) occurs when the Alfv\'{e}n radius is equal to the co-rotation radius. Therefore, in this case, it is possible to estimate the strength of the neutron star's magnetic field by detecting transition (iii). We also discuss the no-accretion X-ray state or recycled pulsar state, in which the Alfv\'{e}n radius is larger than the light cylinder radius.
For many years it has been recognized that the terminal stages of mass transfer in a low-mass X-ray binary (LMXB) should cause the magnetosphere of the accreting neutron star to expand, leading to a braking torque acting on the spinning pulsar. After the discovery of radio millisecond pulsars (MSPs) it was therefore somewhat a paradox (e.g. Ruderman et al. 1989) how these pulsars could retain their fast spins following the Roche-lobe decoupling phase, RLDP. Here I present a solution to this so-called "turn-off problem" which was recently found by combining binary stellar evolution models with torque computations (Tauris 2012). The solution is that during the RLDP the spin equilibrium of the pulsar is broken and therefore it remains a fast spinning object. I briefly discuss these findings in view of the two observed spin distributions in the populations of accreting X-ray millisecond pulsars (AXMSPs) and radio MSPs.
Although the first millisecond pulsars (MSPs) were discovered 30 years ago we still do not understand all details of their formation process. Here, we present new results from Tauris, Langer & Kramer (2012) on the recycling scenario leading to radio MSPs with helium or carbon-oxygen white dwarf companions via evolution of low- and intermediate mass X-ray binaries (LMXBs, IMXBs). We discuss the location of the spin-up line in the (P,Pdot)-diagram and estimate the amount of accreted mass needed to obtain a given spin period and compare with observations. Finally, we constrain the true ages of observed recycled pulsars via calculated isochrones in the (P,Pdot)-diagram.
It is generally considered that the emission of microwave zebra pattern (ZP) structures requires high density and high temperatures, which is similar to the situation of the flaring region where primary energy releases. Therefore, the parameters analysis of ZPs may reveal the physical conditions of the flaring source region. This work investigates the variations of 74 microwave ZP structures observed by Chinese Solar Broadband Radio Spectrometer (SBRS/Huairou) at 2.6-3.8 GHz in 9 solar flares, and found that the ratio between the plasma density scale height LN and the magnetic field scale height LB in emission source displays a tendency of decrease during the flaring processes. The ratio LN/LB is about 3-5 before the maximum of flares. It decreases to about 2 after the maximum. The detailed analysis of three typical X-class flares implied that the variation of LN/LB during the flaring process is most likely due to the topological changes of the magnetic field in the flaring source region, and the step-wise decrease of LN/LB possibly reflects the magnetic field relaxation relative to the plasma density when the flaring energy released. This result may also constrain the solar flare modeling to some extent.
We present a new atmospheric extinction curve for Mauna Kea spanning 3200--9700 \AA. It is the most comprehensive to date, being based on some 4285 standard star spectra obtained on 478 nights spread over a period of 7 years obtained by the Nearby SuperNova Factory using the SuperNova Integral Field Spectrograph. This mean curve and its dispersion can be used as an aid in calibrating spectroscopic or imaging data from Mauna Kea, and in estimating the calibration uncertainty associated with the use of a mean extinction curve. Our method for decomposing the extinction curve into physical components, and the ability to determine the chromatic portion of the extinction even on cloudy nights, is described and verified over the wide range of conditions sampled by our large dataset. We demonstrate good agreement with atmospheric science data obtain at nearby Mauna Loa Observatory, and with previously published measurements of the extinction above Mauna Kea.
We examine the thermal free-free millimetre fluxes expected from non-dusty and non-pulsating K through mid-M giant stars based on our limited understanding of their inhomogeneous chromospheres. We present a semi-analytic model that provides estimates of the radio fluxes for the mm wavelengths (e.g., CARMA, ALMA, JVLA Q-band) based on knowledge of the effective temperatures, angular diameters and chromospheric Mg II h & k emission fluxes. At 250 GHz, the chromospheric optical depths are expected to be significantly less than unity, which means that fluxes across the mm and sub-mm range will have a contribution from the chromospheric mate- rial that gives rise to the ultraviolet emission spectrum, as well as the cool molecular material known to exist above the photosphere. We predict a lower bound to the inferred brightness temperature of red giants based on heating at the basal-flux limit if the upper chromospheres have filling factor 1. Multi-frequency mm observations should provide important new information on the structuring of the inhomogeneous chromospheres, including the boundary layer, and allow tests of competing theoretical models for atmospheric heating. We comment on the suitability of these stars as mm flux calibrators.
The ARGO-YBJ experiment is in stable data taking since November 2007 at the YangBaJing Cosmic Ray Laboratory (Tibet, P.R. China, 4300 m a.s.l., 606 g/cm$^2$). ARGO-YBJ is facing open problems in Cosmic Ray (CR) physics in different ways. The search for CR sources is carried out by the observation of TeV gamma-ray sources both galactic and extra-galactic. The CR spectrum, composition and anisotropy are measured in a wide energy range (TeV - PeV) thus overlapping for the first time direct measurements. In this paper we summarize the current status of the experiment and describe some of the scientific highlights since 2007.
A dormant Swift source J 164449.3+573451 (Sw 164449+57)recently experienced a powerful outburst, caused most probably by a tidal disruption of a star by the super-massive black hole at the center of the source. During the outburst, a quasi periodic oscillation (QPO) was detected in the observed X-ray flux from Sw 164449+57. We show that if the observed QPO belongs to a "3:2 twin peak QPO" (with the second frequency not observed), the mass of the black hole in Sw 164449+57 is rather low, M ~ 10^5 M_sun, and the source belongs to a class of intermediate mass black holes. The low mass of the source has been pointed out previously by several authors.
We compare distance measurements obtained from two distance indicators, Supernovae observations (standard candles) and Baryon acoustic oscillation data (standard rulers). The Union2 sample of supernovae with BAO data from SDSS, 6dFGS and the latest BOSS and WiggleZ surveys is used in search for deviations from the distance duality relation. We find that the supernovae are brighter than expected from BAO measurements. The luminosity distances tend to be smaller then expected from angular diameter distance estimates as also found in earlier works on distance duality, but the trend is not statistically significant. This further constrains the cosmic transparency.
We assess the impact of non-thermally shock-accelerated particles on the magnetohydrodynamic (MHD) jump conditions of relativistic shocks. The adiabatic constant is calculated directly from first principle particle-in-cell simulation data, enabling a semi-kinetic approach to improve the standard fluid model and allowing for an identification of the key parameters that define the shock structure. We find that the evolving upstream parameters have a stronger impact than the corrections due to non-thermal particles. We find that the decrease of the upstream bulk speed yields deviations from the standard MHD model up to 10%. Furthermore, we obtain a quantitative definition of the shock transition region from our analysis. For Weibel-mediated shocks the inclusion of a magnetic field in the MHD conservation equations is addressed for the first time.
We investigated six H II regions with infrared, bright rimmed bubble or
cometary morphology, in search of quantitative evidence for triggered star
formation, both collect and collapse and radiatively driven implosion. We
identified and classified 458 Young Stellar Objects (YSOs) in and around the H
II regions. YSOs were determined by fitting a collection of radiative transfer
model spectral energy distributions (SEDs) to infrared photometry for a large
sample of point sources. We determined areas where there exist enhanced
populations of relatively unevolved YSOs on the bright rims of these regions,
suggesting that star formation has been triggered there. We further
investigated the physical properties of the regions by using radio continuum
emission as a proxy for ionizing flux powering the H II regions, and 13CO (1-0)
observations to measure masses and gravitational stability of molecular clumps.
We used an analytical model of collect and collapse triggered star formation,
as well as a simulation of radiatively driven implosion, and thus we compare
the observed properties of the molecular gas with those predicted in the
triggering scenarios. Notably, those regions in our sample that show evidence
of cometary, or "blister," morphology are more likely to show evidence of
triggering.
Keywords: HII regions -- ISM: bubbles -- Stars: formation -- Stars:
protostars
We present the first measurement of the angular two-point correlation function for AKARI 90-$\mu$m point sources, detected outside of the Milky Way plane and other regions characterized by high Galactic extinction, and categorized as extragalactic sources according to our far-infrared-color based criterion (Pollo et al. 2010). This is the first measurement of the large-scale angular clustering of galaxies selected in the far-infrared after IRAS measurements. Although a full description of clustering properties of these galaxies will be obtained by more detailed studies, using either spatial correlation function, or better information about properties and at least photometric redshifts of these galaxies, the angular correlation function remains the first diagnostics to establish the clustering properties of the catalog and observed galaxy population. We find a non-zero clustering signal in both hemispheres extending up to $\sim 40$ degrees, without any significant fluctuations at larger scales. The observed correlation function is well fitted by a power law function. The notable differences between a northern and southern hemisphere are found, which can be probably attributed to the photometry problems and point out to a necessity of performing a better calibration in the data from southern hemisphere.
We calculate the structure of a standard accretion disk with corona surrounding a massive Kerr black hole in general relativistic frame, in which the corona is assumed to be heated by the reconnection of the strongly buoyant magnetic fields generated in the cold accretion disk. The emergent spectra of the accretion disk-corona systems are calculated by using the relativistic ray-tracing method. We propose a new method to calculate the emergent Comptonized spectra from the coronae. The spectra of the disk-corona systems with a modified $\alpha$-magnetic stress show that both the hard X-ray spectral index and the hard X-ray bolometric correction factor $L_{\rm bol}/L_{\rm X,2-10keV}$ increase with the dimensionless mass accretion rate, which are qualitatively consistent with the observations of active galactic nuclei (AGNs). The fraction of the power dissipated in the corona decreases with increasing black hole spin parameter $a$, which leads to lower electron temperatures of the coronas for rapidly spinning black holes. The X-ray emission from the coronas surrounding rapidly spinning black holes becomes weak and soft. The ratio of the X-ray luminosity to the optical/UV luminosity increases with the viewing angle, while the spectral shape in the X-ray band is insensitive with the viewing angle. We find that the spectral index in the infrared waveband depends on the mass accretion rate and the black hole spin $a$, which deviates from $f_\nu\propto\nu^{1/3}$ expected by the standard thin disk model.
Extracting magnetic and thermodynamic information from spectropolarimetric observations is a difficult and time consuming task. The amount of science-ready data that will be generated by the new family of large solar telescopes is so large that we will be forced to modify the present approach to inference. In this contribution, I propose several possible ways that might be useful for extracting the thermodynamic and magnetic properties of solar plasmas from such observations quickly.
Observations show that propagating magnetohydrodynamic (MHD) waves are ubiquitous in the solar atmosphere. The technique of MHD seismology uses the wave observations combined with MHD wave theory to indirectly infer physical parameters of the solar atmospheric plasma and magnetic field. Here we present an analytical seismological inversion scheme for propagating MHD waves. This scheme uses in a consistent manner the observational information on wavelengths and damping lengths, along with observed values of periods or phase velocities, and is based on approximate asymptotic expressions for the theoretical values of wavelengths and damping lengths. The applicability of the inversion scheme is discussed and an example is given.
We have studied the kinematics of ~2800 candidate close pair galaxies at 0.1<z<1.2 identified from the Canada-France-Hawaii Telescope Legacy Survey fields. Spectra of these systems were obtained using spectrometers on the 6.5m Magellan and 5m Hale telescopes. These data allow us to constrain the rate of dry mergers at intermediate redshifts and to test the `hot halo' model for quenching of star formation. Using virial radii estimated from the correlation between dynamical and stellar masses published by Leauthaud et al. (2011), we find that around 1/5 of our candidate pairs are likely to share a common dark matter halo (our metric for close physical association). These pairs are divided into red-red, blue-red and blue-blue systems using the rest-frame colors classification method introduced in Chou et al. (2011). Galaxies classified as red in our sample have very low star-formation rates, but they need not be totally quiescent, and hence we refer to them as `damp', rather than `dry', systems. After correcting for known selection effects, the fraction of blue-blue pairs is significantly greater than that of red-red and blue-red pairs. Red-red pairs are almost entirely absent from our sample, suggesting that damp mergers are rare at z~0.5. Our data supports models with a short merging timescale (<0.5 Gyr) in which star-formation is enhanced in the early phase of mergers, but quenched in the late phase. Hot halo models may explain this behaviour, but only if virial shocks that heat gas are inefficient until major mergers are nearly complete.
Planned wide-field weak lensing surveys are expected to reduce the statistical errors on the shear field to unprecedented levels. In contrast, systematic errors like those induced by the convolution with the point spread function (PSF) will not benefit from that scaling effect and will require very accurate modeling and correction. While numerous methods have been devised to carry out the PSF correction itself, modeling of the PSF shape and its spatial variations across the instrument field of view has, so far, attracted much less attention. This step is nevertheless crucial because the PSF is only known at star positions while the correction has to be performed at any position on the sky. A reliable interpolation scheme is therefore mandatory and a popular approach has been to use low-order bivariate polynomials. In the present paper, we evaluate four other classical spatial interpolation methods based on splines (B-splines), inverse distance weighting (IDW), radial basis functions (RBF) and ordinary Kriging (OK). These methods are tested on the Star-challenge part of the GRavitational lEnsing Accuracy Testing 2010 (GREAT10) simulated data and are compared with the classical polynomial fitting (Polyfit). We also test all our interpolation methods independently of the way the PSF is modeled, by interpolating the GREAT10 star fields themselves (i.e., the PSF parameters are known exactly at star positions). We find in that case RBF to be the clear winner, closely followed by the other local methods, IDW and OK. The global methods, Polyfit and B-splines, are largely behind, especially in fields with (ground-based) turbulent PSFs. In fields with non-turbulent PSFs, all interpolators reach a variance on PSF systematics $\sigma_{sys}^2$ better than the $1\times10^{-7}$ upper bound expected by future space-based surveys, with the local interpolators performing better than the global ones.
Cosmic muon interactions are important contributors to backgrounds in underground detectors when searching for rare events. Typically neutrons dominate this background as they are particularly difficult to shield and detect in a veto system. Since actual background data is sparse and not well documented, simulation studies must be used to design shields and predict background rates. This means that validation of any simulation code is necessary to assure reliable results. This work studies the validation of the FLUKA simulation code, and reports the results of a simulation of cosmogenic background for a liquid argon two-phase detector embedded within a water tank and liquid scintillator shielding.
We analyze spatially resolved spectroscopic observations of the Eta Carinae binary system obtained with HST/STIS. Eta Car is enshrouded by the dusty Homunculus nebula, which scatters light emitted by the central binary and provides a unique opportunity to study a massive binary system from different vantage points. We investigate the latitudinal and azimuthal dependence of H$\alpha$ line profiles caused by the presence of a wind-wind collision (WWC) cavity created by the companion star. Using two-dimensional radiative transfer models, we find that the wind cavity can qualitatively explain the observed line profiles around apastron. Regions of the Homunculus which scatter light that propagated through the WWC cavity show weaker or no H alpha absorption. Regions scattering light that propagated through a significant portion of the primary wind show stronger P Cygni absorption. Our models overestimate the H alpha absorption formed in the primary wind, which we attribute to photoionization by the companion, not presently included in the models. We can qualitatively explain the latitudinal changes that occur during periastron, shedding light on the nature of Eta Car's spectroscopic events. Our models support the idea that during the brief period of time around periastron when the primary wind flows unimpeded toward the observer, H alpha absorption occurs in directions toward the central object and Homunculus SE pole, but not toward equatorial regions close to the Weigelt blobs. We suggest that observed latitudinal and azimuthal variations are dominated by the companion star via the WWC cavity, rather than by rapid rotation of the primary star.
Metal-rich (red) globular clusters in massive galaxies are, on average, smaller than metal-poor (blue) globular clusters. One of the possible explanations for this phenomenon is that the two populations of clusters have different spatial distributions. We test this idea by comparing clusters observed in unusually deep, high signal-to-noise images of M87 with a simulated globular cluster population in which the red and blue clusters have different spatial distributions, matching the observations. We compare the overall distribution of cluster effective radii as well as the relationship between effective radius and galactocentric distance for both the observed and simulated red and blue subpopulations. We find that the different spatial distributions does not produce a significant size difference between the red and blue subpopulations as a whole, or at a given galactocentric distance. These results suggest that the size difference between red and blue globular clusters is likely due to differences during formation or later evolution
In this paper, we report on our analysis using Hubble Space Telescope astrometry and Keck-I HIRES spectroscopy of the central six stars of Tycho's supernova remnant (SN 1572). With these data, we measured the proper motions, radial velocities, rotational velocities, and chemical abundances of these objects. Regarding the chemical abundances, we do not confirm the unusu- ally high [Ni/Fe] ratio previously reported for Tycho-G. Rather, we find that for all metrics in all stars, none exhibit the characteristics expected from traditional SN Ia single-degenerate-scenario calculations. The only possible exception is Tycho-B, a rare, metal-poor A-type star; however, we are unable to find a suitable scenario for it. Thus, we suggest that SN 1572 cannot be explained by the standard single-degenerate model.
The non-equatorial spherical null geodesics of rotating Kerr black holes are studied analytically. Unlike the extensively studied equatorial circular orbits whose radii are known analytically, no closed-form formula exists in the literature for the radii of generic (non-equatorial) spherical geodesics. We provide here an approximate formula for the radii r_{ph}(a/M;cos i) of these spherical null geodesics, where a/M is the dimensionless angular-momentum of the black hole and cos i is an effective inclination angle (with respect to the black-hole equatorial plane) of the orbit. It is well-known that the equatorial circular geodesics of the Kerr spacetime (the prograde and the retrograde orbits with cos i=\pm 1) are characterized by a monotonic dependence of their radii r_{ph}(a/M;cos i=\pm 1) on the dimensionless spin-parameter a/M of the black hole. We use here our novel analytical formula to reveal that this well-known property of the equatorial circular geodesics is actually not a generic property of the Kerr spacetime. In particular, we find that counter-rotating spherical null orbits in the range (3\sqrt{3}-\sqrt{59})/4 \lesssim \cos i<0 are characterized by a non-monotonic dependence of r_{ph}(a/M;cos i=const) on the dimensionless rotation parameter a/M of the black hole. Furthermore, it is shown that spherical photon orbits of rapidly-rotating black holes are characterized by a critical inclination angle, cos i=\sqrt{4/7}, above which the coordinate radii of the orbits approach the black-hole radius in the extremal limit. We prove that this critical inclination angle signals a transition in the physical properties of the spherical null geodesics: in particular, it separates orbits which are characterized by finite proper distances to the black-hole horizon from orbits which are characterized by infinite proper distances to the horizon.
We provide a general formalism to calculate the infrared correlators of multiple interacting scalar fields in the de Sitter space by means of the stochastic approach. These scalar fields are treated as test fields and hence our result is applicable to the models such as the curvaton scenario where the fields that yield initially isocurvature modes do not contribute to the cosmic energy density during inflationary expansion. The stochastic formalism combined with the argument of conformal invariance of the correlators reflecting the de Sitter isometries allows us to fix the form and amplitude of the three-point functions completely and partially for the four-point functions in terms of calculable quantities. It turns out that naive scaling argument employed in the previous literature does not necessarily hold and we derive the necessary and sufficient condition for the correlator to obey the naive scaling. We also find that correlation functions can in principle exhibit more complicated structure than argued in the literature.
A lot of fundamental tests of gravitational theories rely on highly precise measurements of the travel time and/or the frequency shift of electromagnetic signals propagating through the gravitational field of the Solar System. In practically all of the previous studies, the explicit expressions of such travel times and frequency shifts as predicted by various metric theories of gravity are derived from an integration of the null geodesic differential equations. However, the solution of the geodesic equations requires heavy calculations when one has to take into account the presence of mass multipoles in the gravitational field or the tidal effects due to the planetary motions, and the calculations become quite complicated in the post-post-Minkowskian approximation. This difficult task can be avoided using the time transfer function's formalism. We present here our last advances in the formulation of the one-way frequency shift using this formalism up to the post-post-Minkowskian approximation.
Ideas from causal set theory lead to a fluctuating, time dependent cosmological-constant of the right order of magnitude to match currently quoted "dark energy" values. Although such a term was predicted some time ago, a more detailed analysis of the resulting class of phenomenological models was begun only recently (based on numerical simulation of the cosmological equations with such a fluctuating term). In this paper we continue the investigation by studying the sensitivity of the scheme to some of the ad hoc choices made in setting it up.
Background: In the environment of high neutrino-fluxes provided in
core-collapse supernovae or neutron star mergers, neutrino-induced reactions
with nuclei contribute to the nucleosynthesis processes. A number of
terrestrial neutrino detectors are based on inelastic neutrino-nucleus
scattering and modeling of the respective cross sections allow predictions of
the expected detector reaction rates.
Purpose: To provide a self-consistent microscopic description of
neutrino-nucleus cross sections involving a large pool of Z = 8 - 82 nuclei for
the implementation in models of nucleosynthesis and neutrino detector
simulations.
Methods: Self-consistent theory framework based on relativistic nuclear
energy density functional is employed to determine the nuclear structure of the
initial state and relevant transitions to excited states induced by neutrinos.
The weak neutrino-nucleus interaction is employed in the current-current form
and a complete set of transition operators is taken into account.
Results: We perform large-scale calculations of charged-current
neutrino-nucleus cross sections, including those averaged over supernova
neutrino fluxes, for the set of even-even target nuclei from oxygen toward lead
(Z = 8 - 82), spanning N = 8 - 182 (OPb pool). The model calculations include
allowed and forbidden transitions up to J = 5 multipoles.
Conclusions: The present analysis shows that the self-consistent calculations
result in considerable differences in comparison to previously reported cross
sections, and for a large number of target nuclei the cross sections are
enhanced. Revision in modeling r-process nucleosynthesis based on a
self-consistent description of neutrino-induced reactions would allow an
updated insight into the origin of elements in the Universe and it would
provide the estimate of uncertainties in the calculated element abundance
patterns.
Links to: arXiv, form interface, find, astro-ph, recent, 1210, contact, help (Access key information)
The first short part of this review is a general, but very detailed, critique
of the literature advocating a class of Seyfert galaxies intrinsically lacking
broad emission lines. My conclusion is that there is little or no evidence for
such objects.
Panchromatic properties of all types of radio loud AGN are then reviewed in
detail. Radio galaxies usually show subparsec-scale radio core sources, jets,
and a pair of giant radio lobes. The optical spectra sometimes show only
relatively weak lines of low-ionization ionic species, and no clear nuclear
continuum in the optical or UV region of the spectrum. Some show strong
high-ionization narrow lines. Finally, a few radio galaxies add broad bases
onto the permitted lines. These spectral categories are the same as those for
radio-quiet AGN and quasars.
By the 1980s, data from optical polarization and statistics of the radio
properties required that many narrow line radio galaxies do in fact produce
strong optical/UV continuum. This continuum and the broad line emission are
hidden from the line of sight by dusty, roughly toroidal gas distributions, but
they are seen in polarized flux. The radio galaxies with hidden quasars are
referred to as "thermal."
Do all radio galaxies harbor hidden quasars? We now know the answer using the
radio, infrared, optical and X-ray properties. Near the top of the radio
luminosity function, for FRII, GPS, and CSS galaxies, the answer is yes. At
somewhat lower luminosities, many do not. At the lowest radio luminosities,
most do not. Instead these "nonthermal" weakly-accreting galaxies manifest
their energetic output only as kinetic energy in the form of synchrotron jets.
This applies to all types of radio galaxies, big FR II doubles, as well as the
small young GPS and CSS sources. Only a few FR I sources are of the thermal
type.
The ARCADE 2 collaboration and other experiments have reported a significant excess in the isotropic radio background, whose homogeneity cannot be reconciled with clustered sources. This suggests a cosmological origin prior to structure formation. We investigate several potential mechanisms and show that injection of relativistic electrons through late decays of a metastable particle can give rise to the observed excess radio spectrum either through Compton or synchrotron emission. However, these turn out to be in conflict with CMB bounds on the primordial magnetic field or on the injection of ionizing radiation. The simplest optimal scenario is with MeV-scale particles decaying into e+ e- at a redshift of z ~ 5, which is still in moderate conflict with the CMB constraints. Decays into exotic millicharged particles can alleviate the tension, if they emit synchroton radiation in conjunction with a sufficiently large background magnetic field of a dark U(1)' gauge field.
The Prime Focus Spectrograph (PFS) of the Subaru Measurement of Images and Redshifts (SuMIRe) project has been endorsed by Japanese community as one of the main future instruments of the Subaru 8.2-meter telescope at Mauna Kea, Hawaii. This optical/near-infrared multi-fiber spectrograph targets cosmology with galaxy surveys, Galactic archaeology, and studies of galaxy/AGN evolution. Taking advantage of Subaru's wide field of view, which is further extended with the recently completed Wide Field Corrector, PFS will enable us to carry out multi-fiber spectroscopy of 2400 targets within 1.3 degree diameter. A microlens is attached at each fiber entrance for F-ratio transformation into a larger one so that difficulties of spectrograph design are eased. Fibers are accurately placed onto target positions by positioners, each of which consists of two stages of piezo-electric rotary motors, through iterations by using back-illuminated fiber position measurements with a wide-field metrology camera. Fibers then carry light to a set of four identical fast-Schmidt spectrographs with three color arms each: the wavelength ranges from 0.38 {\mu}m to 1.3 {\mu}m will be simultaneously observed with an average resolving power of 3000. Before and during the era of extremely large telescopes, PFS will provide the unique capability of obtaining spectra of 2400 cosmological/astrophysical targets simultaneously with an 8-10 meter class telescope. The PFS collaboration, led by IPMU, consists of USP/LNA in Brazil, Caltech/JPL, Princeton, & JHU in USA, LAM in France, ASIAA in Taiwan, and NAOJ/Subaru.
Terrestrial planets in the solar system, such as the Earth, are oxygen-rich, with silicates and iron being the most common minerals in their interiors. However, the true chemical diversity of rocky planets orbiting other stars is yet unknown. Mass and radius measurements are used to constrain the interior compositions of super-Earths (exoplanets with masses of 1 - 10 Earth masses), and are typically interpreted with planetary interior models that assume Earth-centric oxygen-rich compositions. Using such models, the super-Earth 55 Cancri e (mass of 8 Earth masses, radius of 2 Earth radii) has been suggested to bear an interior composition consisting of Fe, silicates, and an envelope (>= 10% by mass) of super-critical water. We report that the mass and radius of 55 Cancri e can also be explained by a carbon-rich solid interior made of Fe, C, SiC, and/or silicates and without a volatile envelope. While the data allow Fe mass fractions of up to 40%, a wide range of C, SiC and/or silicate mass fractions are possible. A carbon-rich 55 Cancri e is also plausible if its protoplanetary disk bore the same composition as its host star, which has been reported to be carbon-rich. However, more precise estimates of the stellar elemental abundances and observations of the planetary atmosphere are required to further constrain its interior composition. The possibility of a C-rich interior in 55 Cancri e opens a new regime of geochemistry and geophysics in extraterrestrial rocky planets, compared to terrestrial planets in the solar system.
We examine the velocity distribution function (VDF) in Dark Matter (DM) halos from Milky Way (MW) to cluster mass scales. We identify an empirical model for the VDF with a wider peak and a steeper tail than a Maxwell--Boltzmann distribution, and discuss physical explanations. We quantify sources of scatter in the VDF of cosmological halos and their implication for direct detection of DM. Given modern simulations and observations, we find that the most significant uncertainty in the VDF of the MW arises from the unknown radial position of the solar system relative to the DM halo scale radius.
We identify 42 candidate groups lying between 1.8<z<3.0 from a sample of 3502 galaxies with spectroscopic redshifts in the zCOSMOS-deep redshift survey within the same redshift interval. These systems contain three to five spectroscopic galaxies that lie within 500kpc in projected distance (in physical space) and within 700km/s in velocity. Based on extensive analysis of mock catalogues that have been generated from the Millennium simulation, we examine the likely nature of these systems at the time of observation, and what they will evolve into down to the present epoch. Although few of the "member" galaxies are likely to reside in the same halo at the epoch we observe them, 50% of the systems will eventually bring them all into the same halo, and almost all (93%) will have at least part of the member galaxies in the same halo by the present epoch. Most of the candidate groups can therefore be described as "proto-groups". An estimate of the overdensities is also consistent with the idea that these systems are being seen at the start of the assembly process. We also examine present-day haloes and ask whether their progenitors would have been seen amongst our candidate groups. For present-day haloes between 10^14-10^15Msun/h, 35% should have appeared amongst our candidate groups, and this would have risen to 70% if our survey had been fully-sampled, so we can conclude that our sample can be taken as representative of a large fraction of such systems. There is a clear excess of massive galaxies above 10^10Msun around the locations of the candidate groups in a large independent COSMOS photo-z sample, but we see no evidence in this latter data for any colour differentiation with respect to the field. This is however consistent with the idea that such differentiation arises in satellite galaxies, as indicated at z<1, if the candidate groups are indeed only starting to be assembled.
The CO-H2 conversion factor (Xco; otherwise known as the X-factor) is observed to be remarkably constant in the Milky Way and in the Local Group (aside from the SMC). To date, our understanding of why Xco should be so constant remains poor. Using a combination of extremely high resolution (~ 1 pc) galaxy evolution simulations and molecular line radiative transfer calculations, we suggest that Xco displays a narrow range of values in the Galaxy due to the fact that molecular clouds share very similar physical properties. In our models, this is itself a consequence of stellar feedback competing against gravitational collapse. GMCs whose lifetimes are regulated by radiative feedback show a narrow range of surface densities, temperatures and velocity dispersions with values comparable to those seen in the Milky Way. As a result, the X-factors from these clouds show reasonable correspondence with observed data from the Local Group, and a relatively narrow range. On the other hand, feedback-free clouds collapse to surface densities that are larger than those seen in the Galaxy, and hence result in X-factors that are systematically too large compared to the Milky Way's. We conclude that radiative feedback within GMCs can generate cloud properties similar to those observed in the Galaxy, and hence a roughly constant Milky Way X-factor in normal, quiescent clouds.
A number of theoretically well-motivated additions to the standard cosmological model predict weak signatures in the form of spatially localized sources embedded in the cosmic microwave background (CMB) fluctuations. We present a hierarchical Bayesian statistical formalism and a complete data analysis pipeline for testing such scenarios. We derive an accurate approximation to the full posterior probability distribution over the parameters defining any theory that predicts sources embedded in the CMB, and perform an extensive set of tests in order to establish its validity. The approximation is implemented using a modular algorithm, designed to avoid a posteriori selection effects, which combines a candidate-detection stage with a full Bayesian model-selection and parameter-estimation analysis. We apply this pipeline to theories that predict cosmic textures and bubble collisions, extending previous analyses by using: (1) adaptive-resolution techniques, allowing us to probe features of arbitrary size, and (2) optimal filters, which provide the best possible sensitivity for detecting candidate signatures. We conclude that the WMAP 7-year data do not favor the addition of either cosmic textures or bubble collisions to Lambda CDM, and place robust constraints on the predicted number of such sources. The expected numbers of bubble collisions and cosmic textures on the CMB sky are constrained to be fewer than 4.0 and 5.2 at 95% confidence, respectively.
We have conducted the first blind HI survey covering 480 deg^2 and a
heliocentric velocity range from 300-1900 km/s to investigate the HI content of
the nearby spiral-rich Ursa Major region and to look for previously
uncatalogued gas-rich objects. Here we present the catalog of HI sources. The
HI data were obtained with the 4-beam receiver mounted on the 76.2-m Lovell
telescope (FWHM 12 arcmin) at the Jodrell Bank Observatory (UK) as part of the
HI Jodrell All Sky Survey (HIJASS). We use the automated source finder DUCHAMP
and identify 166 HI sources in the data cubes with HI masses in the range of
10^7 - 10^{10.5} M_sun. Our Ursa Major HI catalogue includes 10 first time
detections in the 21-cm emission line.
We identify optical counterparts for 165 HI sources (99 per cent). For 54 HI
sources (33 per cent) we find numerous optical counterparts in the HIJASS beam,
indicating a high density of galaxies and likely tidal interactions. Four of
these HI systems are discussed in detail.
We find only one HI source (1 per cent) without a visible optical counterpart
out of the 166 HI detections. Green Bank Telescope (FWHM 9 arcmin) follow-up
observations confirmed this HI source and its HI properties. The nature of this
detection is discussed and compared to similar sources in other HI surveys.
We describe the conceptual design of the spectrograph opto-mechanical concept for the SuMIRe Prime Focus Spectrograph (PFS) being developed for the SUBARU telescope. The SuMIRe PFS will consist of four identical spectrographs, each receiving 600 fibers from a 2400 fiber robotic positioner at the prime focus. Each spectrograph will have three channels covering in total, a wavelength range from 380 nm to 1300 nm. The requirements for the instrument are summarized in Section 1. We present the optical design and the optical performance and analysis in Section 2. Section 3 introduces the mechanical design, its requirements and the proposed concepts. Finally, the AIT phases for the Spectrograph System are described in Section 5.
The Prime Focus Spectrograph (PFS) is a wide field multi-fiber spectrograph
using the prime focus of the Subaru telescope, which is capable of observing up
to 2400 astronomical objects simultaneously.
The instrument control software will manage the observation procedure
communicateing with subsystems such as the fiber positioner "COBRA", the
metrology camera system, and the spectrograph and camera systems. Before an
exposure starts, the instrument control system needs to access to a database
where target lists provided by observers are stored in advance, and accurately
position fibers onto astronomical targets as requested therein. This fiber
positioning will be carried out interacting with the metrology system which
measures the fiber positions. In parallel, the control system can issue a
command to point the telescope to the target position and to rotate the
instrument rotator. Finally the telescope pointing and the rotator angle will
be checked by imaging bright stars and checking their positions on the
auto-guide and acquisition cameras. After the exposure finishes, the data are
collected from the detector systems and are finalized as FITS files to archive
with necessary information.
The observation preparation software is required, given target lists and a
sequence of observation, to find optimal fiber allocations with maximizing the
number of guide stars. To carry out these operations efficiently, the control
system will be integrated seamlessly with a database system which will store
information necessary for observation execution such as fiber configurations.
In this article, the conceptual system design of the observation preparation
software and the instrument control software will be presented.
The Prime Focus Spectrograph (PFS) is a new multi-fiber spectrograph on Subaru telescope. PFS will cover around 1.4 degree diameter field with ~2400 fibers. To ensure precise positioning of the fibers, a metrology camera is designed to provide the fiber position information within 5 {\mu}m error. The final positioning accuracy of PFS is targeted to be better than 10 {\mu}m. The metrology camera will locate at the Cassegrain focus of Subaru telescope to cover the whole focal plane. The PFS metrology camera will also serve for the existing multi-fiber infrared spectrograph FMOS.
The peculiar motion of an observer with respect to the CMB rest frame induces an apparent deflection of the observed CMB photons, i.e. aberration, and a shift in their frequency, i.e. Doppler effect. Both effects distort the temperature multipoles a_lm's via a mixing matrix at any l. The common lore when performing a CMB based cosmological parameter estimation is to consider that Doppler affects only the l=1 multipole, and neglect any other corrections. In this paper we reconsider the validity of this assumption, showing that it is actually not robust when sky cuts are included to model CMB foreground contaminations. Assuming a simple fiducial cosmological model with five parameters, we simulated CMB temperature maps of the sky in a WMAP-like and in a Planck-like experiment and added aberration and Doppler effects to the maps. We then analyzed with a MCMC in a Bayesian framework the maps with and without aberration and Doppler effects in order to assess the ability of reconstructing the parameters of the fiducial model. We find that, depending on the specific realization of the simulated data, the parameters can be biased up to one standard deviation for WMAP and almost two standard deviations for Planck. Therefore we conclude that in general it is not a solid assumption to neglect aberration in a CMB based cosmological parameter estimation.
We present a cosmic shear study from the Deep Lens Survey (DLS), a deep BVRz multi-band imaging survey of five 4 sq. degree fields with two National Optical Astronomy Observatory (NOAO) 4-meter telescopes at Kitt Peak and Cerro Tololo. For both telescopes, the change of the point-spread-function (PSF) shape across the focal plane is complicated, and the exposure-to-exposure variation of this position-dependent PSF change is significant. We overcome this challenge by modeling the PSF separately for individual exposures and CCDs with principal component analysis (PCA). We find that stacking these PSFs reproduces the final PSF pattern on the mosaic image with high fidelity, and the method successfully separates PSF-induced systematics from gravitational lensing effects. We calibrate our shears and estimate the errors, utilizing an image simulator, which generates sheared ground-based galaxy images from deep Hubble Space Telescope archival data with a realistic atmospheric turbulence model. For cosmological parameter constraints, we marginalize over shear calibration error, photometric redshift uncertainty, and the Hubble constant. We use cosmology-dependent covariances for the Markov Chain Monte Carlo analysis and find that the role of this varying covariance is critical in our parameter estimation. Our current non-tomographic analysis alone constrains the Omega_M-sigma_8 likelihood contour tightly, providing a joint constraint of Omega_M=0.262+-0.051 and sigma_8=0.868+-0.071. We expect that a future DLS weak-lensing tomographic study will further tighten these constraints because explicit treatment of the redshift dependence of cosmic shear more efficiently breaks the Omega_M-sigma_8 degeneracy. Combining the current results with the Wilkinson Microwave Anisotropy Probe 7-year (WMAP7) likelihood data, we obtain Omega_M=0.278+-0.018 and sigma_8=0.815+-0.020.
The Prime Focus Spectrograph (PFS) is a fiber fed multi-object spectrometer for the Subaru Telescope that will conduct a variety of targeted surveys for studies of dark energy, galaxy evolution, and galactic archaeology. The key to the instrument is a high density array of fiber positioners placed at the prime focus of the Subaru Telescope. The system, nicknamed "Cobra", will be capable of rapidly reconfiguring the array of 2394 optical fibers to the image positions of astronomical targets in the focal plane with high accuracy. The system uses 2394 individual "SCARA robot" mechanisms that are 7.7mm in diameter and use 2 piezo-electric rotary motors to individually position each of the optical fibers within its patrol region. Testing demonstrates that the Cobra positioner can be moved to within 5{\mu}m of an astronomical target in 6 move iterations with a success rate of 95 per cent. The Cobra system is a key aspect of PFS that will enable its unprecedented combination of high-multiplex factor and observing efficiency on the Subaru telescope. The requirements, design, and prototyping efforts for the fiber positioner system for the PFS are described here as are the plans for modular construction, assembly, integration, functional testing, and performance validation.
We describe the conceptual design of the camera cryostats, detectors, and detector readout electronics for the SuMIRe Prime Focus Spectrograph (PFS) being developed for the Subaru telescope. The SuMIRe PFS will consist of four identical spectrographs, each receiving 600 fibers from a 2400 fiber robotic positioner at the prime focus. Each spectrograph will have three channels covering wavelength ranges 3800 {\AA} - 6700 {\AA}, 6500 {\AA} - 10000 {\AA}, and 9700 {\AA} - 13000 {\AA}, with the dispersed light being imaged in each channel by a f/1.10 vacuum Schmidt camera. In the blue and red channels a pair of Hamamatsu 2K x 4K edge-buttable CCDs with 15 um pixels are used to form a 4K x 4K array. For the IR channel, the new Teledyne 4K x 4K, 15 um pixel, mercury-cadmium-telluride sensor with substrate removed for short-wavelength response and a 1.7 um cutoff will be used. Identical detector geometry and a nearly identical optical design allow for a common cryostat design with the only notable difference being the need for a cold radiation shield in the IR camera to mitigate thermal background. This paper describes the details of the cryostat design and cooling scheme, relevant thermal considerations and analysis, and discusses the detectors and detector readout electronics.
Among the current sample of over 2000 radio pulsars known primarily in the disk of our Galaxy, millisecond pulsars now number almost 200. Due to the phenomenal success of blind surveys of the Galactic field, and targeted searches of Fermi gamma-ray sources, for the first time in over a decade, Galactic millisecond pulsars now outnumber their counterparts in globular clusters! In this paper, I briefly review earlier results from studies of the Galactic millisecond pulsar population and present new constraints based on a sample of 60 millisecond pulsars discovered by 20 cm Parkes multibeam surveys. I present a simple model of the population containing $\sim 30,000$ potentially observable millisecond pulsars with a luminosity function, radial distribution and scale height that matches the observed sample of objects. This study represents only a first step towards a more complete understanding of the parent population of millisecond pulsars in the Galaxy and I conclude with some suggestions for further study in this area.
(Abridge) We study statistical intrinsic shape of star-forming BzK galaxies (sBzK galaxies) at z~2 in both rest-frame UV and rest-frame optical wavelengths. The sBzK galaxies are selected down to K(AB)=24.0 mag in the GOODS-South and SXDS fields, where high-resolution images from Hubble Space Telescope are publicly available. 57% (583) of all 1028 galaxies in GOODS-S show a single component in the ACS/F850LP image. As WFC3/F160W images cover only some part of GOODS-S and SXDS, 724/1028 and 2500/29835 sBzK galaxies in the GOODS-S and SXDS have the WFC3 coverage. 86% (626) and 82% (2044) of the sBzK galaxies in WFC3/F160W images appear as a single component in the GOODS-S and SXDS, respectively. Larger fraction of single-component objects in F850LP images represents multiple star-forming regions in galaxies, while they are not so obvious in the F160W image which appears smoother. Most of the single-component sBzK galaxies show S\'ersic indices of n=0.5-2.5, in agreement with those of local disk galaxies. Their effective radii are 1.0-3.0 kpc and 1.5-4.0 kpc in F850LP and F160W images, respectively, regardless of the observed fields. Stellar surface mass density of the sBzK galaxies is also comparable to that of the local disk galaxies. However, the intrinsic shape of sBzK galaxies is not a round disk as seen in the local disk galaxies. By comparing apparent axial ratio (b/a) distributions of the sBzK galaxies with those by assuming tri-axial model with axes A>B>C, we found their intrinsic face-on B/A ratios peak at B/A=0.70 and B/A=0.77-0.79 in the rest-frame UV and optical, respectively and are statistically more bar-like than that of the local disk galaxies. The intrinsic edge-on C/A ratios in both rest-frame UV and optical wavelengths peak at 0.26, which is slightly larger than that of the local disk galaxies.
The Fiber Optical Cable and Connector System (FOCCoS), provides optical connection between 2400 positioners and a set of spectrographs by an optical fibers cable as part of Subaru PFS instrument. Each positioner retains one fiber entrance attached at a microlens, which is responsible for the F-ratio transformation into a larger one so that difficulties of spectrograph design are eased. The optical fibers cable will be segmented in 3 parts at long of the way, cable A, cable B and cable C, connected by a set of multi-fibers connectors. Cable B will be permanently attached at the Subaru telescope. The first set of multi-fibers connectors will connect the cable A to the cable C from the spectrograph system at the Nasmith platform. The cable A, is an extension of a pseudo-slit device obtained with the linear disposition of the extremities of the optical fibers and fixed by epoxy at a base of composite substrate. The second set of multi-fibers connectors will connect the other extremity of cable A to the cable B, which is part of the positioner's device structure. The optical fiber under study for this project is the Polymicro FBP120170190, which has shown very encouraging results. The kind of test involves FRD measurements caused by stress induced by rotation and twist of the fiber extremity, similar conditions to those produced by positioners of the PFS instrument. The multi-fibers connector under study is produced by USCONEC Company and may connect 32 optical fibers. The tests involve throughput of light and stability after many connections and disconnections. This paper will review the general design of the FOCCoS subsystem, methods used to fabricate the devices involved and the tests results necessary to evaluate the total efficiency of the set.
We present a general analysis of the orbit structure of 2D potentials with self-similar elliptical equipotentials by applying the method of Lie transform normalization. We study the most relevant resonances and related bifurcations. We find that the 1:1 resonance is associated only to the appearance of the loops and leads to the destabilization of either one or the other normal modes, depending on the ellipticity of equipotentials. Inclined orbits are never present and may appear only when the equipotentials are heavily deformed. The 1:2 resonance determines the appearance of bananas and anti-banana orbits: the first family is stable and always appears at a lower energy than the second, which is unstable. The bifurcation sequence also produces the variations in the stability character of the major axis orbit and is modified only by very large deformations of the equipotentials. Higher-order resonances appear at intermediate or higher energies and can be described with good accuracy.
Deep Herschel imaging and 12CO(2-1) line luminosities from the IRAM PdBI are combined for a sample of 17 galaxies at z>1 from the GOODS-N field. The sample includes galaxies both on and above the main sequence (MS) traced by star-forming galaxies in the SFR-M* plane. The far-infrared data are used to derive dust masses, Mdust. Combined with an empirical prescription for the dependence of the gas-to-dust ratio on metallicity (GDR), the CO luminosities and Mdust values are used to derive for each galaxy the CO-to-H2 conversion factor, alpha_co. Like in the local Universe, the value of alpha_co is a factor of ~5 smaller in starbursts compared to normal star-forming galaxies (SFGs). We also uncover a relation between alpha_co and dust temperature (Tdust; alpha_co decreasing with increasing Tdust) as obtained from modified blackbody fits to the far-infrared data. While the absolute normalization of the alpha_co(Tdust) relation is uncertain, the global trend is robust against possible systematic biases in the determination of Mdust, GDR or metallicity. Although we cannot formally distinguish between a step and a smooth evolution of alpha_co with the dust temperature, we can conclude that in galaxies of near-solar metallicity, a critical value of Tdust=30K can be used to determine whether the appropriate alpha_co is closer to the starburst value (1.0 Msun(K kms pc^2)^-1, if Tdust>30K) or closer to the Galactic value (4.35 Msun (K kms pc^2)^-1, if Tdust<30K). This indicator has the great advantage of being less subjective than visual morphological classifications of mergers/SFGs, which can be difficult at high z because of the clumpy nature of SFGs. In the absence of far-infrared data, the offset of a galaxy from the main sequence (i.e., log[SSFR(galaxy)/SSFR_MS(M*,z)]) can be used to identify galaxies requiring the use of an alpha_co conversion factor lower than the Galactic value.
On 2007 October 29 the outbursting comet 17P/Holmes passed within 0.79 arcsec of a background star. We recorded the event using optical, narrowband photometry and detect a 3% to 4% dip in stellar brightness bracketing the time of closest approach to the comet nucleus. The detected dimming implies an optical depth tau~0.04 at 1.5 arcsec from the nucleus and an optical depth towards the nucleus center tau_n<13.3. At the time of our observations, the coma was optically thick only within rho<~0.01 arcsec from the nucleus. By combining the measured extinction and the scattered light from the coma we estimate a dust red geometric albedo p_d=0.006+/-0.002 at 16 deg phase angle. Our measurements place the most stringent constraints on the extinction optical depth of any cometary coma.
We investigate the problem of structures formation in accretion disc zone, resulting from the tidally interaction in close binary star system. We aim to examine the area where the incoming flow meets the matter around secondary star and the resulting effects throughout the accretion disc. The research is based on employment of the fluid dynamics equations in conjunction with numerical simulations leading to the design of graphical models of accretion processes. For the simulation we propose box-framed sharing schemes. (i) The tidal transfer of matter through the inner Lagrangian point in close binary stars disturbs the flow in disc's zones and outer disc area. Calculations on the perturbed parameters of density and velocity reveal formation of a thickened zone in the contact area of interacted flows. It appears to be stable for a number of periods and is unaffected by rotation and dissipation processes. (ii) The results also show development of undulations, which grow to vortical patterns in the accretion disc's zone. It is confirmed that under the influence of tidal wave the conditions of reconfiguring of accretion flow structure are generated.
Three pulsar timing arrays are now producing high quality data sets. As reviewed in this paper, these data sets are been processed to 1) develop a pulsar-based time standard, 2) search for errors in the solar system planetary ephemeris and 3) detect gravitational waves. It is expected that the data sets will significantly improve in the near future by combining existing observations and by using new telescopes.
An extreme-mass-ratio burst (EMRB) is a gravitational wave signal emitted when a compact object passes through periapsis on a highly eccentric orbit about a much more massive object, in our case a stellar mass object about a 10^6 M_sol black hole. EMRBs are a relatively unexplored means of probing the spacetime of massive black holes (MBHs). We conduct an investigation of the properties of EMRBs and how they could allow us to constrain the parameters, such as spin, of the Galaxy's MBH. We find that if an EMRB event occurs in the Galaxy, it should be detectable for periapse distances r_p < 65 r_g for a \mu = 10 M_sol orbiting object, where r_g = GM/c^2 is the gravitational radius. The signal-to-noise ratio scales as \rho ~ -2.7 log(r_p/r_g) + log(\mu/M_sol) + 4.9. For periapses r_p < 10 r_g, EMRBs can be informative, and provide good constraints on both the MBH's mass and spin. Closer orbits provide better constraints, with the best giving accuracies of better than one part in 10^4 for both the mass and spin parameter.
HD 50138 presents the B[e] phenomenon, but its nature is not clear yet. This star is known to present spectral variations, which have been associated with outbursts and shell phases. We analyze the line profile variability of HD 50138 and its possible origin, which provide possible hints to its evolutionary stage, so far said to be close to the end of (or slightly beyond) the main sequence. New high-resolution spectra of HD 50138 obtained with the HERMES spectrograph over several nights (five of them consecutively) were analyzed, allowing us to confirm short-term line profile variability. Our new data show short-term variations in the photospheric lines. On the other hand, purely circumstellar lines (such as [O I] lines) do not show such rapid variability. The rotational velocity of HD 50138, V_rot = 90.3 +- 4.3 km/s, and the rotation period, P = 3.64 +- 1.16 d, were derived from the He II 4026A photospheric line. Based on the moment method, we confirm that the origin of this short-term line profile variability is not stellar spots, and it may be caused by pulsations. In addition, we show that macroturbulence may affect the profiles of photospheric lines, as is seen for B supergiants. The location of HD 50138 at the end of (or slightly beyond) the main sequence, the newly detected presence of line profile variability resembling pulsating stars, and macroturbulence make this star a fascinating object.
We present radio-continuum observations of the Galactic supernova remnant (SNR) candidate, G308.3-1.4, made with the Australia Telescope Compact Array, Molonglo Observatory Synthesis Telescope and the Parkes radio telescope. Our results combined with Chandra X-ray images confirm that G308.3-1.4 is a bona fide SNR with a shell morphology. The SNR has average diameter of D = 34 +- 19 pc, radio spectral index of alpha = -0.68 +- 0.16 and linear polarisation of 10 +- 1%; We estimate the SNR magnetic field B = 29 uG. Employing a Sigma-D relation, we estimate a distance to G308.3-1.4 of d = 19 +- 11 kpc. The radio morphology, although complex, suggests a smaller size for the SNR than previously implied in an X-Ray study. These results imply that G308.3-1.4 is a young to middle-aged SNR in the early adiabatic phase of evolution.
Thanks to the high spatial resolution provided by long baseline interferometry, it is possible to understand the complex circumstellar geometry around stars with the B[e] phenomenon. These stars are composed by objects in different evolutionary stages, like high- and low-mass evolved stars, intermediate-mass pre-main sequence stars and symbiotic objects. However, up to now more than 50% of the confirmed B[e] stars are not well classified, being called unclassified B[e] stars. From instruments like VLTI/AMBER and VLTI/MIDI, we have identified the presence of gaseous and dusty circumstellar disks, which have provided us with some hints related to the nature of these objects. Here, we show our results for two galactic stars with the B[e] phenomenon, HD 50138 and CPD-529243, based on interferometric measurements.
Here we report that the activity of comet Hale--Bopp ceased between late 2007 and March, 2009, at about 28 AU distance from the Sun. At that time the comet resided at a distance from the Sun that exceeded the freeze-out distance of regular comets by an order of magnitude. A Herschel Space Observatory PACS scan was taken in mid-2010, in the already inactive state of the nucleus. The albedo has been found to be surprisingly large (8.1$\pm$0.9%{}), which exceeds the value known for any other comets. With re-reduction of archive HST images from 1995 and 1996, we confirm that the pre-perihelion albedo resembled that of an ordinary comet, and was smaller by a factor of two than the post-activity albedo. Our further observations with the Very Large Telescope (VLT) also confirmed that the albedo increased significantly by the end of the activity. We explain these observations by proposing gravitational redeposition of icy grains towards the end of the activity. This is plausible for such a massive body in a cold environment, where gas velocity is lowered to the range of the escape velocity. These observations also show that giant comets are not just the upscaled versions of the comets we know but can be affected by processes that are yet to be fully identified.
The stellar mass and metallicity are among the fundamental parameters of galaxies. An understanding of the interplay between those properties as well as their environmental dependence will give us a general picture of the physics and feedback processes ongoing in groups of galaxies. We study the relationships and environmental dependencies between the stellar mass, and gas metallicity for more than 1900 galaxies in groups up to redshift 0.35 using the Galaxy And Mass Assembly (GAMA) survey. Using a control sample of more than 28,000 star-forming field galaxies, we find evidence for a decrement of the gas metallicity for galaxies in groups.
The magnetar Swift J1834.9-0846 is observed using Nanshan 25 meter radio telescope. No pulsed radio emission is detected. The upper limit on pulsed radio emission from this source is 0.5 mJy. According to the fundamental plane of magnetar radio emissions, this source should have radio emissions. Therefore, our results put constraints on the existence of fundamental plane of magnetar radio emissions. It may be that a small quiescent X-ray luminosity is only a necessary condition for magnetar radio emissions.
Using newly released data from the Wide-field Infrared Survey Explorer, we report the discovery of rapid infrared variability in three radio-loud narrow-line Seyfert 1 galaxies (NLS1s) selected from the 23 sources in the sample of Yuan et al. (2008). J0849+5108 and J0948+0022 clearly show intraday variability, while J1505+0326 has a longer measurable time scale within 180 days. Their variability amplitudes, corrected for measurement errors, are $\sim 0.1-0.2$ mag. The detection of intraday variability restricts the size of the infrared-emitting region to $\sim 10^{-3}$ pc, significantly smaller than the scale of the torus but consistent with the base of a jet. The three variable sources are exceptionally radio-loud, have the highest radio brightness temperature among the whole sample, and all show detected $\gamma$-ray emission in Fermi/LAT observations. Their spectral energy distributions resemble those of low-energy-peaked blazars, with a synchrotron peak around infrared wavelengths. This result strongly confirms the view that at least some radio-loud NLS1s are blazars with a relativistic jet close to our line of sight. The beamed synchrotron emission from the jet contributes significantly to and probably dominates the spectra in the infrared and even optical bands.
The intergalactic magnetic field (IGMF) can be indirectly probed through its effect on electromagnetic cascades initiated by a source of TeV gamma-rays, such as active galactic nuclei (AGN). AGN that are sufficiently luminous at TeV energies, extreme TeV blazars, can produce detectable levels of secondary radiation from Inverse Compton (IC) scattering of the electrons in the cascade, provided that the IGMF is not too large. We review recent work in the literature which utilizes this idea to derive constraints on the IGMF for three TeV-detected blazars-1ES 0229+200, 1ES 1218+304, and RGB J0710+591, and we also investigate four other hard-spectrum TeV blazars in the same context. Through a recently developed detailed Monte Carlo code, incorporating all major effects of QED and cosmological expansion, we research effects of major uncertainties such as the spectral properties of the source, uncertainty in the UV - far IR extragalactic background light (EBL), undersampled Very High Energy (VHE; energy > 100 GeV) coverage, past history of gamma-ray emission, source vs. observer geometry, and jet AGN Doppler factor. The implications of these effects on the recently reported lower limits of the IGMF are thoroughly examined to conclude that presently available data are compatible with a zero IGMF hypothesis.
We have performed a series of cosmic-ray electron observations using the balloon-borne emulsion chambers since 1968. While we previously reported the results from subsets of the exposures, the final results of the total exposures up to 2001 are presented here. Our successive experiments have yielded the total exposure of 8.19 m^2 sr day at the altitudes of 4.0 - 9.4 g/cm^2. The performance of the emulsion chambers was examined by accelerator beam tests and Monte-Carlo simulations, and the on-board calibrations were carried out by using the flight data. In this work we present the cosmic-ray electron spectrum in the energy range from 30 GeV to 3 TeV at the top of the atmosphere, which is well represented by a power-law function with an index of -3.28+-0.10. The observed data can be also interpreted in terms of diffusive propagation models. The evidence of cosmic-ray electrons up to 3 TeV suggests the existence of cosmic-ray electron sources at distances within ~1 kpc and times within ~1x10^5 yr ago.
We examine the metallicity distribution of the Galactic thick disk using F, G, and K dwarf stars selected from the Sloan Digital Sky Survey, Data Release 8. Using the large sample of dwarf stars with proper motions and spectroscopically determined stellar parameters, metallicity gradients in the radial direction for various heights above the Galactic plane and in the vertical direction for various radial distances from the Galaxy center have been found. In particular, we find a vertical metallicity gradient of -0.113 +/- 0.010 (-0.125 +/- 0.008) dex/kpc using an isochrone (photometric) distance determination in the range 1 < |Z| < 3 kpc, which is the vertical height range most consistent with the thick disk of our Galaxy. In the radial direction, we find metallicity gradients between +0.02 and +0.03 dex/kpc for bins in the vertical direction between 1 < |Z| < 3 kpc. Both of these results agree with similar values determined from other populations of stars, but this is the first time a radial metallicity gradient for the thick disk has been found at these vertical heights. We are also able to separate thin and thick disk stars based on kinematic and spatial probabilities in the vertical height range where there is significant overlap of these two populations. This should aid further studies of the metallicity gradients of the disk for vertical heights lower than those studied here but above the solar neighborhood. Metallicity gradients in the thin and thick disks are important probes into possible formation scenarios for our Galaxy and a consistent picture is beginning to emerge from results using large spectroscopic surveys, such as the ones presented here.
We study future observational constraints on cosmic string parameters from various types of next-generation experiments: direct detection of gravitational waves (GWs), pulsar timing array, and the cosmic microwave background (CMB). We consider both GW burst and stochastic GW background searches by ground- and space-based interferometers as well as GW background detection in pulsar timing experiments. We also consider cosmic string contributions to the CMB temperature and polarization anisotropies. These different types of observations offer independent probes of cosmic strings and may enable us to investigate cosmic string properties if the signature is detected. In this paper, we evaluate the power of future experiments to constrain cosmic string parameters, such as the string tension Gmu, the initial loop size alpha, and the reconnection probability p, by performing Fisher information matrix calculations. We find that combining the information from the different types of observations breaks parameter degeneracies and provides more stringent constraints on the parameters. We also find future space-borne interferometers independently provide a highly precise determination of the parameters.
The Magellanic Stream (MS) is a nearby laboratory for studying the fate of cool gas streams injected into a gaseous galactic halo. We investigate properties of the boundary layer between the cool MS gas and the hot Milky Way halo with 21 cm HI observations of a relatively isolated cloud having circular projection in the northern MS. Through averaging and modeling techniques, our observations obtained with the Robert C. Byrd Green Bank Telescope (GBT), reach unprecedented 3\sigma\ sensitivity of ~10^17/cm^2, while retaining the telescope's 9.1' resolution in the essential radial dimension. We find an envelope of diffuse neutral gas with FWHM of 60 km/s, associated in velocity with the cloud core having FWHM of 20 km/s, extending to 3.5 times the core radius with a neutral mass seven times that of the core. We show that the envelope is too extended to represent a conduction-dominated layer between the core and the halo. Its observed properties are better explained by a turbulent mixing layer driven by hydrodynamic instabilities. The fortuitous alignment of the NGC 7469 background source near the cloud center allows us to combine UV absorption and HI emission data to determine a core temperature of 8350 +/- 50 K. We show that the HI column density and size of the core can be reproduced when a slightly larger cloud is exposed to Galactic and extragalactic background ionizing radiation. Cooling in the large diffuse turbulent mixing layer envelope extends the cloud lifetime by at least a factor of two relative to a simple hydrodynamic ablation case, suggesting that the cloud is likely to reach the Milky Way disk.
In an attempt to determine how many planetary nebulae derive from binary
interactions, we have started a project to measure their unbiased binary
fraction. This number, when compared to the binary fraction of the presumed
parent population can give a first handle on the origin of planetary nebulae.
By detecting 27 bona fide central stars in the I band we have found that 30% of
our sample have an I band excess between one and a few sigmas, possibly
denoting companions brighter than M3-4V and with separations smaller than
approximately 1000 AU. By accounting for the undetectable companions, we
determine a de-biased binary fraction of 67-78% for all companions at all
separations. We compare this number to a main sequence binary fraction of
(50+/-4)% determined for spectral types F6V-G2V, appropriate if the progenitors
of today's PN central star population is indeed the F6V-G2V stars. The error on
our estimate could be between 10 and 30%. We conclude that the central star
binary fraction may be larger than expected from the putative parent
population. Using the more sensitive J band of a subset of 11 central stars,
the binary fraction is 54% for companions brighter than approximately M5-6V and
with separations smaller than about 900 AU. De-biassing this number we obtain a
binary fraction of 100-107%. The two numbers should be the same and the
discrepancy is likely due to small number statistics.
We also present an accurately vetted compilation of observed main sequence
star magnitudes, colours and masses, which can serve as a reference for future
studies. We also present synthetic colours of hot stars as a function of
temperature (20-170kK) and gravity (log g= 6-8) for Solar and PG1159
compositions.
Surface composition of near-Earth asteroid (4179) Toutatis is consistent with an undifferentiated L-chondrite composition. This is inconsistent with early observations that suggested high pyroxene iron content and a differentiated body.
The analytical expression for frequency of the maximum of radio emission intensity in pulsars with free electron emission from the stellar surface has been found. We have explained the correlation, known from observations, between the high-frequency cut-off and low-frequency turnover in radio emission spectrum of the pulsars. The explanation is based on peculiarities of electron acceleration in the inner polar gap, which we have analyzed.
The uncertainty about a possible correlation between strength and inclination of the magnetic field and the continuum intensity of the sunspot penumbral fine-structure has been removed by a detailed analysis of a spatially very high resolved spectrum: the darker, lengthy penumbral lanes host a 10% stronger and >30 deg flatter magnetic field as compared to the bright penumbral locations. This finding does not only result from the high spatial resolution but also from the choice of the Fe I 6842.7 line, which obtains its essential contribution from those deep layers near the continuum intensity level where the penumbral structure is seen. The almost perfect correlation establishes that the penumbral structure is formed by two magnetic components mainly differing by their field inclination. The discrepancy with results from other Zeeman lines, as e.g. Fe I 6302.5, indicates a different field structure above the white light penumbral layers.
An attempt to determine spatial location of the main source of short-period comet nuclei was made. There were carried out numerical calculations for orbit evolution of Jupiter family comets, comets with middle-period orbits and bodies of Centaur group. On the basis of the calculations it was shown, that orbital evolution of the solar system small bodies is mainly going in the direction of the semi-major axes increase. It belongs to the bodies which can undergo approaches the planets, and orbital evolution of which is mainly going due to the gravitational forces. Such result is confirmed by qualitative analysis of changes of small body semi-major axes under approaches the planets. The conclusion was drawn that the main source of nuclei of Jupiter family comets is apparently situated at distances from the Sun not more than 6 AU.
Some of the most interesting types of astrophysical objects that have been intensively studied in the recent years are the Anomalous X-ray Pulsars (AXPs) and Soft Gamma-ray Repeaters (SGRs) seen usually as neutron stars pulsars with super strong magnetic fields. However, in the last two years two SGRs with low magnetic fields have been detected. Moreover, fast and very magnetic white dwarf pulsars have also been observed in the last years. Based on these new pulsar discoveries, white dwarf pulsars have been proposed as an alternative explanation to the observational features of SGRs and AXPs. Here we present several properties of these SGRs/AXPs as WD pulsar, in particular the surface magnetic field and the magnetic dipole momentum.
In this research note, we start exploring the influence of the narrow line region (NLR) on the optical/UV continuum polarization of active galactic nuclei (AGN). We have upgraded our previous 3-component model of a thermal Seyfert nucleus that was composed of an equatorial, optically thin electron disc, a circumnuclear dusty torus, and a pair of collimated, optically thin electron winds (Marin et al.2012b). We have added a dusty extension with low optical depth to the outflows to account for continuum scattering and absorption inside the NLR. A spectropolarimetric comparison between our AGN models with and without NLR reprocessing is carried out. It turns out that the NLR can alter and even suppress the observed polarization dichotomy between type-1 and type-2 AGN. For type-2 AGN, it also significantly decreases the expected percentage of polarization and alters its spectral shape. While the NLR makes it more difficult to reproduce the observed polarization in type-1 objects, it helps to explain spectropolarimetry observations of type-2 objects. Further studies including clumpy media need to be carried out.
In this paper we study an anisotropic model generated from a Bianchi III metric, generalization of G\"{o}del's metric, which is an exact solution of Einstein's field equations. In particular, we analyse supernova Ia data, namely the SDSS sample calibrated with the MLCS2k2 fitter, verifying in which limits of distances and redshifts the anisotropy of the model could be observed, and in which limits the model approaches the \Lambda CDM model. We found that redshifts above z = 2 has a particular importance in setting the point at which the anisotropy would be noticed, as well as the point at which the present model begins to diverge from the \Lambda CDM. We conclude that data above this limit, as well as an increasing accuracy in measuring these distances, might indicate the existence of such an anisotropy in the universe.
We investigate the X-ray and UV emission detected by RHESSI and TRACE in the context of a solar flare on the 16th November 2002 with the goal of better understanding the evolution of the flare. We analysed the characteristics of the X-ray emission in the 12-25 and 25-50 keV energy range while we looked at the UV emission at 1600 {\AA}. The flare appears to have two distinct phases of emission separated by a 25-second time delay, with the first phase being energetically more important. We found good temporal and spatial agreement between the 25-50 keV X-rays and the most intense areas of the 1600 {\AA} UV emission. We also observed an extended 100-arcsecond < 25 keV source that appears coronal in nature and connects two separated UV ribbons later in the flare. Using the observational properties in X-ray and UV wavelengths, we propose two explanations for the flare evolution in relation to the spine/fan magnetic field topology and the accelerated electrons. We find that a combination of quasi separatrix layer reconnection and null-point reconnection is required to account for the observed properties of the X-ray and UV emission.
Using solar vector magnetograms of the highest available spatial resolution and signal-to-noise ratio we perform a detailed study of electric current patterns in two solar active regions: a flaring/eruptive, and a flare-quiet one. We aim to determine whether active regions inject non-neutralized (net) electric currents in the solar atmosphere, responding to a debate initiated nearly two decades ago that remains inconclusive. We find that well-formed, intense magnetic polarity inversion lines (PILs) within active regions are the only photospheric magnetic structures that support significant net current. More intense PILs seem to imply stronger non-neutralized current patterns per polarity. This finding revises previous works that claim frequent injections of intense non-neutralized currents by most active regions appearing in the solar disk but also works that altogether rule out injection of non-neutralized currents. In agreement with previous studies, we also find that magnetically isolated active regions remain globally current-balanced. In addition, we confirm and quantify the preference of a given magnetic polarity to follow a given sense of electric currents, indicating a dominant sense of twist in active regions. This coherence effect is more pronounced in more compact active regions with stronger PILs and must be of sub-photospheric origin. Our results yield a natural explanation of the Lorentz force, invariably generating velocity and magnetic shear along strong PILs, thus setting a physical context for the observed pre-eruption evolution in solar active regions.
The GREGOR Fabry-P\'erot Interferometer (GFPI) is one of three first-light instruments of the German 1.5-meter GREGOR solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI uses two tunable etalons in collimated mounting. Thanks to its large-format, high-cadence CCD detectors with sophisticated computer hard- and software it is capable of scanning spectral lines with a cadence that is sufficient to capture the dynamic evolution of the solar atmosphere. The field-of-view (FOV) of 50" x 38" is well suited for quiet Sun and sunspot observations. However, in the vector spectropolarimetric mode the FOV reduces to 25" x 38". The spectral coverage in the spectroscopic mode extends from 530-860 nm with a theoretical spectral resolution R of about 250,000, whereas in the vector spectropolarimetric mode the wavelength range is at present limited to 580-660 nm. The combination of fast narrow-band imaging and post-factum image restoration has the potential for discovery science concerning the dynamic Sun and its magnetic field at spatial scales down to about 50 km on the solar surface.
Spin-orbit coupling is often described in the "MacDonald torque" approach
which has become the textbook standard. Within this method, a concise
expression for the additional tidal potential, derived by MacDonald (1964; Rev.
Geophys. 2, 467), is combined with an assumption that the Q factor is
frequency-independent (i.e., that the geometric lag angle is constant in time).
This makes the approach unphysical because MacDonald's derivation of the said
formula was implicitly based on keeping the time lag frequency-independent,
which is equivalent to setting Q to scale as the inverse tidal frequency. The
contradiction requires the MacDonald treatment of both non-resonant and
resonant rotation to be rewritten.
The non-resonant case was reconsidered by Efroimsky & Williams (2009; CMDA
104, 257), in application to spin modes distant from the major
commensurabilities. We continue this work by introducing the necessary
alterations into the MacDonald-torque-based model of falling into a 1:1
resonance. (For the original version of the model, see Goldreich 1966; AJ 71,
1.)
We also study the effect of the triaxiality on both circulating and librating
rotation near the synchronous state. Circulating rotation may evolve toward the
libration region or toward a spin rate larger than synchronous
(pseudosynchronous spin). Which behaviour depends on the eccentricity, the
triaxiality of the primary, and the mass ratio of the secondary and primary
bodies. The spin evolution will always stall for the oblate case. For
small-amplitude librations, expressions are derived for the libration
frequency, damping rate, and average orientation.
However, the stability of pseudosynchronous spin hinges upon the dissipation
model. Makarov and Efroimsky (2012; arXiv:1209.1616) have found that a more
realistic dissipation model than the corrected MacDonald torque makes
pseudosynchronous spin unstable.
We present a general framework for matching the point-spread function (PSF), photometric scaling, and sky background between two images, a subject which is commonly referred to as difference image analysis (DIA). We introduce the new concept of a spatially varying photometric scale factor which will be important for DIA applied to wide-field imaging data in order to adapt to transparency and airmass variations across the field-of-view. Furthermore, we demonstrate how to separately control the degree of spatial variation of each kernel basis function, the photometric scale factor, and the differential sky background. We discuss the common choices for kernel basis functions within our framework, and we introduce the mixed-resolution delta basis functions to address the problem of the size of the least-squares problem to be solved when using delta basis functions. We validate and demonstrate our algorithm on simulated and real data. We also describe a number of useful optimisations that may be capitalised on during the construction of the least-squares matrix and which have not been reported previously. We pay special attention to presenting a clear notation for the DIA equations which are set out in a way that will hopefully encourage developers to tackle the implementation of DIA software.
The emergence of large-scale magnetic fields observed in the diffuse interstellar medium is explained by a turbulent dynamo. The underlying transport coefficients have previously been extracted from numerical simulations. So far, this was restricted to the kinematic regime, but we aim to extend our analysis into the realm of dynamically important fields. This marks an important step on which derived mean-field models rely to explain observed equipartition strength fields. As in previous work, we diagnose turbulent transport coefficients by means of the test-field method. We derive quenching functions for the dynamo {\alpha} effect, diamagnetic pumping, and turbulent diffusivity, which are compared with theoretical expectations. At late times, we observe the suppression of the vertical wind. Because this potentially affects the removal of small-scale magnetic helicity, new concerns arise about circumventing constraints imposed by the conservation of magnetic helicity at high magnetic Reynolds numbers. While present results cannot safely rule out this possibility, the issue only becomes important at late stages and is absent when the dynamo is quenched by the wind itself.
We present the analysis of an XMM-Newton observation of the M17 nebula. The X-ray point source population consists of massive O-type stars and a population of probable low-mass pre-main sequence stars. CEN1a,b and OI352, the X-ray brightest O-type stars in M17, display hard spectra (kT of 3.8 and 2.6 keV) consistent with a colliding wind origin in binary/multiple systems. We show that the strong interstellar reddening towards the O-type stars of M17 yields huge uncertainties on their Lx/Lbol values. The low-mass pre-main sequence stars exhibit hard spectra resulting from a combination of high plasma temperatures and very large interstellar absorption. We find evidence for considerable long term (months to years) variability of these sources. M17 is one of the few star formation complexes in our Galaxy producing diffuse X-ray emission. We analyze the spectrum of this emission and compare it with previous studies. Finally, we discuss the Optical Monitor UV data obtained simultaneously with the X-ray images. We find very little correspondence between the UV and X-ray sources, indicating that the majority of the UV sources are foreground stars, whilst the bulk of the X-ray sources are deeply embedded in the M17 complex.
CTA 1 (G119.5+10.2) is a composite supernova remnant (SNR) with a shell-type structure, visible in the radio band, surrounding a smaller pulsar wind nebula. Fermi detected a radio-quiet pulsar PSR J0007+7303 within the radio shell. 26.5 hours of VERITAS observation revealed extended TeV emission from CTA 1. The centroid of the TeV emission is located near the Fermi pulsar. The integral flux of the emission was ~4% of the Crab Nebula flux (>1TeV). We present an update on the source analysis with additional exposure and possible interpretations.
The ultracompact X-ray binary 4U 1820-30 is well known for its ~170-d superorbital modulation in X-ray flux and spectrum, and the exclusiveness of bursting behavior to the low hard 'island' state. In May-June 2009, there was an exceptionally long 51-d low state. This state was well covered by X-ray observations and 12 bursts were detected, 9 with the high-throughput RXTE. We investigate the character of these X-ray bursts and find an interesting change in their photospheric expansion behavior. At the lowest inferred mass accretion rates, this expansion becomes very large in 4 bursts and reaches the so-called superexpansion regime. We speculate that this is due to the geometry of the inner accretion flow being spherical and a decreasing accretion rate: when the flow geometry nearest to the neutron star is spherical and the accretion rate is low, the ram pressure of the accretion disk may become too low to counteract that of the photospheric expansion. In effect, this may provide a novel means to probe the accretion flow. Additionally, we observe a peculiar effect: the well-known cessation of X-ray bursts in the high state is too quick to be consistent with a transition to stable helium burning. We suggest an alternative explanation, that the cessation is due to the introduction of a non-nuclear heat source in the neutron star ocean.
A population of obscured supergiant High Mass X-ray Binaries (sgHMXBs) has been discovered by INTEGRAL. X-ray wind tomography of IGR J17252-3616 inferred a slow wind velocity to account for the enhanced obscuration. The main goal of this study is to understand under which conditions high obscuration could occur. We have used an hydrodynamical code to simulate the flow of the stellar wind around the neutron star. A grid of simulations was used to study the dependency of the absorbing column density and of the X-ray light-curves on the model parameters. A comparison between the simulation results and the observations of IGR J17252-3616 provides an estimate on these parameters. We have constrained the wind terminal velocity to 500-600 km/s and the neutron star mass to 1.75-2.15 solar masses. We have confirmed that the initial hypothesis of a slow wind velocity with a moderate mass loss rate is valid. The mass of the neutron star can be constrained by studying its impact on the accretion flow.
This contribution summarizes the splinter session "Non-thermal processes in coronae and beyond" held at the Cool Stars 17 workshop in Barcelona in 2012. It covers new developments in high energy non-thermal effects in the Earth's exosphere, solar and stellar flares, the diffuse emission in star forming regions and reviews the state and the challenges of the underlying atomic databases.
Observations of open star clusters in the solar neighborhood are used to calculate local supernova (SN) rates for the past 510 million years (Myr). Peaks in the SN rates match passages of the Sun through periods of locally increased cluster formation which could be caused by spiral arms of the Galaxy. A statistical analysis indicates that the Solar System has experienced many large short-term increases in the flux of Galactic cosmic rays (GCR) from nearby supernovae. The hypothesis that a high GCR flux should coincide with cold conditions on the Earth is borne out by comparing the general geological record of climate over the past 510 million years with the fluctuating local SN rates. Surprisingly a simple combination of tectonics (long-term changes in sea level) and astrophysical activity (SN rates) largely accounts for the observed variations in marine biodiversity over the past 510 Myr. An inverse correspondence between SN rates and carbon dioxide (CO$_2$) levels is discussed in terms of a possible drawdown of CO$_2$ by enhanced bioproductivity in oceans that are better fertilized in cold conditions - a hypothesis that is not contradicted by data on the relative abundance of the heavy isotope of carbon, $^{13}$C.
Non-Gaussianity in the inflationary perturbations can couple observable scales to modes of much longer wavelength (superhorizon even), leaving as signature a large-angle modulation of the observed CMB power spectrum. This provides an alternative origin for a power asymmetry which is otherwise often ascribed to a breaking of statistical isotropy. The non-Gaussian modulation effect can be significant even for typical ~10^{-5} perturbations, while respecting current constraints on non-Gaussianity, if the squeezed limit of the bispectrum is sufficiently infrared-divergent. Just such a strongly infrared-divergent bispectrum is predicted by inflation models with a non-Bunch-Davies initial state, for instance. Upper limits on the observed CMB power asymmetry place stringent constraints on the duration of inflation in such models.
The violent giant flares of magnetars excite QPOs which persist for hundreds of seconds, as seen in the X-ray tail following the initial burst. Recent studies, based on single-fluid barotropic magnetar models, have suggested that the lower-frequency QPOs correspond to magneto-elastic oscillations of the star. The higher frequencies, however, in particular the strong 625 Hz peak, have proved harder to explain, except as high mode multipoles. In this work we study the time evolutions of non-axisymmetric oscillations of two-fluid Newtonian magnetars with no crust. We consider models with superfluid neutrons and normal protons, and poloidal and toroidal background field configurations. We show that multi-fluid physics (composition-gradient stratification, entrainment) tends to increase Alfven mode frequencies significantly from their values in a single-fluid barotropic model. The higher-frequency magnetar QPOs may then be naturally interpreted as Alfven oscillations of the multi-fluid stellar core. The lower-frequency QPOs are less easily explained within our purely fluid core model, but we discuss the possibility that these are crustal modes.
We describe the VISTA Science Archive (VSA) and its first public release of
data from five of the six VISTA Public Surveys. The VSA exists to support the
VISTA Surveys through their lifecycle: the VISTA Public Survey consortia can
use it during their quality control assessment of survey data products before
submission to the ESO Science Archive Facility (ESO SAF); it supports their
exploitation of survey data prior to its publication through the ESO SAF; and,
subsequently, it provides the wider community with survey science exploitation
tools that complement the data product repository functionality of the ESO SAF.
This paper has been written in conjunction with the first public release of
public survey data through the VSA and is designed to help its users understand
the data products available and how the functionality of the VSA supports their
varied science goals. We describe the design of the database and outline the
database-driven curation processes that take data from nightly
pipeline-processed and calibrated FITS files to create science-ready survey
datasets. Much of this design, and the codebase implementing it, derives from
our earlier WFCAM Science Archive (WSA), so this paper concentrates on the
VISTA-specific aspects and on improvements made to the system in the light of
experience gained in operating the WSA.
A precise characterisation of the red giants in the seismology fields of the CoRoT satellite is a prerequisite for further in-depth seismic modelling. The optical spectra obtained for 19 targets have been used to accurately estimate their fundamental parameters and chemical composition. The extent of internal mixing is also investigated through the abundances of Li, CNO and Na (as well as 12C/13C in a few cases).
We present a systematical analysis of the Chandra observations of 53 nearby highly-inclined (i>60 degree) disk galaxies to study the coronae around them. This sample covers a broad range of galaxy properties: e.g., about three orders of magnitude in the SFR and more than two orders of magnitude in the stellar mass. The Chandra observations of the diffuse soft X-ray emission from 20 of these galaxies are presented for the first time. The data are reduced in a uniform manner, including the excision/subtraction of both resolved and unresolved stellar contributions. Various coronal properties, such as the scale height and luminosity, are characterized for all the sample galaxies. For galaxies with high enough counting statistics, we also examine the thermal and chemical states of the coronal gas. We note on galaxies with distinct multi-wavelength characteristics which may affect the coronal properties. The uniformly processed images, spectra, and brightness profiles, as well as the inferred hot gas parameters, form a large X-ray database for studying the coronae around nearby disk galaxies. We also discuss various complications which may cause biases to this database and their possible corrections or effects, such as the uncertainty in the thermal and chemical states of hot gas, the different galactic disk inclination angles, the presence of AGN, and the contribution of the emission from charge exchange at interfaces between hot and cool gases. Results from a detailed correlation analysis are presented in a companion paper, to gain a more comprehensive statistical understanding of the origin of galactic coronae.
We present initial results from a new high-contrast imaging program dedicated to stars that exhibit long-term Doppler radial velocity accelerations (or "trends"). The goal of the TRENDS (TaRgetting bENchmark-objects with Doppler Spectroscopy and) imaging survey is to directly detect and study the companions responsible for accelerating their host star. In this first paper of the series, we report the discovery of low-mass stellar companions orbiting HD 53665, HD 68017, and HD 71881 using NIRC2 adaptive optics (AO) observations at Keck. Follow-up imaging demonstrates association through common proper-motion. These co-moving companions have red colors with estimated spectral-types of K7--M0, M5, and M3--M4 respectively. We determine a firm lower-limit to their mass from Doppler and astrometric measurements. In the near future, it will be possible to construct three-dimensional orbits and calculate the dynamical mass of HD 68017 B and possibly HD 71881 B. We already detect astrometric orbital motion of HD 68017 B, which has a projected separation of 13.0 AU. Each companion is amenable to AO-assisted direct spectroscopy. Further, each companion orbits a solar-type star, making it possible to infer metallicity and age from the primary. Such benchmark objects are essential for testing theoretical models of cool dwarf atmospheres.
We present an overview of the EXoplanetary Circumstellar Environments and Disk Explorer (EXCEDE), selected by NASA for technology development and maturation. EXCEDE will study the formation, evolution and architectures of exoplanetary systems, and characterize circumstellar environments into stellar habitable zones. EXCEDE provides contrast-limited scattered-light detection sensitivities ~ 1000x greater than HST or JWST coronagraphs at a much smaller effective inner working angle (IWA), thus enabling the exploration and characterization of exoplanetary circumstellar disks in currently inaccessible domains. EXCEDE will utilize a laboratory demonstrated high-performance Phase Induced Amplitude Apodized Coronagraph (PIAA-C) integrated with a 70 cm diameter unobscured aperture visible light telescope. The EXCEDE PIAA-C will deliver star-to-disk augmented image contrasts of < 10E-8 and a 1.2 L/D IWA or 140 mas with a wavefront control system utilizing a 2000-element MEMS DM and fast steering mirror. EXCEDE will provide 120 mas spatial resolution at 0.4 microns with dust detection sensitivity to levels of a few tens of zodis with two-band imaging polarimetry. EXCEDE is a science-driven technology pathfinder that will advance our understanding of the formation and evolution of exoplanetary systems, placing our solar system in broader astrophysical context, and will demonstrate the high contrast technologies required for larger-scale follow-on and multi-wavelength investigations on the road to finding and characterizing exo-Earths in the years ahead.
Using 43 months of public gamma-ray data from the Fermi Large Area Telescope, we find in regions close to the Galactic center at energies of 130 GeV a 4.6 sigma excess that is not inconsistent with a gamma-ray line from dark matter annihilation. When taking into account the look-elsewhere effect, the significance of the observed signature is 3.2 sigma. If interpreted in terms of dark matter particles annihilating into a photon pair, the observations imply a partial annihilation cross-section of about 10^-27 cm^3s^-1 and a dark matter mass around 130 GeV. We review aspects of the statistical analysis and comment on possible instrumental indications.
We study the growth of cosmic structure under the assumption that dark matter self-annihilates with an averaged cross section times relative velocity that grows with the scale factor, an increase known as Sommerfeld-enhancement. Such an evolution is expected in models in which a light force carrier in the dark sector enhances the annihilation cross section of dark matter particles, and has been invoked, for instance, to explain anomalies in cosmic ray spectra reported in the past. In order to make our results as general as possible, we assume that dark matter annihilates into a relativistic species that only interacts gravitationally with the standard model. This assumption also allows us to test whether the additional relativistic species mildly favored by cosmic-microwave background data could originate from dark matter annihilation. We do not find evidence for Sommerfeld-enhanced dark matter annihilation and derive the corresponding upper limits on the annihilation cross-section.
We study the constraints on the cosmic opacity using the latest BAO and Union2 SNIa data in this paper and find that the best fit values seem to indicate that an opaque universe is preferred in redshift regions $0.20-0.35$, $0.35-0.44$ and $0.60-0.73$, whereas, a transparent universe is favored in redshift regions $0.106-0.20$, $0.44-0.57$and $0.57-0.60$. However, our result is still consistent with a transparent universe at the 1$\sigma$ confidence level, even though the best-fit cosmic opacity oscillates between zero and some nonzero values as the redshift varies.
This article studies sufficient accuracy criteria of hybrid post-Newtonian (PN) and numerical relativity (NR) waveforms for parameter estimation of strong binary black-hole sources in second- generation ground-based gravitational-wave detectors. We investigate equal-mass non-spinning binaries with a new 33-orbit NR waveform, as well as unequal-mass binaries with mass ratios 2, 3, 4 and 6. For equal masses, the 33-orbit NR waveform allows us to recover previous results and to extend the analysis toward matching at lower frequencies. For unequal masses, the errors between different PN approximants increase with mass ratio. Thus, at 3.5PN, hybrids for higher-mass-ratio systems would require NR waveforms with many more gravitational-wave (GW) cycles to guarantee no adverse impact on parameter estimation. Furthermore, we investigate the potential improvement in hybrid waveforms that can be expected from 4th order post-Newtonian waveforms, and find that knowledge of this 4th post-Newtonian order would significantly improve the accuracy of hybrid waveforms.
We examine the first ATLAS Collaboration 8 TeV 5.8/fb supersymmetry (SUSY) multijet data observations in the context of No-Scale Flipped SU(5) with extra TeV-Scale vector-like flippon multiplets, dubbed F-SU(5), finding that the recent 8 TeV collider data is statistically consistent with our prior 7 TeV results. Furthermore, we synthesize all currently ongoing experiments searching for beyond the Standard Model (BSM) physics with this fit to the 8 TeV data, establishing a suggestive global coherence within a No-Scale F-SU(5) high-energy framework. The SUSY mass scale consistent with all BSM data consists of the region of the F-SU(5) model space within 660 ~< M_{1/2} ~< 760 GeV, which corresponds to sparticle masses of 133 ~< M(chi_1^0) ~< 160 GeV, 725 ~< M(t_1) ~< 845 GeV, and 890 ~< M(g) ~< 1025 GeV. We suggest that the tight non-trivial correspondence between the SUSY multijets, direct and indirect searches for dark matter, proton decay, rare-decay processes, the observed Higgs boson mass, and the measured dark matter relic density, is strongly indicative of a deeper fundamental relationship. We additionally suggest a simple mechanism for enhancing the capture efficiency of F-SU(5) SUSY multijets, which results in a 93% suppression in ATLAS reported background events, but only a 27% decrease in Monte Carlo simulated F-SU(5) multijet events.
The application of Effective Field Theory (EFT) methods to inflation has taken a central role in our current understanding of the very early universe. The EFT perspective has been particularly useful in analyzing the self-interactions determining the evolution of co-moving curvature perturbations (Goldstone boson modes) and their influence on low-energy observables. However, the standard EFT formalism, to lowest order in spacetime differential operators, does not provide the most general parametrization of a theory that remains weakly coupled throughout the entire low-energy regime. Here we study the EFT formulation by including spacetime differential operators implying a scale dependence of the Goldstone boson self-interactions and its dispersion relation. These operators are shown to arise naturally from the low-energy interaction of the Goldstone boson with heavy fields that have been integrated out. We find that the EFT then stays weakly coupled all the way up to the cutoff scale at which ultraviolet degrees of freedom become operative. This opens up a regime of new physics where the dispersion relation is dominated by a quadratic dependence on the momentum $\omega \sim p^2$. In addition, provided that modes crossed the horizon within this energy range, the prediction of inflationary observables --including non-Gaussian signatures-- are significantly affected by the new scales characterizing it.
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A generic prediction of the single-degenerate model for Type Ia supernovae (SNe Ia) is that a significant amount of material will be stripped from the donor star (~0.5 M_sol for a giant donor and ~0.15 M_sol for a main sequence donor) by the supernova ejecta. This material, excited by gamma-rays from radioactive decay, would then produce relatively narrow (<1000 km s^-1) emission features observable once the supernova enters the nebular phase. Such emission has never been detected, which already provides strong constraints on Type Ia progenitor models. In this Letter we report the deepest limit yet on the presence of H alpha emission originating from the stripped hydrogen in the nebular spectrum of a Type Ia supernova obtained using a high signal-to-noise spectrum of the nearby normal SN Ia 2011fe 274 days after B-band maximum light with the Large Binocular Telescope's Multi-Object Double Spectrograph. We put a conservative upper limit on the H alpha flux of 3.14x10^-17 erg/s/cm^2, which corresponds to a luminosity of 1.57x10^35 erg/s. Assuming the models of Mattila et al. (2005) and the methods of Leonard (2007), this translates into an upper limit of <0.001 M_sol of stripped material, which is an order of magnitude stronger than previous limits by Leonard (2007). SN 2011fe was a typical Type Ia supernova, special only in its proximity, and we argue that lack of hydrogen emission in its nebular spectrum adds yet another strong constraint on the single degenerate class of models for SNe Ia.
Strong evidence is emerging that winds can be driven from the central regions of accretion disks in both active galactic nuclei (AGN) and Galactic black hole binaries (GBHBs). Direct evidence for highly-ionized, Compton-thin inner-disk winds comes from observations of blueshifted (v~0.05-0.1c) iron-K X-ray absorption lines. However, it has been suggested that the inner regions of black hole accretion disks can also drive Compton-thick winds --- such winds would enshroud the inner disk, preventing us from seeing direct signatures of the accretion disk (i.e. the photospheric thermal emission, or the Doppler/gravitationally broadened iron K-alpha line). Here, we show that, provided the source is sub-Eddington, the well-established wind driving mechanisms fail to launch a Compton-thick wind from the inner disk. For the accelerated region of the wind to be Compton-thick, the momentum carried in the wind must exceed the available photon momentum by a factor of at least 2/lambda, where lambda is the Eddington ratio of the source, ruling out radiative acceleration unless the source is very close to the Eddington limit. Compton-thick winds also carry large mass-fluxes, and a consideration of the connections between the wind and the disk show this to be incompatible with magneto-centrifugal driving. Finally, thermal driving of the wind is ruled out on the basis of the large Compton-radii that typify black hole systems. In the absence of some new acceleration mechanism, we conclude that the inner regions of sub-Eddington accretion disks around black holes are indeed naked.
The asymptotic giant branch star R Sculptoris is surrounded by a detached shell of dust and gas. The shell originates from a thermal pulse during which the star undergoes a brief period of increased mass loss. It has hitherto been impossible to constrain observationally the timescales and mass-loss properties during and after a thermal pulse - parameters that determine the lifetime on the asymptotic giant branch and the amount of elements returned by the star. Here we report observations of CO emission from the circumstellar envelope and shell around R Sculptoris with an angular resolution of 1.3 arcsec. What was hitherto thought to be only a thin, spherical shell with a clumpy structure, is revealed to contain a spiral structure. Spiral structures associated with circumstellar envelopes have been seen previously, from which it was concluded that the systems must be binaries. Using the data, combined with hydrodynamic simulations, we conclude that R Sculptoris is a binary system that underwent a thermal pulse approximately 1800 years ago, lasting approximately 200 years. About 0.003 Msun of mass was ejected at a velocity of 14.3 km s-1 and at a rate approximately 30 times higher than the prepulse mass-loss rate. This shows that approximately 3 times more mass is returned to the interstellar medium during and immediately after a pulse than previously thought.
Many cosmological models invoke rolling scalar fields to account for the observed acceleration of the expansion of the universe. These theories generally include a potential V(phi) which is a function of the scalar field phi. Although V(phi) can be represented by a very diverse set of functions, recent work has shown the under some conditions, such as the slow roll conditions, the equation of state parameter w is either independent of the form of V(phi) or is part of family of solutions with only a few parameters. In realistic models of this type the scalar field couples to other sectors of the model leading to possibly observable changes in the fundamental constants such as the fine structure constant alpha and the proton to electron mass ratio mu. This paper explores the limits this puts on the validity of various cosmologies that invoke rolling scalar fields. We find that the limit on the variation of mu puts significant constraints on the product of a cosmological parameter w+1 times a new physics parameter zeta_mu^2, the coupling constant between mu and the rolling scalar field. Even when the cosmologies are restricted to very slow roll conditions either the value of zeta_mu must be at the lower end of or less than its expected values or the value of w+1 must be restricted to values vanishingly close to 0. This implies that either the rolling scalar field is very weakly coupled with the electromagnetic field, small zeta_mu, very weakly coupled with gravity, w+1 ~ 0 or both. These results stress that adherence to the measured invariance in mu is a very significant test of the validity of any proposed cosmology and any new physics it requires. The limits on the variation of mu also produces a significant tension with the reported changes in the value of alpha.
The lightcurve of the explosion of a star with a radius <10-100Rsun is powered mostly by radioactive decay. Observationally such events are dominated by hydrogen deficient progenitors and classified as Type I supernovae: white dwarf thermonuclear explosions (Type Ia) and core collapses of hydrogen-stripped massive stars (Type Ibc). Transient surveys are finding SNe I in increasing numbers and at earlier times, allowing their early emission to be studied in unprecedented detail. Motivated by these developments, we summarize the physics that produces their rising lightcurves and discuss how observations can be utilized to study these exploding stars. The early radioactive-powered lightcurves probe the shallowest 56Ni deposits. If the amount of 56Ni mixing can be deduced, then it places constraints on the progenitor and properties of the explosive burning. In practice we find it is difficult to disentangle whether the explosion occurred recently and one is seeing 56Ni heating near the surface or whether the explosion began in the past and 56Ni heating is deeper. In the latter case there is a "dark phase" between the moment of explosion and the first light observed from the shallowest layers of 56Ni. Because of this, simply extrapolating a lightcurve from 56Ni back in time is not a reliable method for estimating the explosion time. The best solution is to directly identify the moment of explosion, by either observing shock breakout or shock-heated surface cooling, so the depth being probed by the rising lightcurve is known. Since this is typically not available, we identify other diagnostics that are helpful for deciphering how recently an explosion occurred. As an example we apply these arguments to the SN Ic PTF 10vgv. We demonstrate that just a single measurement of the photospheric velocity and temperature during the rise places constraints on its explosion time, radius, and 56Ni mixing.
The near-infrared to optical-ultraviolet (0.1 -- 10 $\mu m$) spectral energy distribution (SED) shapes of 407 X-ray-selected radio-quiet type 1 AGN in the wide-field "Cosmic Evolution Survey" (COSMOS) have been studied for signs of evolution. For a sub-sample of 200 radio-quiet quasars with black hole mass estimation and host galaxy correction, we study the mean SEDs as a function of a broad range of redshift, bolometric luminosity, black hole mass and Eddington ratio, and compare them with the Elvis et al. (1994, E94) type 1 AGN mean SED. The mean SEDs in each bin are very similar to each other, showing no evidence of dependence on any of the analyzed parameters. We also checked the SED dispersion as a function of these four parameters, and found no significant dependance. The dispersion of the XMM-COSMOS SEDs is generally larger than E94 SED dispersion in the ultraviolet, which might be largely due to the broader "window function" for COSMOS quasars, and the X-ray based selection technique.
The Milky Way centre hosts a supermassive Black Hole (BH) with a mass of ~4*10^6 M_Sun. Sgr A*, its electromagnetic counterpart, currently appears as an extremely weak source with a luminosity L~10^-9 L_Edd. The lowest known Eddington ratio BH. However, it was not always so; traces of "glorious" active periods can be found in the surrounding medium. We review here our current view of the X-ray emission from the Galactic Center (GC) and its environment, and the expected signatures (e.g. X-ray reflection) of a past flare. We discuss the history of Sgr A*'s past activity and its impact on the surrounding medium. The structure of the Central Molecular Zone (CMZ) has not changed significantly since the last active phase of Sgr A*. This relic torus provides us with the opportunity to image the structure of an AGN torus in exquisite detail.
The first stars in the universe ionized the ambient primordial gas through various feedback processes. "Second-generation" primordial stars potentially form from this disturbed gas after its recombination. In this Letter, we study the late formation stage of such second-generation stars, where a large amount of gas accretes onto the protostar and the final stellar mass is determined when the accretion terminates. We directly compute the complex interplay between the accretion flow and stellar ultraviolet (UV) radiation, performing radiation-hydrodynamic simulations coupled with stellar evolution calculations. Because of more efficient H2 and HD cooling in the pre-stellar stage, the accretion rates onto the star are ten times lower than in the case of the formation of the first stars. The lower accretion rates and envelope density result in the occurrence of an expanding bipolar HII region at a lower protostellar mass M_* \simeq 10Msun, which blows out the circumstellar material, thereby quenching the mass supply from the envelope to the accretion disk. At the same time the disk loses mass due to photoevaporation by the growing star. In our fiducial case the stellar UV feedback terminates mass accretion onto the star at M_* \simeq 17Msun. Although the derived masses of the second-generation primordial stars are systematically lower than those of the first generation, the difference is within a factor of only a few. Our results suggest a new scenario, whereby the majority of the primordial stars are born as massive stars with tens of solar masses, regardless of their generations.
We present a detailed study of the QSO-galaxy pair [SDSS J163956.35+112758.7 (zq = 0.993) and SDSS J163956.38+112802.1 (zg = 0.079)] based on observations carried out using the Giant Meterwave Radio Telescope (GMRT), the Very Large Baseline Array (VLBA), the Sloan Digital Sky Survey (SDSS) and the ESO New Technology Telescope (NTT). We show that the interstellar medium of the galaxy probed by the QSO line of sight has near-solar metallicity (12+log(O/H) = 8.47+/-0.25) and dust extinction (E(B-V) 0.83+/-0.11) typical of what is usually seen in translucent clouds. We report the detection of absorption in the \lambda 6284 diffuse interstellar band (DIB) with a rest equivalent width of 1.45+/-0.20\AA. Our GMRT spectrum shows a strong 21-cm absorption at the redshift of the galaxy with an integrated optical depth of 15.70+/-0.13 km/s. Follow-up VLBA observations show that the background radio source is resolved into three components with a maximum projected separation of 89 pc at the redshift of the galaxy. One of these components is too weak to provide useful HI 21-cm absorption information. The integrated HI optical depth towards the other two components are higher than that measured in our GMRT spectrum and differ by a factor 2. By comparing the GMRT and VLBA spectra we show the presence of structures in the 21-cm optical depth on parsec scales. We discuss the implications of such structures for the spin-temperature measurements in high-z damped Lyman-alpha systems. The analysis presented here suggests that this QSO-galaxy pair is an ideal target for studying the DIBs and molecular species using future observations in optical and radio wavebands.
We present the first results of an ongoing spectroscopic follow-up program of blue H-alpha excess sources within the Kepler field-of-view, in order to identify new cataclysmic variables. Kepler observations of the identified targets in this work will then provide detailed, time-resolved, studies of accretion. Candidates selected from the Kepler-INT Survey were observed with the 4.2 meter William Herschel Telescope. Out of 38 observed candidates, we found 11 new cataclysmic variables reported here for the first time, as well as 13 new quasars. Our target selection has a success rate of 29% when searching for cataclysmic variables, and we show how this can be improved by including photometry obtained with the Wide-field Infrared Survey Explorer.
We discuss the prospects to measure galaxy-cluster properties via weak lensing of 21-cm fluctuations from the dark ages and the epoch of reionization (EoR). We choose as a figure of merit the smallest cluster mass detectable through such measurements. We construct the minimum-variance quadratic estimator for the cluster mass based on lensing of 21-cm fluctuations at multiple redshifts. We discuss the tradeoff between frequency bandwidth, angular resolution, and number of redshift shells available for a fixed noise level for the radio detectors. Observations of lensing of the 21-cm background from the dark ages will be capable of detecting M>~10^12 Msun/h mass halos, but will require futuristic experiments to overcome the contaminating sources. Next-generation radio measurements of 21-cm fluctuations from the EoR will, however, have the sensitivity to detect galaxy clusters with halo masses M>~10^13 Msun/h, given enough observation time (for the relevant sky patch) and collecting area to maximize their resolution capabilities.
We define the quasar-galaxy mixing diagram by the slopes of the spectral energy distribution (SED) of quasars from $1\mu m$ to 3000 \AA\ and from $1\mu m$ to 3 $\mu m$ in the rest frame. The mixing diagram can easily distinguish among quasar-dominated, galaxy-dominated and reddening-dominated SED shapes. By studying the position of the 413 XMM selected Type 1 AGN in the wide-field "Cosmic Evolution Survey" (COSMOS) in the mixing diagram, we find that a combination of the Elvis et al. (1994, hereafter E94) quasar SED with various contributions from galaxy emission and some dust reddening is remarkably effective in describing the SED shape near $1\mu m$ for large ranges of redshift, luminosity, black hole mass and Eddington ratio of type 1 AGN. In particular, the location in the mixing diagram of the highest luminosity AGN is very close (within 1$\sigma$) to that expected on the basis of the E94 SED. The mixing diagram can also be used to estimate the host galaxy fraction and reddening in the SED. We also show examples of some outliers which might be AGN in different evolutionary stages compared to the majority of AGN in the quasar-host galaxy co-evolution cycle.
The TASTE project is searching for low-mass planets with the Transit Timing Variation (TTV) technique, by gathering high-precision, short-cadence light curves for a selected sample of transiting exoplanets. It has been claimed that the "hot Jupiter" WASP-3b could be perturbed by a second planet. Presenting eleven new light curves (secured at the IAC80 and UDEM telescopes) and re-analyzing thirty-eight archival light curves in a homogeneous way, we show that new data do not confirm the previously claimed TTV signal. However, we bring evidence that measurements are not consistent with a constant orbital period, though no significant periodicity can be detected. Additional dynamical modeling and follow-up observations are planned to constrain the properties of the perturber or to put upper limits to it. We provide a refined ephemeris for WASP-3b and improved orbital/physical parameters. A contact eclipsing binary, serendipitously discovered among field stars, is reported here for the first time.
Because of the objectively existing causes, such as an irregular shape of a celestial body, the lack of the satellites, the low values of albedo at moderate sizes, and a large remoteness from the Sun, creating a more exact the physical properties database of trans-Neptunian dwarf planets in comparison with existing that continues to remain a problem. We offer a new calculation procedure of the physical properties of these objects involving earlier unknown the relationships harmonizing these properties. It allows us to conjecture of they are a group of uniform celestial bodies by their origin beyond the Kuiper belt. The calculated physical properties of these dwarf planets are in a good agreement with the estimates received from observational data and can form the basis for support the validity of this improved physical properties database.
We present VLT/X-shooter observations of a high redshift, type Ia supernova host galaxy, discovered with HST/WFC3 as part of the CANDELS Supernova project. The galaxy exhibits strong emission lines of Ly{\alpha}, [O II], H{\beta}, [O III], and H{\alpha} at z = 1.54992(+0.00008-0.00004). From the emission-line fluxes and SED fitting of broad-band photometry we rule out AGN activity and characterize the host galaxy as a young, low mass, metal poor, starburst galaxy with low intrinsic extinction and high Ly{\alpha} escape fraction. The host galaxy stands out in terms of the star formation, stellar mass, and metallicity compared to its lower redshift counterparts, mainly because of its high specific star-formation rate. If valid for a larger sample of high-redshift SN Ia host galaxies, such changes in the host galaxy properties with redshift are of interest because of the potential impact on the use of SN Ia as standard candles in cosmology.
We present an eclipse timing variations analysis of the post-common envelope binary NSVS 14256825, which is composed by a sdOB star and a dM star in a close orbit (P_{orb} = 0.110374 days). High-speed photometry of this system was performed between July, 2010 and August, 2012. Ten new mid-eclipse times of NSVS 14256825 were analyzed together with all available eclipse times in the literature. We revisited the O--C diagram using a linear ephemeris and detected a clear orbital period variation. We investigated this variation on the assumption that it is a light travel time (LTT) effect. A full orbital motion analysis indicates that two LTT shifts with semi-amplitudes of ~20 s and ~5 s are superimposed on the O--C diagram and are consistent with two circumbinary bodies. The best solution provides the orbital periods, P_c = 3.49 +/- 0.21 years and P_d = 6.86 +/- 0.25 years, and the projected semi-major axes, a_c \sin I_c = 1.9 +/- 0.3 AU and a_d \sin I_d = 2.9 +/- 0.6 AU, for the circumbinary bodies. The masses of the external bodies are M_c ~2.8 M_{Jupiter} and M_d ~8.1 M_{Jupiter}, if we assume their orbits are coplanar with the close binary. Therefore NSVS 14256825 is composed by the close binary and two circumbinary planets in a 2:1 mean motion resonance. The closer planet in NSVS 14256825 has the minimum binary-planet separation among all known circumbinary planets in post-common envelope systems.
Dense populations of stars surround the nuclear regions of galaxies. In this work, we study the interaction of a WR star with relativistic jets in active galactic nuclei. A bow-shaped double-shock structure will form as a consequence of the interaction of the jet and the wind of the star. Particles can be accelerated up to relativistic energies in these shocks and emit high-energy radiation. We compute the produced gamma-ray emission obtaining that this radiation may be significant. This emission is expected to be particularly relevant for nearby non-blazar sources.
Observations show that the underlying rotation curves at intermediate radii in spiral and low-surface brightness galaxies are nearly universal. Further, in these same galaxies, the product of the central density and the core radius ($\rho_{0}r_{0}$) is constant. An empirically motivated model for dark matter halos which incorporates these observational constraints is presented and shown to be in accord with the observations. A model fit to the observations of the galaxy cluster Abell 611 shows that $\rho_{0}r_{0}$ for the dark matter halo in this more massive structure is larger by a factor of $\sim 20$ over that assumed for the galaxies. The model maintains the successful NFW form in the outer regions although the well defined differences in the inner regions suggest that modifications to the standard CDM picture are required.
While clusters of galaxies are considered one of the most important cosmological probes, the standard spherical modelling of the dark matter and the intracluster medium is only a rough approximation. Indeed, it is well established both theoretically and observationally that galaxy clusters are much better approximated as triaxial objects. However, investigating the asphericity of galaxy clusters is still in its infancy. We review here this topic which is currently gathering a growing interest from the cluster community. We begin by introducing the triaxial geometry. Then we discuss the topic of deprojection and demonstrate the need for combining different probes of the cluster's potential. We discuss the different works that have been addressing these issues. We present a general parametric framework intended to simultaneously fit complementary data sets (X-ray, Sunyaev Zel'dovich and lensing data). We discuss in details the case of Abell 1689 to show how different models/data sets lead to different haloe parameters. We present the results obtained from fitting a 3D NFW model to X-ray, SZ, and lensing data for 4 strong lensing clusters. We argue that a triaxial model generally allows to lower the inferred value of the concentration parameter compared to a spherical analysis. This may alleviate tensions regarding, e.g. the over-concentration problem. However, we stress that predictions from numerical simulations rely on a spherical analysis of triaxial halos. Given that triaxial analysis will have a growing importance in the observational side, we advocate the need for simulations to be analysed in the very same way, allowing reliable and meaningful comparisons. Besides, methods intended to derive the three dimensional shape of galaxy clusters should be extensively tested on simulated multi-wavelength observations.
I present a new algorithm, CALCLENS, for efficiently computing weak gravitational lensing shear signals from large N-body light cone simulations over a curved sky. This new algorithm properly accounts for the sky curvature and boundary conditions, is able to produce redshift-dependent shear signals including corrections to the Born approximation by using multiple-plane ray tracing, and properly computes the lensed images of source galaxies in the light cone. The key feature of this algorithm is a new, computationally efficient Poisson solver for the sphere that combines spherical harmonic transform and multgrid methods. As a result, large areas of sky (~10, 000 square degrees) can be ray traced efficiently at high-resolution using only a few hundred cores on widely available machines. Using this new algorithm and curved-sky calculations that only use a slower but more accurate spherical harmonic transform Poisson solver, I study the shear B-mode and rotation mode power spectra. Employing full-sky E/B-mode decompositions, I confirm that the shear B-mode and rotation mode power spectra are equal at high accuracy (~1%), as expected from perturbation theory up to second order. Coupled with realistic galaxy populations placed in large N-body light cone simulations, this new algorithm is ideally suited for the construction of synthetic weak lensing shear catalogs to be used to test for systematic effects in data analysis procedures for upcoming large-area sky surveys. The implementation presented in this work, written in C and employing widely available software libraries to maintain portability, is publicly available at this http URL
Protostellar jets are present in the later stages of the stellar formation. Non-thermal radio emission has been detected from the jets and hot spots of some massive protostars, indicating the presence of relativistic electrons there. We are interested in exploring if these non-thermal particles can emit also at gamma-rays. In the present contribution we model the non-thermal emission produced in the jets associated with the massive protostar IRAS 18162-2048. We obtain that the gamma-ray emission produced in this source is detectable by the current facilities in the GeV domain.
In this contribution we model the non-thermal emission (from radio to gamma-rays) produced in the compact (and recently detected) colliding wind region in the multiple stellar system Cyg OB2 #5. We focus our study on the detectability of the produced gamma-rays.
Magnetic fields present in galaxy NGC 253 are exceptionally strong so that they can influence the rotation of matter and hence the mass-to-light ratio. In this context the issue of the presence of non-baryonic dark matter halo in this galaxy is addressed.
NACO is the famous and versatile diffraction limited NIR imager and spectrograph with which ESO celebrated 10 years of Adaptive Optics at the VLT. Since two years a substantial effort has been put in to understanding and fixing issues that directly affect the image quality and the high contrast performances of the instrument. Experiments to compensate the non-common-path aberrations and recover the highest possible Strehl ratios have been carried out successfully and a plan is hereafter described to perform such measurements regularly. The drift associated to pupil tracking since 2007 was fixed in October 2011. NACO is therefore even better suited for high contrast imaging and can be used with coronagraphic masks in the image plane. Some contrast measurements are shown and discussed. The work accomplished on NACO will serve as reference for the next generation instruments on the VLT, especially those working at the diffraction limit and making use of angular differential imaging (i.e. SPHERE, VISIR, possibly ERIS).
Recently Pop ({\it Solar Phys.} {\bf 276}, 351, 2012) identified a Laplace (or double exponential) distribution in the number of days with a given absolute value in the change over a day, in sunspot number, for days on which the sunspot number does change. We show this phenomenological rule has a physical origin attributable to sunspot formation, evolution, and decay, rather than being due to the changes in sunspot number caused by groups rotating onto and off the visible disc. We also demonstrate a simple method to simulate daily sunspot numbers over a solar cycle using the \cite{2012SoPh..276..351P} result, together with a model for the cycle variation in the mean sunspot number. The procedure is applied to three recent solar cycles. We check that the simulated sunspot numbers reproduce the observed distribution of daily changes over those cycles.
The Surface Detector array of the Pierre Auger Observatory can detect neutrinos with energy between 10^17 eV and 10^20 eV from point-like sources across the sky south of +55 deg and north of -65 deg declinations. A search has been performed for highly inclined extensive air showers produced by the interaction of neutrinos of all flavours in the atmosphere (downward-going neutrinos), and by the decay of tau leptons originating from tau neutrinos interactions in the Earth's crust (Earth-skimming neutrinos). No candidate neutrinos have been found in data up to 2010 May 31. This corresponds to an equivalent exposure of ~3.5 years of a full surface detector array for the Earth-skimming channel and ~2 years for the downward-going channel. An improved upper limit on the diffuse flux of tau neutrinos has been derived. Upper limits on the neutrino flux from point-like sources have been derived as a function of the source declination. Assuming a differential neutrino flux k_PS E^-2 from a point-like source, 90% C.L. upper limits for k_PS at the level of ~5 x 10^-7 and 2.5 x 10^-6 GeV cm^-2 s^-1 have been obtained over a broad range of declinations from the searches of Earth-skimming and downward-going neutrinos, respectively.
We have observed the primary electron spectrum from 30 GeV to 3 TeV using emulsion chambers flown by balloons at the top of the atmosphere, for the purpose of exploring the origin of cosmic rays in the Galaxy. The atmospheric gamma rays have been simultaneously observed in the 30 GeV $\sim$ 8 TeV energy range. In this paper, we estimate the atmospheric electron spectrum in the upper atmosphere ($<$ 10 ${\rm g/cm^2}$) from our observed gamma-ray spectrum using the electromagnetic shower theory in order to derive the primary cosmic-ray electron spectrum. The transport equations of the electron and gamma-ray spectrum are analytically solved and the results are compared with those of Monte Carlo simulation (MC). Since we used the observed atmospheric gamma rays as the source of atmospheric electrons, our solutions are free from ambiguities on the primary cosmic-ray nuclear spectra and nuclear interaction models included in MC. In the energy range above several hundred GeV, the Dalitz electrons produced directly from neutral pions contribute around 10 percent to the whole atmospheric electron spectrum at the depth of 4 ${\rm g/cm^2}$, which increases in importance at the higher altitude and cannot be ignored in TeV electron balloon observations.
We exploit the detection of three distinct stellar subpopulations in the red giant branch of the Fornax dwarf Spheroidal to probe its density distribution. This allows us to resolve directly the evolution with radius of the dark matter mass profile. We find that a cored dark matter halo provides a perfect fit to the data, being consistent with all three stellar populations well within 1-sigma, and for the first time we are able to put constraints on the core size of such a halo. With respect to previous work, we do not strengthen the statistical exclusion of a dark matter cusp in Fornax, but we find that Navarro-Frenk-White haloes would be required to have unrealistically large scale radii in order to be compatible with the data, hence low values of the concentration parameter. We are then forced to conclude that the Fornax dwarf Spheroidal sits within a dark matter halo having a constant density core, with a core size of between 0.6 and 1.8 kpc.
In this review, we look back upon the literature, which had the GREGOR solar telescope project as its subject including science cases, telescope subsystems, and post-focus instruments. The articles date back to the year 2000, when the initial concepts for a new solar telescope on Tenerife were first presented at scientific meetings. This comprehensive bibliography contains literature until the year 2012, i.e., the final stages of commissioning and science verification. Taking stock of the various publications in peer-reviewed journals and conference proceedings also provides the "historical" context for the reference articles in this special issue of Astronomische Nachrichten/Astronomical Notes.
We report high precision transit photometry of GJ1214b in JHKs bands taken simultaneously with the SIRIUS camera on the IRSF 1.4m telescope at Sutherland, South Africa. Our MCMC analyses show that the observed planet-to-star radius ratios in JHKs bands are R_{\rm p}/R_{\rm s,J} = 0.11833 \pm 0.00077, R_{\rm p}/R_{\rm s,H} = 0.11522 \pm 0.00079, R_{\rm p}/R_{\rm s,Ks} = 0.11459 \pm 0.00099, respectively. The radius ratios are well consistent with the previous studies by Bean et al. (2011) within 1\sigma, while our result in Ks band is shallower than and inconsistent at 4\sigma\ level with the previous measurements in the same band by Croll et al. (2011). We have no good explanation for this discrepancy at this point. Our overall results support a flat transmission spectrum in the observed bands, which can be explained by a water-dominated atmosphere or an atmosphere with extensive high-altitude clouds or haze. To solve the discrepancy of the radius ratios and to discriminate a definitive atmosphere model for GJ1214b in the future, further transit observations around Ks band would be especially important.
Cool white dwarfs with Teff < 6000 K are the remnants of the oldest stars that existed in our Galaxy. Their atmospheres, when properly characterized, can provide valuable information on white dwarf evolution and ultimately star formation through the history of the Milky Way. Understanding the atmospheres of these stars requires joined observational effort and reliable atmosphere modeling. We discuss and analyze recent observations of the near-ultraviolet (UV) and near-infrared (IR) spectrum of several cool white dwarfs including DQ/DQp stars showing carbon in their spectra. We present fits to the entire spectral energy distribution (SED) of selected cool stars, showing that the current pure-hydrogen atmosphere models are quite reliable, especially in the near-UV spectral region. Recently, we also performed an analysis of the coolest known DQ/DQp stars investigating further the origin of the C2 Swan bands-like spectral features that characterize the DQp stars. We show that the carbon abundances derived for DQp stars fit the trend of carbon abundance with Teff seen in normal cool DQ stars. This further supports the recent conclusion of Kowalski A&A (2010) that DQp stars are DQ stars with pressure distorted Swan bands. However, we encounter some difficulties in reproducing the IR part of the SED of stars having a mixed He/H atmosphere. This indicates limitations in current models of the opacity in dense He/H fluids.
We present modeled flux and linear polarisation signals of starlight that is reflected by spatially unresolved, horizontally inhomogeneous planets and discuss the effects of including horizontal inhomogeneities on the flux and polarisation signals of Earth-like exoplanets. Our code is based on an efficient adding--doubling algorithm, which fully includes multiple scattering by gases and aerosol/cloud particles. We divide a model planet into pixels that are small enough for the local properties of the atmosphere and surface (if present) to be horizontally homogeneous. Given a planetary phase angle, we sum up the reflected total and linearly polarised fluxes across the illuminated and visible part of the planetary disk, taking care to properly rotate the polarized flux vectors towards the same reference plane. We compared flux and polarisation signals of simple horizontally inhomogeneous model planets against results of the weighted sum approximation, in which signals of horizontally homogeneous planets are combined. Apart from cases in which the planet has only a minor inhomogeneity, the signals differ significantly. In particular, the shape of the polarisation phase function appears to be sensitive to the horizontal inhomogeneities. The same holds true for Earth-like model planets with patchy clouds above an ocean and a sandy continent. Our simulations clearly show that horizontal inhomogeneities leave different traces in flux and polarisation signals. Combining flux with polarisation measurements would help retrieving the atmospheric and surface patterns on a planet.
The binary systems that have been detected in gamma rays have proven very useful to study high-energy processes, in particular particle acceleration, emission and radiation reprocessing, and the dynamics of the underlying magnetized flows. Binary systems, either detected or potential gamma-ray emitters, can be grouped in different subclasses depending on the nature of the binary components or the origin of the particle acceleration: the interaction of the winds of either a pulsar and a massive star or two massive stars; accretion onto a compact object and jet formation; and interaction of a relativistic outflow with the external medium. We evaluate the potentialities of an instrument like the Cherenkov telescope array (CTA) to study the non-thermal physics of gamma-ray binaries, which requires the observation of high-energy phenomena at different time and spatial scales. We analyze the capability of CTA, under different configurations, to probe the spectral, temporal and spatial behavior of gamma-ray binaries in the context of the known or expected physics of these sources. CTA will be able to probe with high spectral, temporal and spatial resolution the physical processes behind the gamma-ray emission in binaries, significantly increasing as well the number of known sources. This will allow the derivation of information on the particle acceleration and emission sites qualitatively better than what is currently available.
Using a model based on the rotational modulation of the visibility of active regions, we analyse the high-accuracy CoRoT lightcurve of the active young star CoRoT102899501. Spectroscopic follow-up observations are used to derive its fundamental parameters. We compare its chromospheric activity level with a model of chrosmospheric activity evolution established by combining relationships between the R'HK index and the Rossby number with a recent model of stellar rotation evolution on the main sequence. We measure the spot coverage of the stellar surface as a function of time, and find evidence for a tentative increase from 5-14% at the beginning of the observing run to 13-29% 35 days later. A high level of magnetic activity on CoRoT102899501 is corroborated by a strong emission in the Balmer and Ca II HK lines (logR'HK ~ -4). The starspots used as tracers of the star rotation constrain the rotation period to 1.625+/-0.002 days and do not show evidence for differential rotation. The effective temperature (Teff=5180+/-80 K), surface gravity (logg=4.35+/-0.1), and metallicity ([M/H]=0.05+/-0.07 dex) indicate that the object is located near the evolutionary track of a 1.09+/-0.12 M_Sun pre-main sequence star at an age of 23+/-10 Myrs. This value is consistent with the "gyro-age" of about 8-25 Myrs, inferred using a parameterization of the stellar rotation period as a function of colour index and time established for the I-sequence of stars in stellar clusters. We conclude that the high magnetic activity level and fast rotation of CoRoT102899501 are manifestations of its stellar youth consistent with its estimated evolutionary status and with the detection of a strong Li I 6707.8 A absorption line in its spectrum. We argue that a magnetic activity level comparable to that observed on CoRoT102899501 could have been present on the Sun at the time of planet formation.
We report on the preparation of hydrogenated amorphous carbon nano-particles whose spectral characteristics include an absorption band at 217.5 nm with the profile and characteristics of the interstellar 217.5 nm feature. Vibrational spectra of these particles also contain the features commonly observed in absorption and emission from dust in the diffuse interstellar medium. These materials are produced under slow deposition conditions by minimizing the flux of incident carbon atoms and by reducing surface mobility. The initial chemistry leads to the formation of carbon chains, together with a limited range of small aromatic ring molecules, and eventually results in carbon nano-particles having an sp2/sp3 ratio = 0.4. Spectroscopic analysis of particle composition indicates that naphthalene and naphthalene derivatives are important constituents of this material. We suggest that carbon nano-particles with similar composition are responsible for the appearance of the interstellar 217.5 nm band and outline how these particles can form in situ under diffuse cloud conditions by deposition of carbon on the surface of silicate grains. Spectral data from carbon nano-particles formed under these conditions accurately reproduces IR emission spectra from a number of Galactic sources. We provide the first detailed fits to observational spectra of Type A and B emission sources based entirely on measured spectra of a carbonaceous material that can be produced in the laboratory.
Pre-main sequence (PMS) binaries are surrounded by circumbinary disks from which matter falls onto both components. The material dragged from the circumbinary disk flows onto each star through independent streams channelled by the variable gravitational field. The action of the bar-like potential is most prominent in high eccentricity systems made of two equal mass stars. AK Sco is a unique PMS system composed of two F5 stars in an orbit with e=0.47. Henceforth, it is an ideal laboratory to study matter infall in binaries and its role in orbit circularization. In this letter, we report the detection of a 1.3mHz ultra low frequency oscillation in the ultraviolet light curve at periastron passage. This oscillation last 7 ks being most likely fed by the gravitational energy released when the streams tails spiralling onto each star get in contact at periastron passage enhancing the accretion flow; this unveils a new mechanism for angular momentum loss during pre-main sequence evolution and a new type of interacting binary.
We analyze heating and cooling processes in accretion disks in binaries. For realistic parameters of the accretion disks in close binaries (with accretion rates from 1e-12 to 1e-7 Msun/year and \alpha from 0.1 to 0.01), the gas temperature in the outer parts of the disk is from 1e4 to 1e6 K. Our previous gas-dynamical studies of mass transfer in close binaries indicate that, for hot disks (with temperatures for the outer parts of the disk of several hundred thousand K), the interaction between the stream from the inner Lagrange point and the disk is shockless. To study the morphology of the interaction between the stream and a cool accretion disk, we carried out three-dimensional modeling of the flow structure in a binary for the case when the gas temperature in the outer parts of the forming disk does not exceed 13600 K. The flow pattern indicates that the interaction is again shockless. The computations provide evidence that, as is the case for hot disks, the zone of enhanced energy release (the "hot line") is located beyond the disk, and originates due to the interaction between the circum-disk halo and the stream.
Turbulence is ubiquitous in many astrophysical systems like galaxies, galaxy clusters and possibly even the IGM filaments. We study fluctuation dynamo action in turbulent systems focusing on one observational signature; the Faraday rotation measure (RM) from background radio sources seen through the magnetic field generated by such a dynamo. We simulate the fluctuation dynamo (FD) in periodic boxes up to resolutions of 512^3, with varying fluid and magnetic Reynolds numbers, and measure the resulting random RMs. We show that the resulting rms value of RM is quite significant, given that the FD produces intermittent fields. When the dynamo saturates, it is of order 40%-50% of the value expected in a model where fields of strength B_rms uniformly fill cells of the largest turbulent eddy but are randomly oriented from one cell to another. This level of RM dispersion obtains across different values of magnetic Reynolds number and Prandtl number explored. We also use the random RMs to probe the structure of the generated fields to distinguish the contribution from intense and diffuse field regions. We find that the strong field regions (say with B > 2B_rms) contribute only of order 15%-20% to the RM. Thus rare structures do not dominate the RM; rather the general 'sea' of volume filling fluctuating fields are the dominant contributors. We also show that the magnetic integral scale, L_{int}, which is directly related to the RM dispersion, increases in all the runs, as Lorentz forces become important to saturate the dynamo. It appears that due to the ordering effect of the Lorentz forces, L_{int} of the saturated field tends to a modest fraction, 1/2-1/3 of the integral scale of the velocity field, for all our runs. These results are then applied to discuss the RM signatures of FD generated fields in young galaxies, galaxy clusters and intergalactic filaments.
Observations of the gas giants show that both planets have dipolar magnetic fields: Jupiter's is very similar to the Earth's and Saturn's is very axisymmetric. We aim to construct realistic numerical models that explain these features. While the small density jump across terrestrial iron cores allows to use the Boussinesq approximation, the picture is different for the gas giants. Here, the density decreases around 5000 from the deep interior to the surface. Though most of this density jump is accommodated in the outer molecular envelopes, it may still be significant in the metallic dynamo region. Among other properties, the electrical conductivity varies significantly with radius, being roughly constant in the metallic hydrogen region and decaying exponentially in the molecular envelope. We solve an anelastic numerical dynamo model to explore the effects of density stratification and electrical conductivity variation on magnetic field generation. We use an anelastic version of the MHD code MagIC with density jumps up to 245 and an electrical conductivity that decays exponentially in the outer 5-30% of the simulated shell. Past simulations using constant conductivity showed that dipole-dominated magnetic fields are only found up to a density jump of 6. An increasing stratification progressively confines the most active convective region close to the outer boundary equator. Mean field models have shown that such a configuration prefers non-axisymmetric modes. The exponential conductivity decay helps by separating magnetic field generation from the dominant convective region. For intermediate stratifications (6< density jump <148), the dipole component dominates during short periods. Stable strongly dipolar solutions are found either when a large stratification, at E=10^-4, more clearly separates the dynamo from the dominant convective region, or when lower Ekman number is considered.
A suitable coupling of the inflaton phi to a vector kinetic term F^2 gives frozen and scale invariant vector perturbations. We compute the cosmological perturbations zeta that result from such coupling by taking into account the classical vector field that unavoidably gets generated at large scales during inflation. This generically results in a too anisotropic power spectrum of zeta. Specifically, the anisotropy exceeds the 1% level (10% level) if inflation lasted ~5 e-folds (~50 e-folds) more than the minimal amount required to produce the CMB modes. This conclusion applies, among others, to the application of this mechanism for magnetogenesis, for anisotropic inflation, and for the generation of anisotropic perturbations at the end of inflation through a waterfall field coupled to the vector (in this case, the unavoidable contribution that we obtain is effective all throughout inflation, and it is independent of the waterfall field). For a tuned duration of inflation, a 1% (10%) anisotropy in the power spectrum corresponds to an anisotropic bispectrum which is enhanced like the local one in the squeezed limit, and with an effective local f_{NL} ~3 (~30). More in general, a significant anisotropy of the perturbations may be a natural outcome of all models that sustain higher than 0 spin fields during inflation.
We consider several early Universe models that allow for production of large curvature perturbations at small scales. As is well known, such perturbations can lead to production of primordial black holes (PBHs). We briefly review the Gaussian case and then focus on two models which produce strongly non-Gaussian perturbations: hybrid inflation waterfall model and the curvaton model. We show that limits on the values of curvature perturbation power spectrum amplitude are strongly dependent on the shape of perturbations and can significantly (by two orders of magnitude) deviate from the usual Gaussian limit of ${\cal P}_\zeta \lesssim 10^{-2}$. We give examples of PBH mass spectra calculations for each case.
We aim to better understand the emission of molecular tracers of the diffuse and dense gas in giant molecular clouds and the influence that metallicity, optical extinction, density, far-UV field, and star formation rate have onto these tracers. Using the IRAM 30m telescope, we detected HCN, HCO+, 12CO, and 13CO in six GMCs along the major axis of M33 at a resolution of ~ 114pc and out to a radial distance of 3.4kpc. Optical, far-infrared, and submillimeter data from Herschel and other observatories complement these observations. To interpret the observed molecular line emission, we created two grids of models of photon-dominated regions, one for solar and one for M33-type subsolar metallicity. The observed HCO+/HCN line ratios range between 1.1 and 2.5. Similarly high ratios have been observed in the Large Magellanic Cloud. The HCN/CO ratio varies between 0.4% and 2.9% in the disk of M33. The 12CO/13CO line ratio varies between 9 and 15 similar to variations found in the diffuse gas and the centers of GMCs of the Milky Way. Stacking of all spectra allowed HNC and C2H to be detected. The resulting HCO+/HNC and HCN/HNC ratios of ~ 8 and 6, respectively, lie at the high end of ratios observed in a large set of (ultra-)luminous infrared galaxies. HCN abundances are lower in the subsolar metallicity PDR models, while HCO+ abundances are enhanced. For HCN this effect is more pronounced at low optical extinctions. The observed HCO+/HCN and HCN/CO line ratios are naturally explained by subsolar PDR models of low optical extinctions between 3 and 10 mag and of moderate densities of n = 3x10^3 - 3x10^4 cm^-3, while the FUV field strength has only little effect on the modeled line ratios. The line ratios are almost equally well reproduced by the solar-metallicity models, indicating that variations in metallicity only play a minor role in influencing these line ratios.
Precise measurements of the cosmic microwave background (CMB) are crucial in cosmology, because any proposed model of the universe must account for the features of this radiation. Of all CMB measurements that the scientific community has not yet been able to perform, the CMB B-mode polarization is probably the most challenging from the instrumental point of view. The signature of primordial gravitational waves, which give rise to a B-type polarization, is one of the goals in cosmology today and amongst the first objectives in the field. For this purpose, high-performance low-temperature bolometric cameras, made of thousands of pixels, are currently being developed by many groups, which will improve the sensitivity to B-mode CMB polarization by one or two orders of magnitude compared to the Planck satellite HFI detectors. We present here a new bolometer structure that is able to increase the pixel sensitivities and to simplify the fabrication procedure. This innovative device replaces delicate membrane-based structures and eliminates the mediation of phonons: the incoming energy is directly captured and measured in the electron bath of an appropriate sensor and the thermal decoupling is achieved via the intrinsic electron-phonon decoupling of the sensor at very low temperature. Reported results come from a 204-pixel array of Nb$_{x}$Si$_{1-x}$ transition edge sensors with a meander structure fabricated on a 2-inch silicon wafer using electron-beam co-evaporation and a cleanroom lithography process. To validate the application of this device to CMB measurements, we have performed an optical calibration of our sample in the focal plane of a dilution cryostat test bench. We have demonstrated a light absorption close to 20% and an NEP of about 7$\times10^{-16}$ W/$\sqrt{Hz}$, which is highly encouraging given the scope for improvement in this type of detectors.
We report on searches for neutrino sources at energies above 200 GeV in the Northern sky of the galactic plane, using the data collected by the South Pole neutrino telescopes IceCube and AMANDA. The galactic region considered here includes the Local Arm towards the Cygnus region and our closest approach to the Perseus Arm. The data have been collected between 2007 and 2009 when AMANDA was an integrated part of IceCube, which was still under construction and operated with 22-strings (2007-8) and 40-strings (2008-9) of optical modules deployed in the ice. By combining the larger IceCube detector with the lower energy threshold of the more compact AMANDA detector, we obtain an improved sensitivity at energies below $\sim$10 TeV with respect to previous searches. The analyses presented here are: a scan for point sources within the galactic plane; a search optimized for multiple and extended sources in the Cygnus region, which might be below the sensitivity of the point source scan; and studies of seven pre-selected neutrino source candidates. For one of them, Cygnus X-3, a time-dependent search for neutrinos in coincidence with observed radio and X-ray flares has been performed. No evidence of a signal is found, and upper limits are reported for each of the searches. We investigate neutrino spectra proportional to E$^{-2}$ and E$^{-3}$ to cover the entire range of possible spectra. The soft E$^{-3}$ spectrum results in an energy distribution similar to a source with cut-off below $\sim$50 TeV. For the considered region of the galactic plane, the 90% confidence level muon neutrino flux upper limits are in the range E$^3$dN/dE$\sim 5.4 - 19.5 \times 10^{-11} \rm{TeV^{2} cm^{-2} s^{-1}}$ for point-like neutrino sources in the energy region [180.0 GeV - 20.5 TeV]. These represent the most stringent upper limits for soft-spectra neutrino sources within the Galaxy reported to date.
From previous studies of the effect of primordial magnetic fields on early structure formation, we know that the presence of primordial magnetic fields during early structure formation could induce more perturbations at small scales (at present 1-10 Mpc/h) as compared to the usual LCDM theory. Matter power spectrum over these scales are effectively probed by cosmological observables such as shear correlation and Ly-alpha clouds, In this paper we discuss the implications of primordial magnetic fields on the distribution of Ly-alpha clouds. We simulate the line of sight density fluctuation including the contribution coming from the primordial magnetic fields. We compute the evolution of Ly-alpha opacity for this case and compare our theoretical estimates of Ly-alpha opacity with the existing data to constrain the parameters of the primordial magnetic fields. We also discuss the case when the two density fields are correlated. Our analysis yields an upper bounds of roughly 0.3-0.6 nG on the magnetic field strength for a range of nearly scale invariant models, corresponding to magnetic field power spectrum index n \simeq -3.
The next generation of wide-area sky surveys offer the power to place extremely precise constraints on cosmological parameters and to test the source of cosmic acceleration. These observational programs will employ multiple techniques based on a variety of statistical signatures of galaxies and large-scale structure. These techniques have sources of systematic error that need to be understood at the percent-level in order to fully leverage the power of next-generation catalogs. Simulations of large-scale structure provide the means to characterize these uncertainties. We are using XSEDE resources to produce multiple synthetic sky surveys of galaxies and large-scale structure in support of science analysis for the Dark Energy Survey. In order to scale up our production to the level of fifty 10^10-particle simulations, we are working to embed production control within the Apache Airavata workflow environment. We explain our methods and report how the workflow has reduced production time by 40% compared to manual management.
We have analyzed a long-look Suzaku observation of the Seyfert 1.2 Mkn~590. We aimed to measure the Compton reflection strength, Fe K complex properties and soft excess emission as had been observed previously in this source. The Compton reflection strength was measured to be in the range 0.2-1.0 depending on the model used. A moderately strong Fe \ka emission line was detected with an equivalent width of ~120+/-25 eV and an Fe Kb line was identified with an equivalent width of ~30+/-20 eV, although we could not rule out contribution from ionized Fe emission at this energy. Surprisingly, we found no evidence for soft excess emission. Comparing our results with a 2004 observation from XMM-Newton we found that either the soft excess has decreased by a factor of 20-30 in 7 years or the photon index has steepened by 0.10 (with no soft excess present) while the continuum flux in the range 2-10 keV has varied only minimally (10%). This result could support recent claims that the soft excess is independent of the X-ray continuum.
We present an empirical working model for sunspot umbrae which equally describes observed continuum intensities and line profiles. The wings of the infrared Ca II lines depend sensitively on the temperature gradient at -0.6 < log(tau-0.5) < +0.3 but not essentially on the absolute value of T. These lines are observed to remain almost unchanged from photosphere to umbra and are thus insensitive to parasitic light. It is also shown that the infrared K I 7699 line is suitable for umbral spectroscopy since it is not seriously blended, its continuum is well defined and it is less influenced by parasitic light as compared to lines in the visible spectrum, due to the smaller umbal contrast. Calculations show that the umbral gradient dT/d(tau), required to fit the Ca II triplet lines, strongly conflicts with the observed profiles of K I 7699, NaD2 and Fe I 5434 (g=0), even when assuming vanishing Fe II lines for a maximum correction of parasitic light. It is shown that the discrepancy from the different line profiles may be removed by adopting an opacity enhancement as introduced by Zwaan (1974) from a discussion of continuum contrasts alone. The finally proposed umbral working model is very close to a scaled model of the quiet sun with T(eff)= 4000 K thus resembling a M0 rather than a K5 stellar atmosphere
We present correlation results for the radio halo power in galaxy clusters with the integrated thermal Sunyaev-Zel'dovich (SZ) effect signal, including new results obtained at sub-GHz frequencies. The radio data is compiled from several published works, and the SZ measurements are taken from the Planck ESZ cluster catalog. The tight correlation between the radio halo power and the SZ effect demonstrates a clear correspondence between the thermal and non-thermal electron populations in the intra-cluster medium, as already has been shown in X-ray based studies. The radio power varies roughly as the square of the global SZ signal, but when the SZ signal is scaled to within the radio halo radius the correlation becomes approximately linear, with reduced intrinsic scatter. We do not find any strong indication of a bi-modal division in the radio halo cluster population, as has been reported in the literature, which suggests that such duality could be an artifact of X-ray selection. We compare the SZ signal dependence of radio halos with simplified predictions from theoretical models, and discuss some implications and shortcomings of the present work.
Recent analysis revealed that supergranules (convection cells seen at the Sun's surface) are advected by the zonal flows at depths equal to the widths of the cells themselves. Here we probe the structure of the meridional circulation by cross-correlating maps of the Doppler velocity signal using a series of successively longer time lags between maps. We find that the poleward meridional flow decreases in amplitude with time lag and reverses direction to become an equatorward return flow at time lags > 24 hours. These cross-correlation results are dominated by larger and deeper cells at longer time lags. (The smaller cells have shorter lifetimes and do not contribute to the correlated signal at longer time lags.) We determine the characteristic cell size associated with each time lag by comparing the equatorial zonal flows measured at different time lags with the zonal flows associated with different cell sizes from a Fourier analysis. This association gives a characteristic cell size of ~50 Mm at a 24 hour time lag. This indicates that the poleward meridional flow returns equatorward at depths > 50 Mm -- just below the base of the surface shear layer. A substantial and highly significant equatorward flow (4.6 +/- 0.4 m/s) is found at a time lag of 28 hours corresponding to a depth of ~70 Mm. This represents one of the first positive detections of the Sun's meridional return flow and illustrates the power of using supergranules to probe the Sun's internal dynamics.
The magnetosphere of a rotating pulsar naturally develops a current sheet beyond the light cylinder (LC). Magnetic reconnection in this current sheet inevitably dissipates a nontrivial fraction of the pulsar spin-down power within a few LC radii. We develop a basic physical picture of reconnection in this environment and discuss its implications for the observed pulsed gamma-ray emission. We argue that reconnection proceeds in the plasmoid-dominated regime, via an hierarchical chain of multiple secondary islands/flux ropes. The inter-plasmoid reconnection layers are subject to strong synchrotron cooling, leading to significant plasma compression. Using the conditions of pressure balance across these current layers, the balance between the heating by magnetic energy dissipation and synchrotron cooling, and Ampere's law, we obtain simple estimates for key parameters of the layers --- temperature, density, and layer thickness. In the comoving frame of the relativistic pulsar wind just outside of the equatorial current sheet, these basic parameters are uniquely determined by the strength of the reconnecting upstream magnetic field. For the case of the Crab pulsar, we find them to be of order 10 GeV, $10^{13} cm^{-3}$, and 10 cm, respectively. After accounting for the bulk Doppler boosting due to the pulsar wind, the synchrotron and inverse-Compton emission from the reconnecting current sheet can explain the observed pulsed high-energy (GeV) and VHE (~100 GeV) radiation, respectively. Also, we suggest that the rapid relative motions of the secondary plasmoids in the hierarchical chain may contribute to the production of the pulsar radio emission.
Recent observations by Mauerhan et al. have shown the unprecedented transition of the previously identified luminous blue variable (and supernova impostor) SN 2009ip to a real Type IIn supernova (SN) explosion. We present high-cadence optical imaging of SN 2009ip obtained between 2012 UT Sep. 23.6 and Oct. 9.6, using 0.3-0.4 meter aperture telescopes from the Coral Towers Observatory in Cairns, Australia. The light curves show well-defined phases, including very rapid brightening early on (0.5 mag in 6 hr observed during the night of Sep. 24), a transition to a much slower rise between Sep. 25 and Sep. 28, and a plateau/peak around Oct. 7. These changes are coincident with the reported spectroscopic changes that, most likely, mark the start of a strong interaction between the fast SN ejecta and a dense circumstellar medium formed during the earlier LBV eruptions. In the 16-day observing period SN 2009ip brightened by 3.7 mag from I = 17.4 mag on Sep. 23.6 (MI = -14.2) to I = 13.7 mag (MI = -17.9) on Oct. 9.6, radiating ~2x10^49 erg in the optical wavelength range. Currently, SN 2009ip is more luminous than most Type IIP SNe and comparable to other Type IIn SNe.
We investigate how the azimuthal ambiguity in solar vector magnetogram data can be resolved by using the divergence-free property of magnetic fields. In a previous article, by Crouch, Barnes, and Leka (Solar Phys. 260, 271, 2009), error-free synthetic data were used to test several methods that each make a different assumption about how the divergence-free property can be used to resolve the ambiguity. In this paper this testing is continued with an examination of the effects of Poisson photon noise and limited instrumental spatial resolution. We find that all currently available methods based on the divergence-free property can produce undesirable results when photon noise or unresolved structure are present in the data. We perform a series of experiments aimed at improving the performance of the global minimisation method, which is the most promising of the methods. We present a two-step approach that produces reasonable results in tests using synthetic data. The first step of this approach involves the global minimisation of a combination of the absolute value of the approximation for the divergence and a smoothness constraint, which is designed to minimise the difference between the magnetic field in neighbouring pixels. In the second step, pixels with measurements known to be strongly affected by photon noise are revisited with a smoothing algorithm that also seeks to minimise the difference between the magnetic field in neighbouring pixels.
Like the Lovelock Lagrangian which is a specific homogeneous polynomial in Riemann curvature, for an alternative derivation of the gravitational equation of motion, it is possible to define a specific homogeneous polynomial analogue of the Riemann curvature, and then the trace of its Bianchi derivative yields the corresponding polynomial analogue of the divergence free Einstein tensor defining the differential operator for the equation of motion. We propose that the general equation of motion is $G^{(n)}_{ab} = -\Lambda g_{ab} +\kappa_n T_{ab}$ for $d=2n+1, \, 2n+2$ dimensions with the single coupling constant $\kappa_n$, and $n=1$ is the usual Einstein equation. It turns out that gravitational behavior is essentially similar in the critical dimensions for all $n$. All static vacuum solutions asymptotically go over to the Einstein limit, Schwarzschild-dS/AdS. The thermodynamical parameters bear the same relation to horizon radius, for example entropy always goes as $r_h^{d-2n}$ and so for the critical dimensions it always goes as $r_h, \, r_h^2$. In terms of the area, it would go as $A^{1/n}$. The generalized analogues of the Nariai and Bertotti-Robinson solutions arising from the product of two constant curvature spaces, also bear the same relations between the curvatures $k_1=k_2$ and $k_1=-k_2$ respectively.
Analytical expressions for the orbital precessions affecting the relative motion of the components of a local binary system induced by Lorentz-violating Preferred Frame Effects (PFE) are explicitly computed in terms of the PPN parameters {\alpha}1, {\alpha}2. A linear combination of the supplementary perihelion precessions of all the inner planets of the Solar System, able to remove the a-priori bias of unmodelled/mismodelled standard effects such as the general relativistic Lense-Thirring precessions and the classical rates due to the Sun's oblateness J2, allows to infer {\alpha}1 <= 10^-6, {\alpha}2 <= 10^-5. Such bounds should be improved in the near future after processing the data that are being collected by the MESSENGER spacecraft, currently orbiting Mercury. Further improvements may come in the mid-future from the approved BepiColombo mission to Mercury (Abridged).
In this note we study the 2PN/RM gauge invariance structure of a \textit{Brans-Dicke-like} Scalar-Tensor Theories (STT) without potential. Since the spherical isotropic metric plays an important role in the literature, its 2PN/RM STT version is deduced from the general equations given in \cite{moiCQG11}, by using the invariance structure properties. It is found that the second order Eddington parameter $\epsilon$ can be written in terms of the usual post-Newtonian parameter $\gamma$ and $\beta$ as $ \epsilon=4/3 \gamma^2 + 4/3 \beta - 1/6 \gamma -3/2$
Short GRBs are believed to originate from the coalescence of two NSs or a NS and a BH. If this scenario is correct, short GRBs will be accompanied by the emission of strong GWs, detectable by GW observatories such as LIGO and Virgo. As compared with blind, all-sky, all-time GW searches, externally triggered searches for GW counterparts to short GRBs have the advantages of both significantly reduced detection threshold due to known time and sky location and preferentially higher GW amplitude because of face-on orientation. Based on the distribution of SNR in candidate CBC events in the most recent joint LIGO--Virgo data, we find an effective sensitive volume for GRB-triggered searches that ~2 times greater than for blind searches. For NSNS systems, a jet angle of 20 degrees, and an effective gamma-ray satellite field-of-view of 10% of the sky, this doubles the number of NSNS--short GRB associations to 4% of all NSNS detections. We also investigate the power of tests for statistical excesses in lists of sub-threshold events, and show that these are unlikely to reveal a sub-threshold population until finding individual sources is already routine.
Energy calibration of superheated droplet detector is discussed in terms of the effective recoil nucleus threshold energy and the reduced superheat. This provides a universal energy calibration curve valid for different liquids used in this type of detector. Two widely used liquids, R114 and C4F10, one for neutron detection and the other for WIMPs dark matter search experiment, have been compared. Liquid having recoil nuclei with larger values of LET provides better neutron and gamma discrimination. Gamma response of C4F10 has also been studied and the results are discussed. Behaviour of nucleation parameter with the effective recoil nucleus threshold energy and the reduced superheat have been explored.
We analyze the state space of a Bianchi I universe with anisotropic sources. Here we consider an extended state space which includes null geodesics in this background. The evolution equations for all the state observables are derived. Dynamical system approach is used to study the evolution of these equations. The asymptotic stable fixed points for all the evolution equations are found. We also check our analytic results with numerical analysis of these dynamical equations. The evolution of the state observables are studied both in cosmic time and using a dimensionless time variable. Finally the cosmic microwave background anisotropy maps are generated, assuming that the universe is anisotropic and dominated by one of the anisotropic sources since decoupling. We find that they contribute dominantly to CMB quadrupole.
What does it mean to say that space expands? One approach to this question is the study of relative velocities. In this context, a non local test particle is "superluminal" if its relative velocity exceeds the local speed of light of the observer. The existence of superluminal relative velocities of receding test particles, in a particular cosmological model, suggests itself as a possible criterion for expansion of space in that model. In this point of view, superluminal velocities of distant receding galaxy clusters result from the expansion of space between the observer and the clusters. However, there is a fundamental ambiguity that must be resolved before this approach can be meaningful. The notion of relative velocity of a nonlocal object depends on the choice of coordinates, and this ambiguity suggests the need for coordinate independent definitions. In this work, we review four (inequivalent) geometrically defined and universal notions of relative velocity: Fermi, kinematic, astrometric, and spectroscopic relative velocities. We apply this formalism to test particles undergoing radial motion relative to comoving observers in expanding Robertson-Walker cosmologies, and include previously unpublished results on Fermi coordinates for a class of inflationary cosmologies. We compare relative velocities to each other, and show how pairs of them determine geometric properties of the spacetime, including the scale factor with sufficient data. Necessary and sufficient conditions are given for the existence of superluminal recessional Fermi speeds in general Robertson-Walker cosmologies. We conclude with a discussion of expansion of space.
The axion is a pseudo-Nambu-Goldstone boson. It appears after the spontaneous breaking of the Peccei-Quinn symmetry, which was proposed to solve the strong-CP problem. Other pseudo-Nambu-Goldstone bosons, postulated in some extensions of the standard model of particle physics, are called axion-like particles (ALPs) if they share certain characteristics with the axion, in particular a coupling to two photons. Thus far, axion and ALP searches have been unsuccessful, indicating that their couplings have to be extremely weak. However, axions and ALPs could be responsible for some observable effects in astrophysics and cosmology, which can also be exploited to constrain the parameter space of these particles. We focus on limits coming from cosmology, which is an optimal field for studying axions and ALPs. In particular, we first investigate the possibility of a primordial population of axions and ALPs arising during the earliest epochs of the universe. The importance of this analysis lies on the fact that axions and ALPs are ideal dark matter candidates because of their faint interactions and their peculiar production mechanisms. Finally, we consider the consequences of the decay of such a population on specific cosmological observables, namely the photon spectrum of galaxies, the cosmic microwave background, the effective number of neutrino species, and the abundance of primordial elements. Our bounds constitute the most stringent probes of early decays and exclude a part of the ALP parameter space that is otherwise very difficult to test experimentally.
In this work we present a systematic study of Micromegas detectors in high pressure gaseous Xenon using trimethylamine (TMA) as quencher gas. Gas gains and energy resolutions for 22.1 keV X-rays are measured for pressures between 1 and 10 bar and various relative concentrations of TMA from 0.3 % to 15 %. We observe stable operation at all pressures, and a strongly enhanced gas gain, suggestive of Penning-like energy-transfer processes. The effect is present at all pressures and it is strongest at TMA concentrations ranging from 1.5 % to 3 %. Operating in this concentration range, the maximum gain reached values as high as x10^3 (x10^2) at 1 (10) bar. Besides, the energy resolution achievable for 22.1 keV X-rays is substantially better than the one previously obtained in pure Xe, going down to 7.3 % (9.6 %) FWHM for 1 (10) bar. These results are of interest for calorimetric applications of high pressure gas Xe TPCs, in particular for the search of the neutrinoless double beta decay of Xe-136. The resolutions achieved would extrapolate into 0.7 % (0.9 %) FWHM at the Qbb value of Xe-136 for 1 (10) bar.
The accelerating expansion of the Universe points to a small positive vacuum energy density and negative vacuum pressure. A strong candidate is the cosmological constant in Einstein's equations of General Relativity. The vacuum dark energy density extracted from astrophysics is 10^56 times smaller than the value expected from the Higgs potential in Standard Model particle physics. The dark energy scale is however close to the range of possible values expected for the light neutrino mass. We investigate this physics in a simple toy model where the chirality of the neutrino is treated by analogy as an Ising-like "spin" degree of freedom.
Thermodynamic properties of strange quark matter in strong magnetic fields $H$ up to $10^{20}$ G are considered within the MIT bag model at zero temperature implying the constraints of total baryon number conservation, charge neutrality and chemical equilibrium. The effects of the pressure anisotropy, exhibiting in the difference between the pressures along and perpendicular to the field direction, become essential at $H>H_{th}$, with the estimate $10^{17}<H_{th}\lesssim10^{18}$ G. The longitudinal pressure vanishes in the critical field $H_c$, which can be somewhat less or larger than $10^{18}$ G, depending on the total baryon number density and bag pressure. As a result, the longitudinal instability occurs in strange quark matter, which precludes: (1) a significant drop in the content of $s$ quarks, which, otherwise, could happen at $H\sim10^{20}$ G; (2) the appearance of positrons in weak processes in a narrow interval near $H\sim2\cdot10^{19}$ G (replacing electrons). The occurrence of the longitudinal instability leaves the possibility only for electrons to reach a fully polarized state, while for all quark flavors the polarization remains mild even for the fields near $H_c$. The anisotropic equation of state is determined under the conditions relevant to the interiors of magnetars.
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