We use two 4.5micron Spitzer (IRAC) maps of the NGC 1333 region taken over approx. 7 yr interval to determine proper motions of its associated outflows. This is a first, successful attempt at obtaining proper motions of stellars outflow from Spitzer observations. For the outflow formed by the Herbig-Haro objects HH7, 8 and 10, we find proper motions of approx. 9-13 km/s, which are consistent with previously determined optical proper motions of these objects. We determine proper motions for a total of 8 outflows, ranging from approx. 10 to 100 km/s. The derived proper motions show that out of these 8 outflows, 3 have tangential velocities less or equal to 20 km/s. This result shows that a large fraction of the observed outflows have low intrinsic velocities, and that the low proper motions are not merely a projection effect.
I present a systematic study of gamma-ray flares in blazars. For this purpose, I propose a very simple and practical definition of a flare as a period of time, associated with a given flux peak, during which the flux is above half of the peak flux. I select a sample of 40 brightest gamma-ray flares observed by Fermi/LAT during the first 4 years of its mission. The sample is dominated by 4 blazars: 3C 454.3, PKS 1510-089, PKS 1222+216 and 3C 273. For each flare, I calculate a light curve and variations of the photon index. For the whole sample, I study the distributions of the peak flux, duration, time asymmetry, average photon index and photon index scatter. I find that: 1) flares produced by 3C 454.3 are longer and have more complex light curves than those produced by other blazars; 2) flares shorter than 2.3 days tend to be time-asymmetric with the flux peak preceding the flare midpoint. These differences can be largely attributed to a smaller viewing angle of 3C 454.3 as compared to other blazars. Intrinsically, the gamma-ray emitting regions in blazar jets may be structured and consist of several domains. I find no regularity in the spectral gamma-ray variations of flaring blazars.
We present APEX/P-ArT\'eMiS 450\mu m continuum observations of RCW 36 and the adjacent ridge, a high-mass high-column density filamentary structure at the centre of the Vela C molecular cloud. These observations, at higher resolution than Herschel's SPIRE camera, reveal clear fragmentation of the central star-forming ridge. Combined with PACS far-infrared and SPIRE sub-millimetre observations from the Herschel HOBYS project we build a high resolution column density map of the region mapped with P-ArT\'eMiS. We extract the radial density profile of the Vela C ridge which with a ~ 0.1pc central width is consistent with that measured for low-mass star-forming filaments in the Herschel Gould Belt survey. Direct comparison with Serpens South, of the Gould Belt Aquila complex, reveals many similarities between the two regions. Despite likely different formation mechanisms and histories, the Vela C ridge and Serpens South filament share common characteristics, including their filament central widths.
We report the discovery of X-ray emission at the position of the old classical nova DK Lacertae using the Swift satellite. Three observations were conducted using the X-ray telescope 62 years after the discovery of the nova, yielding 46 source signals in an exposure time of 4.8 ks. A background-subtracted count rate was 9+/-2x10^{-3} counts s^{-1}, corresponding to a detection significance level of 5-sigma. The X-ray spectrum was characterized by a continuum extending up to about 7 keV, which can be modeled by a power-law component with a photon index of 1.4--5.6, or by a thermal bremsstrahlung component with a temperature of 0.7--13.3 keV, convolved with interstellar absorption with an equivalent hydrogen column density of 0.3--2.4x10^{22} cm^{-2}. Assuming a distance of 3900 pc to the source, the luminosity was 10^{32}--10^{34} ergs s^{-1} in the 0.3--10 keV energy band. The origin of X-rays is considered to be either mass accretion on the white dwarf or adiabatic shocks in nova ejecta, with the former appearing much more likely. In either case, DK Lacertae represents a rare addition to the exclusive club of X-ray emitting old novae.
PINGSoft, is a set of IDL routines designed to visualise, manipulate, and analyse integral field spectroscopy (IFS) data regardless of the original instrument and spaxel shape. PINGSoft 2 is a relatively major upgrade with respect to the first version: the overall functionality and layout have been improved, while the command syntax has been simplified. This version includes new routines that offer powerful spatial and spectral visualisation of the data, improved extraction routines, and new analysis tools. PINGSoft is optimised for a fast visualisation rendering, it supports RSS and 3D cube formats, it is able to run on practically any computer platform with minimal library requirements, and is adapted to work natively with the CALIFA survey data. The PINGSoft 2 IDL Integral Field Spectroscopy Software is freely available at this http URL
We compute black hole masses and bolometric luminosities for 57 active galactic nuclei (AGN) in the redshift range 1.25 < z < 2.67, selected from the GOODS-South deep multi-wavelength survey field via their X-ray emission. We determine host galaxy morphological parameters by separating the galaxies from their central point sources in deep HST images, and host stellar masses and colors by multi-wavelength SED fitting. 90% of GOODS AGN at these redshifts have detected rest-frame optical nuclear point sources; bolometric luminosities range from 2e43 - 2e46 erg/s. The black holes are growing at a range of accretion rates, with at least 50% of the sample having L/L_Edd < 0.1. 70% of host galaxies have stellar masses M* > 1e10 M_sun, with a range of colors suggesting a complex star formation history. We find no evolution of AGN bolometric luminosity within the sample, and no correlation between AGN bolometric luminosity and host stellar mass, color or morphology. Fully half the sample of host galaxies is disk-dominated, with another 25% having strong disk components. Fewer than 15% of the systems appear to be at some stage of a major merger. These moderate-luminosity AGN hosts are therefore inconsistent with a dynamical history dominated by mergers strong enough to destroy disks, indicating minor mergers or secular processes dominate the co-evolution of galaxies and their central black holes at z ~ 2.
In this work we analyse late-time (t > 100 d) optical spectra of low-redshift (z < 0.1) Type Ia supernovae (SNe Ia) which come mostly from the Berkeley Supernova Ia Program dataset. We also present spectra of SN 2011by for the first time. The sample studied consists of 34 SNe Ia with 60 nebular spectra, which represents one of the largest sets of late-time SN Ia spectra ever analysed. The full width at half-maximum intensity (FWHM) and velocities of the [Fe III] {\lambda}4701, [Fe II] {\lambda}7155, and [Ni II] {\lambda}7378 emission features are measured in most of the spectra that are spectroscopically normal, have signal-to-noise ratios >20/px, and are older than 160 d past maximum brightness. The velocities of all three features are seen to be relatively constant with time, increasing only a few to ~20 km/s/d. The nebular velocity (v_neb, calculated by taking the average of the [Fe II] {\lambda}7155 and [Ni II] {\lambda}737 velocities) is correlated with the velocity gradient and near-maximum-brightness photospheric velocity; most high velocity gradient objects have redshifted nebular lines while most low velocity gradient objects have blueshifted nebular lines. A marginal correlation is found between v_neb and {\Delta}m_15(B), but for a given light-curve shape there is a large range of observed nebular velocities. The BSNIP data also indicate a strong correlation between observed (B-V)_max (which is likely mostly the intrinsic SN colour) and v_neb (a purely intrinsic quantity). Employing a relatively rudimentary search, evidence for light echoes in the late-time spectra is found for a handful of objects, though the presence of light echoes is not yet confirmed.
We report the discovery of a massive ultra-compact quiescent galaxy that has been strongly-lensed into multiple images by a foreground galaxy at z = 0.960. This system was serendipitously discovered as a set of extremely Ks-bright high-redshift galaxies with red J - Ks colors using new data from the UltraVISTA YJHKs near-infrared survey. The system was also previously identified as an optically-faint lens/source system using the COSMOS ACS imaging by Faure et al. (2008, 2011). Photometric redshifts for the three brightest images of the source galaxy determined from twenty-seven band photometry place the source at z = 2.4 +/- 0.1. We provide an updated lens model for the system which is a good fit to the positions and morphologies of the galaxies in the ACS image. The lens model implies that the magnification of the three brightest images is a factor of 4 - 5. We use the lens model, combined with the Ks-band image to constrain the size and Sersic profile of the galaxy. The best-fit model is an ultra-compact galaxy (Re = 0.64^{+0.08}_{-0.18} kpc, lensing-corrected), with a Sersic profile that is intermediate between a disk and bulge profile (n = 2.2^{+2.3}_{-0.9}). We present aperture photometry for the source galaxy images which have been corrected for flux contamination from the central lens. The best-fit stellar population model is a massive galaxy (Log(M_{star}/M_{sol}) = 10.8^{+0.1}_{-0.1}, lensing-corrected) with an age of 1.0^{+1.0}_{-0.4} Gyr, moderate dust extinction (Av = 0.8^{+0.5}_{-0.6}), and a low specific star formation rate (Log(SSFR) < -11.0 yr^{-1}). This is typical of massive "red-and-dead" galaxies at this redshift and confirms that this source is the first bona fide strongly-lensed massive ultra-compact quiescent galaxy to be discovered. We conclude with a discussion of the prospects of finding a larger sample of these galaxies.
Building on results from the Magnetism in Massive Stars (MiMeS) project, this paper shows how a two-parameter classification of massive-star magnetospheres in terms of the magnetic wind confinement (which sets the Alfv\'en radius RA) and stellar rotation (which sets the Kepler co-rotation radius RK) provides a useful organisation of both observational signatures and theoretical predictions. We compile the first comprehensive study of inferred and observed values for relevant stellar and magnetic parameters of 64 confirmed magnetic OB stars with Teff > 16 kK. Using these parameters, we locate the stars in the magnetic confinement-rotation diagram, a log-log plot of RK vs. RA. This diagram can be subdivided into regimes of centrifugal magnetospheres (CM), with RA > RK, vs. dynamical magnetospheres (DM), with RK > RA. We show how key observational diagnostics, like the presence and characteristics of Halpha emission, depend on a star's position within the diagram, as well as other parameters, especially the expected wind mass-loss rates. In particular, we identify two distinct populations of magnetic stars with Halpha emission: namely, slowly rotating O-type stars with narrow emission consistent with a DM, and more rapidly rotating B-type stars with broader emission associated with a CM. For O-type stars, the high mass-loss rates are sufficient to accumulate enough material for line emission even within the relatively short free-fall timescale associated with a DM: this high mass-loss rate also leads to a rapid magnetic spindown of the stellar rotation. For the B-type stars, the longer confinement of a CM is required to accumulate sufficient emitting material from their relatively weak winds, which also lead to much longer spindown timescales. [abbreviated]
Dark matter annihilation or de-excitation, decay of metastable species, or other new physics may inject energetic electrons and photons into the photon-baryon fluid during and after recombination. As such particles cool, they partition their energy into a large number of efficiently ionizing electrons and photons, which in turn modify the ionization history. Recent work has provided a simple method for constraining arbitrary energy deposition histories using the cosmic microwave background (CMB); in this note, we present results describing the energy deposition histories for photons and electrons as a function of initial energy and injection redshift. With these results, the CMB bounds on any process injecting some arbitrary spectrum of electrons, positrons and/or photons with arbitrary redshift dependence can be immediately computed.
In this Letter we revisit arguments suggesting that the Bardeen-Petterson effect can coalign the spins of a central supermassive black hole binary accreting from a circumbinary (or circumnuclear) gas disc. We improve on previous estimates by adding the dependence on system parameters, and noting that the nonlinear nature of warp propagation in a thin viscous disc affects alignment. This reduces the disc's ability to communicate the warp, and can severely reduce the effectiveness of disc-assisted spin alignment. We test our predictions with a Monte Carlo realization of random misalignments and accretion rates and we find that the outcome depends strongly on the spin magnitude. We estimate a generous upper limit to the probability of alignment by making assumptions which favour it throughout. Even with these assumptions, about 40% of black holes with $a \gtrsim 0.5$ do not have time to align with the disc. If the residual misalignment is not small and it is maintained down to the final coalescence phase this can give a powerful recoil velocity to the merged hole. Highly spinning black holes are thus more likely of being subject to strong recoils, the occurrence of which is currently debated.
This document summarizes the results of a community-based discussion of the potential science impact of the Mayall+BigBOSS highly multiplexed multi-object spectroscopic capability. The KPNO Mayall 4m telescope equipped with the DOE- and internationally-funded BigBOSS spectrograph offers one of the most cost-efficient ways of accomplishing many of the pressing scientific goals identified for this decade by the "New Worlds, New Horizons" report. The BigBOSS Key Project will place unprecedented constraints on cosmological parameters related to the expansion history of the universe. With the addition of an open (publicly funded) community access component, the scientific impact of BigBOSS can be extended to many important astrophysical questions related to the origin and evolution of galaxies, stars, and the IGM. Massive spectroscopy is the critical missing ingredient in numerous ongoing and planned ground- and space-based surveys, and BigBOSS is unique in its ability to provide this to the US community. BigBOSS data from community-led projects will play a vital role in the education and training of students and in maintaining US leadership in these fields of astrophysics. We urge the NSF-AST division to support community science with the BigBOSS multi-object spectrograph through the period of the BigBOSS survey in order to ensure public access to the extraordinary spectroscopic capability.
We analyze environmental correlations using mark clustering statistics with the mock galaxy catalogue constructed by Muldrew et al. (Paper I). We find that mark correlation functions are able to detect even a small dependence of galaxy properties on the environment, quantified by the overdensity $1+\delta$, while such a small dependence would be difficult to detect by traditional methods. We then show that rank ordering the marks and using the rank as a weight is a simple way of comparing the correlation signals for different marks. With this we quantify to what extent fixed-aperture overdensities are sensitive to large-scale halo environments, nearest-neighbor overdensities are sensitive to small-scale environments within haloes, and colour is a better tracer of overdensity than is luminosity.
Minute-timescale TeV flares have been observed in several blazars. The fast flaring requires compact regions in the jet that boost their emission towards the observer at an extreme Doppler factor of delta>50. For TeV photons to avoid annihilation in the broad line region of PKS 1222+216, the flares must come from large (pc) scales challenging most models proposed to explain them. Here we elaborate on the magnetic reconnection minijet model for the blazar flaring, focusing on the inherently time-dependent aspects of the process of magnetic reconnection. I argue that, for the physical conditions prevailing in blazar jets, the reconnection layer fragments leading to the formation a large number of plasmoids. Occasionally a plasmoid grows to become a large, "monster" plasmoid. I show that radiation emitted from the reconnection event can account for the observed "envelope" of \sim day-long blazar activity while radiation from monster plasmoids can power the fastest TeV flares. The model is applied to several blazars with observed fast flaring. The inferred distance of the dissipation zone is R_diss \sim0.3-1 pc. The required magnetization of the jet at this distance is modest: sigma \sim a few.
This white paper describes the LSST Dark Energy Science Collaboration (DESC), whose goal is the study of dark energy and related topics in fundamental physics with data from the Large Synoptic Survey Telescope (LSST). It provides an overview of dark energy science and describes the current and anticipated state of the field. It makes the case for the DESC by laying out a robust analytical framework for dark energy science that has been defined by its members and the comprehensive three-year work plan they have developed for implementing that framework. The analysis working groups cover five key probes of dark energy: weak lensing, large scale structure, galaxy clusters, Type Ia supernovae, and strong lensing. The computing working groups span cosmological simulations, galaxy catalogs, photon simulations and a systematic software and computational framework for LSST dark energy data analysis. The technical working groups make the connection between dark energy science and the LSST system. The working groups have close linkages, especially through the use of the photon simulations to study the impact of instrument design and survey strategy on analysis methodology and cosmological parameter estimation. The white paper describes several high priority tasks identified by each of the 16 working groups. Over the next three years these tasks will help prepare for LSST analysis, make synergistic connections with ongoing cosmological surveys and provide the dark energy community with state of the art analysis tools. Members of the community are invited to join the LSST DESC, according to the membership policies described in the white paper. Applications to sign up for associate membership may be made by submitting the Web form at this http URL with a short statement of the work they wish to pursue that is relevant to the LSST DESC.
Submillimeter cameras now have up to $10^4$ pixels (SCUBA 2). The proposed CCAT 25-meter submillimeter telescope will feature a 1 degree field-of-view. Populating the focal plane at 350 microns would require more than $10^6$ photon-noise limited pixels. To ultimately achieve this scaling, simple detectors and high-density multiplexing are essential. We are addressing this long-term challenge through the development of frequency-multiplexed superconducting microresonator detector arrays. These arrays use lumped-element, direct-absorption resonators patterned from titanium nitride films. We will discuss our progress toward constructing a scalable 350 micron pathfinder instrument focusing on fabrication simplicity, multiplexing density, and ultimately a low per-pixel cost.
We analyse the Catalina Real-time Transient Survey light curves of 835 spectroscopically confirmed white dwarf plus main-sequence binaries from the Sloan Digital Sky Survey (SDSS) with g<19, in search of new eclipsing systems. We identify 29 eclipsing systems, 12 of which were previously unknown. This brings the total number of eclipsing white dwarf plus main-sequence binaries to 49. Our set of new eclipsing systems contains two with periods of 1.9 and 2.3 days making them the longest period eclipsing white dwarf binaries known. We also identify one system which shows very large ellipsoidal modulation (almost 0.3 magnitudes), implying that the system is both very close to Roche-lobe overflow and at high inclination. However, our follow up photometry failed to firmly detect an eclipse meaning that this system either contains a cool white dwarf and hence the eclipse is very shallow and undetectable in our red-sensitive photometry or that it is non-eclipsing. Radial velocity measurements for the main-sequence stars in three of our newly identified eclipsing systems imply that their white dwarf masses are lower than those inferred from modelling their SDSS spectra. 13 non-eclipsing post common envelope binaries were also identified, from either reflection or ellipsoidal modulation effects. The white dwarfs in our newly discovered eclipsing systems span a wide range of parameters, including; low mass (~0.3Msol), very hot (80,000K) and a DC white dwarf. The spectral types of the main-sequence stars range from M2 to M6. This makes our sample ideal for testing white dwarf and low-mass star mass-radius relationships as well as close binary evolution.
We present an update of our low-resolution spectroscopic follow-up and model atmosphere analysis of hot subdwarf stars from the Galaxy Evolution Explorer (GALEX) survey. Targets were selected on the basis of colour indices calculated from the GALEX GR6 N_UV, Guide Star Catalogue (GSC2.3.2) V and the Two Micron All Sky Survey (2MASS) J and H photometry. High signal-to-noise ratio spectra were obtained at the European Southern Observatory (ESO) and the Kitt Peak National Observatory (KPNO) over the course of three years. Detailed H, He and CNO abundance analysis helped us improve our T_eff, log g and He abundance determination and to constrain CNO abundances. We processed 191 observations of 180 targets and found 124 sdB and 42 sdO stars in this sample while some blue horizontal branch stars were also found in this programme. With quantitative binary decomposition of 29 composite spectra we investigated the incidence of A, F and G type companions. The incidence of late G and K type companions and their effects on subdwarf atmospheric parameters were also examined.
Here we introduce CRASH3, the latest release of the 3D radiative transfer code CRASH. In its current implementation CRASH3 integrates into the reference algorithm the code Cloudy to evaluate the ionisation states of metals, self-consistently with the radiative transfer through H and He. The feedback of the heavy elements on the calculation of the gas temperature is also taken into account, making of CRASH3 the first 3D code for cosmological applications which treats self-consistently the radiative transfer through an inhomogeneous distribution of metal enriched gas with an arbitrary number of point sources and/or a background radiation. The code has been tested in idealized configurations, as well as in a more realistic case of multiple sources embedded in a polluted cosmic web. Through these validation tests the new method has been proven to be numerically stable and convergent. We have studied the dependence of the results on a number of physical quantities such as the source characteristics (spectral range and shape, intensity), the metal composition, the gas number density and metallicity.
We compare the central mass distribution of galaxies simulated with three different models of the interstellar medium (ISM) with increasing complexity: primordial (H+He) cooling down to 10^4 K, additional cooling via metal lines and to lower temperatures, and molecular hydrogen (H_2) with shielding of atomic and molecular hydrogen in addition to metal line cooling. In order to analyze the effect of these models, we follow the evolution of four field galaxies with V_peak < 120 km/s to a redshift of zero using high-resolution Smoothed Particle Hydrodynamic simulations in a fully cosmological LCDM context. The spiral galaxies produced in simulations with either primordial cooling or H_2 physics have bulge magnitudes and scale lengths very similar to observed galaxies and realistic, rising rotation curves. In contrast, the metal line cooling simulation produced galaxies with more massive and concentrated bulges and with the peaked rotation curves typical of most previous LCDM simulations of spiral galaxies. The less-massive bulges and non-peaked rotation curves in the galaxies simulated with primordial cooling or H_2 are linked to changes in the angular momentum distribution of the baryons. These galaxies had smaller amounts of low-angular momentum baryons because of increased gas loss from stellar feedback. When there is only primordial cooling, the star forming gas is hotter and the feedback-heated gas cools more slowly than when metal line cooling is included and so requires less energy to be expelled. When H_2 is included, the accompanying shielding produces large amounts of clumpy, cold gas where H_2 forms. Star formation in clumpy gas results in more concentrated supernova feedback and greater efficiency of mass loss. The higher feedback efficiency causes a decrease of low-angular momentum material and formation of realistic bulges. (abridged)
We report the detection of strong and compact molecular line emission (in the CO J=3-2, 4-3, 6-5, 7-6, 13CO J=3-2, HCN and HCO+ J=4-3 transitions) from a cometary-shaped object (Carina-frEGG1) in the Carina star-forming region (SFR) previously classified as a photoevaporating protoplanetary disk (proplyd). We derive a molecular mass of 0.35 Msun for Carina-frEGG1, which shows that it is not a proplyd, but belongs to a class of free-floating evaporating gas globules (frEGGs) recently found in the Cygnus SFR by Sahai, Morris & Claussen (2012). Archival Adaptive Optics near-IR (Ks) images show a central hourglass-shaped nebula. The derived source luminosity (about 8-18 Lsun), the hourglass morphology, and the presence of collimated jets seen in HST images, imply the presence of a jet-driving, young, low-mass star deeply embedded in the dust inside Carina-frEGG1. Our results suggest that the true nature of many or most such cometary-shaped objects seen in massive SFRs and previously labelled as proplyds has been misunderstood, and that these are really frEGGs.
We have studied the fascinating dynamics of the nearby Vela pulsar's nebula in a campaign comprising eleven 40ks observations with Chandra X-ray Observatory (CXO). The deepest yet images revealed the shape, structure, and motion of the 2-arcminute-long pulsar jet. We find that the jet's shape and dynamics are remarkably consistent with that of a steadily turning helix projected on the sky. We discuss possible implications of our results, including free precession of the neutron star and MHD instability scenarios.
We present the first scientific results from the Sydney-AAO Multi-Object IFS (SAMI) at the Anglo-Australian Telescope. This unique instrument deploys 13 fused fibre bundles (hexabundles) across a one-degree field of view allowing simultaneous spatially-resolved spectroscopy of 13 galaxies. During the first SAMI commissioning run, targeting a single galaxy field, one object (ESO 185-G031) was found to have extended minor axis emission with ionisation and kinematic properties consistent with a large-scale galactic wind. The importance of this result is two-fold: (i) fibre bundle spectrographs are able to identify low-surface brightness emission arising from extranuclear activity; (ii) such activity may be more common than presently assumed because conventional multi-object spectrographs use single-aperture fibres and spectra from these are nearly always dominated by nuclear emission. These early results demonstrate the extraordinary potential of multi-object hexabundle spectroscopy in future galaxy surveys.
We report the discovery of 23 lithium-rich post-main-sequence stars, identified from moderate-resolution SDSS spectroscopy and confirmed with high-resolution spectra taken at the Hobby-Eberly Telescope. These new Li-rich stars cover a broad range in mass and evolutionary phase, including bright giants and post-AGB stars. The process responsible for preserving or producing excess lithium in a small fraction of evolved stars remains unclear.
We present Herschel/HIFI observations of nine transitions of \hho and \hheo towards six high-mass star-forming regions, obtained as part of the PRISMAS Key Program. Water vapor in translucent clouds is detected in absorption along every sightline. We derive the column density of \hho or \hheo for the lower energy level of each transition observed. The total water column density is about a few $10^{13} \rm{cm^{-2}}$. We find that the abundance of water relative to hydrogen nuclei is $1\times10^{-8}$ in agreement with models for oxygen chemistry with high cosmic ray ionization rates. Relative to \hh, the abundance of water is remarkably constant at $5\times10^{-8}$. The abundance of water in excited levels is at most 15%, implying that the excitation temperature $T_{ex}$ in the ground state transitions is below 10 K. The column densities derived from the two ortho ground state transitions indicates that $T_{ex}\simeq5$ K and that the density $n($\hh$)$ in the clouds is $\le10^4 \rm{cm^{-3}}$. For most clouds we derive a water ortho-to-para ratio consistent with the value of 3 expected in thermodynamic equilibrium in the high temperature limit. Two clouds with large column densities exhibit a ratio significantly below 3. This may argue that the history of water molecules includes a cold phase, either when the molecules were formed on cold grains, or when they later become at least partially thermalized with the cold gas ($\sim25$ K) in the shielded, low temperature regions of the clouds; evidently, they have not yet fully thermalized with the warmer ($\sim50$ K) translucent portions of the clouds.
We review the observational evidence that the warm ionized medium (WIM) is a major and physically distinct component of the Galactic interstellar medium. Although up to ~20% of the faint, high-latitude H-alpha emission in the Milky Way may be scattered light emitted in midplane H II regions, recent scattered light models do not effectively challenge the well-established properties of the WIM.
For the first time, we systematically explored the population of discrete X-ray sources in the outskirt of early-type galaxies. Based on a broad sample of 20 galaxies observed with Chandra we revealed over density of X-ray sources in their outskirts. They appear as halos of resolved sources around galaxies, distributing much broader than the stellar light, and extended out to at least ~ 10 re (re is the effective radius). These halos are composed of sources fainter than ~ 5.e38 erg/s, whereas the more luminous sources appear to follow the distribution of stellar light, suggesting that the excess source population consists of neutron star binaries. Dividing the galaxy sample into four groups according to their stellar mass and specific frequency of globular cluster, we find that the extended halos are present in all groups except for the low mass galaxies with low globular cluster content. We propose that the extended halos may be comprised of two independent components: (i) LMXBs located in blue (metal-poor) globular clusters (GCs), which GCs are known to have a broader distribution than the stellar light; (ii) neutron star LMXBs kicked out of the main body of the parent galaxy by the supernova explosion. The available deep optical and X-ray data of NGC 4365 supports this conclusion. For this galaxy we identified 60.1 \pm 10.8 excess sources in the (4-10)re region of which ~ 40% are located in globular clusters, whereas ~ 60% are field LMXBs. We interpret the latter as kicked NS LMXBs. We discuss implications of these results for the natal kick distributions of black holes and neutron stars.
We study the implications on compact star properties of a soft nuclear equation of state determined from kaon production at subthreshold energies in heavy-ion collisions. On one hand, we apply these results to study radii and moments of inertia of light neutron stars. Heavy-ion data provides constraints on nuclear matter at densities relevant for those stars and, in particular, to the density dependence of the symmetry energy of nuclear matter. On the other hand, we derive a limit for the highest allowed neutron star mass of three solar masses. For that purpose, we use the information on the nucleon potential obtained from the analysis of the heavy-ion data combined with causality on the nuclear equation of state.
(Abridged) We describe a new method to extract spectra of stars from observations of crowded stellar fields with integral field spectroscopy (IFS). Our approach extends the well-established concept of crowded field photometry in images into the domain of 3-dimensional spectroscopic datacubes. The main features of our algorithm are: (1) We assume that a high-fidelity input source catalogue already exists and that it is not needed to perform sophisticated source detection in the IFS data. (2) Source positions and properties of the point spread function (PSF) vary smoothly between spectral layers of the datacube, and these variations can be described by simple fitting functions. (3) The shape of the PSF can be adequately described by an analytical function. Even without isolated PSF calibrator stars we can therefore estimate the PSF by a model fit to the full ensemble of stars visible within the field of view. (4) By using sparse matrices to describe the sources, the problem of extracting the spectra of many stars simultaneously becomes computationally tractable. We present extensive performance and validation tests of our algorithm using realistic simulated datacubes that closely reproduce actual IFS observations of the central regions of Galactic globular clusters. We investigate the quality of the extracted spectra under the effects of crowding. The main effect of blending between two nearby stars is a decrease in the S/N in their spectra. The effect increases with the crowding in the field in a way that the maximum number of stars with useful spectra is always ~0.2 per spatial resolution element. This balance breaks down when exceeding a total source density of ~1 significantly detected star per resolution element. We close with an outlook by applying our method to a simulated globular cluster observation with the upcoming MUSE instrument at the ESO-VLT.
We present results of convective turbulent dynamo simulations including a coronal layer in a spherical wedge. We find an equatorward migration of the radial and azimuthal fields similar to the behavior of sunspots during the solar cycle. The migration of the field coexist with a spoke-like differential rotation and anti-solar (clockwise) meridional circulation. Even though the migration extends over the whole convection zone, the mechanism causing this is not yet fully understood.
The Galactic center dust ridge consists of a narrow string of massive condensations identified in submillimeter dust continuum emission. To determine whether new high-mass stars are forming in this region, we performed new observations at 870 $\mu$m with the Atacama Pathfinder Experiment telescope and at 8.4 GHz with the Very Large Array. We complement our data with recent maser and mid-infrared results. The ridge's clouds are dark at mid-infrared wavelengths, indicating the presence of cold, high column density material. In combination with existing temperature measurements in the dust ridge, we determined the masses of the largest clouds. The results show that the dust ridge contains a very massive reservoir of molecular material. We find five radio sources at 8.4 GHz in the general dust ridge vicinity but outside of the dust ridge clouds, which are probably all excited by massive young stars, whose properties we constrain. Our observations exclude the existence of zero age main sequence stars with spectral types earlier than B0.5 within the dust ridge clouds. The only indication of ongoing high-mass star formation inside the clouds are class II methanol masers that are found in two of the clouds. Except for a weak water maser, found in previous observations, no signs of star formation are detected in the massive cloud M0.25+0.012.
We present HI 21cm observations of the Orion Nebula, obtained with the Karl G. Jansky Very Large Array, at an angular resolution of 7.2"x5.7" and a velocity resolution of 0.77 km/s. Our data reveal HI absorption towards the radio continuum of the HII region, and HI emission arising from the Orion Bar photon-dominated region (PDR) and from the Orion-KL outflow. In the Orion Bar PDR, the HI signal peaks in the same layer as the H2 near-infrared vibrational line emission, in agreement with models of the photodissociation of H2. The gas temperature in this region is approximately 540K, and the HI abundance in the interclump gas in the PDR is 5-10% of the available hydrogen nuclei. Most of the gas in this region therefore remains molecular. Mechanical feedback on the Veil manifests itself through the interaction of ionized flow systems in the Orion Nebula, in particular the Herbig-Haro object HH202, with the Veil. These interactions give rise to prominent blueward velocity shifts of the gas in the Veil. The unambiguous evidence for interaction of this flow system with the Veil shows that the distance between the Veil and the Trapezium stars needs to be revised downwards to about 0.4pc. The depth of the ionized cavity is about 0.7pc, which is much smaller than the depth and the lateral extent of the Veil. Our results reaffirm the blister model for the M42 HII region, while also revealing its relation to the neutral environment on a larger scale.
The study of the transition between galactic and extragalactic cosmic rays can shed more light on the end of the Galactic cosmic rays spectrum and the beginning of the extragalactic one. Three models of transition are discussed: ankle, dip and mixed composition models. All these models describe the transition as an intersection of a steep galactic component with a flat extragalactic one. Severe bounds on these models are provided by the Standard Model of Galactic Cosmic Rays according to which the maximum acceleration energy for Iron nuclei is of the order of $E_{\rm Fe}^{\rm max} \approx 1\times 10^{17}$ eV. In the ankle model the transition is assumed at the ankle, a flat feature in the all particle spectrum which observationally starts at energy $E_a \sim (3 - 4)\times 10^{18}$ eV. This model needs a new high energy galactic component with maximum energy about two orders of magnitude above that of the Standard Model. The origin of such component is discussed. As observations are concerned there are two signatures of the transition: change of energy spectra and mass composition. In all models a heavy galactic component is changed at the transition to a lighter or proton component.
We discuss the problem of ultra high energy particles propagation in astrophysical backgrounds. We present two different computational schemes based on both kinetic and Monte Carlo approaches. The kinetic approach is an analytical computation scheme based on the hypothesis of continuos energy losses while the Monte Carlo scheme takes into account also the stochastic nature of particle interactions. These schemes, that give quite reliable results, enable the computation of fluxes keeping track of the different primary and secondary components, providing a fast and useful workbench to study Ultra High Energy Cosmic Rays.
We present simulations of the evolution of self-gravitating dense gas on kiloparsec-size scales in a galactic disc, designed to study dense clump formation from giant molecular clouds (GMCs). These dense clumps are expected to be the precursors to star clusters and this process may be the rate limiting step controling star formation rates in galactic systems as described by the Kennicutt-Schmidt relation. The evolution of the GMCs and clumps is determined by self-gravity balanced by turbulent pressure support and the large scale galactic shear. While the cloud structures and densities significantly changes during their evolution, they remain roughly in virial equilibrium for time scales exceeding the free-fall time of GMCs, indicating that energy from the galactic shear continuously cascades down. We implement star formation at a slow, inefficient rate of 2% per local free-fall time, but this yields global star formation rates that are more than two orders of magnitude larger than the observed Kennicutt-Schmidt relation due to the over-production of dense clump gas. To explain this discrepancy, we anticipate magnetic fields to provide additional support. Low-resolution simulations indeed show that the magnetic field reduces the star formation rate.
Context. Millimetric observations have measured large degrees of molecular deuteration in several species seen around low-mass protostars. The Herschel Space Telescope, launched in 2009, is now providing new measures of the deuterium fractionation of water, the main constituent of interstellar ices. Aims. We aim at theoretically studying the formation and the deuteration of water which is believed to be formed on interstellar grain surfaces in molecular clouds. Methods. We used our gas-grain astrochemical model GRAINOBLE which considers the multilayer formation of interstellar ices. We varied several input parameters to study their impact on water deuteration. We included the treatment of ortho and para states of key species, including H2, that affects the deuterium fractionation of all molecules. The model also includes relevant laboratory and theoretical works on water formation and deuteration on grain surfaces. In particular, we computed the transmission probabilities of surface reactions using the Eckart model and we considered ice photodissociation following molecular dynamics simulations. Results. The use of a multilayer approach allowed us to study the influence of various parameters on the abundance and the deuteration of water. Deuteration of water is found to be very sensitive to the ortho-to-para ratio of H2 and the total density, but it also depends on the gas/grain temperatures and the visual extinction of the cloud. Since the deuteration is very sensitive to the physical conditions, the comparison with sub-millimetric observation towards the low-mass protostar IRAS 16293 allowed us to suggest that water ice is formed together with CO2 in molecular clouds with limited density while formaldehyde and methanol are mainly formed in a later phase, where the condensation becomes denser and colder.
We point out the difficulties in carrying out direct numerical simulation of the solar dynamo problem and argue that kinematic mean-field models are our best theoretical tools at present for explaining various aspects of the solar cycle in detail. The most promising kinematic mean-field model is the flux transport dynamo model, in which the toroidal field is produced by differential rotation in the tachocline, the poloidal field is produced by the Babcock--Leighton mechanism at the solar surface and the meridional circulation plays a crucial role. Depending on whether the diffusivity is high or low, either the diffusivity or the meridional circulations provides the main transport mechanism for the poloidal field to reach the bottom of the convection zone from the top. We point out that the high-diffusivity flux transport dynamo model is consistent with various aspects of observational data. The irregularities of the solar cycle are primarily produced by fluctuations in the Babcock--Leighton mechanism and in the meridional circulation. We summarize recent work on the fluctuations of meridional circulation in the flux transport dynamo, leading to explanations of such things as the Waldmeier effect.
We present CO (J = 1 - 0) and CO (J = 2 - 1) spectra for 19 bright, late-type galaxies (spirals) in the central region of the galaxy cluster Abell 1367 (z = 0.02) from observations made with the IRAM 30 - m telescope. All 19 spirals were observed at the position of their optical center and for a subset, at multiple positions. For each spiral the integrated CO (J = 1 - 0) intensity from the central pointing, in few cases supplemented with intensities from offset pointings, was used to estimate its molecular hydrogen mass and H_2 deficiency. Accepting the considerable uncertainties involved in determining H_2 deficiencies, spirals previously identified by us to have redder colours and higher HI deficiencies as a result of environmental influence, were found to be more H_2 deficient compared to members of the sample in less advanced evolutionary states. For eight of the observed spirals multiple pointing observations were made to investigate the distribution of their molecular gas. For these spirals we fitted Gaussians to the CO intensities projected in a line across the galaxy. In two cases, CGCG 097-079 and CGCG 097-102(N), the offset between the CO and optical intensity maxima was significantly larger than the pointing uncertainty and the FWHMs of the fits were significantly greater than those of the other spirals, irrespective of optical size. Both signatures are indicators of an abnormal molecular gas distribution. In the case of CGCG 097-079, which is considered an archetype for ram pressure stripping, our observations indicate the CO intensity maximum lies ~ 15.6 +/- 8.5 arcsec (6 kpc) NW of the optical centre at the same projected position as the HI intensity maximum.
We present a new optimal method to set up initial conditions for Smooth Particle Hydrodynamics (SPH) simulations, which may also be of interest for N-body simulations. This new method is based on weighted Voronoi tesselations (WVTs) and can meet arbitrarily complex spatial resolution requirements. We conduct a comprehensive review of existing SPH setup methods, and outline their advantages, limitations and drawbacks.
Almost all hydrodynamic accretion disk models parametrize viscosity with the dimensionless parameter alpha. There is no detailed model for alpha, so it is usually taken to be a constant. However, global simulations of magnetohydrodynamic disks find that alpha varies with distance from the central object. Also, Newtonian simulations tend to find smaller alpha's than general relativistic simulations. We seek a one-dimensional model for alpha that can reproduce these two observations. We are guided by data from six general relativistic magnetohydrodynamic accretion disk simulations. The variation of alpha in the inner, laminar regions of the flow results from stretching of mean magnetic field lines by the flow. The variation of alpha in the outer, turbulent regions results from the dependence of the magnetorotational instability on the dimensionless shear rate. We give a one-dimensional prescription for alpha(r) that captures these two effects and reproduces the radial variation of alpha observed in the simulations. For thin disks, the prescription simplifies to the formula alpha(r)=0.025[q(r)/1.5]^6, where the shear parameter, q(r), is an analytical function of radius in the Kerr metric. The coefficient and exponent are inferred from our simulations and will change as better simulation data becomes available. We conclude that the alpha-viscosity prescription can be extended to the radially varying alpha's observed in simulations. It is possible that Newtonian simulations find smaller alpha's than general relativistic simulations because the shear parameter is lower in Newtonian flows.
The unification of active galactic nuclei (AGN) is a model that has been
difficult to test due to the lack of knowledge on the intrinsic luminosities of
the objects. We present a test were we probe the model by statistical
investigation of the neighbours to AGN at redshifts 0.03 < z < 0.2 within a
projected distance of 350 kpc and |\Delta z|<0.001, 0.006, 0.012 and 0.03
between AGN and neighbour.
1658 Type-1 (broad-line) AGN-galaxy pairs and 5698 Type-2 AGN-galaxy pairs
with spectroscopic redshifts from the Data Release 7 of Sloan Digital Sky
Survey were used together with a complementary set of pairs with photometric
redshifts on the neighbour galaxies (13519 Type-1 AGN-galaxy and 58743 Type-2
AGN-galaxy pairs). Morphologies for the AGN host galaxies were derived from the
Galaxy Zoo project.
Our results suggest that broad-line AGN and narrow-line AGN reside in widely
different environments where the neighbours to Type-2 AGN are more star-forming
and bluer than those of Type-1 AGN. There is a colour-dependency only
detectable in the neighbours with photometric redshifts for the Type-2 AGN. We
see that the ratio between Type-1/Type-2 neighbours to Type-2 AGN decreases
steadily at short separations with a statistical significance of 4.5 sigma. The
lack of change in the morphology of the Type-2 AGN hosts having a close
companion (contrary to the case of Type-1 AGN hosts) suggests that the innate
state of Type-2 AGN is extremely short-lived and is not preserved in subsequent
mergers. Finally, we perform a hypothetical luminosity test to investigate
whether a mass bias in our selection could explain the observed differences in
our samples. Our conclusion is that AGN unification is consistently not
supported by the environment of the two types of AGN, but that an evolutionary
connection between them might exist.
Galaxy redshift surveys are becoming increasingly important as a dark energy probe. We improve the forecasting of dark energy constraints from galaxy redshift surveys by using the "dewiggled" galaxy power spectrum, P_{dw}(k), in the Fisher matrix calculations. Since P_{dw}(k) is a good fit to real galaxy clustering data over most of the scale range of interest, our approach is more realistic compared to previous work in forecasting dark energy constraints from galaxy redshift surveys. We find that our new approach gives results in excellent agreement when compared to the results from the actual data analysis of the clustering of the Sloan Digital Sky Survey DR7 luminous red galaxies. We provide forecasts of the dark energy constraints from a plausible Stage IV galaxy redshift survey.
We use a cosmological simulation of the formation of the Local Group of Galaxies to identify a mechanism that enables the removal of baryons from low-mass halos without appealing to feedback or reionization. As the Local Group forms, matter bound to it develops a network of filaments and pancakes. This moving web of gas and dark matter drifts and sweeps a large volume, overtaking many halos in the process. The dark matter content of these halos is unaffected but their gas can be efficiently removed by ram-pressure. The loss of gas is especially pronounced in low-mass halos due to their lower binding energy and has a dramatic effect on the star formation history of affected systems. This "cosmic web stripping" may help to explain the scarcity of dwarf galaxies compared with the numerous low-mass halos expected in \Lambda CDM and the large diversity of star formation histories and morphologies characteristic of faint galaxies. Although our results are based on a single high-resolution simulation, it is likely that the hydrodynamical interaction of dwarf galaxies with the cosmic web is a crucial ingredient so far missing from galaxy formation models.
Bound electron contribution to the Doppler-shift of gamma-ray spectra in the positron-electron annihilation process of molecular methane has been studied in gas phase. Two accurate ab initio quantum mechanical schemes, i.e. the delocalized molecular orbital (MO) and the localized natural bond orbital (NBO) schemes, are applied to study the multi-centred methane molecule. The present ab initio calculations of methane indicate that the C-H bonds are polarized with the partial negative charge of -0.36 a.u. on the carbon atom and the partial positive charge of +0.09 a.u. on each of the hydrogen atoms. The positively charged hydrogen atoms produce repulsive Coulomb potentials to a positron. Both the MO and NBO schemes further reveal that the 2a1 electrons of methane, that is, the 2a1 electron component of the C-H bonds rather than the whole C-H bonds of methane, predominates the positron-electron annihilation gamma-ray spectra of the molecule. Electrons of a molecule which are dominant the positron-electron annihilation processes are called positrophilic electrons in the present study. It is further shown that the negative electrostatic potential (ESP) of methane facilitates with the density of the positrophilic 2a1 electrons of methane. Other valence electrons (e.g. 1t2) in the C-H bonds play a minor spectator role in the annihilation process of methane.
I will talk on my recent works. Axino, related to the SUSY transformation of axion, can mix with Goldstino in principle. In this short talk, I would like to explain what is the axino mass and its plausible mass range. The axino mass is known to have a hierarchical mass structure depending on accidental symmetries. With only one axino, if G_A=0 where G=K+ 2ln|W|, we obtain axino mass= gravitino mass. For G_A nonzero, the axino mass depends on the details of the Kaehler potential. I also comment on the usefulness of a new parametrization of the CKM matrix.
We examine a gravitational lens model inspired by modified gravity theories, exotic matter and energy. We study an asymptotically flat, static and spherically symmetric spacetime that is modified in such a way that the spacetime metric depends on the inverse distance to the power of positive n in the weak field approximation. It is shown analytically and numerically that demagnifying gravitational lenses could appear, provided the impact parameter of light $\beta$ and the power n satisfy $\beta > 2/(n+1)$ in the units of the Einstein ring radius. Unusually, the total amplification of the lensed images, though they are caused by the gravitational pull, could be less than the unity. Therefore, time-symmetric extinction parts in numerical light curves by gravitational microlensing (Abe, Astrophys. J. 725, 787, 2010) may be an evidence of an Ellis wormhole (being an example of traversable wormholes) but they do not always prove it. Such a gravitational extinction of the light might be used for hunting a clue of exotic matter and energy that are described by an equation of state more general than the Ellis wormhole case. Numerical calculations for n=3 and 10 cases show $\sim 10$ and $\sim 60$ percent depletion of the light, respectively.
We consider a maximal extension of the Hilbert-Einstein action and analyze several interesting features of the theory. More specifically, the motion is non-geodesic and takes place in the presence of an extra force. These models could lead to some major differences, as compared to the predictions of General Relativity or other modified theories of gravity, in several problems of current interest, such as cosmology, gravitational collapse or the generation of gravitational waves. Thus, the study of these phenomena may also provide some specific signatures and effects, which could distinguish and discriminate between the various gravitational models.
We propose a simple extension of the standard model by adding a fourth generation vector-like lepton doublet and show that if the fourth neutrino is a massive pseudo-Dirac fermion with mass in the few hundred GeV range and mass splitting of about 100 keV, its lighter component can be a viable inelastic dark matter candidate. Its relic abundance is produced by the CP violating out-of-equilibrium decay of the type-II seesaw scalar triplet, which also gives rise to the required baryon asymmetry of the Universe via type-II leptogenesis, thus providing a simultaneous explanation of dark matter and baryon abundance observed today. Moreover, the induced vacuum expectation value of the same scalar triplet is responsible for the sub-eV Majorana masses to the three active neutrinos. A stable fourth generation of neutrinos is elusive at collider, however might be detected by current dark matter direct search experiments.
Gerbert of Aurillac wrote to Constantine of Fleury in 978 a letter to describe in detail the procedure to point the star nearest to the North celestial pole. This was made to align a sphere equipped with tubes to observe the celestial pole, the polar circles, the solstices and equinoxes. The use of tubes in astronomical observation is later reported by Alhazen in his treatise on optics (1011-1021). The description of pointing to the celestial pole indicates that the instrument must be accurately aligned with the true pole, materialized at that epoch by a star of fifth magnitude, at the limit of naked eye visibility, and then the instrument must remain fixed. Solstices and Equinoxes are points of the orbit of the Sun, so the sphere could be used as a tool for observing the Sun and probably determine the duration of the tropical year. This sphere was much more than a didactic tool, given the long procedure for the accurate alignement. Moreover "Rogatus a pluribus" (asked by his many students), Gerbert wrote a treatise on acoustic tubes (fistulae) in 980: Mensura Fistularum. He knew the difference in behavior of the fistulae compared with the acoustic strings, already studied by the Pythagoreans, and the treaty is intended to present the law that governs the length of the organ pipes in two octaves, compared to the corresponding acoustic strings. In terms of modern physics we know that acoustic tubes require an "end correction" to be tuned, which is proportional to the diameter of the tube. This proportionality is the same for every note. The mathematical law is simple, but Gerbert preferred to create a law in which the proportions of pipes and strings should be calculated through a series of fractions linked to the number 12 and its multiples.
Accurate measurement of polarization in spectral lines is important for the reliable inference of magnetic fields on the Sun. For ground based observations, polarimetric precision is severely limited by the presence of Earth's atmosphere. Atmospheric turbulence (seeing) produces signal fluctuations which combined with the non-simultaneous nature of the measurement process cause intermixing of the Stokes parameters known as seeing induced polarization cross-talk. Previous analysis of this effect (Judge et al., 2004) suggests that cross-talk is reduced not only with increase in modulation frequency but also by compensating the seeing induced image aberrations by an Adaptive Optics (AO) system. However, in those studies the effect of higher order image aberrations than those corrected by the AO system was not taken into account. We present in this paper an analysis of seeing induced cross-talk in the presence of higher order image aberrations through numerical simulation. In this analysis we find that the amount of cross-talk among Stokes parameters is practically independent of the degree of image aberration corrected by an AO system. However, higher order AO corrections increase the signal-to-noise ratio by reducing the seeing caused image smearing.
In a recent paper Sule et al. (Astronomical Notes, vol. 332 (2011), 655) argued that an early 17th-century Indian mural of the constellation Sagittarius with a dragon-headed tail indicated that the bright supernova of 1604 was also sighted by Indian astronomers. In this paper it will be shown that this identification is based on a misunderstanding of traditional Islamic astrological iconography and that the claim that the mural represents an early 17th-century Indian sighting of the supernova of 1604 has to be rejected.
Conversion of gravitational waves into electromagnetic radiation is discussed. The probability of transformations of gravitons into photons in presence of cosmological background magnetic field is calculated at the recombination epoch and during subsequent cosmological stages. The produced electromagnetic radiation is concentrated in the X-ray part of the spectrum. It is shown that if the early Universe was dominated by primordial black holes (PBHs) prior to Big Bang Nucleosynthesis (BBN), the relic gravitons emitted by PBHs would transform to an almost isotropic background of electromagnetic radiation due to conversion of gravitons into photons in cosmological magnetic fields. Such extragalactic radiation could be noticeable or even dominant component of Cosmic X-ray Background.
We consider dark matter (DM) that interacts with ordinary matter exclusively through an electromagnetic anapole, which is the only allowed electromagnetic form factor for Majorana fermions. We show that unlike DM particles with an electric or magnetic dipole moment, anapole dark matter particles annihilate exclusively into fermions via purely p-wave interactions, while tree-level annihilations into photons are forbidden. We calculate the anapole moment needed to produce a thermal relic abundance in agreement with cosmological observations, and show that it is consistent with current XENON100 detection limits on the DM-nucleus cross-section for all masses, while lying just below the detection threshold for a mass ~ 30-40 GeV.
Generating small sterile neutrino masses via the same seesaw mechanism that suppresses active neutrino masses requires a specific structure in the neutral fermion mass matrix. We present a model where this structure is enforced by a new U(1)' gauge symmetry, spontaneously broken at the TeV scale. In order not to spoil the neutrino structure, the additional fermions necessary for anomaly cancellations need to carry exotic charges, and turn out to form multicomponent cold dark matter. The active-sterile mixing then connects the new particles and the Standard Model---opening a new portal in addition to the usual Higgs- and kinetic-mixing portals---which leads to dark matter annihilation almost exclusively into neutrinos.
Links to: arXiv, form interface, find, astro-ph, recent, 1211, contact, help (Access key information)
In this paper, the third of a series, we study the growth rate and luminosity of black holes (BHs) in motion with respect to their surrounding medium by running a large set of 2D axis-symmetric radiation-hydrodynamic simulations. Contrary to the case without radiation feedback, we find that the accretion rate increases with increasing BH velocity v reaching a maximum value at v = 2c_s ~ 50 km/s, where c_s is the sound speed inside the "cometary-shaped" HII region around the BH, before decreasing as v^{-3}. The increase of the accretion rate with v is produced by the formation of a D-type (density) ionization front (I-front) preceded by a standing bow-shock that reduces the downstream gas velocity to transonic values. Since the I-front is beyond the classical Bondi radius for the hot ionized gas, the accretion flow in the BH frame of reference is similar to the stationary case. Interestingly, there is a range of densities and velocities in which the dense shell downstream of the bow-shock is unstable; its central part is destroyed and reformed periodically, producing a periodic accretion rate with peak values about 10 times the mean. This effect can significantly increase the detectability of accreting intermediate mass BHs from the ISM in nearby galaxies. For v>2c_s, the central part of the bow-shock is not able to regenerate, the I-front becomes R-type and the accretion rate approaches the classical Bondi-Hoyle-Lyttleton solution. We find that the maximum accretion rate for a moving BH is larger than that of a stationary BH of the same mass, accreting from the same medium if the medium temperature is T<10^4 K. This result could have an important impact on our understanding of the growth of seed BHs in the multi-phase medium of the first galaxies and for building and early X-ray background that may affect the formation of the first galaxies and the reionization process.
We present the results of a weak gravitational lensing analysis to determine whether the stellar mass or the velocity dispersion is more closely related to the amplitude of the lensing signal around galaxies - and hence to the projected distribution of dark matter. The lensing signal on scales smaller than the virial radius corresponds most closely to the lensing velocity dispersion in the case of a singular isothermal profile, but is on larger scales also sensitive to the clustering of the haloes. We select over 4000 lens galaxies at a redshift z<0.2 with concentrated (or bulge-dominated) surface brightness profiles from the ~300 square degree overlap between the Red-sequence Cluster Survey 2 (RCS2) and the data release 7 (DR7) of the Sloan Digital Sky Survey (SDSS). We consider both the spectroscopic velocity dispersion and a model velocity dispersion (a combination of the stellar mass, the size and the Sersic index of a galaxy). Comparing the model and spectroscopic velocity dispersion we find that they correlate well for galaxies with concentrated brightness profiles. We find that the stellar mass and the spectroscopic velocity dispersion trace the amplitude of the lensing signal on small scales equally well. The model velocity dispersion, however, does significantly worse. A possible explanation is that the halo properties that determine the small-scale lensing signal - mainly the total mass - also depend on the structural parameters of galaxies, such as the effective radius and Sersic index, but we lack data for a definitive conclusion.
We present a brief overview of a splinter session on M dwarf stars as planet hosts that was organized as part of the Cool Stars 17 conference. The session was devoted to reviewing our current knowledge of M dwarf stars and exoplanets in order to prepare for current and future exoplanet searches focusing in low mass stars. We review the observational and theoretical challenges to characterize M dwarf stars and the importance of accurate fundamental parameters for the proper characterization of their exoplanets and our understanding on planet formation.
It has long been expected that in some scenarios when a white dwarf (WD) grows to the Chandrasekhar limit, it can undergo an accretion induced collapse (AIC) to form a rapidly rotating neutron star. Nevertheless, the detection of such events has so far evaded discovery, likely because the optical, supernova-like emission is expected to be dim and short-lived. Here we propose a novel signature of AIC: a transient radio source lasting for a few months. Rapid rotation along with flux freezing and dynamo action can grow the WD's magnetic field to magnetar strengths during collapse. The spindown of this newly born magnetar generates a pulsar wind nebula (PWN) within the ~0.001-0.1Msun of ejecta surrounding it. Our calculations show that synchrotron emission from the PWN may be detectable in the radio, even if the magnetar has a rather modest magnetic field of ~2*10^14 G and an initial spin period of ~10 ms. An all-sky survey with a detection limit of 1 mJy at 1.4 GHz would see ~4(f/10^-2) above threshold at any given time, where f is the ratio of the AIC rate to Type Ia supernova rate. A similar scenario may result from binary neutron stars if some mergers produce massive neutron stars rather than black holes. We conclude with a discussion of the detectability of these types of radio sources in an era of facilities with high mapping speeds.
Recent observations of quasars powered by supermassive black holes (SMBHs) out to z > 7 allow to constrain both the initial seed masses and the growth of the most massive black holes (BHs) in the early universe. The combination of the limited role of mergers in growing seed BHs as inferred from recent cosmological simulations, the sub-Eddington accretion rates of BHs expected at the earliest times, and the large radiative efficiencies of the most massive BHs inferred from observations of active galactic nuclei at high redshift, all suggest that the initial BH seeds may have been as massive as > 10^5 solar masses. This is consistent with the prediction of the direct collapse scenario of SMBH seed formation, in which a supermassive primordial star forms in a region of the universe with a high molecule-dissociating background radiation field, and collapses directly into a 10^4 --10^6 solar mass seed BH. This also corroborates the results of recent cosmological simulations which suggest that these massive BHs were the seeds of a large fraction of the SMBHs residing in the centers of galaxies today.
We present an online catalog of distance determinations for 4781 K giants, most of which are members of the Milky Way's stellar halo. Their spectra from SDSS/SEGUE provide metallicities with accuracies \Delta [Fe/H]\approx\pm0.2 dex and giant-dwarf distinction. The distance moduli are derived from a comparison of each star's apparent magnitude with the absolute magnitude of empirically calibrated color-luminosity fiducials, at the observed (g-r)_0 color and spectroscopic [Fe/H]. We employ a probabilistic approach that makes it straightforward to propagate the errors in metallicities, magnitudes, and colors properly into distance uncertainties. We also fold in {\it prior} information about the giant-branch luminosity function and different metallicity distributions of the SEGUE K-giant targeting sub-categories. We show that the metallicity prior plays little role in the distance estimates, but that neglecting the luminosity prior would lead to a systematic distance modulus bias of up to 0.2 mag. We find a median distance precision of 12%, with distance estimates most precise for the least metal-poor stars near the tip of the red-giant branch. We use globular and open clusters to verify the precision and accuracy of our distance estimates. The stars in our publicly available catalog are up to 110 kpc distant from the Galactic center, with 270 stars beyond 50 kpc, forming the largest sample of distant tracers in the Galactic halo.
Gas giant planets orbiting within 0.1 AU of their host stars, unlikely to have formed in situ, are evidence for planetary migration. It is debated whether the typical hot Jupiter smoothly migrated inward from its formation location through the proto-planetary disk or was perturbed by another body onto a highly eccentric orbit, which tidal dissipation subsequently shrank and circularized during close stellar passages. Socrates and collaborators predicted that the latter class of model should produce a population of super-eccentric proto-hot Jupiters readily observable by Kepler. We find a paucity of such planets in the Kepler sample, disagreeing with the theoretical prediction with 98.7% confidence. Observational effects are unlikely to explain this discrepancy. We find that the fraction of hot Jupiters with orbital period P > 3 days produced by the stellar binary Kozai mechanism does not exceed 0.15 +0.29/-0.11. Our results may indicate that disk migration is the dominant channel for producing hot Jupiters with P > 3 days. Alternatively, the typical hot Jupiter may have been perturbed to a high eccentricity by interactions with a planetary rather than stellar companion and began tidal circularization much interior to the ice line after multiple scatterings. A final alternative is that tidal circularization occurs much more rapidly early in the tidal circularization process at high eccentricities than later in the process at low eccentricities, contrary to current tidal theories.
The Be star \delta\ Scorpii is an interesting binary system, whose primary companion created a circumstellar disk after the periastron passage of the secondary in 2000, being since then classified as Be. This work presents the results of a long-term monitoring of this star in broad-band imaging polarimetry. The observational data collected since 2006 in the Pico dos Dias Observatory (Brazil) show a variable polarization that seems to correlate with the photometric light curve. From this data we see that the disk density varied since 2006; furthermore, the data suggests that there was some disturbance of the disk during the last periastron passage in July, 2011.
We describe the experimental setup and the results of RAuger, a small radio-antenna array, consisting of three fully autonomous and self-triggered radio-detection stations, installed close to the center of the Surface Detector (SD) of the Pierre Auger Observatory in Argentina. The setup has been designed for the detection of the electric field strength of air showers initiated by ultra-high energy cosmic rays, without using an auxiliary trigger from another detection system. Installed in December 2006, RAuger was terminated in May 2010 after 65 registered coincidences with the SD. The sky map in local angular coordinates (i.e., zenith and azimuth angles) of these events reveals a strong azimuthal asymmetry which is in agreement with a mechanism dominated by a geomagnetic emission process. The correlation between the electric field and the energy of the primary cosmic ray is presented for the first time, in an energy range covering two orders of magnitude between 0.1 EeV and 10 EeV. It is demonstrated that this setup is relatively more sensitive to inclined showers, with respect to the SD. In addition to these results, which underline the potential of the radio-detection technique, important information about the general behavior of self-triggering radio-detection systems has been obtained. In particular, we will discuss radio self-triggering under varying local electric-field conditions.
The GJ 581 system has been amply studied since its discovery in 2005: the number of known planets in the system has increased and their orbital parameters are among the most precisely determined for radial velocity detected exoplanets. We have acquired MOST space-based photometry during 2007 and 2009, with the aims of measuring the stellar variability and searching for transits of GJ 581e, respectively. We quantify our sensitivity to shallow transit signals using Monte Carlo simulations, and perform a transit search within the 3$\sigma$ transit windows corresponding to both the circular and Keplerian orbit ephemerides. Our analysis rules out transits for a planet with an orbital period of 3.15 days (GJ 581 e) having a radius larger than 1.62 $R_{\oplus}$ (or a density lower than 2.39 g cm$^{-3}$ for an orbital inclination of 90$^{\circ}$) to 2$\sigma$ confidence. Thus, if the planet transits, we can exclude hydrogen, helium and water theoretical model compositions. The MOST photometry also allows us to rule out transits of GJ 581b within the Keplerian orbit-derived transit window for impact parameter values smaller than $\sim$0.4 and confirm previous results which exclude transits for this planet within the circular orbit-derived transit window, for all plausible interior compositions. We find that the stellar brightness of GJ 581 is stable to within 1%, a characteristic which is favourable to the development of life in the habitable zone of the system. In the 2009 photometry, we detect a stellar signal with a period of 5.586 $\pm$ 0.051 days, which is close to the orbital period of GJ 581b ($P=$5.37 days). However, further monitoring of the system is necessary to verify the nature of this variation.
Large-scale reionization simulations are described which combine the results of cosmological N-body simulations that model the evolving density and velocity fields and identify the galactic halo sources, with ray-tracing radiative transfer calculations which model the nonequilibrium ionization of the intergalactic medium. These simulations have been used to predict some of the signature effects of reionization on cosmic radiation backgrounds, including the CMB, near-IR, and redshifted 21cm backgrounds. We summarize some of our recent progress in this work, and address the question of whether observations of such signature effects can be used to distinguish the relative contributions of galaxies of different masses to reionization.
We present the application of a new method to compute the Wiener filter solution of large and complex data sets. Contrary to the iterative solvers usually employed in signal processing, our algorithm does not require the use of preconditioners to be computationally efficient. The new scheme is conceptually very simple and therefore easy to implement, numerically absolutely stable, and guaranteed to converge. We introduce a messenger field to mediate between the different preferred bases in which signal and noise properties can be specified most conveniently, and rephrase the signal reconstruction problem in terms of this auxiliary variable. We demonstrate the capabilities of the algorithm by applying it to cosmic microwave background (CMB) radiation data obtained by the WMAP satellite.
We present the status of MUSIC, the MUltiwavelength Sub/millimeter Inductance Camera, a new instrument for the Caltech Submillimeter Observatory. MUSIC is designed to have a 14', diffraction-limited field-of-view instrumented with 2304 detectors in 576 spatial pixels and four spectral bands at 0.87, 1.04, 1.33, and 1.98 mm. MUSIC will be used to study dusty star-forming galaxies, galaxy clusters via the Sunyaev-Zeldovich effect, and star formation in our own and nearby galaxies. MUSIC uses broadband superconducting phased-array slot-dipole antennas to form beams, lumped-element on-chip bandpass filters to define spectral bands, and microwave kinetic inductance detectors to senseincoming light. The focal plane is fabricated in 8 tiles consisting of 72 spatial pixels each. It is coupled to the telescope via an ambient temperature ellipsoidal mirror and a cold reimaging lens. A cold Lyot stop sits at the image of the primary mirror formed by the ellipsoidal mirror. Dielectric and metal mesh filters are used to block thermal infrared and out-of-band radiation. The instrument uses a pulse tube cooler and 3He/3He/4He closed-cycle cooler to cool the focal plane to below 250 mK. A multilayer shield attenuates Earth's magnetic field. Each focal plane tile is read out by a single pair of coaxes and a HEMT amplifier. The readout system consists of 16 copies of custom-designed ADC/DAC and IF boards coupled to the CASPER ROACH platform. We focus on recent updates on the instrument design and results from the commissioning of the full camera in 2012.
The helium-merger gamma-ray burst progenitor is produced by the rapid accretion onto a compact remnant (neutron star or black hole) when it undergoes a common envelope inspiral with its companion's helium core. This merger phase produces a very distinct environment around these outbursts and recent observations suggest that, in some cases, we are detecting the signatures of the past merger in the GRB afterglow. These observations allow us, for the first time, to study the specific features of the helium merger progenitor. In this paper, we couple population synthesis calculations to our current understanding of gamma-ray burst engines and common envelope evolution to make observational predictions for the helium-merger gamma-ray burst population. Many mergers do not produce GRB outbursts and we discuss the implications of these mergers with the broader population of astrophysical transients.
Tidal dissipation in compact white dwarf (WD) binary systems significantly influences the physical conditions (such as surface temperature and rotation rate) of the WDs prior to mass transfer or merger. In these systems, the dominant tidal effects involve the excitation of gravity waves and their dissipation in the outer envelope of the star. We calculate the amplitude of tidally excited gravity waves in low-mass (0.3M_\odot) helium-core (He) WDs as a function of the tidal forcing frequency \omega. Like carbon-oxygen (CO) WDs studied in our previous paper, we find that the dimensionless tidal torque F(\omega) (inversely proportional to the effective tidal quality factor) has an erratic dependence on \omega. On average, F(\omega) scales approximately as \omega^6, and is several orders of magnitude smaller for He WDs than for CO WDs. We find that tidal torques can begin to synchronize the WD rotation when the orbital period is less than about a hour, although a nearly constant asynchronization is maintained even at small periods. We examine where the tidally excited gravity waves experience non-linear breaking or resonant absorption at a critical layer, allowing us to estimate the location and magnitude of tidal heating in the WD envelope. We then incorporate tidal heating in the MESA stellar evolution code, calculating the physical conditions of the WD as a function of orbital period for different WD models. We find that tidal heating makes a significant contribution to the WD luminosity for short-period (~10 min) systems such as SDSS J0651+2844. We also find that for WDs containing a hydrogen envelope, tidal heating can trigger runaway hydrogen shell burning, leading to a nova-like event before the onset of mass transfer.
A new view of disk evolution is emerging from self-consistent numerical simulation modeling of the formation of circumstellar disks from the direct collapse of prestellar cloud cores. This has implications for many aspects of star and planet formation, including the growth of dust and high-temperature processing of materials. A defining result is that the early evolution of a disk is crucially affected by the continuing mass loading from the core envelope, and is driven into recurrent phases of gravitational instability. Nonlinear spiral arms formed during these episodes fragment to form gaseous clumps in the disk. These clumps generally migrate inward due to gravitational torques arising from their interaction with a trailing spiral arm. Occasionally, a clump can open up a gap in the disk and settle into a stable orbit, revealing a direct pathway to the formation of companion stars, brown dwarfs, or giant planets. At other times, when multiple clumps are present, a low mass clump may even be ejected from the system, providing a pathway to the formation of free-floating brown dwarfs and giant planets in addition to low mass stars. Finally, it has been suggested that the inward migration of gaseous clumps can provide the proper conditions for the transport of high-temperature processed solids from the outer disk to the inner disk, and even possibly accelerate the formation of terrestrial planets in the inner disk. All of these features arising from clump formation and migration can be tied together conceptually in a Migrating Embryo model for disk evolution that can complement the well-known Core Accretion model for planet formation.
Stars form within molecular clouds but our understanding of this fundamental process remains hampered by the complexity of the physics that drives their evolution. We review our observational and theoretical knowledge of molecular clouds trying to confront the two approaches wherever possible. After a broad presentation of the cold interstellar medium and molecular clouds, we emphasize the dynamical processes with special focus to turbulence and its impact on cloud evolution. We then review our knowledge of the velocity, density and magnetic fields. We end by openings towards new chemistry models and the links between molecular cloud structure and star--formation rates.
We consider the prospects for measuring the pairwise kinetic Sunyaev-Zel'dovich (kSZ) signal from galaxy clusters discovered in large photometric surveys such as the Dark Energy Survey (DES). We project that the DES cluster sample will, in conjunction with existing mm-wave data from the South Pole Telescope (SPT), yield a detection of the pairwise kSZ signal at the 8-13 sigma level, with sensitivity peaking for clusters separated by ~100 Mpc distances. A next-generation version of SPT would allow for a 18-30 sigma detection and would be limited by variance from the kSZ signal itself and residual thermal Sunyaev-Zel'dovich (tSZ) signal. Throughout our analysis we assume photometric redshift errors, which wash out the signal for clusters separated by <~50 Mpc; a spectroscopic survey of the DES sample would recover this signal and allow for a 26-43 sigma detection, and would again be limited by kSZ/tSZ variance. Assuming a standard model of structure formation, these high-precision measurements of the pairwise kSZ signal will yield detailed information on the gas content of the galaxy clusters. Alternatively, if the gas can be sufficiently characterized by other means (e.g. using tSZ, X-ray, or weak lensing), then the relative velocities of the galaxy clusters can be isolated, thereby providing a precision measurement of gravity on 100 Mpc scales. We briefly consider the utility of these measurements for constraining theories of modified gravity.
Filamentary structures are ubiquitous from large-scale molecular clouds (few parsecs) to small-scale circumstellar envelopes around Class 0 sources (~1000 AU to ~0.1 pc). In particular, recent observations with the Herschel Space Observatory emphasize the importance of large-scale filaments (few parsecs) and star formation. The small-scale flattened envelopes around Class 0 sources are reminiscent of the large-scale filaments. We propose an observationally derived scenario for filamentary star formation that describes the evolution of filaments as part of the process for formation of cores and circumstellar envelopes. If such a scenario is correct, small-scale filamentary structures (0.1 pc in length) with higher densities embedded in starless cores should exist, although to date almost all the interferometers have failed to observe such structures. We perform synthetic observations of filaments at the prestellar stage by modeling the known Class 0 flattened envelope in L1157 using both the Combined Array for Research in Millimeter-wave Astronomy (CARMA) and the Atacama Large Millimeter/Submillimeter Array (ALMA). We show that with reasonable estimates for the column density through the flattened envelope, the CARMA D-array at 3mm wavelengths is not able to detect such filamentary structure, so previous studies would not have detected them. However, the substructures may be detected with CARMA D+E array at 3 mm and CARMA E array at 1 mm as a result of more appropriate resolution and sensitivity. ALMA is also capable of detecting the substructures and showing the structures in detail compared to the CARMA results with its unprecedented sensitivity. Such detection will confirm the new proposed paradigm of non-spherical star formation.
Recent research on global climate changes points to three distinct sources of climate disturbance: anthropogenic; natural changes in the oceans and atmosphere; and irregularities in the solar cycles. One of the most direct ways to survey an exogenous component of the climatic variability is through the measurement of variations in the diameter and shape of the solar disk. At Observatorio Nacional/MCTI, Rio de Janeiro, after several years of diameter observation using a CCD Solar Astrolabe, these measurements are now performed by a state-of-the-art Solar Heliometer. The heliometric method is one of the most successful techniques to measure small variations of angles. Its principle has been used for the latest space borne astrometric missions, aiming to milli-arcsecond precision. The success of this method relies in the fact that it minimizes the dependence of angular measurements to the thermal and mechanical stability of the instrument. However in the classic heliometer the objective is split into two halves to which is applied a linear displacement along the cut, thus still leaving room for a residual dependence with the focus, due to non-concentricity of the beams of the two images. The focus variation, as well as the effects brought by the large temperature variations during solar observations, was tackled in the Solar Heliometer by having all optical elements and their niches made on CCZ, and the telescope tube on carbon fiber, both materials of negligible thermal coefficient. Additionally, the measures are made perpendicular to the separation direction and the plate scale can be known at every time from the solar motion itself. We present the results from the first year of measurements, in special exploring the upheaval of solar activity on late 2011.
Clusters of galaxies are the most massive objects in the Universe and precise knowledge of their mass structure is important to understand the history of structure formation and constrain still unknown types of dark contents of the Universe. X-ray spectroscopy of galaxy clusters provides rich information about the physical state of hot intracluster gas and the underlying potential structure. In this paper, starting from the basic description of clusters under equilibrium conditions, we review properties of clusters revealed primarily through X-ray observations considering their thermal and dynamical evolutions. The future prospects of cluster studies using upcoming X-ray missions are also mentioned.
Mid-infrared spectroscopic measurements from the Infrared Spectrometer on Spitzer (IRS) are given for 125 hard X-ray AGN (14-195 keV) from the Swift Burst Alert Telescope sample and for 32 AGN with black hole masses from reverberation mapping. The 9.7 um silicate feature in emission or absorption defines an infrared AGN classification describing whether AGN are observed through dust clouds, indicating that 55% of the BAT AGN are observed through dust. The mid-infrared dust continuum luminosity is shown to be an excellent indicator of intrinsic AGN luminosity, scaling closely with the hard X-ray luminosity, log vLv(7.8 um)/L(X) = -0.31 +- 0.35 and independent of classification determined from silicate emission or absorption. Dust luminosity scales closely with black hole mass, log vLv(7.8 um) = (37.2 +- 0.5) + 0.87 log BHM for luminosity in erg per sec and BHM in solar masses. The 100 most luminous type 1 quasars as measured in vLv(7.8 um) are found by comparing Sloan Digital Sky Survey optically discovered quasars with photometry at 22 um from the Wide-Field Infrared Survey Explorer, scaled to rest frame 7.8 um using an empirical template determined from IRS spectra. The most luminous SDSS/WISE quasars have the same maximum infrared luminosities for all 1.5 < z < 5, reaching total infrared luminosity L(IR) = 10^14.4 solar luminosities. Comparing with Dust Obscured Galaxies from Spitzer and WISE surveys, we find no evidence of hyperluminous obscured quasars whose maximum infrared luminosities exceed the maximum infrared luminosities of optically discovered quasars. Bolometric luminosities L(bol) estimated from rest frame optical or ultraviolet luminosities are compared to L(IR).
The origin of the giant stellar arcs in the LMC remains a controversial issue, discussed since 1966. No other stellar arc is so perfect a segment of a circle, moreover, there is another similar arc nearby. Many hypotheses were advanced to explain these arcs, and all but one of these were disproved. It was proposed in 2004 that origin of these arcs was due to the bow shock from the jet, which is intermittently fired by the Milky Way nucleus and during the last episode of its activity the jet was pointed to the LMC. Quite recently evidence for such a jet has really appeared. We suppose it was once energetic enough to trigger star formation in the LMC, and if the jet opening angle was about 2{\deg}, it could push out HI gas from the region of about 2 kpc in size, forming a cavity LMC4, but also squeezed two dense clouds, which occurred in the same area, causing the formation of stars along their surfaces facing the core of the MW. In result, spherical segments of the stellar shells might arise, visible now as the arcs of Quadrant and Sextant, the apices of which point to the center of the MW. This orientation of both arcs can be the key to unlocking their origin. Here we give data which confirm the above hypothesis, amongst which are radial velocities of stars inside and outside the larger one of the LMC arcs. The probability is low that a jet from an AGN points to a nearby galaxy and triggers star formation there, but a few other examples are now known or suspected.
The infrared channel of the Wide-Field Camera 3 on the Hubble Space Telescope revealed multiple main sequences of very low-mass stars in the globular clusters NGC 2808 and Omega Centauri. In this paper I summarize the observational facts and provide a possible interpretation.
We present a numerical simulation of cosmic ray transport in the heliosphere and show that AMS-02 should observe a decrease in the positron fraction above 40GeV compared to the fraction observed by PAMELA.
HD 140283 is a nearby (V=7.7) subgiant metal-poor star, extensively analysed in the literature. Although many spectra have been obtained for this star, none showed a signal-to-noise (S/N) ratio high enough to enable a very accurate derivation of abundances from weak lines. The detection of europium proves that the neutron-capture elements in this star originate in the r-process, and not in the s-process, as recently claimed in the literature. Based on the OSMARCS 1D LTE atmospheric model and with a consistent approach based on the spectrum synthesis code Turbospectrum, we measured the europium lines at 4129 {\AA} and 4205 {\AA}, taking into account the hyperfine structure of the transitions. The spectrum, obtained with a long exposure time of seven hours at the Canada-France-Hawaii Telescope (CFHT), has a resolving power of 81000 and a S/N ratio of 800 at 4100 {\AA}. We were able to determine the abundance A(Eu)=-2.35 dex, compatible with the value predicted for the europium from the r-process. The abundance ratio [Eu/Ba]=+0.58 dex agrees with the trend observed in metal-poor stars and is also compatible with a strong r-process contribution to the origin of the neutron-capture elements in HD 140283.
The paper considers the evolution of the supernova envelopes produced by Population III stars with masses of $M_*\sim 25-200 M_\odot$ located in non-rotating protogalaxies with masses of $M\sim 10^7 M_\odot$ at redshifts $z=12$, with dark-matter density profiles in the form of modified isothermal spheres. The supernova explosion occurs in the ionization zone formed by a single parent star. The properties of the distribution of heavy elements (metals) produced by the parent star are investigated, as well as the efficiency with which they are mixed with the primordial gas in the supernova envelope. In supernovae with high energies ($E\simgt 5\times 10^{52}$ erg), an appreciable fraction of the gas can be ejected from the protogalaxy, but nearly all the heavy elements remain in the protogalaxy. In explosions with lower energies ($E\simlt 3\times 10^{52}$ erg), essentially no gas and heavy elements are lost from the protogalaxy: during the first one to threemillion years, the gas and heavy elements are actively carried from the central region of the protogalaxy ($r\sim 0.1 r_{vir}$, where $r_{vir}$ is the virial radius of the protogalaxy), but an appreciable fraction of the mass of metals subsequently returns when the hot cavity cools and the envelope collapses. Supernovae with high energies ($E\simgt 5\times 10^{52}$ erg) are characterized by a very low efficiency of mixing of metals; their heavy elements are located in the small volume occupied by the disrupted envelope (in a volume comparable with that of the entire envelope), with most of the metals remaining inside the hot, rarified cavity of the envelope. (abridged)
We present Plateau de Bure Interferometer observations of far infra-red emission lines in BRI 0952-0115, a lensed quasar at z=4.4 powered by a super-massive black hole (M_BH=2x10^9 M_sun). In this source, the resolved map of the [CII] emission at 158 micron allows us to reveal the presence of a companion galaxy, located at \sim 10 kpc from the quasar, undetected in optical observations. From the CO(5-4) emission line properties we infer a stellar mass M*<2.2x10^10 M_sun, which is significantly smaller than the one found in local galaxies hosting black holes with similar masses (M* \sim 10^12 M_sun). The detection of the [NII] emission at 205 micron suggests that the metallicity in BRI 0952-0115 is consistent with solar, implying that the chemical evolution has progressed very rapidly in this system. We also present PdBI observations of the [CII] emission line in SDSSJ1148+5251, one of the most distant quasar known, at z=6.4. We detect broad wings in the [CII] emission line, indicative of gas which is outflowing from the host galaxy. In particular, the extent of the wings, and the size of the [CII] emitting region associated to them, are indicative of a quasar-driven massive outflow with the highest outflow rate ever found (dM/dt>3500 M_sun/yr).
The significance of jets and accretion disks in Astrophysics may be growing far beyond any single example of recent finds in the scientific journals. This brief review will summarize recent, significant manifestations of accretion disk powered jets in the universe. We then introduce supplemental contemporary finds in physics and astrophysics which might bear tangential or direct implications for astrophysics toward rethinking the universe with a major role of relativistic jets powered by accretion disks.
Using our updated stellar evolutionary code, we quantitatively evaluate the effects of the uncertainties in the main physical inputs on the evolutionary characteristics of low mass stars from the main sequence to the zero age horizontal branch (ZAHB). We calculated more than 3000 stellar tracks and isochrones, with updated solar mixture, by changing the following physical inputs within their current range of uncertainty: 1H(p,nu e+)2H, 14N(p,gamma)15O, and triple-alpha reaction rates, radiative and conductive opacities, neutrino energy losses, and microscopic diffusion velocities. We performed a systematic variation on a fixed grid, in a way to obtain a full crossing of the perturbed input values. The effect of the variations of the chosen physical inputs on relevant stellar evolutionary features, such as the turn-off luminosity, the central hydrogen exhaustion time, the red-giant branch (RGB) tip luminosity, the helium core mass, and the ZAHB luminosity in the RR Lyrae region are statistically analyzed. For a 0.9 Msun model, the cumulative uncertainty on the turn-off, the RGB tip, and the ZAHB luminosities accounts for $\pm$ 0.02 dex, $\pm$ 0.03 dex, and $\pm$ 0.045 dex respectively, while the central hydrogen exhaustion time varies of about $\pm$ 0.7 Gyr. The most relevant effect is due to the radiative opacities uncertainty; for the later evolutionary stages the second most important effect is due to the triple-alpha reaction rate uncertainty. For an isochrone of 12 Gyr, we find that the isochrone turn-off log luminosity varies of $\pm$ 0.013 dex, the mass at the isochrone turn-off varies of $\pm$ 0.015 Msun, and the difference between ZAHB and turn-off log-luminosity varies of $\pm$ 0.05 dex. The effect of the physical uncertainty affecting the age inferred from turn-off luminosity and from the vertical method are of $\pm$ 0.375 Gyr and $\pm$ 1.25 Gyr respectively.
Solar five-minute oscillations have been detected in the power spectra of two six-day time intervals from soft X-ray measurements of the Sun observed as a star using the Extreme Ultraviolet Spectrophotometer (ESP) onboard the Solar Dynamics Observatory (SDO) Extreme Ultraviolet Variability Experiment (EVE). The frequencies of the largest amplitude peaks were found matching within 3.7 microHz the known low-degree (l = 0--3) modes of global acoustic oscillations, and can be explained by a leakage of the global modes into the corona. Due to strong variability of the solar atmosphere between the photosphere and the corona the frequencies and amplitudes of the coronal oscillations are likely to vary with time. We investigate the variations in the power spectra for individual days and their association with changes of solar activity, e.g. with the mean level of the EUV irradiance, and its short-term variations due to evolving active regions. Our analysis of samples of one-day oscillation power spectra for a 49-day period of low and intermediate solar activity showed little correlation with the mean EUV irradiance and the short-term variability of the irradiance. We suggest that some other changes in the solar atmosphere, e.g. magnetic fields and/or inter-network configuration may affect the mode leakage to the corona.
Context. The APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) is the first systematic survey of the inner Galactic plane in the sub-millimetre. The observations were carried out with the Large APEX Bolometer Camera (LABOCA), an array of 295 bolometers observing at 870 microns (345 GHz). Aims. Here we present a first version of the compact source catalogue extracted from this survey. This catalogue provides an unbiased database of dusty clumps in the inner Galaxy. Methods. The construction of this catalogue was made using the source extraction routine SExtractor. We have cross-associated the obtained sources with the IRAS and MSX catalogues, in order to constrain their nature. Results. We have detected 6639 compact sources in the range from 330 < l < 21 degrees and |b| < 1.5 degrees. The catalogue has a 99% completeness for sources with a peak flux above 6 sigma, which corresponds to a flux density of ~0.4 Jy/beam. The parameters extracted for sources with peak fluxes below the 6 sigma completeness threshold should be used with caution. Tests on simulated data find the uncertainty in the flux measurement to be ~12%, however, in more complex regions the flux values can be overestimated by a factor of 2 due to the additional background emission. Using a search radius of 30" we found that 40% of ATLASGAL compact sources are associated with an IRAS or MSX point source, but, ~50% are found to be associated with MSX 21 microns fluxes above the local background level, which is probably a lower limit to the actual number of sources associated with star formation. Conclusions. Although infrared emission is found towards the majority of the clumps detected, this catalogue is still likely to include a significant number of clumps that are devoid of star formation activity and therefore excellent candidates for objects in the coldest, earliest stages of (high-mass) star formation.
The launch of Hinode satellite led to the discovery of rising plumes, dark in chromospheric lines, in quiescent prominences that propagate from large (~10 Mm) bubbles that form at the base of the prominences. These plumes present a very interesting opportunity to study Magnetohydrodynamic (MHD) phenomena in quiescent prominences, but obstacles still remain. One of the biggest issues is that of the magnetic field strength, which is not easily measurable in prominences. In this paper we present a method that may be used to determine a prominence's plasma \beta when rising plumes are observed. Using the classic fluid dynamic solution for flow around a circular cylinder with an MHD correction, the compression of the prominence material can be estimated. This has been successfully confirmed through simulations; application to a prominence gave an estimate of the plasma beta as \beta=0.47 to 1.13 with an error of 0.080 for the range \gamma=1.4 to 1.7. Using this method it may be possible to estimate the plasma beta of observed prominences, therefore helping our understanding of a prominence's dynamics in terms of MHD phenomena.
The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is under construction and will be commissioned in September 2016. A low frequency 7-beam receiver working around 400 MHz is proposed for FAST early science. It will be optimized for a whole FAST sky drift-scan pulsar survey. Simulations show that about 1500 new normal pulsars will be discovered, as while as about 200 millisecond pulsars.
We introduce the MALT-45 (Millimetre Astronomer's Legacy Team - 45 GHz) Galactic plane survey and describe pilot survey results with the Australia Telescope Compact Array (ATCA). The pilot survey was conducted to test the instrumentation and observational technique of MALT-45, before commencing the full survey. We mapped two half-square degree regions within the southern Galactic plane around the G333 giant molecular cloud, using fast mosaic mapping. Using the new Compact Array Broadband Backend (CABB) on the ATCA, we were able to observe two 2048 MHz spectral windows, centred on frequencies 43.2 and 48.2 GHz. Although only a coarse spectral resolution of around 7 km/s was available to us, we detect widespread, extended emission in the CS (1-0) ground state transition. We also detect eight Class I CH3OH masers at 44 GHz and three SiO masers in vibrationally excited (1-0) transitions. We also detect the H53a radio recombination line, non-vibrationally excited SiO (1-0) and emission in the CH3OH 1_1-0_0 A+ line.
Recently, a New HDE model with action principle was proposed (Li and Miao, arXiv:1210.0966). This model completely solves the causality and circular problems in the original HDE model, and is similar to the original model except a new term that can be interpreted as dark radiation. In this paper, we make further investigations on this model from the aspect of cosmological observations. Numerically, we confirm that the equations of motion force the $L(z=-1)=0$, making the cut-off $aL$ exactly the future event horizon. We also perform detailed analysis on the dynamical properties of the model, divided into the $c<6$ and $c\geq6$ cases ($c$ is a dimensionless parameter which should be decided by the data). From a combination of the present Union2.1+BAO+CMB+$H_0$ data, we find the model yields $\chi^2_{\rm min}=548.798$ (in a non-flat Universe), comparable to the results of the original HDE model (549.461) and the concordant $\Lambda$CDM model (550.354). At 95.4% CL, we get $1.41<c<3.09$ and correspondingly $-2.25<w(z=-1)<-1.39$, implying the Big Rip fate of the Universe at a high confidence level. Besides, for the constraints on dark radiation, we also get a rough estimation $N_{\rm \rm eff}=3.54^{+0.32+0.67}_{\rm -0.45-0.76}$, with the central value slightly larger than the standard value 3.046.
The Milky Way appears to be missing baryons, as the observed mass in stars and gas is well below the cosmic mean. One possibility is that a substantial fraction of the Galaxy's baryons are embedded within an extended, million-degree hot halo, an idea supported indirectly by observations of warm gas clouds in the halo and gas-free dwarf spheroidal satellites. X-ray observations have established that hot gas does exist in our Galaxy beyond the local hot bubble; however, it may be distributed in a hot disk configuration. Moreover, recent investigations into the X-ray constraints have suggested that any Galactic corona must be insignificant. Here we re-examine the observational data, particularly in the X-ray and radio bands, in order to determine whether it is possible for a substantial fraction of the Galaxy's baryons to exist in ~ 10^6 K gas. In agreement with past studies, we find that a baryonically closed halo is clearly ruled out if one assumes that the hot corona is distributed with a cuspy NFW profile. However, if the hot corona of the galaxy is in an extended, low-density distribution with a large central core, as expected for an adiabatic gas in hydrostatic equilibrium, then it may contain up to 10^11 M_sun of material, possibly accounting for all of the missing Galactic baryons. We briefly discuss some potential avenues for discriminating between a massive, extended hot halo and a local hot disk.
The properties of tidally induced arms provide a means to study molecular cloud formation and the subsequent star formation under environmental conditions which in principle are different from quasi stationary spiral arms. We report the properties of a newly discovered molecular gas arm of likely tidal origin at the south of NGC 4039 and the overlap region in the Antennae galaxies, with a resolution of 1"68 x 0"85, using the Atacama Large Millimeter/submillimeter Array science verification CO(2-1) data. The arm extends 3.4 kpc (34") and is characterized by widths of ~ 200 pc (2") and velocity widths of typically \DeltaV ~ 10-20 km/s . About 10 clumps are strung out along this structure, most of them unresolved, with average surface densities of \Sigma_gas ~ 10-100 Msun pc^{-2}, and masses of (1-8) x 10^6 Msun. These structures resemble the morphology of beads on a string, with an almost equidistant separation between the beads of about 350 pc, which may represent a characteristic separation scale for giant molecular associations. We find that the star formation efficiency at a resolution of 6" (600 pc) is in general a factor of 10 higher than in disk galaxies and other tidal arms and bridges. This arm is linked, based on the distribution and kinematics, to the base of the western spiral arm of NGC 4039, but its morphology is different to that predicted by high-resolution simulations of the Antennae galaxies.
We propose a model for the gamma-ray binary LS 5039 in which the X-ray emission is due to the inverse Compton (IC) process instead of the synchrotron radiation. Although the synchrotron model has been discussed in previous studies, it requires a strong magnetic field which leads to a severe suppression of the TeV gamma-ray flux in conflict with H.E.S.S. observations. In this paper, we calculate the IC emission by low energy electrons (\gamma_e \lesssim 10^3) in the Thomson regime. We find that IC emission of the low energy electrons can explain the X-ray flux and spectrum observed with Suzaku if the minimum Lorentz factor of injected electrons \gamma_min is around 10^3. In addition, we show that the Suzaku light curve is well reproduced if \gamma_min varies in proportion to the Fermi flux when the distribution function of injected electrons at higher energies is fixed. We conclude that the emission from LS 5039 is well explained by the model with the IC emission from electrons whose injection properties are dependent on the orbital phase. Since the X-ray flux is primarily determined by the total number of cooling electrons, this conclusion is rather robust, although some mismatches between the model and observations at the GeV band remain in the present formulation.
Estimates of cosmological parameters using galaxy clusters have the scatter in the observable at a given mass as a fundamental parameter. This work computes the amplitude of the scatter for a newly introduced mass proxy, the product of the cluster total luminosity times the mass-to-light ratio, usually referred as stellar mass. The analysis of 12 galaxy clusters with excellent total masses shows a tight correlation between the stellar mass, or stellar fraction, and total mass within r500 with negligible intrinsic scatter: the 90% upper limit is 0.06 dex, the posterior mean is 0.027 dex. This scatter is similar to the one of best-determined mass proxies, such as Yx, i.e. the product of X-ray temperature and gas mass. The size of the cluster sample used to determine the intrinsic scatter is small, as in previous works proposing low-scatter proxies because very accurate masses are needed to infer very small values of intrinsic scatter. Three-quarters of the studied clusters have lgM <~14 Msol, which is advantageous from a cosmological perspective because these clusters are far more abundant than more massive clusters. At the difference of other mass proxies such as Yx, stellar mass can be determined with survey data up to at least z=0.9 using upcoming optical near-infrared surveys, such as DES and Euclid, or even with currently available surveys, covering however smaller solid angles. On the other end, the uncertainty about the predicted mass of a single cluster is large, 0.21 to 0.32 dex, depending on cluster richness. This is largely because the proxy itself has ~0.10 dex errors for clusters of lgM<~ 14 Msol mass.
We compare the results of three binary population synthesis codes to understand the differences in their results. As a first result we find that when equalizing the assumptions the results are similar. The main differences arise from deviating physical input.
We present the discovery of four new transiting hot jupiters, detected mainly from SuperWASP-North and SOPHIE observations. These new planets, WASP-52b, WASP-58b, WASP-59b, and WASP-60b, have orbital periods ranging from 1.7 to 7.9 days, masses between 0.46 and 0.94 M_Jup, and radii between 0.73 and 1.49 R_Jup. Their G1 to K5 dwarf host stars have V magnitudes in the range 11.7-13.0. The depths of the transits are between 0.6 and 2.7%, depending on the target. With their large radii, WASP-52b and 58b are new cases of low-density, inflated planets, whereas WASP-59b is likely to have a large, dense core. WASP-60 shows shallow transits. In the case of WASP-52 we also detected the Rossiter-McLaughlin anomaly via time-resolved spectroscopy of a transit. We measured the sky-projected obliquity lambda = 24 (+17/-9) degrees, indicating that WASP-52b orbits in the same direction as its host star is rotating and that this prograde orbit is slightly misaligned with the stellar equator. These four new planetary systems increase our statistics on hot jupiters, and provide new targets for follow-up studies.
We report the discovery of blue-shifted metastable He I* absorption lines at 3188 A and 3889 A with multiple components on high-resolution spectra (R ~ 60,000) of V1280 Scorpii. Similar multiple absorption lines associated with Na I D doublet and Ca II H and K are observed. Na I D doublet absorption lines have been observed since 2009, while the metastable He I* absorption lines were absent in 2009 and were detected in 2011 (four years after the burst). We find different time variations in depths and velocities of blue-shifted absorption components among He I*, Na I, and Ca II. The complex time evolutions of these lines can be explained by assuming changes in density and recombination/ionization rate when the ejecta expand and the photosphere contracts to become hotter. The multiple absorption lines originate in the ejected materials consisting of clumpy components, which obscure a significant part of the continuum emitting region. We estimate the total mass of the ejected material to be on the order of ~ 10^{-4} Mo, using metastable He I* 3188 and 3899 absorption lines.
The Ultra Luminous X-ray (ULX) source HLX-1 in the galaxy ESO 243-49 has an observed maximum unabsorbed X-ray luminosity of 1.3e42 erg/s (0.2-10.0 keV). From the conservative assumption that this value exceeds the Eddington limit by at most a factor of 10, the minimum mass is then 500 solar masses. The X-ray luminosity varies by a factor of 40 with an apparent recurrence timescale of approximately one year. This X-ray variability is associated with spectral state transitions similar to those seen in black hole X-ray binaries. Here we discuss our recent modelling of all the X-ray data for HLX-1 and show that it supports the idea that this ULX is powered by sub- and near Eddington accretion onto an intermediate mass black hole. We also present evidence for transient radio emission which is consistent with a discrete jet ejection event as well as comment on the nature of the environment around HLX-1 in light of recent Hubble Space Telescope photometry.
The XENON100 experiment, in operation at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy, was designed to search for evidence of dark matter interactions inside a volume of liquid xenon using a dual-phase time projection chamber. This paper describes the Slow Control System (SCS) of the experiment with emphasis on the distributed architecture as well as on its modular and expandable nature. The system software was designed according to the rules of Object-Oriented Programming and coded in Java, thus promoting code reusability and maximum flexibility during commissioning of the experiment. The SCS has been continuously monitoring the XENON100 detector since mid 2008, remotely recording hundreds of parameters on a few dozen instruments in real time, and setting emergency alarms for the most important variables.
We discuss the linear response to low-frequency tidal forcing of fluid bodies that are slowly and uniformly rotating, are neutrally stratified and may contain a solid or fluid core. This problem may be regarded as a simplified model of astrophysical tides in convective regions of stars and giant planets. The response can be separated into non-wavelike and wavelike parts, where the former is related instantaneously to the tidal potential and the latter may involve resonances or other singularities. The imaginary part of the potential Love number of the body, which is directly related to the rates of energy and angular momentum exchange in the tidal interaction and to the rate of dissipation of energy, may have a complicated dependence on the tidal frequency. However, a certain frequency-average of this quantity is independent of the dissipative properties of the fluid and can be determined by means of an impulse calculation. The result is a strongly increasing function of the size of the core when the tidal potential is a sectoral harmonic, especially when the body is not strongly centrally condensed. However, the same is not true for tesseral harmonics, which receive a richer response and may therefore be important in determining tidal evolution even though they are usually subdominant in the expansion of the tidal potential. We also discuss analytically the low-frequency response of a slowly rotating homogeneous fluid body to tidal potentials proportional to spherical harmonics of degrees less than five. Tesseral harmonics of degrees greater than two, such as are present in the case of a spin-orbit misalignment, can resonate with inertial modes of the full sphere, leading to an enhanced tidal interaction.
We present deep CO observations of NGC6240 performed with the IRAM Plateau de Bure Interferometer (PdBI). NGC6240 is the prototypical example of a major galaxy merger in progress, caught at an early stage, with an extended, strongly-disturbed butterfly-like morphology and the presence of a heavily obscured active nucleus in the core of each progenitor galaxy. The CO line shows a skewed profile with very broad and asymmetric wings detected out to velocities of -600 km/s and +800 km/s with respect to the systemic velocity. The PdBI maps reveal the existence of two prominent structures of blueshifted CO emission. One extends eastward, i.e. approximately perpendicular to the line connecting the galactic nuclei, over scales of ~7 kpc and shows velocities up to -400 km/s. The other extends southwestward out to ~7 kpc from the nuclear region, and has a velocity of -100 km/s with respect to the systemic one. Interestingly, redshifted emission with velocities 400 to 800 km/s is detected around the two nuclei, extending in the east-west direction, and partly overlapping with the eastern blue-shifted structure, although tracing a more compact region of size ~1.7 kpc. The overlap between the southwestern CO blob and the dust lanes seen in HST images, which are interpreted as tidal tails, indicates that the molecular gas is deeply affected by galaxy interactions. The eastern blueshifted CO emission is co-spatial with an Halpha filament that is associated with strong H2 and soft X-ray emission. The analysis of Chandra X-ray data provides strong evidence for shocked gas at the position of the Halpha emission. Its association with outflowing molecular gas supports a scenario where the molecular gas is compressed into a shock wave that propagates eastward from the nuclei. If this is an outflow, the AGN are likely the driving force.
We analyzed archival spectra acquired with the Hubble Space Telescope for a study of interstellar C2. Absorption from the electronic transitions, D ^1Sigma^+_u -- X ^1Sigma^+_g (0,0) as well as F ^1Pi_u -- X ^1Sigma^+_g (0,0) and (1,0), was the focus of the study. Our profile syntheses revealed that the lines of the F-X bands were broadened as a result of a perturbation involving the upper levels. Further evidence for the perturbation came from anomalies in line strength and position for the F-X (0,0) band. The perturbation likely arises from a combination of triplet-singlet interactions involving spin-orbit mixing between ^3Pi_u states and F ^1Pi_u and an avoided crossing between the ^3Pi_u states. Tunneling through a potential barrier caused by the 3 and 4 ^1Pi_u states and spin-orbit mixing with other close-lying triplet states of ungerade symmetry are less likely. Except for the broadening, lines in the F-X (1,0) band appear free from anomalies and can be used to study interstellar C2; new results for 10 sight lines are presented.
We present ATCA observations of the H2O maser line and radio continuum at 18.0GHz and 22.8GHz, toward a sample of 192 massive star forming regions containing several clumps already imaged at 1.2mm. The main aim of this study is to investigate the water maser and centimeter continuum emission (likely tracing thermal free-free emission) in sources at different evolutionary stages, using the evolutionary classifications proposed by Palla et al (1991) and Molinari et al (2008). We used the recently comissioned CABB backend at ATCA obtaining images with 20arcsec resolution in the 1.3cm continuum and H2O maser emission, in all targets. For the evolutionary analysis of the sources we used the millimeter continuum emission from Beltran et al (2006) and the infrared emission from the MSX Point Source Catalogue. We detect centimeter continuum emission in 88% of the observed fields with a typical rms noise level of 0.45mJy/beam. Most of the fields show a single radio continuum source, while in 20% of them we identify multiple components. A total of 214 centimeter continuum sources have been identified, likely tracing optically thin HII regions, with physical parameters typical of both extended and compact HII regions. Water maser emission was detected in 41% of the regions, resulting in a total of 85 distinct components. The low angular (20arcsec) and spectral (14km/s) resolutions do not allow a proper analysis of the water maser emission, but suffice to investigate its association with the continuum sources. We have also studied the detection rate of HII regions in the two types of IRAS sources defined by Palla et (1991) on the basis of the IRAS colours: High and Low. No significant differences are found, with large detection rates (>90%) for both High and Low sources. We classify the millimeter and infrared sources in our fields in three evolutionary stages following the scheme presented by ...
The 1968 discovery of the Crab and Vela pulsars in their respective supernova remnants (SNRs) confirmed Baade and Zwicky's 1934 prediction that supernovae form neutron stars. Observations of Pulsar Wind Nebulae (PWNe), particularly with the Chandra X-ray Observatory, have in the past decade opened a new window to focus on the neutron stars' relativistic winds, study their interaction with their hosting SNRs, and find previously missed pulsars. While the Crab has been thought for decades to represent the prototype of PWNe, we now know of different classes of neutron stars and PWNe whose properties differ from the Crab. In this talk, I review the current status of neutron stars/PWNe-SNRs associations, and highlight the growing diversity of PWNe with an X-ray eye on their association with highly magnetized neutron stars. I conclude with an outlook to future high-energy studies.
Core-collapse supernovae (CC SNe), especially those of type II-plateau (II-P), are thought to be important contributors to cosmic dust production. The most obvious indicator of the presence of newly-formed and/or pre-existing dust is the time-dependent mid-infrared (MIR) excess coming from the environment of SNe. Our goal was to collect publicly available, previously unpublished measurements on type II-P (or peculiar IIP) SNe from the Spitzer database. The temporal changes of the observed fluxes may be indicative of the underlying supernova, while spectral energy distribution (SED) fitting to the fluxes in different IRAC channels may reveal the physical parameters of the mid-IR radiation, presumably due to warm dust. IRS spectra were extracted and calibrated with SPICE, while photometric SEDs were assembled using IRAF and MOPEX. Calculated SEDs from observed fluxes were fit with simple dust models to get basic information on the dust presumed as the source of MIR radiation. We found twelve SNe satisfying the criterion above, observed at late-time epochs (typically after +300 days). In three cases we could not identify any point source at the SN position on late time IRAC images. We found two SNe, 2005ad and 2005af, which likely have newly-formed dust in their environment, while in the other seven cases the observed MIR flux may originate from pre-existing circumstellar or interstellar dust. Our results support the previous observational conclusions that warm new dust in the environment of SNe contributes only marginally to cosmic dust content.
From new observations and literature data we investigate the presence of HI, dust, and optical cores in the central kiloparsec of low-power radio galaxies. The goal of this pilot study is to identify physical relations between these components, which can help us to study kinematics and feeding mechanisms in future samples of active galaxies. Our results are consistent with neutral gas being associated with dust on sub-kiloparsec scales. Objects that have HI absorption always have significant amounts of dust in their host galaxy. If there is no visible dust in the host galaxy, there is also no HI absorption. The presence of an unresolved optical core correlates with the HI column density, with the core being absent in high column density sources. This work opens a path for studying the kinematics of cold material in the central regions of active galaxies by combining information of HI absorption and molecular lines. Consistent with previous work, we find no evidence for a compact, parsec-scale obscuring torus in low-power radio galaxies.
An increasing number of OB stars have been shown to possess magnetic fields.
Although the sample remains small, it is surprising that the magnetic and X-ray
properties of these stars appear to be far less correlated than expected. This
contradicts model predictions, which generally indicate that the X-rays from
magnetic stars to be harder and more luminous than their non-magnetic
counterparts. Instead, the X-ray properties of magnetic OB stars are quite
diverse.
$\tau$ Sco is one example where the expectations are better met. This bright
main sequence, early B star has been studied extensively in a variety of
wavebands. It has a surface magnetic field of around 500 G, and Zeeman Doppler
tomography has revealed an unusual field configuration. Furthermore, tau Sco
displays an unusually hard X-ray spectrum, much harder than similar,
non-magnetic OB stars. In addition, the profiles of its UV P Cygni wind lines
have long been known to possess a peculiar morphology.
Recently, two stars, HD 66665 and HD 63425, whose spectral types and UV wind
line profiles are similar to those of $\tau$ Sco, have also been determined to
be magnetic. In the hope of establishing a magnetic field - X-ray connection
for at least a sub-set of the magnetic stars, we obtained XMM-Newton EPIC
spectra of these two objects. Our results for HD 66665 are somewhat
inconclusive. No especially strong hard component is detected; however, the
number of source counts is insufficient to rule out hard emission. longer
exposure is needed to assess the nature of the X-rays from this star. On the
other hand, we do find that HD 63425 has a substantial hard X-ray component,
thereby bolstering its close similarity to tau Sco.
We have developed a new model for analysing light curves of planetary transits when there are starspots on the stellar disc. Because the parameter space contains a profusion of local minima we developed a new optimisation algorithm which combines the global minimisation power of a genetic algorithm and the Bayesian statistical analysis of the Markov chain. With these tools we modelled three transit light curves of WASP-19. Two light curves were obtained on consecutive nights and contain anomalies which we confirm as being due to the same spot. Using these data we measure the star's rotation period and velocity to be $11.76 \pm 0.09$ d and $3.88 \pm 0.15$\kms, respectively, at a latitude of 65$^\circ$. We find that the sky-projected angle between the stellar spin axis and the planetary orbital axis is $\lambda = 1.0^{\circ} \pm 1.2^{\circ}$, indicating axial alignment. Our results are consistent with and more precise than published spectroscopic measurements of the Rossiter-McLaughlin effect.
The neutron rich isotope 22Ne may be a significant impurity in carbon and oxygen white dwarfs and could impact how the stars freeze. We perform molecular dynamics simulations to determine the influence of 22Ne in carbon-oxygen-neon systems on liquid-solid phase equilibria. Both liquid and solid phases are present simultaneously in our simulation volumes. We identify liquid, solid, and interface regions in our simulations using a bond angle metric. In general we find good agreement for the composition of liquid and solid phases between our MD simulations and the semi analytic model of Medin and Cumming. The trace presence of a third component, neon, does not appear to strongly impact the chemical separation found previously for two component carbon and oxygen systems. This suggests that small amounts of 22Ne may not qualitatively change how the material in white dwarf stars freezes. However, we do find systematically lower melting temperatures (higher Gamma) in our MD simulations compared to the semi analytic model. This difference seems to grow with impurity parameter Q_imp and suggests a problem with simple corrections to the linear mixing rule for the free energy of multicomponent solid mixtures that is used in the semi analytic model.
We study the capture of galactic dark matter particles in the Solar System produced by rotation of Jupiter. It is shown that the capture cross section is much larger than the area of Jupiter orbit being inversely diverging at small particle energy. We show that the dynamics of captured particles is chaotic and is well described by a simple symplectic dark map. This dark map description allows to simulate the scattering and dynamics of $10^{14}$ dark matter particles during the life time of the Solar System and to determine dark matter density profile as a function of distance from the Sun. The mass of captured dark matter in the radius of Neptune orbit is estimated to be $2 \cdot 10^{15} g$. The radial density of captured dark matter is found to be approximately constant behind Jupiter orbit being similar to the density profile found in galaxies.
The DEAP-1 \SI{7}{kg} single phase liquid argon scintillation detector was
operated underground at SNOLAB in order to test the techniques and measure the
backgrounds inherent to single phase detection, in support of the DEAP-3600
Dark Matter detector. Backgrounds in DEAP are controlled through material
selection, construction techniques, pulse shape discrimination and event
reconstruction. This report details the analysis of background events observed
in three iterations of the DEAP-1 detector, and the measures taken to reduce
them.
The $^{222}$Rn decay rate in the liquid argon was measured to be between 16
and \SI{26}{\micro\becquerel\per\kilogram}. We found that the background
spectrum near the region of interest for Dark Matter detection in the final
DEAP-1 detector generation is well described considering events from three
sources: radon daughters decaying on the surface of the active volume, the
expected rate of electromagnetic events misidentified as nuclear recoils due to
inefficiencies in the pulse shape discrimination arising from the prototype
design, and leakage of events from outside the fiducial volume due to imperfect
position reconstruction. These backgrounds statistically account for all
observed events, and they will be strongly reduced in the DEAP-3600 detector
due to its higher light yield and simpler geometry.
FK Comae is a rapidly rotating magnetically active star, the light curve of which is modulated by cool spots on its surface. It was the first star where the flip-flop phenomenon was discovered. Therefore, it is of interest to perform a more thorough study of the evolution of the spot activity in FK Com. In this study, we analyse 15 years of photometric observations with two different time series analysis methods, with a special emphasis on detecting flip-flop type events from the data. We apply the continuous period search and carrier fit methods on long-term standard Johnson-Cousins V-observations from the years 1995-2010. The observations were carried out with two automated photometric telescopes, Phoenix-10 and Amadeus T7 located in Arizona. We identify complex phase behaviour in 6 of the 15 analysed data segments. We identify five flip-flop events and two cases of phase jumps, where the phase shift is \Delta \phi < 0.4. In addition we see two mergers of spot regions and two cases where the apparent phase shifts are caused by spot regions drifting with respect to each other. Furthermore we detect variations in the rotation period corresponding to a differential rotation coefficient of |k| > 0.031. The flip-flop cannot be interpreted as a single phenomenon, where the main activity jumps from one active longitude to another. In some of our cases the phase shifts can be explained by differential rotation: Two spot regions move with different angular velocity and even pass each other. Comparison between the methods show that the carrier fit utility is better in retrieving slow evolution especially from a low amplitude light curve, while the continuous period search is more sensitive in case of rapid changes.
SuperSpec is a pathfinder for future lithographic spectrometer cameras, which promise to energize extra-galactic astrophysics at (sub)millimeter wavelengths: delivering 200--500 km/s spectral velocity resolution over an octave bandwidth for every pixel in a telescope's field of view. We present circuit simulations that prove the concept, which enables complete millimeter-band spectrometer devices in just a few square-millimeter footprint. We evaluate both single-stage and two-stage channelizing filter designs, which separate channels into an array of broad-band detectors, such as bolometers or kinetic inductance detector (KID) devices. We discuss to what degree losses (by radiation or by absorption in the dielectric) and fabrication tolerances affect the resolution or performance of such devices, and what steps we can take to mitigate the degradation. Such design studies help us formulate critical requirements on the materials and fabrication process, and help understand what practical limits currently exist to the capabilities these devices can deliver today or over the next few years.
We present new CRIRES spectroscopic observations of BrGamma in the nuclear region of the Circinus galaxy, obtained with the aim of measuring the black hole (BH) mass with the spectroastrometric technique. The Circinus galaxy is an ideal benchmark for the spectroastrometric technique given its proximity and secure BH measurement obtained with the observation of its nuclear H2O maser disk. The kinematical data have been analyzed both with the classical method based on the analysis of the rotation curves and with the new method developed by us and based on spectroastrometry. The classical method indicates that the gas disk rotates in the gravitational potential of an extended stellar mass distribution and a spatially unresolved mass of (1.7 +- 0.2) 10^7 Msun, concentrated within r < 7 pc. The new method is capable of probing gas rotation at scales which are a factor ~3.5 smaller than those probed by the rotation curve analysis. The dynamical mass spatially unresolved with the spectroastrometric method is a factor ~2 smaller, 7.9 (+1.4 -1.1) 10^6 Msun indicating that spectroastrometry has been able to spatially resolve the nuclear mass distribution down to 2 pc scales. This unresolved mass is still a factor ~4.5 larger than the BH mass measurement obtained with the H2O maser emission indicating that it has not been possible to resolve the sphere of influence of the BH. Based on literature data, this spatially unresolved dynamical mass distribution is likely dominated by molecular gas and it has been tentatively identified with the circum-nuclear torus which prevents a direct view of the central BH in Circinus. This mass distribution, with a size of ~2pc, is similar in shape to that of the star cluster of the Milky Way suggesting that a molecular torus, forming stars at a high rate, might be the earlier evolutionary stage of the nuclear star clusters which are common in late type spirals.
The meridional circulation at high latitudes is crucial to the build-up and reversal of the Sun's polar magnetic fields. Here we characterize the axisymmetric flows by applying a magnetic feature cross-correlation procedure to high resolution magnetograms obtained by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We focus on Carrington Rotations 2096-2107 (April 2010 to March 2011) - the overlap interval between HMI and the Michelson Doppler Investigation (MDI). HMI magnetograms averaged over 720 seconds are first mapped into heliographic coordinates. Strips from these maps are then cross-correlated to determine the distances in latitude and longitude that the magnetic element pattern has moved, thus providing meridional flow and differential rotation velocities for each rotation of the Sun. Flow velocities were averaged for the overlap interval and compared to results obtained from MDI data. This comparison indicates that these HMI images are rotated counter-clockwise by 0.075 degrees with respect to the Sun's rotation axis. The profiles indicate that HMI data can be used to reliably measure these axisymmetric flow velocities to at least within 5 degrees of the poles. Unlike the noisier MDI measurements, no evidence of a meridional flow counter-cell is seen in either hemisphere with the HMI measurements: poleward flow continues all the way to the poles. Slight North-South asymmetries are observed in the meridional flow. These asymmetries should contribute to the observed asymmetries in the polar fields and the timing of their reversals.
We consider the general spatial three body problem and study the dynamics of planetary systems consisting of a star and two planets which evolve into 2/1 mean motion resonance and into inclined orbits. Our study is focused on the periodic orbits of the system given in a suitable rotating frame. The stability of periodic orbits characterize the evolution of any planetary system with initial conditions in their vicinity. Stable periodic orbits are associated with long term regular evolution, while unstable periodic orbits are surrounded by regions of chaotic motion. We compute many families of symmetric periodic orbits by applying two schemes of analytical continuation. In the first scheme, we start from the 2/1 (or 1/2) resonant periodic orbits of the restricted problem and in the second scheme, we start from vertical critical periodic orbits of the general planar problem. Most of the periodic orbits are unstable, but many stable periodic orbits have been, also, found with mutual inclination up to $50^\circ$ - $60^\circ$, which may be related with the existence of real planetary systems.
We present a simulation analysis of flexion and shear measurement using shapelet decomposition, and identify apparent qualitative differences between flexion and shear measurement noise in deep survey data. Taking models of galaxies from the Hubble Space Telescope Ultra Deep Field (HUDF) as a basis set and applying a correction for the HUDF PSF we generate lensed simulations of deep, optical imaging data from Hubble's Advanced Camera for Surveys (ACS) with realistic galaxy morphologies. We find that flexion and shear estimates differ in our measurement pipeline: whereas intrinsic galaxy shape is the largest contribution to noise in shear estimates, noise in flexion estimates is dominated by pixel noise due to finite photon counts and detector read noise. This pixel noise also increases more rapidly as galaxy signal-to-noise decreases than is found for shear estimates. We provide simple power law fitting functions for this behaviour, for both flexion and shear, allowing the effect to be properly accounted for in future forecasts for flexion measurement. Using the simulations we also quantify the systematic biases of our shapelet flexion and shear measurement pipeline for deep Hubble datasets such as GEMS, STAGES or COSMOS. Flexion measurement biases are found to be significant, but consistent with previous studies.
We present here a detailed spectral study of the X-ray emission of the persistent source and the low-fluence bursts of SGR J0501+4516 observed during a deep XMM-Newton observation near the peak of its 2008 outburst. For the persistent emission we employ a physically motivated continuum emission model and spectroscopically determine important source properties; such as, the surface magnetic field strength and the magnetospheric scattering optical depth. We find that the magnetar surface temperature near the peak of its activity is 0.38 keV, corresponding to an emission area of 131 km^2 at a distance of 2 kpc. The surface magnetic field strength determined spectroscopically, B=2.2E14 G, is consistent with the dipole field strength inferred from the source spin and spin down rate. We fit the stacked spectra of 129 very faint bursts with a modified blackbody model and find a temperature of 1.16 keV, corresponding to an emission area of 93 km^2. We also find an evidence for cooling during the burst decay phase.
We present a new diagnostic allowing one to measure the anisotropy of ion temperatures and non-thermal velocities as well as Doppler shifts with respect to the ambient magnetic field. Our spectral data come from observations of a low latitude, on-disk coronal hole. A potential field source surface model was used to calculate the angle between the magnetic field lines and the line of sight for each spatial bin of the observation. A fit was performed to determine the line widths and Doppler shifts parallel and perpendicular to the magnetic field. For each line width component we derived parallel and perpendicular ion temperatures and non-thermal velocities. The perpendicular ion temperature was cooler than off-limb polar coronal hole measurements. The parallel ion temperature was consistent with a uniform temperature of 1.8 +/- 0.2 x 10^{6} K for each ion. Since parallel ion heating is expected to be weak, this ion temperature should reflect the proton temperature. A comparison between our results and others implies a large proton temperature gradient around 1.02 R_sun. The non-thermal velocities are thought to be proportional to the amplitudes of various waves. Our results for the perpendicular non-thermal velocity agree with Alfv\'en wave amplitudes inferred from off-limb polar coronal hole line width measurements. Our parallel non-thermal velocity results are consistent with slow magnetosonic wave amplitudes inferred from Fourier analysis of time varying intensity fluctuations. Doppler shift measurements yield outflows of ~5 km s^-1 for ions formed over a broad temperature range. This differs from other studies which found a strong Doppler shift dependence on formation temperature.
The Painleve test is very useful to construct not only the Laurent-series solutions but also the elliptic and trigonometric ones. Such single-valued functions are solutions of some polynomial first order differential equations. To find the elliptic solutions we transform an initial nonlinear differential equation in a nonlinear algebraic system in parameters of the Laurent-series solutions of the initial equation. The number of unknowns in the obtained nonlinear system does not depend on number of arbitrary coefficients of the used first order equation. In this paper we describe the corresponding algorithm, which has been realized in REDUCE and Maple.
We discuss the possibility of having multiple Kaluza-Klein (KK) dark matter candidates which arise naturally in generic Type-IIB string theory compactification scenarios. These dark matter candidates reside in various throats of the Calabi-Yau manifold. In principle, they can come with varied range of masses in four-dimensions depending upon the hierarchical warping of the throats. We show that consistency with cosmological bounds and four-dimensional effective theory description imposes strong constraints on the parameter space and the geometry of the throats. With a rather model-independent approach, we find that the mass scales allowed for the KK dark matter particles in various throats can vary between 0.1 eV and 10 TeV. Thus, there could be simultaneously more than one kind of cold (and possibly warm and hot) dark matter components residing in the Universe. This multiple dark matter scenario could weaken the bound on a conventional supersymmetric dark matter candidate and even act as an extra relativistic degree of freedom.
We find static charged black hole solutions in nonlinear massive gravity. In the parameter space of two gravitational potential parameters $(\alpha, \beta)$ we show that below the Compton wavelength the black hole solutions reduce to that of Reissner-Nordstr\"om via the Vainshtein mechanism in the weak field limit. In the simplest case with $\alpha=\beta=0$ the solution exhibits the vDVZ discontinuity but ordinary General Relativity is recovered deep inside the horizon due to the existence of electric charge. For $\alpha\neq0$ and $\beta=0$, the post-Newtonian parameter of the charged black hole evolves to that of General Relativity via the Vainshtein mechanism within a macroscopic distance; however, a logarithmic correction to the metric factor of the time coordinate is obtained. When $\alpha$ and $\beta$ are both nonzero, there exist two branches of solutions depending on the positivity of $\beta$. When $\beta<0$, the strong coupling of the scalar graviton weakens gravity at distances smaller than the Vainshtein radius. However, when $\beta>0$ the metric factors exhibit only small corrections compared to the solutions obtained in General Relativity, and under a particular choice of $\beta=\alpha^2/6$ the standard Reissner-Nordstr\"om-de Sitter solution is recovered.
We present a simple way to obtain exact solutions of Einstein-scalar field equations on spatially flat Friedmann-Robertson-Walker space-times. The scalar equation turns out to be integrable if the Hubble parameter is written as an appropriate function of the scalar field and its velocity. Eventually, the field equations are reduced to find `generating functions' for a given scalar potential. Once a generating function is found as a function of the scalar field, the evolution of the field and the Universe can be easily obtained with a simple integration. As examples, we obtain the solution spectra in the cases of the constant and the exponential potentials, and find exact solutions for various scalar potentials such as the $\lambda \phi^4$, the power law, and the double-well hyperbolic functions. We additionally analyze the stability of the generating equation. We show that the existence of a fixed point of the equation of motion affect on the evolution so that the Universe experiences a long inflation. We additionally show that small change of the scalar potential cannot get rid of the appearance of the long inflation.
We construct generic spherically symmetric thin shells by using the cut-and-paste procedure. We take considerable effort to make the analysis as general and unified as practicable; investigating both the internal physics of the transition layer and its interaction with "external forces" arising due to interactions between the transition layer and the bulk spacetime. We demonstrate in full generality that stability of the thin shell is equivalent to choosing suitable properties for the material residing on the junction interface. Applications to gravastars and wormhole geometries are also explored.
We propose a method for constructing the specific heat for the universe by following standard definitions of classical thermodynamics, in a spatially flat homogeneous and isotropic spacetime. We use cosmography to represent the specific heat in terms of measurable quantities, and show that a negative specific heat at constant volume and a zero specific heat at constant pressure are compatible with observational data. We derive the most general cosmological model which is compatible with the values obtained for the specific heat of the universe, and show that it overcomes the fine-tuning and the coincidence problems of the $\Lambda$CDM model.
Random fields in nature often have, to a good approximation, Gaussian characteristics. For such fields, the relative densities of umbilical points -- topological defects which can be classified into three types -- have certain fixed values. Phenomena described by nonlinear laws can however give rise to a non-Gaussian contribution, causing a deviation from these universal values. We consider a Gaussian field with a perturbation added to it, given by a nonlinear function of that field, and calculate the change in the relative density of umbilical points. This allows us not only to detect a perturbation, but to determine its size as well. This geometric approach offers an independent way of detecting non-Gaussianity, which even works in cases where the field itself cannot be probed directly.
A review of some of the issues that have arisen over the years concerning the energy distribution among scales for magnetohydrodynamics (MHD) turbulence is given here. A variety of tools are employed to that effect, and a central role is played by taking into consideration the ideal (non-dissipative) invariants, namely the total energy, the magnetic helicity and the cross-correlations between the velocity and the magnetic field (concentrating on the three-dimensional case). These concepts, based mostly on theory, models and direct numerical simulations, are briefly put in the context of observations, in particular the solar wind, and some of the remaining open questions are delineated as well. New results on ideal MHD dynamics in three dimensions on equivalent grids of up to $6144^3$ points using the Taylor-Green flow generalized to MHD are also mentioned.
The cosmological backreaction from perturbations is clearly gauge-dependent, and obviously depends on the choice of averaged Hubble rate. We consider two common choices of Hubble rate and advocate the use of comoving volume-preserving gauges. We highlight two examples valid to an appropriate order in perturbation theory, uniform curvature gauge, which is as close to volume-preserving as possible, and a spatially-traceless uniform cold dark matter gauge which preserves the volume to linear order. We demonstrate the strong gauge- and frame-dependences in averaging. In traceless uniform CDM gauge the backreaction exhibits a strong ultra-violet divergence and can be tuned to an arbitrary magnitude with an appropriate choice of smoothing scale. In uniform curvature gauge we find that for a choice of Hubble rate locked to the spatial surface the backreaction vanishes identically, while for a Hubble rate defined from a fluid's expansion scalar the effective energy density at the current epoch in an Einstein-de Sitter universe is Omega_eff~5e-4, slightly bigger than but in broad agreement with previous results in conformal Newtonian gauge.
In two recent papers (R. Kshetri, JINST 2012 7 P04008; ibid., P07006), a probabilistic formalism was introduced to predict the response of encapsulated type composite germanium detectors like the SPI (spectrometer for INTEGRAL satellite). Predictions for the peak-to-total and peak-to-background ratios are given at 1.3 MeV for the addback mode of operation. The application of the formalism to clover germanium detector is discussed in two separate papers (R. Kshetri, JINST 2012 7 P07008; ibid., P08015). Using the basic approach developed in those papers, for the first time we present a procedure for calculating the peak-to-total ratio of the cluster detector for gamma-energies up to 8 MeV. Results are shown for both bare and suppressed detectors as well as for the single crystal and addback modes of operation. We have considered the experimental data of (i) peak-to-total ratio at 1.3 MeV, and (ii) single detector efficiency and addback factor for other energies up to 8 MeV. Using this data, an approximate method of calculating the peak-to-total ratio of other composite detectors, is shown. Experimental validation of our approach (for energies up to 8 MeV) has been confirmed considering the data of the SPI spectrometer. We have discussed about comparisons between various modes of operation and suppression cases. The present paper is the fifth in the series of papers on composite germanium detectors and for the first time discusses about the change in fold distribution and peak-to-total ratio for sophisticated detectors consisting of several modules of miniball, cluster and SPI detectors. Our work could provide a guidance in designing new composite detectors and in performing experimental studies with the existing detectors for high energy gamma-rays.
We present a new method to study light scattering on non-absorbing spherical particles. This method is based on the Ramsauer approach, a model known in atomic an nuclear physics. Its main advantage is its intuitive understanding of the underlying physics phenomena. We show that although the approximations are numerous, the Ramsauer analytical solutions describe fairly well the scattering phase function and the total cross section. Then this model is applied to the Henyey-Greenstein parameterisation of scattering phase function to give a relation between its asymmetry parameter and the mean particle size.
When the equations that govern the dynamics of a random field are nonlinear, the field can develop with time non-Gaussian statistics even if its initial condition is Gaussian. Here, we provide a general framework for calculating the effect of the underlying nonlinear dynamics on the relative densities of maxima and minima of the field. Using this simple geometrical probe, we can identify the size of the non-Gaussian contributions in the random field, or alternatively the magnitude of the nonlinear terms in the underlying equations of motion. We demonstrate our approach by applying it to an initially Gaussian field that evolves according to the deterministic KPZ equation, which models surface growth and shock dynamics.
In hybrid inflation, the inflaton generically has a tadpole due to gravitational effects in supergravity, which significantly changes the inflaton dynamics in high-scale supersymmetry. We point out that the tadpole can be cancelled if there is a supersymmetry breaking singlet with gravitational couplings, and in particular, the cancellation is automatic in no-scale supergravity. We consider the LARGE volume scenario as a concrete example and discuss the compatibility between the hybrid inflation and the moduli stabilization. We also point out that the dark radiation generated by the overall volume modulus decay naturally relaxes a tension between the observed spectral index and the prediction of the hybrid inflation.
Links to: arXiv, form interface, find, astro-ph, recent, 1211, contact, help (Access key information)
We search for massive and compact galaxies (superdense galaxies, hereafter SDGs) at z=0.03-0.11 in the Padova-Millennium Galaxy and Group Catalogue, a spectroscopically complete sample representative of the local Universe general field population. We find that compact galaxies with radii and mass densities comparable to high-z massive and passive galaxies represent 4.4% of all galaxies with stellar masses above 3 X 10^10 M_sun, yielding a number density of 4.3 X 10^-4 h^3 Mpc^-3. Most of them are S0s (70%) or ellipticals (23%), are red and have intermediate-to-old stellar populations, with a median luminosity-weighted age of 5.4 Gyr and a median mass-weighted age of 9.2 Gyr. Their velocity dispersions and dynamical masses are consistent with the small radii and high stellar mass estimates. Comparing with the WINGS sample of cluster galaxies at similar redshifts, the fraction of superdense galaxies is three times smaller in the field than in clusters, and cluster SDGs are on average 4 Gyr older than field SDGs. We confirm the existence of a universal trend of smaller radii for older luminosity-weighted ages at fixed galaxy mass. On top of the well known dependence of stellar age on galaxy mass, the luminosity-weighted age of galaxies depends on galaxy compactness at fixed mass, and, for a fixed mass and radius, on environment. This effect needs to be taken into account in order not to overestimate the evolution of galaxy sizes from high- to low-z. Our results and hierarchical simulations suggest that a significant fraction of the massive compact galaxies at high-z have evolved into compact galaxies in galaxy clusters today. When stellar age and environmental effects are taken into account, the average amount of size evolution of individual galaxies between high- and low-z is mild, a factor ~1.6. (abridged)
It has become common understanding that the recession of galaxies and the corresponding redshift of light received from them can only be explained by an expansion of the space between them and us. In this paper, for the presently favored case of a universe without spatial curvature, it is shown that this interpretation is restricted to comoving coordinates. It is proven by construction that within the framework of general relativity other coordinates exist in relation to which these phenomena can be explained by a motion of the cosmic substrate across space, caused by an explosion like big bang or by inflation preceding an almost big bang. At the place of an observer, this motion occurs without any spatial expansion. It is shown that in these "explosion coordinates" the usual redshift comes about by a Doppler shift and a subsequent gravitational shift. Making use of this interpretation, it can easily be understood why in comoving coordinates light rays of short spatial extensions expand and thus constitute an exemption from the rule that small objects up to the size of the solar system or even galaxies do not participate in the expansion of the universe. It is also discussed how the two interpretations can be reconciled with each other.
The effects that interactions produce on galaxy disks and how they modify the subsequent formation of bars need to be distinguished to fully understand the relationship between bars and environment. To this aim we derive the bar fraction in three different environments ranging from the field to Virgo and Coma clusters, covering an unprecedentedly large range of galaxy luminosities (or, equivalently, stellar masses). We confirm that the fraction of barred galaxies strongly depends on galaxy luminosity. We also show that the difference between the bar fraction distributions as a function of galaxy luminosity (and mass) in the field and Coma cluster are statistically significant, with Virgo being an intermediate case. The fraction of barred galaxies shows a maximum of about 50% at $M_r\,\simeq\,-20.5$ in clusters, whereas the peak is shifted to $M_r\,\simeq\,-19$ in the field. We interpret this result as a variation of the effect of environment on bar formation depending on galaxy luminosity. We speculate that brighter disk galaxies are stable enough against interactions to keep their cold structure, thus, the interactions are able to trigger bar formation. For fainter galaxies the interactions become strong enough to heat up the disks inhibiting bar formation and even destroying the disks. Finally, we point out that the controversy regarding whether the bar fraction depends on environment could be resolved by taking into account the different luminosity ranges probed by the galaxy samples studied so far.
We apply halo abundance matching to obtain galaxy virial masses, M_h, and radii, Rvir, for the 169 isolated galaxies in the "MgII Absorber-Galaxy Catalog" (MAGIICAT, Nielsen et al.). All galaxies have spectroscopic redshifts (0.1 < z < 1.1) and their circumgalactic medium (CGM) is probed in MgII absorption within projected galactocentric distances D < 200 kpc. We examine the behavior of equivalent width, W(2796), and covering fraction, f_c, as a function of D, D/Rvir, and M_h. We find: [1] systematic segregation of M_h on the W(2796)-D plane (4.2 sigma); high-mass halos are found at higher D with larger W(2796) compared to lower mass halos. On the W(2796)-D/Rvir plane, mass segregation vanishes and we find W(2796) ~ (D/Rvir)^-2 (9.5 sigma); [2] higher mass halos have larger f_c at a given D, whereas f_c is independent of M_h at all D/Rvir; [3] f_c is constant with M_h over the range 10.4 < log(M_h/Msun) < 13.3 within a given D or D/Rvir. The combined results suggest that the MgII absorbing CGM is self-similar with halo mass, even above log(M_h/Msun)~12, where cold mode accretion is theoretically predicted to be quenched. If theory is correct, either outflows or sub-halos must contribute to absorption in high-mass halos such that low- and high-mass halos are observationally indistinguishable using MgII absorption strength once impact parameter is scaled by halo mass. Alternatively, the data may indicate that predictions of a universal shut down of cold-mode accretion in high-mass halos may require revision.
Nonlinear redshift-space distortions, the Finger-of-God (FoG) effect, can complicate the interpretation of the galaxy power spectrum. Here, we demonstrate the method proposed by Hikage et al. (2012) to use complimentary observations to directly constrain this effect on the data. We use catalogs of Luminous Red Galaxies (LRGs) and photometric galaxies from the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) to measure the redshift-space power spectrum of LRGs, the cross-correlation of LRGs with the shapes of background photometric galaxies (galaxy-galaxy weak lensing), and the projected cross-correlation of LRGs with photometric galaxies having similar photometric redshifts to the LRG spectroscopic redshift. All of these measurements use a reconstructed halo field. While we use the position of each LRG for single LRG systems, we compare the measurements using different halo-center proxies for multiple-LRG systems (4.5 per cent of all the halos): the brightest LRG position (BLRG), the faintest LRG position (FLRG) and their geometrical mean position (Mean), respectively, in each system. We find significant differences in the measured correlations of different centers, showing consistent off-centering effects in the three observables. By comparing the measurements with the halo model, we find that about 40 (70) per cent of BLRGs (FLRGs) are off-centered satellite galaxies in the multiple-LRG systems. The satellite LRGs have typical off-centering radius of about 400 kpc/h, and velocity dispersion of about 500 km/s in host halos with a mean mass of 1.6x10^14 Ms/h. We show that, if LRGs in the single LRG systems have similar offsets, the residual FoG contamination in the LRG power spectrum can be significant at k=0.1 h/Mpc, which may cause a bias in cosmological parameters determined by the shape of the power spectrum, such as the neutrino mass.
We present a study of rest-frame UV-to-optical color distributions for z~4 galaxies based on the combination of deep HST/ACS+WFC3/IR data with Spitzer/IRAC imaging. In particular, we use new, ultra-deep data from the IRAC Ultradeep Field program (IUDF10). Our sample contains a total of ~2600 galaxies selected as B-dropout Lyman Break Galaxies (LBGs) in the HUDF and one of its deep parallel fields, the HUDF09-2, as well as GOODS-North and South. This sample is used to investigate the UV continuum slopes beta and Balmer break colors (J_125-[4.5]) as a function of rest-frame optical luminosity. The [4.5] filter is chosen to avoid potential contamination by strong rest-frame optical emission lines. We find that galaxies at M_z<-21.5 (roughly corresponding to L*[z~4]) are significantly redder than their lower luminosity counterparts. The UV continuum slopes and the J_125-[4.5] colors are well correlated. The most simple explanation for this correlation is that the dust reddening at these redshifts is better described by an SMC-like extinction curve, rather than the typically assumed Calzetti reddening. After correcting for dust, we find that the galaxy population shows mean stellar population ages in the range 10^8.5 to 10^9 yr, with a dispersion of ~0.5 dex, and only weak trends as a function of luminosity. In contrast to some results from the literature, we find that only a small fraction of galaxies shows Balmer break colors which are consistent with extremely young ages, younger than 100 Myr. Under the assumption of smooth star-formation histories, this fraction is only 12-19% for galaxies at M_z<-19.75. Our results are consistent with a gradual build-up of stars and dust in galaxies at z>4, with only a small fraction of stars being formed in short, intense bursts of star-formation.
We use interferometric CO observations to compare the extent, surface brightness profiles and kinematics of the molecular gas in CO-rich Atlas3D early-type galaxies (ETGs) and spiral galaxies. We find that the molecular gas extent is smaller in absolute terms in ETGs than in late-type galaxies, but that the size distributions are similar once scaled by the galaxies optical/stellar characteristic scale-lengths. Virgo cluster ETGs have less extended molecular gas reservoirs than field counterparts. Approximately half of ETGs have molecular gas surface brightness profiles that follow the stellar light profile. These systems often have relaxed gas out to large radii, suggesting they are unlikely to have had recent merger/accretion events. A third of the sample galaxies show molecular gas surface brightness profiles that fall off slower than the light, and sometimes show a truncation. We suggest that ram pressure stripping and/or the presence of hot gas has compressed/truncated the gas in these systems. The remaining galaxies have rings, or composite profiles, that we argue can be caused by the effects of bars. We investigated the kinematics of the molecular gas using position-velocity diagrams, and compared the observed kinematics with dynamical model predictions, and the observed stellar and ionised gas velocities. We confirm that the molecular gas reaches beyond the turnover of the circular velocity curve in ~70% of our CO-rich Atlas3D ETGs. In general we find that in most galaxies the molecular gas is relaxed and dynamically cold. Molecular gas is a better direct tracer of the circular velocity than the ionised gas, justifying its use as a kinematic tracer for Tully-Fisher and similar analyses. (abridged)
In this letter we propose a test to detect the linearity of the dark energy equation of state, and apply it to two different Type Ia Supernova (SN Ia) data sets, Union2.1 and SNLS3. We find that: a. current SN Ia data are well described by a dark energy equation of state linear in the cosmic scale factor a, at least up to a redshift z = 1, independent of the pivot points chosen for the linear relation; b. there is no significant evidence of any deviation from linearity. This apparent linearity may reflect the limit of dark energy information extractable from current SN Ia data.
The ultimate fates of binary companions to stars (including whether the companion survives and the final orbit of the binary) are of interest in light of an increasing number of recently discovered, low-mass companions to white dwarfs (WDs). In this Letter, we study the evolution of a two-body system wherein the orbit adjusts due to structural changes in the primary, dissipation of orbital energy via tides, and mass loss during the giant phases. For companions ranging from Jupiter's mass to ~0.3 Msun and primaries ranging from 1--3 Msun, we determine the minimum initial semimajor axis required for the companion to avoid engulfment by the primary during post-main-sequence evolution, typically several times the maximum radius on the Asymptotic Giant Branch. We present regions in secondary mass and orbital period space where an engulfed companion might be expected to survive the common envelope phase (CEP), and compare with known M dwarf+WD short-period binaries. Finally, we note that engulfed Earth-like planets cannot survive a CEP. Detection of a first-generation terrestrial planet in the white dwarf habitable zone requires scattering from a several-AU orbit to a high-eccentricity orbit (with a periastron of ~Rsun) from which it is damped into a circular orbit via tidal friction, possibly rendering it an uninhabitable, charred ember.
Imperfect photometric calibration of galaxy surveys due to either astrophysical or instrumental effects leads to biases in measuring galaxy clustering and the resulting cosmological parameter measurements. More interestingly (and disturbingly), the spatially varying calibration also generically leads to violations of statistical isotropy of the galaxy clustering signal. Here we develop, for the first time, a formalism to propagate the effects of photometric calibration variations with arbitrary spatial dependence across the sky to the observed power spectra and to the cosmological parameter constraints. We develop an end-to-end pipeline to study the effects of calibration, and illustrate our results using specific examples including Galactic dust extinction and survey-dependent magnitude limits as a function of zenith angle of the telescope. We establish requirements on the control of calibration so that it doesn't significantly bias constraints on dark energy and primordial non-Gaussianity. Two principal findings are: 1) largest-angle photometric calibration variations (dipole, quadrupole and a few more modes, though not the monopole) are the most damaging, and 2) calibration will need to be understood at the 0.1%-1% level (i.e. rms variations mapped out to accuracy between 0.001 and 0.01 mag), though the precise requirement strongly depends on the faint-end slope of the luminosity function and the redshift distribution of galaxies in the survey.
Here we present new adaptive optics observations of the Quaoar-Weywot system. With these new observations we determine an improved system orbit. Due to a 0.39 day alias that exists in available observations, four possible orbital solutions are available with periods of $\sim11.6$, $\sim12.0$, $\sim12.4$, and $\sim12.8$ days. From the possible orbital solutions, system masses of $1.3-1.5\pm0.1\times10^{21}$ kg are found. These observations provide an updated density for Quaoar of $2.7-5.0{g cm$^{-3}$}$. In all cases, Weywot's orbit is eccentric, with possible values $\sim0.13-0.16$. We present a reanalysis of the tidal orbital evolution of the Quoaor-Weywot system. We have found that Weywot has probably evolved to a state of synchronous rotation, and have likely preserved their initial inclinations over the age of the Solar system. We find that for plausible values of the effective tidal dissipation factor tides produce a very slow evolution of Weywot's eccentricity and semi-major axis. Accordingly, it appears that Weywot's eccentricity likely did not tidally evolve to its current value from an initially circular orbit. Rather, it seems that some other mechanism has raised its eccentricity post-formation, or Weywot formed with a non-negligible eccentricity.
We investigate the gravitational effect of a scalar field within scalar-tensor gravity as an alternative of the dark matter. Motivated by results of chameleon models, $f(R)$ gravity and symmetron models, we study a phenomenological scenario where the scalar field has a mass and a coupling constant to the ordinary matter which scale with the local properties of the considered astrophysical system. We analyze the compatibility of this "alternative gravity" scenario at galaxy and galaxy cluster scales. Main results are: 1) the velocity dispersion of elliptical galaxies can be fit remarkably well by a scalar field, with model significance similar to the one obtained if a classical Navarro-Frenk-White dark halo profile is considered; 2) in particular, the analysis of the stellar dynamics and the gas equilibrium on elliptical galaxies has shown that the scalar field can couple with ordinary matter with different strength (different coupling constants) depending on the clustering state of matter components; 3) spiral galaxies and clusters of galaxies combined together show evident correlations among theory parameters (coupling constants and scalar field interaction length) which suggests the generality of the results at all scales and the way toward an unification of the theory for all gravitating systems; 4) the gravitational effects of the scalar field and its viability as an alternative to the dark matter are confirmed by some preliminary test on strong lensing at galaxy cluster scales.
We use hydrodynamical simulations from the OWLS project to investigate the dependence of the physical properties of galaxy populations at redshift 2 on metal-line cooling and feedback from star formation and active galactic nuclei (AGN). We find that if the sub-grid feedback from star formation is implemented kinetically, the feedback is only efficient if the initial wind velocity exceeds a critical value. This critical velocity increases with galaxy mass and also if metal-line cooling is included. This suggests that radiative losses quench the winds if their initial velocity is too low. If the feedback is efficient, then the star formation rate is inversely proportional to the amount of energy injected per unit stellar mass formed (which is proportional to the initial mass loading for a fixed wind velocity). This can be understood if the star formation is self-regulating, i.e. if the star formation rate (and thus the gas fraction) increase until the outflow rate balances the inflow rate. Feedback from AGN is efficient at high masses, while increasing the initial wind velocity with gas pressure or halo mass allows one to generate galaxy-wide outflows at all masses. Matching the observed galaxy mass function requires efficient feedback. In particular, the predicted faint-end slope is too steep unless we resort to highly mass loaded winds for low-mass objects. Such efficient feedback from low-mass galaxies (M_* << 10^10 Msun) also reduces the discrepancy with the observed specific star formation rates, which are higher than predicted unless the feedback transitions from highly efficient to inefficient just below the observed stellar mass range.
We report the discovery of the second and third pulsating extremely low mass white dwarfs (WDs), SDSS J111215.82+111745.0 (hereafter J1112) and SDSS J151826.68+065813.2 (hereafter J1518). Both have masses < 0.25 Msun and effective temperatures below 10,000 K, establishing these putatively He-core WDs as a cooler class of pulsating hydrogen-atmosphere WDs (DAVs, or ZZ Ceti stars). The short-period pulsations evidenced in the light curve of J1112 may also represent the first observation of acoustic (p-mode) pulsations in any WD, which provide an exciting opportunity to probe this WD even deeper than allowed by the long-period g-modes also present. J1112 is a 9590 +/- 140 K and log(g) = 6.36 +/- 0.06 WD. The star displays sinusoidal variability at five distinct periodicities between 1792-2855 s. In this star we also see short-period variability, strongest at 134.3 s, well short of expected g-modes for such a low-mass WD. The other new pulsating WD, J1518, is a 9900 +/- 140 K and log(g) = 6.80 +/- 0.05 WD. The light curve of J1518 is highly non-sinusoidal, with at least seven significant periods between 1335-3848 s. Consistent with the expectation that ELM WDs must be formed in binaries, these two new pulsating He-core WDs, in addition to the prototype SDSS J184037.78+642312.3, have close companions. However, the observed variability is inconsistent with tidally induced pulsations and is so far best explained by the same hydrogen partial-ionization driving mechanism at work in classic C/O-core ZZ Ceti stars.
We studied the stellar populations, distribution of dark matter, and dynamical structure of a sample of 25 early-type galaxies in the Coma and Abell 262 clusters. We derived dynamical mass-to-light ratios and dark matter densities from orbit-based dynamical models, complemented by the ages, metallicities, and \alpha-elements abundances of the galaxies from single stellar population models. Most of the galaxies have a significant detection of dark matter and their halos are about 10 times denser than in spirals of the same stellar mass. Calibrating dark matter densities to cosmological simulations we find assembly redshifts z_{DM} \approx 1-3. The dynamical mass that follows the light is larger than expected for a Kroupa stellar initial mass function, especially in galaxies with high velocity dispersion \sigma_{eff} inside the effective radius r_{eff}. We now have 5 of 25 galaxies where mass follows light to 1-3 r_{eff}, the dynamical mass-to-light ratio of all the mass that follows the light is large (\approx 8-10 in the Kron-Cousins R band), the dark matter fraction is negligible to 1-3 r_{eff}. This could indicate a "massive" initial mass function in massive early-type galaxies. Alternatively, some of the dark matter in massive galaxies could follow the light very closely suggesting a significant degeneracy between luminous and dark matter.
We investigate the X-ray properties of BzK-selected galaxies at z $\sim$ 2 using deep X-ray data in the Chandra Deep Field South and North (CDFS and CDFN). Of these we directly detect in X-rays 49 sBzKs in CDFS and 32 sBzKs in CDFN. Stacking the undetected sources also reveals a significant X-ray signal. Investigating the X-ray detection rate and stacked flux versus the IR excess parameter (i.e. SFRtotal/SFRUV,corr), we find no strong evidence for an increased X-ray detection rate, or a harder X-ray spectrum in IR Excess sBzKs. This is particularly the case when one accounts for the strong correlation between the IR excess parameter and the bolometric IR luminosity (LIR), e.g. when controlling for LIR, the IR Non-Excess sBzKs show a detection rate at least as high. While both direct detections and stacking suggest that the AGN fraction in sBzK galaxies is high, there is no clear evidence for widespread Compton thick activity in either the sBzK population generally, or the IR Excess sBzK subsample. The very hard X-ray signal obtained for the latter in earlier work was most likely contaminated by a few hard X-ray sources now directly detected in deeper X-ray data. The X-ray detection fraction of passive BzK galaxies in our sample is if anything higher than that of sBZKs, so there is no evidence for coeval black hole growth and star formation from X-ray analysis of the BzK populations. Because increased AGN activity in the IR excess population is not indicated by our X-ray analysis, it appears that the bulk of the IR Excess sBzK population are luminous star-forming galaxies whose SFRs are either overestimated at 24 microns, underestimated in the UV, or both. This conclusion reinforces recent results from Herschel which show similar effects.
We report the discovery of KELT-3b, a moderately inflated transiting hot Jupiter with a mass of 1.462 (+0.067, -0.066) M_J, and radius of 1.358 (+0.068, -0.069) R_J, with an orbital period of 2.703390 +/- 0.000010 days. The host star, KELT-3, is a V=9.8 late F star with M_* = 1.282 (+0.062, -0.060) M_sun, R_* = 1.482 (+0.062, -0.064) R_sun, T_eff = 6304 +/- 49 K, log(g) = 4.204 (+0.031, -0.029), and [Fe/H] = 0.048 (+0.079, -0.081), and has a likely proper motion companion. KELT-3b is the third transiting exoplanet discovered by the KELT survey, and is orbiting one of the 20 brightest known transiting planet host stars, making it a promising candidate for detailed characterization studies. Although we infer that KELT-3 is significantly evolved, a preliminary analysis of the stellar and orbital evolution of the system suggests that the planet has likely always received a level of incident flux above the empirically-identified threshold for radius inflation suggested by Demory & Seager (2011).
The relative strength between forward and reverse shock emission in early gamma-ray burst afterglow reflects that of magnetic energy densities in the two shock regions. We numerically show that with the current standard treatment, the fireball magnetization is underestimated by up to two orders of magnitude. This discrepancy is especially large in the sub-relativistic reverse shock regime (i.e. the thin shell and intermediate regime) where most optical flashes were detected. We provide new analytic estimates of the reverse shock emission based on a better shock approximation, which well describe numerical results in the intermediate regime. We show that the reverse shock temperature at the onset of afterglow is constant, $(\bar{\Gamma}_d-1)\sim 8\times10^{-2}$, when the dimensionless parameter $\xi_{0}$ is more than several. Our approach is applied to case studies of GRB 990123 and 090102, and we find that magnetic fields in the fireballs are even stronger than previously believed.
We calculate the diffuse intensity of cosmic ray (CR) nuclei and their secondaries in the Boron-Carbon group produced by supernova remnants (SNR). The trajectories of charged particles in the SNR are modeled as a random walk in the test particle approximation. Secondary production by CRs colliding with gas in the SNR is included as a Monte Carlo process, while we use Galprop to account for the propagation and interactions of CRs in the Galaxy. In the vicinity of a source, we find an approximately constant B/C ratio as a function of energy. As a result, the B/C ratio at Earth does not rise with energy, but flattens instead in the high energy limit. This prediction can be soon tested by the AMS-2 collaboration.
We use state-of-the-art simulations to explore the physical evolution of galaxies in the first billion years of cosmic time. First, we demonstrate that our model, without any tuning, reproduces the basic statistical properties of the observed Lyman-break galaxy (LBG) population at z = 6 - 8, including the evolving ultra-violet (UV) luminosity function (LF), the stellar-mass density (SMD), and the average specific star-formation rates (sSFR) of LBGs with M_{UV} < -18 (AB mag). Encouraged by this success we present predictions for the behaviour of fainter LBGs extending down to M_{UV} <= -15 (as will be probed with the James Webb Space Telescope) and have interrogated our simulations to try to gain insight into the physical drivers of the observed population evolution. We find that mass growth due to star formation in the mass-dominant progenitor builds up about 90% of the total z ~ 6 LBG stellar mass, dominating over the mass contributed by merging throughout this era. Our simulation suggests that the apparent "luminosity evolution" depends on the luminosity range probed: the steady brightening of the bright end of the LF is driven primarily by genuine physical luminosity evolution and arises due to a fairly steady increase in the UV luminosity (and hence star-formation rates) in the most massive LBGs. However, at fainter luminosities the situation is more complex, due in part to the more stochastic star-formation histories of lower-mass objects; at this end, the evolution of the UV LF involves a mix of positive and negative luminosity evolution (as low-mass galaxies temporarily brighten then fade) coupled with both positive and negative density evolution (as new low-mass galaxies form, and other low-mass galaxies are consumed by merging). We also predict the average sSFR of LBGs should rise from sSFR = 4.5 Gyr^-1 at z = 6 to about 11 Gyr^-1 by z = 9.
We identify 69 X-ray sources discovered by the Galactic Bulge Survey (GBS) that are coincident with, or very close to bright stars in the Tycho-2 catalog. Additionally, two other GBS sources are resolved binary companions to Tycho-2 stars where both components are separately detected in X-rays. Most of these are likely to be real matches, but we identify nine objects with large and significant X-ray to optical offsets as either detections of resolved binary companions or chance alignments. We collate known spectral types for these objects, and also examine 2MASS colors, variability information from the All-Sky Automated Survey (ASAS), and X-ray hardness ratios for the brightest objects. Nearly a third of the stars are found to be optically variable, divided roughly evenly between irregular variations and periodic modulations. All fall among the softest objects identified by the GBS. The sample forms a very mixed selection, ranging in spectral class from O9 to M3. In some cases the X-ray emission appears consistent with normal coronal emission from late-type stars, or wind emission from early-types, but the sample also includes one known Algol, one W UMa system, two Be stars, and several X-ray bright objects likely to be coronally active stars or binaries. Surprisingly, a substantial fraction of the spectroscopically classified, non-coincidental sample (12 out of 38 objects) have late B or A type counterparts. Many of these exhibit redder near-IR colors than expected for their spectral type and/or variability, and it is likely that the X-rays originate from a late-type companion star in most or all of these objects.
Searches for slow radio transients and variables have generally focused on extragalactic populations, and the basic parameters of Galactic populations remain poorly characterized. We present a large 3 GHz survey performed with the Allen Telescope Array (ATA) that aims to improve this situation: ASGARD, the ATA Survey of Galactic Radio Dynamism. ASGARD observations spanned 2 years with weekly visits to 23 deg^2 in two fields in the Galactic Plane, totaling 900 hr of integration time on science fields and making it significantly larger than previous efforts. The typical blind unresolved source detection limit was 10 mJy. We describe the observations and data analysis techniques in detail, demonstrating our ability to create accurate wide-field images while effectively modeling and subtracting large-scale radio emission, allowing standard transient-and-variability analysis techniques to be used. We present early results from the analysis of two pointings: one centered on the microquasar Cygnus X-3 and one overlapping the Kepler field of view (l = 76{\deg}, b = +13.5{\deg}). Our results include images, catalog statistics, completeness functions, variability measurements, and a transient search. Out of 134 sources detected in these pointings, the only compellingly variable one is Cygnus X-3, and no transients are detected. We estimate number counts for potential Galactic radio transients and compare our current limits to previous work and our projection for the fully-analyzed ASGARD dataset.
In the present work the part of the quasar UV-optical bump within the wavelength range 1210-1450\AA\ was studied with the help of composite spectra compiled from the samples of SDSS DR7 spectra with the similar spectral index \alpha_{\lambda} within 1270-1480 \AA. This division allowed to see weak emission lines, which were not detected in previous studies of the quasar composite spectra, but were known from individual optical or composite UV spectra from the Hubble Space Telescope. Although the physical explanation of the difference in spectral indices between quasars and their dependence on quasar parameters is still not clear, it is obvious that this difference has to be taken into account when generating composite spectra, e.g. for redshift measurements. It was also shown that the equivalent width of the emission lines does not depend on the spectral index.
The large-scale surveys such as PTF, CRTS and Pan-STARRS-1 that have emerged within the past 5 years or so employ digital databases and modern analysis tools to accentuate research into Time Domain Astronomy (TDA). Preparations are underway for LSST which, in another 6 years, will usher in the second decade of modern TDA. By that time the Digital Access to a Sky Century @ Harvard (DASCH) project will have made available to the community the full sky Historical TDA database and digitized images for a century (1890--1990) of coverage. We describe the current DASCH development and some initial results, and outline plans for the "production scanning" phase and data distribution which is to begin in 2012. That will open a 100-year window into temporal astrophysics, revealing rare transients and (especially) astrophysical phenomena that vary on time-scales of a decade. It will also provide context and archival comparisons for the deeper modern surveys
Recent numerical analysis of Keplerian disk formation in turbulent, magnetized cloud cores by Santos-Lima, de Gouveia Dal Pino, & Lazarian (2012) demonstrated that reconnection diffusion is an efficient process to remove the magnetic flux excess during the build up of a rotationally supported disk. This process is induced by fast reconnection of the magnetic fields in a turbulent flow. In a similar numerical study, Seifried et al. (2012) concluded that reconnection diffusion or any other non-ideal MHD effects would not be necessary and turbulence shear alone would provide a natural way to build up a rotating disk without requiring magnetic flux loss. Their conclusion was based on the fact that the mean mass-to-flux ratio ({\mu}) evaluated over a spherical region with a radius much larger than the disk is nearly constant in their models. In this letter we compare the two sets of simulations and show that this averaging over large scales can mask significant real increases of {\mu} in the inner regions where the disk is built up. We demonstrate that turbulence-induced reconnection diffusion of the magnetic field happens in the initial stages of the disk formation in the turbulent envelope material that is accreting. Our analysis is suggestive that reconnection diffusion is present in both sets of simulations and provides a simple solution for the "magnetic braking catastrophe" which is discussed in the literature in relation to the formation of protostellar accretion disks.
KIC 6131659 is a long-period (17.5 days) eclipsing binary discovered by the Kepler mission. We analyzed six quarters of Kepler data along with supporting ground-based photometric and spectroscopic data to obtain accurate values for the mass and radius of both stars, namely M_1=0.922 +/- 0.007 M_sun, R_1=0.8800 +/- 0.0028 R_sun, and M_2=0.685 +/- 0.005 M_sun, R_2=0.6395 +/- 0.0061 R_sun. There is a well-known issue with low mass (M <<0.8 M_sun) stars (in cases where the mass and radius measurement uncertainties are smaller than two or three percent) where the measured radii are almost always 5 to 15 percent larger than expected from evolutionary models, i.e. the measured radii are all above the model isochrones in a mass-radius plane. In contrast, the two stars in KIC 6131659 were found to sit on the same theoretical isochrone in the mass-radius plane. Until recently, all of the well-studied eclipsing binaries with low-mass stars had periods less than about three days. The stars in such systems may have been inflated by high levels of stellar activity induced by tidal effects in these close binaries. KIC 6131659 shows essentially no evidence of enhanced stellar activity, and our measurements support the hypothesis that the unusual mass-radius relationship observed in most low-mass stars is influenced by strong magnetic activity created by the rapid rotation of the stars in tidally-locked, short-period systems. Finally, using short cadence data, we show that KIC 6131657 has one of the smallest measured non-zero eccentricities of a binary with two main sequence stars, where e cos omega=(4.57 +/-0.02)*10^-5.
We simulate the evolution of a 10^9 Msun dark matter halo in a cosmological setting with an adaptive-mesh refinement code as an analogue to local low luminosity dwarf irregular and dwarf spheroidal galaxies. The primary goal of our study is to investigate the roles of reionization and supernova feedback in determining the star formation histories of low mass dwarf galaxies. We include a wide range of physical effects, including metal cooling, molecular hydrogen formation and cooling, photoionization and photodissociation from a metagalactic background, a simple prescription for self-shielding, star formation, and a simple model for supernova driven energetic feedback. We carry out simulations excluding each major effect in turn. We find that reionization is primarily responsible for expelling most of the gas in our simulations, but that supernova feedback is required to disperse the dense, cold gas in the core of the halo. Moreover, we show that the timing of reionization can produce an order of magnitude difference in the final stellar mass of the system. For our full physics run with reionization at z=9, we find a stellar mass of about 10^5 Msun at z=0, and a mass-to-light ratio within the half-light radius of approximately 130 Msun/Lsun, consistent with observed low-luminosity dwarfs. However, the resulting median stellar metallicity is 0.06 Zsun, considerably larger than observed systems. In addition, we find star formation is truncated between redshifts 4 and 7, at odds with the observed late time star formation in isolated dwarf systems but in agreement with Milky Way ultrafaint dwarf spheroidals. We investigate the efficacy of energetic feedback in our simple thermal-energy driven feedback scheme, and suggest that it may still suffer from excessive radiative losses, despite reaching stellar particle masses of about 100 Msun, and a comoving spatial resolution of 11 pc.
In the framework of the Magnetism in Massive Stars (MiMeS) project, a HARPSpol Large Program at the 3.6m-ESO telescope has recently started to collect high-resolution spectropolarimetric data of a large number of Southern massive OB stars in the field of the Galaxy and in many young clusters and associations. In this contribution, we present details of the HARPSpol survey, the first HARPSpol discoveries of magnetic fields in massive stars, and the magnetic properties of two previously known magnetic stars.
We perform several suites of highly detailed dynamical simulations to investigate the architectures of the 24 Sextantis and HD 200964 planetary systems. The best fit orbital solution for the two planets in the 24 Sex system places them on orbits with periods that lie very close to 2:1 commensurability, while that for the HD 200964 system places the two planets therein in orbits whose periods lie close to a 4:3 commensurability. In both cases, the proposed best-fit orbits are mutually crossing - a scenario that is only dynamically feasible if the planets are protected from close encounters by the effects of mutual mean motion resonance. Our simulations reveal that the best fit orbits for both systems lie within narrow islands of dynamical stability, and are surrounded by much larger regions of extreme instability. As such, we show that the planets are only feasible if they are currently trapped in mutual mean-motion resonance - the 2:1 resonance in the case of 24 Sex b and c, and the 4:3 resonance in the case of HD 200964 b and c. In both cases, the region of stability is strongest and most pronounced when the planetary orbits are mutually coplanar. As the inclination of planet c with respect to planet b is increased, the stability of both systems rapidly collapses.
We report the discovery of a unique gravitational lens system, SDSSJ2222+2745, producing five spectroscopically confirmed images of a z_s=2.82 quasar lensed by a foreground galaxy cluster at z_l=0.49. We also present photometric and spectroscopic evidence for a sixth lensed image of the same quasar. The maximum separation between the quasar images is 15.1". Both the large image separations and the high image multiplicity of the lensed quasar are in themselves exceptionally rare, and observing the combination of these two factors is an exceptionally unlikely occurrence in present datasets. This is only the third known case of a quasar lensed by a cluster, and the only one with six images. The lens system was discovered in the course of the Sloan Giant Arcs Survey, in which we identify candidate lenses in the Sloan Digital Sky Survey and target these for follow up and verification with the 2.56m Nordic Optical Telescope. Multi-band photometry obtained over multiple epochs from September 2011 to September 2012 reveal significant variability at the ~10-30% level in some of the quasar images, indicating that measurements of the relative time delay between quasar images will be feasible. In this lens system we also identify a bright (g = 21.5) giant arc corresponding to a strongly lensed background galaxy at z_s=2.30. We fit parametric models of the lens system, constrained by the redshift and positions of the quasar images and the redshift and position of the giant arc. The predicted time delays between different pairs of quasar images range from ~100 days to ~6 years.
We study the CMB constraint on non-Gaussianity in CDM isocurvature perturbations. Non-Gaussian isocurvature perturbations can be produced in various models at the very early stage of the Universe. Since the isocurvature perturbations little affect the structure formation at late times, CMB is the best probe of isocurvature non-Gaussianity at least in the near future. In this paper, we focus on uncorrelated isocurvature perturbations and constrain their non-Gaussianity. For this purpose, we employ several state-of-art techniques for the analysis of CMB data and simulation. We use the WMAP 7 year data of temperature anisotropy. When the adiabatic perturbations are assumed to be Gaussian, we obtained a constraint on the isocurvature non-Gaussianity alpha^2 f_{NL}^{(ISO)}=40+-66 for the scale invariant isocurvature power spectrum, where alpha is the ratio of the power spectrum of isocurvature perturbations to that of the adiabatic ones. When we assume that the adiabatic perturbations can also be non-Gaussian, we obtain f_{NL}=38+-24 and alpha^2 f_{NL}^{(ISO)}=-8+-72. We also discuss implications our results on the axion CDM isocurvature model.
We report on Gemini/GMOS observations of two newly discovered globular clusters in the outskirts of M31. These objects, PAndAS-7 and PAndAS-8, lie at a galactocentric radius of ~87 kpc and are projected, with separation ~19 kpc, onto a field halo substructure known as the South-West Cloud. We measure radial velocities for the two clusters which confirm that they are almost certainly physically associated with this feature. Colour-magnitude diagrams reveal strikingly short, exclusively red horizontal branches in both PA-7 and PA-8; both also have photometric [Fe/H] = -1.35 +/- 0.15. At this metallicity, the morphology of the horizontal branch is maximally sensitive to age, and we use the distinctive configurations seen in PA-7 and PA-8 to demonstrate that both objects are very likely to be at least 2 Gyr younger than the oldest Milky Way globular clusters. Our observations provide strong evidence for young globular clusters being accreted into the remote outer regions of M31 in a manner entirely consistent with the established picture for the Milky Way, and add credence to the idea that similar processes play a central role in determining the composition of globular cluster systems in large spiral galaxies in general.
NSVS 02502726 has been known as a double-lined, detached eclipsing binary that consists of two low-mass stars. We obtained $BVRI$ photometric follow-up observations in 2009 and 2011 to measure improved physical properties of the binary star. Each set of light curves, including the 2008 data given by \cCakirli et al., was simultaneously analyzed with the previously published radial-velocity curves using the Wilson-Devinney binary code. The conspicuous seasonal light variations of the system are satisfactorily modelled by a two-spot model with one starspot on each component and by changes of the spot parameters with time. Based on 23 eclipse timings calculated from the synthetic model and one ephemeris epoch, an orbital period study of NSVS 02502726 reveals that the period has experienced a continuous decrease of $-5.9\times10^{-7}$ d yr$^{-1}$ or a sinusoidal variation with a period and semi-amplitude of 2.51 yrs and 0.0011 d, respectively. The timing variations could be interpreted as either the light-travel-time effect due to the presence of an unseen third body, or as the combination of this effect and angular momentum loss via magnetic stellar wind braking. Individual masses and radii of both components are determined to be $M_1$=0.689$\pm$0.016 M$_\odot$, $M_2$=0.341$\pm$0.009 M$_\odot$, $R_1$=0.707$\pm$0.007 R$_\odot$, and $R_2$=0.657$\pm$0.008 R$_\odot$. The results are very different from those of \cCakirli et al. with the primary's radius (0.674$\pm$0.006 R$_\odot$) smaller the secondary's (0.763$\pm$0.007 R$_\odot$). We compared the physical parameters presented in this paper with current low-mass stellar models and found that the measured values of the primary star are best fitted to a 79-Myr isochrone. The primary is in good agreement with the empirical mass-radius relation from low-mass binaries, but the secondary is oversized by about 85%.
We demonstrate the possibility of detecting tidal stripping of dark matter subhalos within galaxy groups using weak gravitational lensing. We have run ray-tracing simulations on galaxy catalogues from the Millennium Simulation to generate mock shape catalogues. The ray-tracing catalogues assume a halo model for galaxies and groups, using various models with different distributions of mass between galaxy and group halos to simulate different stages of group evolution. Using these mock catalogues, we forecast the lensing signals that will be detected around galaxy groups and satellite galaxies, as well as test two different methods for isolating the satellites' lensing signals. A key challenge is to determine the accuracy to which group centres can be identified. We show that with current and ongoing surveys, it will possible to detect stripping in groups of mass 10^12--10^15 Msun.
The anti-correlations between the equivalent widths of emission lines and the continuum luminosity in AGNs, known as the Baldwin effect are well established for broad lines, but are less well studied for narrow lines. In this paper we explore the Baldwin effect of narrow emission lines over a wide range of ionization levels and critical densities using a large sample of broad-line, radio-quiet AGNs taken from Sloan Digital Sky Survey (SDSS) Data Release 4. These type1 AGNs span three orders of magnitude in continuum luminosity. We show that most narrow lines show a similar Baldwin effect slope of about -0.2 while the significant deviations of the slopes for [NII] 6583, [OII] 3727, [NeV] 3425, and the narrow component of Ha can be explained by the influence of metallicity, star-formation contamination and possibly by difference in the shape of the UV-optical continuum. The slopes do not show any correlation with either the ionization potential or the critical density. We show that a combination of 50% variations in continuum near 5100A and a log-normal distribution of observed luminosity can naturally reproduce a constant Baldwin effect slope of -0.2 for all narrow lines. The variations of the continuum could be due to variability, intrinsic anisotropic emission, or an inclination effect.
Results from the Suzaku X-ray broad-band observations of clusters of galaxies are summarized. Aiming at understanding the physics of gas heating/particle acceleration and the cluster dynamical evolution, we search for non-thermal hard X-ray emission from merging clusters, particularly A2163 and the Bullet Cluster, based on the Suzaku and XMM-Newton/Chandra joint analyzes. The observed hard X-ray emission is well represented by the single- or multi-temperature thermal models including super-hot (kT~20 keV) gas. On the other hand, no significant non-thermal hard X-ray emission has been detected. Together with the presently available literature, the hard X-ray properties have been studied for about 10 clusters with Suzaku. The present status on Suzaku measurements of non-thermal X-ray emission and the cluster magnetic field are summarized and compared with those from the RXTE, BeppoSAX, and Swift satellites. The future prospects are briefly mentioned.
(abridged),In this paper, we suggest to add the "amplitude" of GRB prompt emission as the third dimension into the consideration of GRB classification with the prompt $\gamma$-ray data. We define three new parameters with the prompt emission data. The first parameter is defined as $f={F_{p}}/{F_{B}}$, where $F_{p}$ and $F_{B}$ are the peak flux and the background flux, respectively. The second parameter is defined by $f_{\rm eff}={F^{\prime}_{p}}/{F_{B}}$, where ${F^{\prime}_{p}}$ the peak flux of the a pseudo-GRB, which is generated by scaling the original lightcurve down until the measured $T_{90}$ above the background is just less than 2 s. This is an "effective amplitude" of a real long GRB that is observed as a "short" GRB with its "tip-of-iceberg" above the background. The third parameter is defined as $f_{\rm eff,z}={F^{\prime}_{p,z}}/{F_{B}}$, where ${F^{\prime}_{p,z}}$ is the peak flux of another pseudo-GRB, which is generated by progressively moving a GRB to a higher redshift $z$, until its measured "rest frame" duration $T_{90}/(1+z)$ is just below 2 s. We systematically derive these parameters for the {\em Swift} GRBs detected between December 2004 to December 2011. We find that most short GRBs are likely not "tip-of-iceberg" of long GRBs. However, one needs to be cautious if a short GRB has $f<2$, since it could be either intrinsically short or intrinsically long with the extended emission episodes buried beneath the background. We also find that most long GRBs would show up as rest-frame short GRBs if they have a high enough redshift. This interprets the interesting observational fact that the three highest-$z$ GRBs (080913, 090423, 090429B) all have a rest frame duration shorter than 2 s, but are all likely Type II GRBs.
The structure and evolution of the stellar velocity ellipsoid plays an important role in shaping galaxies undergoing bar driven secular evolution and the eventual formation of a boxy/peanut bulge such as present in the Milky Way. Using high resolution N-body simulations, we show that during the formation of such a boxy/peanut bulge, the meridional shear stress of stars, which can be measured by the meridional tilt of the velocity ellipsoid, reaches a characteristic peak in its time evolution. It is shown that the onset of a bar buckling instability is closely connected to the maximum meridional tilt of the stellar velocity ellipsoid. Our findings bring new insight to this complex gravitational instability of the bar which complements the buckling instability studies based on orbital models. We briefly discuss the observed diagnostics of the stellar velocity ellipsoid during such a phenomenon.
Simple MCBR models of chemical evolution are extended to the limit of dominant gas inflow or outflow with respect to gas locked up into long-lived stars and remnants. For an assigned empirical differential oxygen abundance distribution, which can be linearly fitted, a family of theoretical curves is built up with assigned prescriptions. For curves with increasing cut parameter, the gas mass fraction locked up into long-lived stars and remnants is found to attain a maximum and then decrease towards zero as the flow tends to infinity, while the remaining parameters show a monotonic trend. The theoretical integral oxygen abundance distribution is also expressed. An application is performed to the empirical distribution deduced from two different samples of disk stars, for both the thin and the thick disk. The constraints on formation and evolution are discussed in the light of the model. The evolution is tentatively subdivided into four stages, A, F, C, E. The empirical distribution related to any stage is fitted by all curves for a wide range of the cut parameter. The F stage may safely be described by a steady inflow regime, implying a flat theoretical distribution, in agreement with the results of hydrodynamical simulations. Finally, (1) the change of fractional mass due to the extension of the linear fit to the empirical distribution, towards both the (undetected) low-metallicity and high-metallicity tail, is evaluated and (2) the idea of a thick disk-thin disk collapse is discussed, in the light of the model.
Based on a 21.5 ks \chandra\ observation of A2556, we identify an edge on the surface brightness profile (SBP) at about 160$h_{71}^{-1}$ kpc northeast of the cluster center, and it corresponds to a shock front whose Mach number $\mathcal{M}$ is calculated to be $1.25_{-0.03}^{+0.02}$. No prominent substructure, such as sub-cluster, is found in either optical or X-ray band that can be associated with the edge, suggesting that the conventional super-sonic motion mechanism may not work in this case. As an alternative solution, we propose that the nonlinear steepening of acoustic wave, which is induced by the turbulence of the ICM at the core of the cluster, can be used to explain the origin of the shock front. Although nonlinear steepening weak shock is expected to occur frequently in clusters, why it is rarely observed still remains a question that requires further investigation, including both deeper X-ray observation and extensive theoretical studies.
The most massive star clusters include several generations of stars with a different chemical composition (mainly revealed by an Na-O anti-correlation) while low-mass star clusters appear to be chemically homogeneous. We are investigating the chemical composition of several clusters with masses of a few 10^4 Msun to establish the lower mass limit for the multiple stellar population phenomenon. Using FLAMES@VLT spectra we determine abundances of Fe, O, Na, and several other elements (alpha, Fe-peak, and neutron-capture elements) in the old open cluster Berkeley 39. This is a massive open cluster: M~10^4 Msun, approximately at the border between small globular clusters and large open clusters. Our sample size of about 30 stars is one of the largest studied for abundances in any open cluster to date, and will be useful to determine improved cluster parameters, such as age, distance, and reddening when coupled with precise, well-calibrated photometry. We find that Berkeley 39 is slightly metal-poor, <[Fe/H]>=-0.20, in agreement with previous studies of this cluster. More importantly, we do not detect any star-to-star variation in the abundances of Fe, O, and Na within quite stringent upper limits. The r.m.s. scatter is 0.04, 0.10, and 0.05 dex for Fe, O, and Na, respectively. This small spread can be entirely explained by the noise in the spectra and by uncertainties in the atmospheric parameters. We conclude that Berkeley 39 is a single-population cluster.
We present the first catalogue of known variable stars in open cluster regions and with up to two times the given cluster radius. This gives basic information about the distribution of variable stars in cluster fields for the complete sky. Knowledge of the variable star contents in open clusters is a significant advantage in their study. Analysing variability of cluster members and fields stars as well, allows us to study the characteristics of stars and clusters together. This catalogue of variable stars in open cluster fields is the first step in supporting such studies. We took all variable and suspected variable stars into account from the most complete collection, "The AAVSO Variable Star Index", and did a cross-match of these stars with the most complete catalogue of galactic open clusters named DAML02. Our on-line catalogue presently contains 18 065 variable stars. We present the basic statistical distribution according to types of variability.
We report on Chandra X-ray and Gemini-North near-infrared K-band observations of the eclipsing accretion-powered millisecond X-ray pulsar SWIFT J1749.4-2807 in quiescence. Using the Chandra observation we derive a source position of Right Ascencion: 17:49:31.73 and Declination:-28:08:05.08. The position is accurate to 0.6" (90 per cent confidence). We find one source at a magnitude K=18.44+-0.03 with a position fully consistent with the accurate Chandra X-ray localization and a second source at K=19.2+-0.1 that falls close to the edge of the error circle in the deep K-band images. The presence of a few weaker sources as suggested by previous H-band observations presented in the literature cannot the ruled out. There is marginal evidence that the brighter of the these two sources is variable. Follow-up spectroscopy of this potential counterpart will show if this source is the true counterpart to SWIFT J1749.4-2807. If so, baring the presence of complicating effects such as heating of the mass-donor star, it would allow for the mass of the neutron star to be measured through the measurement of periodic radial velocity variations.
Magnetars are an extreme, highly magnetized class of isolated neutron stars whose large X-ray luminosity is believed to be driven by their high magnetic field. In this work we study for the first time the possible very high energy gamma-ray emission above 100 GeV from magnetars, observing the sources 4U 0142+61 and 1E 2259+586. We observed the two sources with atmospheric Cherenkov telescopes in the very high energy range (E > 100 GeV). 4U 0142+61 was observed with the MAGIC I telescope in 2008 for ~25 h and 1E 2259+586 was observed with the MAGIC stereoscopic system in 2010 for ~14 h. The data were analyzed with the standard MAGIC analysis software. Neither magnetar was detected. Upper limits to the differential and integral flux above 200 GeV were computed using the Rolke algorithm. We obtain integral upper limits to the flux of 1.52*10^-12cm^-2 s^-1 and 2.7*10^-12cm^-2 s^-1 with a confidence level of 95% for 4U 0142+61 and 1E 2259+586, respectively. The resulting differential upper limits are presented together with X-ray data and upper limits in the GeV energy range.
We present wide area, deep, high-resolution 153 MHz GMRT observations of the NOAO Bootes field, adding to the extensive, multi-wavelength data of this region. The observations, data reduction, and catalogue construction and description are described here. The seven pointings produced a final mosaic covering 30 square degrees with a resolution of 25". The rms noise is 2 mJy/beam in the centre of the image, rising to 4-5 mJy/beam on the edges, with an average of 3 mJy/beam. Seventy-five per cent of the area has an rms < 4 mJy/beam. The extracted source catalogue contains 1289 sources detected at 5\sigma, of which 453 are resolved. We estimate the catalogue to be 92 per cent reliable and 95 per cent complete at an integrated flux density limit of 14 mJy. The flux densities and astrometry have been corrected for systematic errors. We calculate the differential source counts {which are in good agreement with those in the literature and provide an important step forward in quantifying the source counts at these low frequencies and low flux densities}. The GMRT 153 MHz sources have been matched to the 1.4 GHz NVSS and 327 MHz WENSS catalogues and spectral indices were derived.
We present phase-resolved spectroscopy and photometry of a source discovered with the Chandra Galactic Bulge Survey (GBS), CXOGBSJ174444.7-260330 (aka CX93 and CX153 in the previously published GBS list). We find two possible values for the orbital period P, differing from each other by 13 seconds. The most likely solution is P =5.69014(6) hours. The optical lightcurves show ellipsoidal modulations, whose modeling provides an inclination of 32+-1 degrees for the most likely P. The spectra are dominated by a K5V companion star (the disc veiling is <~5%). Broad and structured emission from the Balmer lines is also detected, as well as fainter emission from HeI. From the absorption lines we measure K2 =117+-8km/s and v sin i = 69+-7km/s. By solving the system mass function we find M1=0.8+-0.2Msun for the favored P and i, consistent with a white dwarf accretor, and M2=0.6+-0.2Msun. We estimate a distance in the range 400-700 pc. Although in a low accretion state, both spectroscopy and photometry provide evidence of variability on a timescale of months or faster. Besides finding a new, long orbital period cataclysmic variable in a low accretion state, this work shows that the design of the GBS works efficiently to find accreting X-ray binaries in quiescence, highlighting that the spectra of CVs in a low-accretion state can at times appear suggestive of a quiescent neutron star or a black hole system.
For a sample of metal-poor stars (-3.3< [Fe/H] <-2.2) that have high-resolution spectroscopic abundance determinations, we have measured equivalent widths (EW) of the Ca II K, Mg I b and near-infrared (NIR) Ca II triplet lines using low-resolution spectra of the Sloan Digital Sky Survey (SDSS), calculated effective temperatures from (g-z)0 color, deduced stellar surface gravities by fitting stellar isochrones, and determined metallicities based on the aforementioned quantities. Metallicities thus derived from the Ca II K line are in much better agreement with the results determined from high-resolution spectra than the values given in the SDSS Data Release 7 (DR7). The metallicities derived from the Mg I b lines have a large dispersion owing to the large measurement errors, whereas those deduced from the Ca II triplet lines are too high due to both non-local thermodynamical equilibrium (NLTE) effects and measurement errors. Abundances after corrected for the NLTE effect for the Mg I b lines and Ca II triplet lines are also presented. Following this method, we have identified six candidates of ultra-metal-poor stars with [Fe/H] <-4.0 from a sample of 166 metal-poor star candidates. One of them, SDSS J102915+172927, was recently confirmed to be an ultra-metal-poor ([Fe/H] < -4.0) star with the lowest metallicity ever measured. Follow-up high-resolution spectroscopy for the other five ultra-metal-poor stars in our sample will therefore be of great interest.
Multi-color light curves and radial velocities for TYC\,1031\,1262\,1 have been obtained and analyzed. TYC\,1031\,1262\,1 includes a Cepheid with a period of 4.15270$\pm$0.00061 days. The orbital period of the system is about 51.2857$\pm$0.0174 days. The pulsation period indicates a secular period increase with an amount of 2.46$\pm$0.54 min/yr. The observed B, V, and R magnitudes were cleaned for the intrinsic variations of the primary star. The remaining light curves, consisting of eclipses and proximity effects, are obtained and analyzed for orbital parameters. The system consists of two evolved stars, F8II+G6II, with masses of M$_1$=1.640$\pm$0.151 {\Msun} and M$_2$=0.934$\pm$0.109 {\Msun} and radii of R$_1$=26.9$\pm$0.9 {\Rsun} and R$_2$=15.0$\pm$0.7 {\Rsun}. The pulsating star is almost filling its corresponding Roche lobe which indicates the possibility of mass loss or transfer having taken place. We find an average distance of d=5070$\pm$250\,pc using the BVR and JHK magnitudes and also the V-band extinction. Kinematic properties and the distance to the galactic plane with an amount of 970 pc indicate that it belongs to the thick-disk population. Most of the observed and calculated parameters of the TYC\,1031\,1262\,1 lead to a classification of an Anomalous Cepheid.
Context: The formation and evolution of disk galaxies are long standing questions in Astronomy. Understanding the properties of globular cluster systems can lead to important insights on the evolution of its host galaxy. Aims: We aim to obtain the stellar population parameters - age and metallicity - of a sample of M31 and Galactic globular clusters. Studying their globular cluster systems is an important step towards understanding their formation and evolution in a complete way. Methods: Our analysis employs a modern pixel-to-pixel spectral fitting technique to fit observed integrated spectra to updated stellar population models. By comparing observations to models we obtain the ages and metallicities of their stellar populations. We apply this technique to a sample of 38 globular clusters in M31 and to 41 Galactic globular clusters, used as a control sample. Results: Our sample of M31 globular clusters spans ages from 150 Myr to the age of the Universe. Metallicities [Fe/H] range from -2.2 dex to the solar value. The age-metallicity relation obtained can be described as having two components: an old population with a flat age-[Fe/H] relation, possibly associated with the halo and/or bulge, and a second one with a roughly linear relation between age and metallicity, higher metallicities corresponding to younger ages, possibly associated with the M31 disk. While we recover the very well known Galactic GC metallicity bimodality, our own analysis of M31's metallicity distribution function (MDF) suggests that both GC systems cover basically the same [Fe/H] range yet M31's MDF is not clearly bimodal. These results suggest that both galaxies experienced different star formation and accretion histories.
Aims. We report on the recent observations of the supernova remnant SNR 1987A
in the Large Magellanic Cloud with XMM-Newton. Carefully monitoring the
evolution of the X-ray light curve allows to probe the complex circumstellar
medium structure observed around the supernova progenitor star.
Methods. We analyse all XMM-Newton observations of SNR 1987A from January
2007 to December 2011, using data from the EPIC-pn camera. Spectra from all
epochs are extracted and analysed in a homogeneous way. Using a multi-shock
model to fit the spectra across the 0.2-10 keV band we measure soft and hard
X-ray fluxes with high accuracy. In the hard X-ray band we examine the presence
and properties of Fe K ines. Our findings are interpreted in the framework of a
hydrodynamics-based model.
Results. The soft X-ray flux of SNR 1987A continuously increased in the
recent years. Although the light curve shows a mild flattening, there is no
sudden break as reported in an earlier work, a picture echoed by a revision of
the Chandra light curve. We therefore conclude that material in the equatorial
ring and out-of-plane HII regions are still being swept-up. We estimate the
thickness of the equatorial ring to be at least 4.5x10^16 cm (0.0146 pc). This
lower limit will increase as long as the soft X-ray flux has not reached a
turn-over. We detect a broad Fe K line in all spectra from 2007 to 2011. The
widths and centroid energies of the lines indicate the presence of a collection
of iron ionisation stages. Thermal emission from the hydrodynamic model does
not reproduce the low-energy part of the line (6.4-6.5 keV), suggesting that
fluorescence from neutral and/or low ionisation Fe might be present.
With the HOPS, MALT90 and HiGAL Galactic plane surveys we are mapping a significant fraction of the dense, star-forming, molecular gas in the Galaxy. I present results from two projects based on this combined dataset, namely, (i) looking for variations in the star formation (SF) rate across the Galaxy as a function of environment, and (ii) searching for molecular cloud progenitors of the most extreme (massive and dense) stellar clusters. We find the SF rate per unit mass of dense gas in the inner 500pc of the Galaxy is at least an order of magnitude lower than that in the disk, directly challenging the predictions of proposed universal column/volume density relations. In particular, the region 1 degrees < l < 3.5 degrees, |b| < 0.5 degrees contains ~1E7 Msun of dense molecular gas -- enough to form 1000 Orion-like clusters -- but the present-day star formation rate within this gas is only equivalent to that in Orion. I present follow up studies of one molecular cloud we have studied as part of project (ii) which also lies in the inner 500 pc of the Galaxy and is clearly extreme compared to the rest of the Galactic population. With a mass of 1E5 Msun,a radius of only ~3pc and almost no signs of star formation it appears to be the progenitor of an Arches-like stellar cluster. Despite detailed observational followup searches, this object still appears to be unique in the Galaxy, making it extremely important for testing massive cluster formation models.
The question of the origin of the gas supplying the accretion process is pertinent especially in the context of enhanced activity of Galactic Center during the past few hundred years, seen now as echo from the surrounding molecular clouds, and the currently observed new cloud approaching Sgr A*. We discuss the so-called Galactic Center mini-spiral as a possible source of material feeding the supermassive black hole on a 0.1 parsec scale. The collisions between individual clumps reduce their angular momentum. and set some of the clumps on a plunging trajectory. We conclude that the amount of material contained in the mini-spiral is sufficient to sustain the luminosity of Sgr A* at the required level. The accretion episodes of relatively dense gas from the mini-spiral passing through a transient ring mode at $\sim 10^4$ Rg provide a viable scenario for the bright phase of Galactic Center.
Recent measurement of mass of PSR J1614-2230 rules out most of existing
models of equation of state (EOS) of dense matter with high-density softening
due to hyperonization, based on the recent hyperon-nucleon and hyperon-hyperon
interactions, leading to a "hyperon puzzle".
We study a specific solution of "hyperon puzzle", consisting in replacing a
too soft hyperon core by a sufficiently stiff quark core. We construct an
analytic approximation fitting very well modern EOSs of 2SC and CFL color
superconducting phases of quark matter. This allows us for simulating continua
of sequences of first-order phase transitions from hadronic matter to the 2SC,
and then to the CFL state of color superconducting quark matter.
We obtain constraints in the parameter space of the EOS of superconducting
quark cores, resulting from M_max> 2 M_sol. We also derive constraints that
would result from significantly higher measured masses. For 2.4 M_sol required
stiffness of the CFL quark core should have been close to the causality limit,
the density jump at the phase transition being very small.
Condition M_max > 2 M_sol puts strong constraints on the EOSs of the 2SC and
CFL phases of quark matter. Density jumps at the phase transitions have to be
sufficiently small and sound speeds in quark matter - sufficiently large. A
strict condition of thermodynamic stability of quark phase results in the
maximum mass of hybrid stars similar to that of purely baryon stars. Therefore,
to get M_max>2 M_sol for stable hybrid stars, both sufficiently strong
additional hyperon repulsion at high density baryon matter and a sufficiently
stiff EOS of quark matter would be needed. However, it is likely that the high
density instability of quark matter (reconfinement) indicates actually the
inadequacy of the point-particle model of baryons in dense matter at very high
densities.
The most characteristic property of active galaxies, including quasars, are prominent broad emission lines. I will discuss an interesting possibility that dust is responsible for this phenomenon. The dust is known to be present in quasars in the form of a dusty/molecular torus which results in complexity of the appearance of active galaxies. However, this dust is located further from the black hole than the Broad Line Region. We propose that the dust is present also closer in and it is actually responsible for formation of the broad emission lines. The argument is based on determination of the temperature of the disk atmosphere underlying the Broad Line Region: it is close to 1000 K, independently from the black hole mass and accretion rate of the object. The mechanism is simple and universal but leads to a considerable complexity of the active nucleus surrounding. The understanding the formation of BLR opens a way to use it reliably - in combination with reverberation measurement of its size - as standard candles in cosmology.
Comparison of peculiar velocities of galaxies with their gravitational accelerations (induced by the density field) is one of the methods to constrain the redshift distortion parameter \beta=(\Omega_m^0.55)/b, where \Omega_m is the non-relativistic matter density parameter and b is the linear bias. In particular, one can use the motion of the Local Group (LG) for that purpose. Its peculiar velocity is known from the dipole component of the cosmic microwave background, whereas its acceleration can be estimated with the use of an all-sky galaxy catalog, from the so-called clustering dipole. At the moment, the biggest dataset of that kind is the Two Micron All Sky Survey Extended Source Catalog (2MASS XSC) containing almost 1 million galaxies and complete up to ~300 Mpc/h. We applied 2MASS data to measure LG acceleration and used two methods to estimate the beta parameter. Both of them yield \beta~0.4 with an error of several per cent, which is the most precise determination of this parameter from the clustering dipole to date.
Accurate parameter estimation of gravitational waves from coalescing compact binary sources is a key requirement for gravitational-wave astronomy. Evaluating the posterior probability density function of the binary's parameters (component masses, sky location, distance, etc.) requires computing millions of waveforms. The computational expense of parameter estimation is dominated by waveform generation and scales linearly with the waveform computational cost. Previous work showed that gravitational waveforms from non-spinning compact binary sources are amenable to a truncated singular value decomposition, which allows them to be reconstructed via interpolation at fixed computational cost. However, the accuracy requirement for parameter estimation is typically higher than for searches, so it is crucial to ascertain that interpolation does not lead to significant errors. Here we provide a proof of principle to show that interpolated waveforms can be used to recover posterior probability density functions with negligible loss in accuracy with respect to non-interpolated waveforms. This technique has the potential to significantly increase the efficiency of parameter estimation.
Previous SiO maps of the innermost regions of HH212 set strong constraints on the structure and origin of this jet. They rule out a fast wide-angle wind, and tentatively favor a magneto-centrifugal disk wind launched out to 0.6 AU. We aim to assess the SiO content at the base of the HH212 jet to set an independent constraint on the location of the jet launch zone with respect to the dust sublimation radius. We present the first sub-arcsecond (0"44x0"96) CO map of the HH212 jet base, obtained with the IRAM Plateau de Bure Interferometer. Combining this with previous SiO(5-4) data, we infer the CO(2-1) opacity and mass-flux in the high-velocity jet and arrive at a much tighter lower limit to the SiO abundance than possible from the (optically thick) SiO emission alone. Gas-phase SiO at high velocity contains at least 10% of the elemental silicon if the jet is dusty, and at least 40% if the jet is dust-free, if CO and SiO have similar excitation temperatures. Such a high SiO content is challenging for current chemical models of both dust-free winds and dusty interstellar shocks. Updated chemical models (equatorial dust-free winds, highly magnetized dusty shocks) and observations of higher J CO lines are required to elucidate the dust content and launch radius of the HH212 high-velocity jet.
Cometary globule (CG) 1 and CG 2 are "classic" CGs in the Gum Nebula. They have compact heads and long dusty tails that point away from the centre of the Gum Nebula. We study the structure of CG 1 and CG 2 and the star formation in them to find clues to the CG formation mechanism. The two possible mechanisms, radiation-driven implosion (RDI) and a supernova (SN) blast wave, produce a characteristic mass distribution where the major part of the mass is situated in either the head (RDI) or the tail (SN). CG 1 and CG 2 were imaged in the near infrared (NIR) JsHKs bands. NIR photometry was used to locate NIR excess objects and to create extinction maps of the CGs. The A_V maps allow us to analyse the large-scale structure of CG 1 and CG 2. Archival images from the WISE and Spitzer satellites and HIRES-processed IRAS images were used to study the small-scale structure. In addition to the previously known CG 1 IRS 1 we discovered three new NIR-excess objects, two in CG 1 and one in CG 2. CG 2 IRS 1 is the first detection of star formation in CG 2. Spectral energy distribution (SED) fitting suggests the NIR-excess objects are young low-mass stars. CG 1 IRS 1 is probably a class I protostar in the head of CG 1. CG 1 IRS 1 drives a bipolar outflow, which is very weak in CO, but the cavity walls are seen in reflected light in our NIR and in the Spitzer 3.6 and 4.5 mum images. Strong emission from excited polycyclic aromatic hydrocarbon particles and very small grains were detected in the CG 1 tail. The total mass of CG 1 in the observed area is 41.9 Msun of which 16.8 Msun lies in the head. For CG 2 these values are 31.0 Msun total and 19.1 Msun in the head. The observed mass distribution does not offer a firm conclusion for the formation mechanism of these CGs: CG 1 is in too evolved a state, and in CG 2 part of the globule tail was outside the observed area. (abridged)
We present here new measurements of the longitudinal magnetic field (B_e) in the binary system HD9996, where the primary companion is an Ap star. Series of 63 B_e observations was obtained in years 1994-2011 with the 1m optical telescope of the Special Astrophysical Observatory (Russia). New magnetic data allowed us to refine the long-term magnetic period of HD9996 to P_mag=21.8 years. Compilation of archival photometric data showed the existence of long term variations of HD9996 in time scale of 22-23 yr consistent with P_mag}. We identify P_mag with the precession period of the primary Ap star and summarize search for a short-term rotational period and the rotational line broadening in this star.
An emergent gravity metric incorporating $k-$essence scalar fields $\phi$ having a Born-Infeld type lagrangian is mapped into a metric whose structure is similar to that of a blackhole of large mass $M$ that has swallowed a global monopole. However, here the field is not that of a monopole but rather that of a $k-$essence scalar field. If $\phi_{emergent}$ be solutions of the emergent gravity equations of motion under cosmological boundary conditions at $\infty$, then for $r\rightarrow\infty$ the rescaled field $\frac {\phi_{emergent}}{2GM-1}$ has exact correspondence with $\phi$ with $\phi(r,t)=\phi_{1}(r)+\phi_{2}(t)$. The Hawking temperature of this metric is $T_{\mathrm emergent}= \frac{\hbar c^{3}}{8\pi GM k_{\mathrm B}}(1-K)^{2}\equiv \frac{\hbar}{8\pi GM k_{\mathrm B}}(1-K)^{2}$, taking the speed of light $c=1$. Here $K=\dot\phi_{2}^{2}$ is the kinetic energy of the $k-$essence field $\phi$ and $K$ is always less than unity, $k_{\mathrm B}$ is the Boltzmann constant. This is phenomenologically interesting in the context of Belgiorno {\it et al's} gravitational analogue experiment.
We report results of an extensive analysis of the X-ray nova XTE J1859+226 observed with BeppoSAX and RXTE during its 1999 outburst. We modelled the source spectrum with a multicolour blackbody-like feature plus the generic Comptonization model BMC which has the advantage of providing spectral description of the emitted-radiation properties without assumptions on the underlying physical process. The multicolour component is attributed to the geometrically thin accretion disk, while the Comptonization spectrum is claimed to originate in the innermost sub-Keplerian region of the system (transition layer). We find that XTE J1859+226 covers all the spectral states typical of black-hole sources during its evolution across the outburst, however during the very high state, when the disk contribution to the total luminosity is more than 70% and the root mean square variability > 5%, the high-energy photon index is closer to a hard state value (Gamma ~ 1.8). The BMC normalization and photon index Gamma well correlate with the radio emission, and we also observed a possible saturation effect of Gamma at the brightest radio emission levels. A strong positive correlation was found between the fraction of Comptonized seed photons and the observed integrated root mean square variability, which strengthens the idea that most of the fast variability in these systems is provided by the innermost Compton cloud, which may be also identified as a jet.
Rotational splittings are currently measured for several main sequence stars and a large number of red giants with the space mission Kepler. This will provide stringent constraints on rotation profiles. Our aim is to obtain seismic constraints on the internal transport and surface loss of angular momentum of oscillating solar-like stars. To this end, we study the evolution of rotational splittings from the pre-main sequence to the red-giant branch for stochastically excited oscillation modes. We modified the evolutionary code CESAM2K to take rotationally induced transport in radiative zones into account. Linear rotational splittings were computed for a sequence of $1.3 M_{\odot}$ models. Rotation profiles were derived from our evolutionary models and eigenfunctions from linear adiabatic oscillation calculations. We find that transport by meridional circulation and shear turbulence yields far too high a core rotation rate for red-giant models compared with recent seismic observations. We discuss several uncertainties in the physical description of stars that could have an impact on the rotation profiles. For instance, we find that the Goldreich-Schubert-Fricke instability does not extract enough angular momentum from the core to account for the discrepancy. In contrast, an increase of the horizontal turbulent viscosity by 2 orders of magnitude is able to significantly decrease the central rotation rate on the red-giant branch. Our results indicate that it is possible that the prescription for the horizontal turbulent viscosity largely underestimates its actual value or else a mechanism not included in current stellar models of low mass stars is needed to slow down the rotation in the radiative core of red-giant stars.
We study the collapse and virialization of an isolated spherical cloud of self-gravitating particles initially at rest and characterised by a power-law density profile, with exponent 0<= \alpha < 3, or by a Plummer, an Hernquist, a NFW, a Gaussian profile. We find that in all cases the virialized structure formed after the collapse has a density profile decaying, at large enough radii, as ~ r^{-4}, and a radial velocity dispersion profile decaying as ~r^{-1}. We show that these profiles originate from the physical mechanism responsible of the ejection of a fraction of cloud's mass and energy during the collapse and that this same mechanism washes out the dependence on the initial conditions. When a large enough initial velocity dispersion is given to the cloud particles, ejection does not occur anymore and consequently the virialized halo density and velocity profiles display features which reflect the initial conditions.
The four-planet system around GJ 581 has received attention because it has been claimed that there are possibly two additional low-mass companions as well - one of them being a planet in the middle of the stellar habitable zone. We re-analyse the available HARPS and HIRES Doppler data in an attempt to determine the false positive rate of our Bayesian data analysis techniques and to count the number of Keplerian signals in the GJ 581 data. We apply the common Lomb-Scargle periodograms and posterior sampling techniques in the Bayesian framework to estimate the number of signals in the radial velocities. We also analyse the HARPS velocities sequentially after each full observing period to compare the sensitivities and false positive rates of the two signal detection techniques. By relaxing the assumption that the radial velocity noise is white, we also demonstrate the consequences that noise correlations have on the obtained results and the significances of the signals. According to our analyses, the number of Keplerian signals favoured by the publicly available HARPS and HIRES radial velocity data of GJ 581 is four. This result relies on the sensitivity of the Bayesian statistical analysis techniques but also depends on the assumed noise model. We also show that the radial velocity noise is actually not white and that this feature has to be accounted for when analysing radial velocities in a search for low-amplitude signals corresponding to low-mass planets. ...
Looking for the primary rainbow in starlight that is reflected by exoplanets appears to be a promising method to search for liquid water clouds in exoplanetary atmospheres. Ice water clouds, that consist of water crystals instead of water droplets, could potentially mask the rainbow feature in the planetary signal by covering liquid water clouds. Here, we investigate the strength of the rainbow feature for exoplanets that have liquid and icy water clouds in their atmosphere, and calculate the rainbow feature for a realistic cloud coverage of Earth. We calculate flux and polarization signals of starlight that is reflected by horizontally and vertically inhomogeneous Earth--like exoplanets, covered by patchy clouds consisting of liquid water droplets or water ice crystals. The planetary surfaces are black. On a planet with a significant coverage of liquid water clouds only, the total flux signal shows a weak rainbow feature. Any coverage of the liquid water clouds by ice clouds, however, dampens the rainbow feature in the total flux, and thus the discovery of liquid water in the atmosphere. On the other hand, detecting the primary rainbow in the polarization signal of exoplanets appears to be a powerful tool for detecting liquid water in exoplanetary atmospheres, even when these clouds are partially covered by ice clouds. In particular, liquid water clouds covering as little as 10%-20% of the planetary surface, with more than half of these covered by ice clouds, still create a polarized rainbow feature in the planetary signal. Indeed, calculations of flux and polarization signals of an exoplanet with a realistic Earth--like cloud coverage, show a strong polarized rainbow feature.
We develop an absolute flux density scale for cm-wavelength astronomy by combining accurate flux density ratios determined by the VLA between the planet Mars and a set of potential calibrators with the Rudy thermophysical emission model of Mars, adjusted to the absolute scale established by WMAP. The radio sources 3C123, 3C196, 3C286 and 3C295 are found to be varying at a level of less than ~5% per century at all frequencies between 1 and 50 GHz, and hence are suitable as flux density standards. We present polynomial expressions for their spectral flux densities, valid from 1 to 50 GHz, with absolute accuracy estimated at 1-3% depending on frequency. Of the four sources, 3C286 is the most compact and has the flattest spectral index, making it the most suitable object on which to establish the spectral flux density scale. The sources 3C48, 3C138, 3C147, NGC7027, NGC6542, and MWC349 show significant variability on various timescales. Polynomial coefficients for the spectral flux density are developed for 3C48, 3C138, and 3C147 for each of the seventeen observation dates, spanning 1983 through 2012. The planets Venus, Uranus, and Neptune are included in our observations, and we derive their brightness temperatures over the same frequency range.
Spectroscopic observations at the Russian 6-m telescope are used to study the two polar ring galaxies (PRGs) from the catalogue by Moiseev et al.: SPRC-7 and SPRC-260. We have analyzed the kinematics of the stellar component of the central galaxies as well as the ionized gas kinematics in the external ring structures. The disc-halo decomposition of rotation curves in two perpendicular directions are considered. The observed 2D velocity fields are compared with the model predictions for different dark halo shapes. Based on these data, we constrain that for potential of DM halo semiaxis ratios is $s=0.8$, $q=1$ for SPRC-7 and $s=0.95$, $q=1.1$ for SPRC-260. Using 3D hydrodynamic simulations we also study the dynamics and evolution of the polar component in the potential of the galactic disc and dark halo for these two galaxies. We show that the polar component is dynamically quasi-stable on the scale of $\sim10$ dynamical times (about a few Gyr). This is demonstrate the possibility for the growth of a spiral structure, which then steadily transforms to a lopsided gaseous system in the polar pane.
We present an improved version of SOAP (Boisse et al. 2012) named "SOAP-T", which can generate the radial velocity variations and light-curves for systems consisting of a rotating spotted star with a transiting planet. This tool can be used to study the anomalies inside transit light-curves and the Rossiter-McLaughlin effect, to better constrain the orbital configuration and properties of planetary systems and active zones of their host stars. Tests of the code are presented to illustrate its performance and to validate its capability when compared with analytical models and real data. Finally, we apply SOAP-T to the active star, HAT-P-11, observed by the NASA Kepler space telescope and use this system to discuss the capability of this tool in analyzing light-curves for the cases where the transiting planet overlaps with the star's spots.
New BVR light curves of the eclipsing binary system NSV 5904 have been constructed based on CCD observations obtained using 1.88-m telescope of Kottamia observatory during the phase of telescope testing and adjusting its optical quality on May, 2009. New times of minima and epoch have been determined from these light curves. Using the Binary Maker 3.0 (BM3) package, a preliminary determination of the photometric orbital and physical parameters of NSV 5904 are given.
We study transient spiral structures in an isothermal, thin, galactic disc. We find no instability that can grow everywhere from infinitesimal disturbances, but spiral structure does grow in the disc due to an arbitrarily strong, asymmetric, central source. An initially finite spiral undergoes transient swing amplification as it is gradually wound-up by differential rotation. An independent sequence in negative time describes a leading spiral swinging to a trailing spiral. The dynamical coupling is established between the swinging potential and the arm particles, by ensuring that this potential constrains a locally rotating distribution function centred on the arms. This swing amplification propagates in radius at the constant rotational speed of the disc, and leaves behind an exponential density decline in space and time.
We are performing a transient, microsecond timescale radio sky survey, called "Astropulse," using the Arecibo telescope. Astropulse searches for brief (0.4 {\mu}s to 204.8 {\mu}s), wideband (relative to its 2.5 MHz bandwidth) radio pulses centered at 1,420 MHz. Astropulse is a commensal (piggyback) survey, and scans the sky between declinations of -1.33 and 38.03 degrees. We obtained 1,540 hours of data in each of 7 beams of the ALFA receiver, with 2 polarizations per beam. Examination of timescales on the order of a few microseconds is possible because we used coherent dedispersion. The more usual technique, incoherent dedispersion, cannot resolve signals below a minimum timescale. However, coherent dedispersion requires more intensive computation than incoherent dedispersion. The required processing power was provided by BOINC, the Berkeley Open Infrastructure for Network Computing.
We used archival Spitzer Space Telescope mid-infrared data to search for young stellar objects (YSOs) in the immediate vicinity of two bright-rimmed clouds, BRC 27 (part of CMa R1) and BRC 34 (part of the IC 1396 complex). These regions both appear to be actively forming young stars, perhaps triggered by the proximate OB stars. In BRC 27, we find clear infrared excesses around 22 of the 26 YSOs or YSO candidates identified in the literature, and identify 16 new YSO candidates that appear to have IR excesses. In BRC 34, the one literature-identified YSO has an IR excess, and we suggest 13 new YSO candidates in this region, including a new Class I object. Considering the entire ensemble, both BRCs are likely of comparable ages, within the uncertainties of small number statistics and without spectroscopy to confirm or refute the YSO candidates. Similarly, no clear conclusions can yet be drawn about any possible age gradients that may be present across the BRCs.
Ion-neutral collisions may lead to the damping of Alfven waves in chromospheric and prominence plasmas. Neutral helium atoms enhance the damping in certain temperature interval, where the ratio of neutral helium and neutral hydrogen atoms is increased. Therefore, the height-dependence of ionization degrees of hydrogen and helium may influence the damping rate of Alfven waves. We aim to study the effect of neutral helium in the damping of Alfven waves in stratified partially ionized plasma of the solar chromosphere. We consider a magnetic flux tube, which is expanded up to 1000 km height and then becomes vertical due to merging with neighboring tubes, and study the dynamics of linear torsional Alfven waves in the presence of neutral hydrogen and neutral helium atoms. We start with three-fluid description of plasma and consequently derive single-fluid magnetohydrodynamic (MHD) equations for torsional Alfven waves. Thin flux tube approximation allows to obtain the dispersion relation of the waves in the lower part of tubes, while the spatial dependence of steady-state Alfven waves is governed by Bessel type equation in the upper part of tubes. Consecutive derivation of single-fluid MHD equations results in a new Cowling diffusion coefficient in the presence of neutral helium which is different from previously used one. We found that shorter-period (< 5 s) torsional Alfven waves damp quickly in the chromospheric network due to ion-neutral collision. On the other hand, longer-period (> 5 s) waves do not reach the transition region as they become evanescent at lower heights in the network cores. Propagation of torsional Alfven waves through the chromosphere into the solar corona should be considered with caution: low-frequency waves are evanescent due to the stratification, while high-frequency waves are damped due to ion neutral collisions.
This study of SDSS0804 is primarily concerned with the double-hump shape in the light curve and its connection with the accretion disk in this bounce-back system. Time-resolved photometric and spectroscopic observations were obtained to analyze the behavior of the system between superoutbursts. A geometric model of a binary system containing a disk with two outer annuli spiral density waves was applied to explain the light curve and the Doppler tomography. Observations were carried out during 2008-2009, after the object's magnitude decreased to V~17.7(0.1) from the March 2006 eruption. The light curve clearly shows a sinusoid-like variability with a 0.07 mag amplitude and a 42.48 min periodicity, which is half of the orbital period of the system. In Sept. 2010, the system underwent yet another superoutburst and returned to its quiescent level by the beginning of 2012. This light curve once again showed a double-humps, but with a significantly smaller ~0.01mag amplitude. Other types of variability like a "mini-outburst" or SDSS1238-like features were not detected. Doppler tomograms, obtained from spectroscopic data during the same period of time, show a large accretion disk with uneven brightness, implying the presence of spiral waves. We constructed a geometric model of a bounce-back system containing two spiral density waves in the outer annuli of the disk to reproduce the observed light curves. The Doppler tomograms and the double-hump-shape light curves in quiescence can be explained by a model system containing a massive >0.7Msun white dwarf with a surface temperature of ~12000K, a late-type brown dwarf, and an accretion disk with two outer annuli spirals. According to this model, the accretion disk should be large, extending to the 2:1 resonance radius, and cool (~2500K). The inner parts of the disk should be optically thin in the continuum or totally void.
We present previously unpublished photometry of supernovae 2003gs and 2003hv. Using spectroscopically-derived corrections to the U-band photometry, we reconcile U-band light curves made from imagery with the Cerro Tololo 0.9-m, 1.3-m and Las Campanas 1-m telescopes. Previously, such light curves showed a 0.4 mag spread at one month after maximum light. This gives us hope that a set of corrected ultraviolet light curves of nearby objects can contribute to the full utilization of rest frame U-band data of supernovae at redshift ~0.3 to 0.8. As pointed out recently by Kessler et al. in the context of the Sloan Digital Sky Survey supernova search, if we take the published U-band photometry of nearby Type Ia supernovae at face value, there is a 0.12 mag U-band anomaly in the distance moduli of higher redshift objects. This anomaly led the Sloan survey to eliminate from their analyses all photometry obtained in the rest frame U-band. The Supernova Legacy Survey eliminated observer frame U-band photometry, which is to say nearby objects observed in the U-band, but they used photometry of high redshift objects no matter in which band the photons were emitted.
The cryogenic detectors in the form of bolometers are presently used for different applications, in particular for very rare or hypothetical events associated with new forms of matter, specifically related to the existence of Dark Matter. In the detection of particles with a semiconductor as target and detector, usually two signals are measured: ionization and heat. The amplification of the thermal signal is obtained with the prescriptions from Luke-Neganov effect. The energy deposited in the semiconductor lattice as stable defects in the form of Frenkel pairs at cryogenic temperatures, following the interaction of a dark matter particle, is evaluated and consequences for measured quantities are discussed. This contribution is included in the energy balance of the Luke effect. Applying the present model to germanium and silicon, we found that for the same incident weakly interacting massive particle the energy deposited in defects in germanium is about twice the value for silicon.
It is well known that the mass lens systems have the invariance in the singed magnification sums. In this paper, we discuss the signed magnification sums of the general spherical lens models including the singular isothermal sphere, the Schwarzschild black hole and the Ellis wormhole which is an example of the transversable wormholes of the Morris-Thorne class. We show that the signed magnification sum is a very useful tool to distinguish the exotic lens objects. For an example, we show that we can distinguish the Schwarzschild black hole with the Ellis wormhole by the signed magnification sum.
We consider the minimal scalar singlet dark matter stabilised by a $Z_3$ symmetry. Due to the cubic term in the scalar potential, semi-annihilations, besides annihilations, contribute to the dark matter relic density. Unlike in the $Z_2$ case, the dark matter spin independent direct detection cross section is not linked to the annihilation cross section any more. We study the extrema of the potential and show that a too large cubic term would break the $Z_3$ symmetry spontaneously, implying a lower bound on the direct detection cross section, and allowing the whole parameter space to be tested by XENON1T. In a small region of the parameter space the model can avoid the instability of the standard model vacuum up to the unification scale. If the semi-annihilations are large, however, new physics will be needed at TeV scale because the model becomes non-perturbative. The singlet dark matter mass cannot be lower than 53.8 GeV due to the constraint from Higgs boson decay into dark matter.
We revisit the issue on signatures of pre-inflationary background anisotropy by considering the quantization of a massless and minimally coupled scalar field in an axially symmetric Kasner background, mimicking cosmological perturbations. We show that the power spectrum of the scalar field fluctuation has a negligible difference from the standard inflation in the non-planar directions, but it has a sharp peak around the symmetry plane. For the non-planar high-momentum modes, we use the WKB approximation for the first period and the asymptotic approximation based on the de Sitter solution for the next period. At the boundary, two mode functions have the same accuracy with error of $O({H_{i}}/k)$. We calculate the approximation up to the order of $({H_{i}}/k)^6$ and show that the power spectrum of the scalar field fails to get corrections until we execute the approximation up to $6^{\rm th}$ order.
A fundamental property in wormhole physics is the flaring-out condition of the throat, which through the Einstein field equation entails the violation of the null energy condition. In the context of modified theories of gravity, it has also been shown that the normal matter can be imposed to satisfy the energy conditions, and it is the higher order curvature terms, interpreted as a gravitational fluid, that sustain these non-standard wormhole geometries, fundamentally different from their counterparts in general relativity. We review recent work in wormhole physics in the context of modified theories of gravity.
We investigate the magnetic moment operator for constituent fermion masses for chirally symmetric theories. Constituent fermion masses are generated through a yukawa interaction of the fermion with a scalar (or /and psuedoscalar) field via the vacuum expectation value (VEV) of the scalar (or and psuedoscalar) field. We especially consider the high baryon density $\pi_0$ condensed phase, in which chiral symmetry is spontaneously broken, with space varying expectation values of the $ \sigma$ and $\pi_0$ fields. This phase has a spin polarized fermi sea as the ground state. We show that there is indeed generated a macroscopic magnetization in this phase, contrary to what one would have found, if one just used a primitive phenomenological magnetic moment formula for explicit/ current fermion masses. Furthermore, this analysis reveals that the magnetization of this state goes up as the VEV, that determines the 'mass', comes down with increasing baryon density. The consequent high magnetic field that is generated will destabilize this state at a threshold density. This is important in the context of neutron stars, as such a high density state may be responsible for very high magnetic fields in the dense core of neutron stars. This could potentially be the origin of magnetars - the stars with the largest magnetic fields in the universe.
In the first section we present the atomic part where a C2+ atomic target was
prepared and used to generate theoretical data to investigate recombination
lines arising from electron-ion collisions in thin plasma. R-matrix method was
used to describe the C2+ plus electron system. Theoretical data concerning
bound and autoionizing states were generated in the intermediate-coupling
approximation. The data were used to generate dielectronic recombination data
for C+ which include transition lines, oscillator strengths, radiative
transition probabilities, emissivities and dielectronic recombination
coefficients. The data were cast in a line list containing 6187
optically-allowed transitions which include many C II lines observed in
astronomical spectra. This line list was used to analyze the spectra from a
number of astronomical objects, mainly planetary nebulae, and identify their
electron temperature. The electron temperature investigation was also extended
to include free electron energy analysis to investigate the long-standing
problem of discrepancy between the results of recombination and forbidden lines
analysis and its possible connection to the electron distribution.
In the second section we present the results of our molecular investigation;
the generation of a comprehensive, calculated line list of frequencies and
transition probabilities for H2D+. The line list contains over 22 million
rotational-vibrational transitions occurring between more than 33 thousand
energy levels and covers frequencies up to 18500 cm-1. About 15% of these
levels are fully assigned with approximate rotational and vibrational quantum
numbers. A temperature-dependent partition function and cooling function are
presented. Temperature-dependent synthetic spectra for the temperatures T=100,
500, 1000 and 2000 K in the frequency range 0-10000 cm-1 were also generated
and presented graphically.
We illustrate the formation of a thin-long structure of heavy nuclei by three-nucleus simultaneous collisions within time-dependent density functional theory. The impact parameter dependence for such formation is systematically demonstrated through clarifications of the difference between binary and ternary collision events. A new method for producing thin-long heavy nuclei in the laboratory is suggested, as well as the possible formation of the thin-long structure in hot dense matter such as that encountered in core collapse supernovae.
If one is not ready to pay a large fine-tuning price within supersymmetric models given the current measurement of the Higgs boson mass, one can envisage a scenario where the supersymmetric spectrum is made of heavy scalar sparticles and much lighter fermionic superpartners. We offer a cosmological explanation of why nature might have chosen such a mass pattern: the opposite mass pattern is not observed experimentally because it is not compatible with the plausible idea that the universe went through a period of primordial inflation.
Cosmological perturbations are generally described by quantum fields on (curved but) classical space-times. While this strategy has a large domain of validity, it can not be justified in the quantum gravity era where curvature and matter densities are of Planck scale. Using techniques from loop quantum gravity, the standard theory of cosmological perturbations is extended to overcome this limitation. The new framework sharpens conceptual issues by distinguishing between the true and apparent trans-Planckian difficulties and provides sufficient conditions under which the true difficulties can be overcome within a quantum gravity theory. In a companion paper, this framework is applied to the standard inflationary model, with interesting implications to theory as well as observations.
Links to: arXiv, form interface, find, astro-ph, recent, 1211, contact, help (Access key information)
In order to determine what processes govern the assembly history of galaxies with rotating disks, we examine the stellar mass Tully-Fisher relation over a wide range in redshift partitioned according to whether or not galaxies contain a prominent bulge. Using our earlier Keck spectroscopic sample, for which bulge/total parameters are available from analyses of HST images, we find that bulgeless disk galaxies with z > 0.8 present a significant offset from the local Tully-Fisher relation whereas, at all redshifts probed, those with significant bulges fall along the local relation. Our results support the suggestion that bulge growth may somehow expedite the maturing of disk galaxies onto the Tully-Fisher relation. We discuss a variety of physical hypotheses that may explain this result in the context of kinematic observations of star-forming galaxies at redshifts z = 0 and z > 2.
An improved estimator for the amplitude fnl of local-type non-Gaussianity from the cosmic microwave background (CMB) bispectrum is discussed. The standard estimator is constructed to be optimal in the zero-signal (i.e., Gaussian) limit. When applied to CMB maps which have a detectable level of non-Gaussianity the standard estimator is no longer optimal, possibly limiting the sensitivity of future observations to a non-Gaussian signal. Previous studies have proposed an improved estimator by using a realization-dependent normalization. Under the approximations of a flat sky and a vanishingly thin last-scattering surface, these studies showed that the variance of this improved estimator can be significantly smaller than the variance of the standard estimator when applied to non-Gaussian CMB maps. Here this technique is generalized to the full sky and to include the full radiation transfer function, yielding expressions for the improved estimator that can be directly applied to CMB maps. The ability of this estimator to reduce the variance as compared to the standard estimator in the face of a significant non-Gaussian signal is re-assessed using the full CMB transfer function. As a result of the late time integrated Sachs-Wolfe effect, the performance of the improved estimator is degraded. If CMB maps are first cleaned of the late-time ISW effect using a tracer of foreground structure, such as a galaxy survey or a measurement of CMB weak lensing, the new estimator does remove a majority of the excess variance, allowing a higher significance detection of fnl.
The relation between galaxy stellar mass and gas-phase metallicity is a sensitive diagnostic of the main processes that drive galaxy evolution, namely cosmological gas inflow, metal production in stars, and gas outflow via galactic winds. We employed the direct method to measure the metallicities of ~200,000 star-forming galaxies from the SDSS that were stacked in bins of (1) stellar mass and (2) both stellar mass and star formation rate (SFR) to significantly enhance the signal-to-noise ratio of the weak [O III] 4363 and [O II] 7320, 7330 auroral lines required to apply the direct method. These metallicity measurements span three decades in stellar mass from log(Mstar/Msun) = 7.4--10.5, which allows the direct method mass--metallicity relation to simultaneously capture the high-mass turnover and extend a full decade lower in mass than previous studies that employed more uncertain strong line methods. The direct method mass-metallicity relation rises steeply at low mass (O/H ~ Mstar^{1/2}) until it turns over at log(Mstar/Msun) = 8.9 and asymptotes to 12 + log(O/H) = 8.8 at high mass. The direct method mass--metallicity relation has a steeper slope, a lower turnover mass, and a factor of two to three greater dependence on SFR than strong line mass--metallicity relations. Furthermore, the SFR-dependence appears monotonic with stellar mass, unlike strong line mass-metallicity relations. We also measure the N/O abundance ratio, an important tracer of star formation history, and find the clear signature of primary and secondary nitrogen enrichment. N/O correlates tightly with oxygen abundance, and even more so with stellar mass.
The Coma cluster is one of the nearest galaxy clusters, and the first one in which a radio halo and a peripheral relic were discovered. While its halo and the central parts of the intracluster medium have been studied extensively, X-ray observations of the plasma near its relic have been scarce. Here, we present results from a re-analysis of a 22-ks archival XMM-Newton observation. Across the relic, we detect a shock of Mach number about 2. This excludes the previously suggested hypothesis that the relic was formed by turbulence. Furthermore, multiwavelenth observations and numerical models do not support the scenario in which the shock at the Coma relic is an outgoing cluster-merger shock. Instead, our results lend support to the idea that the relic coincides with an infall shock front formed just as the NGC 4839 group falls onto the cluster along a cosmic filament.
Dynamical modeling and strong lensing data indicate that the total density profiles of early-type galaxies are close to isothermal, i.e., rho_tot ~ r^gamma with gamma approx -2. To understand the origin of this universal slope we study a set of simulated spheroids formed in isolated binary mergers with controlled initial conditions as well as the formation within the cosmological framework. On average, the total stellar plus dark matter density profiles can be described by a power law with an index of gamma approx -2.1 with a tendency towards steeper slopes for more compact, lower-mass ellipticals. In the binary mergers the amount of gas involved in the merger determines the steepness of the slope. This agrees with results from the cosmological simulations where ellipticals with steeper slopes have a higher fraction of stars formed in-situ. At higher redshifts, the slopes of the ellipticals extracted from the cosmological simulations are generally steeper. Each gas-poor merger event evolves the slope towards gamma ~ -2, once this slope is reached further merger events do not change the slope anymore. Independent of their individual slopes or evolution scenarios, all our ellipticals have flat intrinsic combined stellar and dark matter velocity dispersion profiles. We conclude that flat velocity dispersion profiles and total density distributions with a slope of gamma ~ -2 for the combined system of stars and dark matter act as a natural attractor. In addition, the variety of complex formation histories as present in cosmological simulations, including major as well as minor merger events, is essential to generate the full range of observed density slopes seen for present day elliptical galaxies.
Photoevaporating protoplanetary discs (proplyds) in the vicinity of hot massive stars, such as those found in Orion, are important objects of study for the fields of star formation, early disc evolution, planetary formation, and H II region astrophysics. Their element abundances are largely unknown, unlike those of the main-sequence stars or the host Orion nebula. We present a spectroscopic analysis of the Orion proplyd HST 10, based on integral field observations with the Very Large Telescope/FLAMES fibre array at a resolution of 0.31" x 0.31". The proplyd and its vicinity are imaged in a variety of emission lines across a 6.6" x 4.2" area. The reddening, electron density and temperature are mapped out from various line diagnostics. The abundances of helium, and eight heavy elements are measured relative to hydrogen using the direct method based on the [O III] electron temperature. The abundance ratios of O/H and S/H are derived without resort to ionization correction factors. We construct dynamic photoevaporation models of HST 10 with the Cloudy microphysics code that validate the oxygen and sulfur abundances. With the exception of [O I] 6300-A and [S II] 4069-A, the model fit is satisfactory for all spectral lines arising from the proplyd. The models show that the classic ionization correction factor for neon significantly underestimates (0.4 dex) this element's abundance in the low ionization conditions of HST 10. Apart from iron, whose gas-phase abundance is ~0.3 dex lower than in the local Orion nebula, most other elements in the proplyd do not show substantially different gas-phase abundances from the nebula. The abundances of carbon, oxygen and neon in HST 10 are practically the same as those in B-type stars in Orion.
Using stellar kinematics measurements, we investigate whether massive, quiescent galaxies were denser at z~2 than they are today. We present X-Shooter spectra from the UV to NIR and dynamical mass measurements of 5 quiescent massive (>10^11 Msun) galaxies at z~2. This triples the sample of z>1.5 galaxies with well constrained (delta sigma<100 km/s) velocity dispersion measurements. From spectral population synthesis modeling we find that these galaxies have stellar ages that range from 0.5-2 Gyr, with no sign of on-going star formation. We measure velocity dispersions (290-450 km/s) and find that they are 1.6-2.1 times higher than those of galaxies in the SDSS at fixed mass. Sizes are measured using GALFIT from HST-WFC3 H_160 and UDS K-band images. The dynamical masses correspond well to the SED-based stellar masses, with dynamical masses that are ~15% higher. We find that M_*/M_dyn may decrease slightly with time, which could reflect the increase of the dark matter fraction within an effective radius. We combine different stellar kinematic studies from the literature, and examine the structural evolution from z~2 to z~0: we confirm that at fixed dynamical mass, the effective radius increases by a factor of ~2.8, and the velocity dispersion decreases by a factor of ~1.7 with time. The mass density within one effective radius decreases by a factor of ~21, while within a fixed physical radius (1 kpc) it decreases only mildly (factor of ~2.3). When we allow for an evolving mass limit by selecting a population of galaxies at fixed number density, a stronger size growth with time is found (factor of ~4), velocity dispersion decreases by a factor of ~1.4, and interestingly, the mass density within 1 kpc is consistent with no evolution. This finding suggests that massive quiescent galaxies at z~2 grow in an inside-out matter, consistent with the expectations from minor mergers.
The cosmic dispersion in the abundances of the heavy elements strontium and barium in halo stars is well known. Strontium and barium are detected in most cool, metal-poor giants, but are these elements always detectable? To identify stars that could be considered probable candidates for lacking these elements, I examine the stellar abundance data available in the literature for 1148 field stars and 226 stars in dwarf galaxies, 776 of which have metallicities lower than [Fe/H]<-2.0. Strontium or barium have been detected in all field, globular cluster, and dwarf galaxy environments studied. All upper limits are consistent with the lowest detected ratios of [Sr/H] and [Ba/H]. The frequent appearance of these elements raises the intriguing prospect that at least one kind of neutron-capture reaction operates as often as the nucleosynthesis mechanisms that produce lighter elements, like magnesium, calcium, or iron, although the yields of heavy elements may be more variable.
The Crab pulsar has been widely studied across the electromagnetic spectrum from radio to gamma-ray energies. The exact nature of the emission processes taking place in the pulsar is a matter of broad debate. Above a few GeV the energy spectrum turns over suddenly. The shape of this cutoff can provide unique insight in to the particle acceleration processes taking place in the pulsar magnetosphere. Here we discuss the detection of pulsed gamma-rays from the Crab Pulsar above 100 GeV with the VERITAS telescopes in the context of measurements made with the Fermi space telescope below 10 GeV. Limits on the level of flux enhancement of emission correlated with giant radio pulses and dispersion due to Lorentz invariance violation effects will also be presented.
We present optical spectroscopy of projected QSO pairs to investigate the
MgII and the CIV absorption features imprinted on the spectrum of the
background object by the gaseous halo surrounding the foreground QSO. We
observed 13 projected pairs in the redshift range 0.7<z<2.2 spanning projected
separations between 60 kpc and 120 kpc. In the spectra of the background QSOs,
we identify MgII intervening absorption systems associated to the foreground
QSOs in 7 out of 10 pairs, and 1 absorption system out of 3 is found for CIV.
The distribution of the equivalent width as a function of the impact parameter
shows that, unlike the case of normal galaxies, some strong absorption systems
(EWr > 1 Ang) are present also beyond a projected radius of ~70 kpc. If we take
into account the mass of the galaxies as an additional parameter that influence
the extent of the gaseous haloes, the distribution of the absorptions connected
to the QSOs is consistent to that of galaxies. In the spectra of the foreground
QSOs we do not detect any MgII absorption lines originated by the gas
surrounding the QSO itself, but in 2 cases these features are present for CIV.
The comparison between the absorption features observed in the transverse
direction and those along the line of sight allows us to comment on the
distribution of the absorbing gas and on the emission properties of the QSOs.
Based on observations undertaken at the European Southern Observatory (ESO)
Very Large Telescope (VLT) under Programmes 085.B-0210(A) and 086.B-0028(A).
We report the discovery of a peculiar horizontal branch (HB) in NGC 6440 and NGC 6569, two massive and metal-rich Galactic globular clusters (GGCs) located in the Galactic bulge, within 4 kpc from the Galactic Center. In both clusters, two distinct clumps are detected at the level of the cluster HB, separated by only ~ 0.1 magnitudes in the Ks band. They were detected with IR photometric data collected with the "VISTA Variables in the Via Lactea" (VVV) Survey, and confirmed in independent IR catalogs available in the literature, and HST optical photometry. Our analysis demonstrates that these clumps are real cluster features, not a product of field contamination or interstellar reddening. The observed split HBs could be a signature of two stellar sub-populations with different chemical composition and/or age, as recently found in Terzan 5, but it cannot be excluded that they are caused by evolutionary effects, in particular for NGC 6440. This interpretation, however, requires an anomalously high helium content (Y > 0.30). Our discovery suggests that such a peculiar HB morphology could be a common feature of massive, metal-rich bulge GGCs.
NGC 1266 is a nearby field galaxy observed as part of the ATLAS3D survey (Cappellari et al. 2011). NGC 1266 has been shown to host a compact (< 200 pc) molecular disk and a mass-loaded molecular outflow driven by the AGN (Alatalo et al. 2011). Very Long Basline Array (VLBA) observations at 1.65 GHz revealed a compact (diameter < 1.2 pc), high bright- ness temperature continuum source most consistent with a low-level AGN origin. The VLBA continuum source is positioned at the center of the molecular disk and may be responsible for the expulsion of molecular gas in NGC 1266. Thus, the candidate AGN-driven molecular outflow in NGC 1266 supports the picture in which AGNs do play a significant role in the quenching of star formation and ultimately the evolution of the red sequence of galaxies.
We have discovered 12 new molecular hydrogen emission-line objects (MHOs) in the vicinity of the candidate massive young stellar object Mol 121, in addition to five that were previously known. H2 2.12-micron/H2 2.25-micron flux ratios indicate another region dominated by fluorescence from a photo-dissociation region (PDR), and one region that displays an anomalously low H2 2.12-micron/H2 2.25-micron flux ratio (<1) and coincides with a previously reported deeply embedded source (DES). Continuum observations at 3 mm reveal five dense cores; the brightest core is coincident with the DES. The next brightest cores are both associated with cm continuum emission. One of these is coincident with the IRAS source; the other lies at the centroid of a compact outflow defined by bipolar MHOs. The brighter of these bipolar MHOs exhibits [Fe II] emission and both MHOs are associated with CH3OH maser emission observed at 95 GHz and 44 GHz. Masses and column densities of all five cores are consistent with theoretical predictions for massive star formation. Although it is impossible to associate all MHOs with driving sources in this region, it is evident that there are several outflows along different position angles, and some unambiguous associations can be made. We discuss implications of observed H2 2.12-micron/H2 2.25-micron and [Fe II] 1.64-micron/H2 2.12-micron flux ratios and compare the estimated total H2 luminosity with the bolometric luminosity of the region. We conclude that the outflows are driven by massive young stellar objects embedded in cores that are likely to be in different evolutionary stages.
We detail the rich molecular story of NGC 1266, its serendipitous discovery within the ATLAS3D survey (Cappellari et al. 2011) and how it plays host to an AGN-driven molecular outflow, potentially quenching all of its star formation (SF) within the next 100 Myr. While major mergers appear to play a role in instigating outflows in other systems, deep imaging of NGC 1266 as well as stellar kinematic observations from SAURON, have failed to provide evidence that NGC 1266 has recently been involved in a major interaction. The molecular gas and the instantaneous SF tracers indicate that the current sites of star formation are located in a hypercompact disk within 200 pc of the nucleus (Fig. 1; SF rate ~ 2 Msuns/yr). On the other hand, tracers of recent star formation, such as the H{\beta} absorption map from SAURON and stellar population analysis show that the young stars are distributed throughout a larger area of the galaxy than current star formation. As the AGN at the center of NGC 1266 continues to drive cold gas out of the galaxy, we expect star formation rates to decline as the star formation is ultimately quenched. Thus, NGC 1266 is in the midst of a key portion of its evolution and continued studies of this unique galaxy may help improve our understanding of how galaxies transition from the blue to the red sequence (Alatalo et al. 2011).
We use the pulsational properties of the RR Lyrae variables in the globular cluster NGC 1851 to obtain detailed constraints of the various sub-stellar populations present along its horizontal branch. On the basis of detailed synthetic horizontal branch modeling, we find that minor helium variations (Y~0.248-0.280) are able to reproduce the observed periods and amplitudes of the RR Lyrae variables, as well as the frequency of fundamental and first-overtone RR Lyrae stars. Comparison of number ratios amongst the blue and red horizontal branch components and the two observed subgiant branches also suggest that the RR Lyrae variables originated from the progeny of the bright subgiant branch. The RR Lyrae variables with a slightly enhanced helium (Y~0.270-0.280) have longer periods at a given amplitude, as is seen with Oosterhoff II (OoII) RR Lyrae variables, whereas the RR Lyrae variables with Y~0.248-0.270 have shorter periods, exhibiting properties of Oosterhoff I (OoI) variables. This correlation does suggest that the pulsational properties of RR Lyrae stars can be very useful for tracing the various sub-populations and can provide suitable constraints on the multiple population phenomenon. It appears of great interest to explore whether this conclusion can be generalized to other globular clusters hosting multiple populations.
We report conclusive verification of the detection of associated HI 21cm absorption in the early-type host of the compact radio source PMN J2054-4242. We estimate an equivalent spectral-line width of 415 +/- 20 km/s, and observed peak optical depth of 2.5 +/- 0.2 per cent, making this one of the broadest and weakest 21cm absorption-lines yet discovered. For Tspin/f > 100K the column density is NHI > 2 x 10^{21} cm^{-2}. The observed spectral-line profile is redshifted by v = 179 +/- 46 km/s, with respect to the spectroscopic optical measurement, perhaps indicating that the HI gas is infalling toward the central active galactic nucleus. The broad width of the line suggests that the cold gas is either rotating at very high velocity, or that the infall is accelerating (perhaps as a blended series of line-of-sight gas clouds). Our initial tentative detection would likely have been dismissed by visual inspection, and hence its verification here is an excellent test of our spectral-line detection technique, currently under development in anticipation of future next-generation 21cm absorption-line surveys. We find that other such broad-line dominated detections in the literature are comparatively rare, presenting us with the following question: are these systems intrisically more scarce in nature, or are the existing data and analysis techniques not yet of sufficient quality to detect these low peak signal-to-noise systems?
We continue our study of the physical properties of the recurrent nova T Pyx, focussing on the structure of the ejecta in the nebular stage of expansion during the 2011 outburst. The nova was observed contemporaneously with the Nordic Optical Telescope (NOT), at high resolution spectroscopic resolution (R ~ 65000) on 2011 Oct. 11 and 2012 Apr. 8 (without absolute flux calibration), and with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope, at high resolution (R ~ 30000) on 2011 Oct. 10 and 2012 Mar. 28 (absolute fluxes). We use standard plasma diagnostics (e.g. [O III] and [N II] line ratios and the H$\beta$ line fluxes) to constrain electron densities and temperatures. Using Monte Carlo modeling of the ejecta, we derive the structure and filling factor from comparisons to the optical and ultraviolet line profiles. The ejecta can be modeled using an axisymmetric conical -- bipolar -- geometry with a low inclination of the axis to the line of sight, i=15+/-5 degrees, compatible with published results from high angular resolution optical spectro-interferometry. The structure is similar to that observed in the other short orbital period recurrent novae during their nebular stages. We show that the electron density scales as $t^{-3}$ as expected from a ballistically ejected constant mass shell; there is no need to invoke a continuing mass outflow following the eruption. The derived mass for the ejecta with filling factor f ~ 3%, M_ej ~ 2E-6$M_sun is similar to that obtained for other recurrent nova ejecta but inconsistent with the previously reported extended optically thick epoch of the explosion. We suggest that the system underwent a common envelope phase following the explosion that produced the recombination event. Implications for the dynamics of the recurrent novae are discussed. (truncated)
We consider a scalar-tensor model of dark energy with kinetic and Gauss Bonnet couplings. We study the conditions for the existence of quintessential and phantom power-law expansion, and also analyze these conditions in absence of potential (closely related to string theory). A mechanism to avoid the Big Rip singularity in various asymptotic limits of the model has been studied. It was found that the kinetic and Gauss-Bonnet couplings might prevent the Big Rip singularity in a phantom scenario. The autonomous system for the model has been used to study the stability properties of the power-law solution, and the centre manifold analysis was used to treat zero eigenvalues.
A novel concept is presented in this paper for a human mission to the lunar L2 (Lagrange) point that would be a proving ground for future exploration missions to deep space while also overseeing scientifically important investigations. In an L2 halo orbit above the lunar farside, the astronauts aboard the Orion Crew Vehicle would travel 15% farther from Earth than did the Apollo astronauts and spend almost three times longer in deep space. Such a mission would serve as a first step beyond low Earth orbit and prove out operational spaceflight capabilities such as life support, communication, high speed re-entry, and radiation protection prior to more difficult human exploration missions. On this proposed mission, the crew would teleoperate landers and rovers on the unexplored lunar farside, which would obtain samples from the geologically interesting farside and deploy a low radio frequency telescope. Sampling the South Pole-Aitken basin, one of the oldest impact basins in the solar system, is a key science objective of the 2011 Planetary Science Decadal Survey. Observations at low radio frequencies to track the effects of the Universe's first stars/galaxies on the intergalactic medium are a priority of the 2010 Astronomy and Astrophysics Decadal Survey. Such telerobotic oversight would also demonstrate capability for human and robotic cooperation on future, more complex deep space missions such as exploring Mars.
We present a set of 3-dimensional, radiation-magnetohydrodynamic calculations of the gravitational collapse of massive (300 Msun), star-forming molecular cloud cores. We show that the combined effects of magnetic fields and radiative feedback strongly suppress core fragmentation, leading to the production of single star systems rather than small clusters. We find that the two processes are efficient at suppressing fragmentation in different regimes, with the feedback most effective in the dense, central region and the magnetic field most effective in more diffuse, outer regions. Thus, the combination of the two is much more effective at suppressing fragmentation than either one considered in isolation. Our work suggests that typical massive cores, which have mass-to-flux ratios of about 2 relative to critical, likely form a single star system, but that cores with weaker fields may form a small star cluster. This result helps us understand why the observed relationship between the core mass function and the stellar initial mass function holds even for ~100 Msun cores with many thermal Jeans masses of material. We also demonstrate that a ~40 AU Keplerian disk is able to form in our simulations, despite the braking effect caused by the strong magnetic field.
We present a statistical survey of almost 10 000 radio Type III bursts observed by the Nancay Radioheliograph from 1998 to 2008, covering nearly a full solar cycle. In particular, sources sizes, positions, and fluxes were examined. We find an east-west asymmetry in source positions which could be attributed to a 6(+/-)1 degree eastward tilt of the magnetic field, that source FWHM sizes s roughly follow a solar-cycle averaged distribution dN/ds = 14 {\nu}^{-3.3} s^{-4} arcmin^{-1} day^{-1}, and that source fluxes closely follow a solar-cycle averaged dN/dS_{\nu} = 0.34 {\nu}^{-2.9} S_{\nu}^{-1.7} sfu^{-1} day^{-1} distribution (when {\nu} is in GHz, s in arcmin, and S_{\nu} in sfu). Fitting a barometric density profile yields a temperature of 0.6 MK, while a solar wind-like (\propto h^{-2}) density profile yields a density of 1.2x10^6 cm^{-3} at an altitude of 1 RS, assuming harmonic emission. Finally, we found that the solar-cycle averaged radiated Type III energy could be similar in magnitude to that radiated by nanoflares via non-thermal bremsstrahlung processes, and we hint at the possibility that escaping electron beams might carry as much energy away from the corona as is introduced into it by accelerated nanoflare electrons.
We report the detection of radio emission from the unusually active L5e + T7 binary 2MASS J13153094-2649513AB made with the Australian Telescope Compact Array. Observations at 5.5 GHz reveal an unresolved source with a continuum flux of 370+/-50 microJy, corresponding to a radio luminosity of L_rad = nuL_nu = (9+/-3)x10^23 erg/s and log10(L_rad/L_bol) = -5.44+/-0.22. No detection is made at 9.0 GHz to a 5 sigma limit of 290 microJy, consistent with a power law spectrum S_nu ~ nu^-a with a > 0.5. The emission is quiescent, with no evidence of variability or bursts over 3 hr of observation, and no measurable polarization (V/I < 34%). 2MASS J1315-2649AB is one of the most radio-luminous ultracool dwarfs detected in quiescent emission to date, comparable in strength to other cool sources detected in outburst. Its detection indicates no decline in radio flux through the mid-L dwarfs. It is unique among L dwarfs in having strong and persistent Halpha and radio emission, indicating the coexistence of a cool, neutral photosphere (low electron density) and a highly active chromosphere (high electron density and active heating). These traits, coupled with the system's mature age and substellar secondary, makes 2MASS J1315-2649AB an important test for proposed radio emission mechanisms in ultracool dwarfs.
I discuss a search for red giant stars in the Galactic halo with light-element abundances similar to second-generation globular cluster stars, and discuss the implications of such a population for globular cluster formation models and the balance between in situ star formation and accretion for the assembly of the Galactic halo.
The research about asteroids attracts more and more attention recently, especially focusing on their physical structures, such as the spin axis, the rotation period and the shape. The long distance between Earth observers and asteroids makes it impossible to get the shape and other parameters of asteroids directly with the exception of the NEAs (Near Earth Asteroids) and others passed by some spacecrafts. Generally photometric measurement is still the main way to obtain the research data for asteroids now, i.e. the lightcurves recording the brightness and positions of asteroids. Supposing that the shape of the asteroid is a triaxial ellipsoid with a stable spinning status, a new method is present in this article to reconstruct the shape models of asteroids from the lightcurves, with the other physical parameters together. By applying a special curvature function, the method calculates the brightness integration on a unit sphere and Lebedev Quadrature is employed for the discretization. At last the method searches the optimal solution by Levenberg-Marquardt algorithm to minimize the residual of the brightness. By adopting this method not only related physical parameters of asteroids can be obtained at a reasonable accuracy, but also a simple shape model of Ellipsoid can be generated for reconstructing more sophisticated shape model further.
We present our monitoring campaign of the outburst of the black-hole candidate Swift J1753.5-0127, observed with the Rossi X-ray Timing Explorer and the Swift satellites. After ~4.5 years since its discovery, the source had a transition to the hard intermediate state. We performed spectral and timing studies of the transition showing that, unlike the majority of the transient black holes, the system did not go to the soft states but it returned to the hard state after a few months. During this transition Swift J1753.5-0127 features properties which are similar to those displayed by the black hole Cygnus X-1. We compared Swift J1753.5-0127 to one dynamically confirmed black hole and two neutron stars showing that its power spectra are in agreement with the binary hosting a black hole. We also suggest that the prolonged period at low flux that followed the initial flare is reminiscent of that observed in other X-ray binaries, as well as in cataclysmic variables.
The BVRcIc CCD photometry in the fields of six open clusters toward the Perseus spiral arm is presented. These data along with JHKs magnitudes taken from 2MASS catalog, have been used to determine cluster's ages, distances and color excesses. In addition, the gaps in mass function of Be 97, King 12 and NGC 7788 clusters have been revealed in mass intervals of 1.3-1.5, 1.4-1.6 and 1.5-1.7 solar masses, respectively.
We revised the treatment of interstellar dust in the KOSMA-\tau\ PDR model code to achieve a consistent description of the dust-related physics in the code. The detailed knowledge of the dust properties is then used to compute the dust continuum emission together with the line emission of chemical species. We coupled the KOSMA-\tau\ PDR code with the MCDRT (multi component dust radiative transfer) code to solve the frequency-dependent radiative transfer equations and the thermal balance equation in a dusty clump under the assumption of spherical symmetry, assuming thermal equilibrium in calculating the dust temperatures, neglecting non-equilibrium effects. We updated the calculation of the photoelectric heating and extended the parametrization range for the photoelectric heating toward high densities and UV fields. We revised the computation of the H2 formation on grain surfaces to include the Eley-Rideal effect, thus allowing for high-temperature H2 formation. We demonstrate how the different optical properties, temperatures, and heating and cooling capabilities of the grains influence the physical and chemical structure of a model cloud. The most influential modification is the treatment of H2 formation on grain surfaces that allows for chemisorption. This increases the total H2 formation significantly and the connected H2 formation heating provides a profound heating contribution in the outer layers of the model clumps. The contribution of PAH surfaces to the photoelectric heating and H2 formation provides a boost to the temperature of outer cloud layers, which is clearly traced by high-J CO lines. Increasing the fraction of small grains in the dust size distribution results in hotter gas in the outer cloud layers caused by more efficient heating and cooler cloud centers, which is in turn caused by the more efficient FUV extinction.
Most studies of high-mass star formation focus on massive luminous clumps, but the physical properties of their larger scale environment are poorly known. In this work, we aim at characterising the effects of clustered star formation and feedback of massive stars on the surrounding medium by studying the distribution of warm gas through mid-J 12CO and 13CO data. We present APEX 12CO(6-5), (7-6), 13CO(6-5), (8-7) and HIFI 13CO(10-9) maps of the star forming region G327.36-0.6. We infer the physical properties of the emitting gas on large scales through a LTE analysis, while we apply a more sophisticated LVG approach on selected positions. Maps of all lines are dominated in intensity by the PDR around the Hii region G327.3-0.5. Mid-J 12CO emission is detected over the whole extent of the maps with excitation temperatures ranging from 20K up to 80K in the gas around the Hii region, and H2 column densities from few 10^21 cm-2 in the inter-clump gas to 3 10^22 cm-2 towards the hot core G327.3-0.6. The warm gas (traced by 12 and 13CO(6-5) emission) is only a small percentage (10%) of the total gas in the IRDC, while it reaches values up to 35% of the total gas in the ring surrounding the Hii region. The 12CO ladders are qualitatively compatible with PDR models for high density gas, but the much weaker than predicted 13CO emission suggests that it comes from a large number of clumps along the line of sight. All lines are detected in the inter-clump gas when averaged over a large region with an equivalent radius of 50" (~0.8pc), implying that the mid-J 12CO and 13CO inter-clump emission is due to high density components with low filling factor. Finally, the detection of the 13CO(10-9) line allows to disentangle the effects of gas temperature and gas density on the CO emission, which are degenerate in the APEX observations alone.
We present a general method for accelerating by more than an order of magnitude the convolution of pixelated function on the sphere with a radially-symmetric kernel. Our method splits the kernel into a compact real-space, and a compact spherical harmonic space component that can then be convolved in parallel using an inexpensive commodity GPU and a CPU, respectively. We provide models for the computational cost of both real-space and Fourier space convolutions and an estimate for the approximation error. Using these models we can determine the optimum split that minimizes the wall clock time for the convolution while satisfying the desired error bounds. We apply this technique to the problem of simulating a cosmic microwave background sky map at the resolution typical of the high resolution maps of the cosmic microwave background anisotropies produced by the Planck space craft. For the main Planck CMB science channels we achieve a speedup of over a factor of ten, assuming an acceptable fractional rms error of order 10^-5 in the (power spectrum of the) output map.
We upgraded the chemical network from the UMIST Database for Astrochemistry 2006 to include isotopes such as ^{13}C and ^{18}O. This includes all corresponding isotopologues, their chemical reactions and the properly scaled reaction rate coefficients. We study the fractionation behavior of astrochemically relevant species over a wide range of model parameters, relevant for modelling of photo-dissociation regions (PDRs). We separately analyze the fractionation of the local abundances, fractionation of the total column densities, and fractionation visible in the emission line ratios. We find that strong C^+ fractionation is possible in cool C^+ gas. Optical thickness as well as excitation effects produce intensity ratios between 40 and 400. The fractionation of CO in PDRs is significantly different from the diffuse interstellar medium. PDR model results never show a fractionation ratio of the CO column density larger than the elemental ratio. Isotope-selective photo-dissociation is always dominated by the isotope-selective chemistry in dense PDR gas. The fractionation of C, CH, CH^+, and HCO^+ is studied in detail, showing that the fractionation of C, CH and CH^+ is dominated by the fractionation of their parental species. The light hydrides chemically derive from C^+, and, consequently, their fractionation state is coupled to that of C^+. The fractionation of C is a mixed case depending on whether formation from CO or HCO^+ dominates. Ratios of the emission lines of [C II], [C I], ^{13}CO, and H^{13}CO^+ provide individual diagnostics to the fractionation status of C^+, C, and CO.
One of the important unknowns of current cosmology concerns the effects of the large scale distribution of matter on the formation and evolution of dark matter haloes and galaxies. One main difficulty in answering this question lies in the absence of a robust and natural way of identifying the large scale environments and their characteristics. This work summarizes the NEXUS+ formalism which extends and improves our multiscale scale-space MMF method. The new algorithm is very successful in tracing the Cosmic Web components, mainly due to its novel filtering of the density in logarithmic space. The method, due to its multiscale and hierarchical character, has the advantage of detecting all the cosmic structures, either prominent or tenuous, without preference for a certain size or shape. The resulting filamentary and wall networks can easily be characterized by their direction, thickness, mass density and density profile. These additional environmental properties allows to us to investigate not only the effect of environment on haloes, but also how it correlates with the environment characteristics.
We present a method for the production of segmented optics. It is a novel processing developed at INAF-Osservatorio Astronomico di Brera (INAF-OAB) employing commercial of-the-shelf materials. It is based on the shaping of thin glass foils by means of forced bending, this occurring at room temperature (cold-shaping). The glass is then assembled into a sandwich structure for retaining the imposed shape. The principal mechanical features of the mirrors are the very low weight, rigidity and environmental robustness. The cost and production time also turns to be very competitive. In this paper we sum up the results achieved during the r&d performed in the past years. We have investigated the theoretical limits of the structural components by means of parametric finite elements analyses; we also discuss the effects caused by the most common structural loads. Finally, the process implementation, the more significant validation tests and the mass production at the industry is described.
Using photometric and spectroscopic observations of the double-lined
early-type eclipsing binary system ALS 1135, a member of the distant OB
association Bochum 7, we derived the new physical and orbital parameters of its
components. The masses of both components were derived with an accuracy better
than 1 per cent, their radii, with an accuracy better than 3 per cent. Since
the primary's mass is equal to about 25 sun masses, its radius was subsequently
used to derive the age of the system which is equal to 4.3+/-0.5 Myr. The
result shows that this method represents a viable alternative to isochrone
fitting.
A photometric search of the field of ALS 1135 resulted in the discovery of 17
variable stars, including seven pulsating ones. One of them is an SPB star
belonging to Vel OB1, the other six are delta Scuti stars. Of the six delta
Scuti stars three might belong to Vel OB1, the other two are likely members of
Bochum 7. Given the age of Bochum 7, these two stars are probably pre-main
sequence pulsators. In addition, we provide UBVI_C photometry for about 600
stars in the observed field.
The Mass loss of Evolved StarS (MESS) sample offers a selection of 78 Asymptotic Giant Branch (AGB) stars and Red Supergiants (RSGs) observed with the PACS photometer on-board Herschel at 70 and 160 {\mu}m. For most of these objects, the dusty AGB wind differs from spherical symmetry and the wind shape can be subdivided into four classes. In the present paper we concentrate on the influence of a companion on the morphology of the stellar wind. Literature was searched to find binaries in the MESS sample and these are subsequently linked to their wind-morphology class to assert that the binaries are not distributed equally among the classes. In the second part of the paper we concentrate on the circumstellar environment of the two prominent objects R Aqr and W Aql. Each shows a characteristic signature of a companion interaction with the stellar wind. For the symbiotic star R Aqr, PACS revealed two perfectly opposing arms which in part reflect the previously observed ring-shaped nebula in the optical. However, from the far-IR there is evidence that the emitting region is elliptical rather than circular. The outline of the wind of W Aql seems to follow a large Archimedean spiral formed by the orbit of the companion but also shows strong indications of an interaction with the interstellar medium. The nature of the companion of W Aql was investigated and the magnitude of the orbital period supports the size of the spiral outline.
We describe regularized methods for image reconstruction and focus on the question of hyperparameter and instrument parameter estimation, i.e. unsupervised and myopic problems. We developed a Bayesian framework that is based on the \post density for all unknown quantities, given the observations. This density is explored by a Markov Chain Monte-Carlo sampling technique based on a Gibbs loop and including a Metropolis-Hastings step. The numerical evaluation relies on the SPIRE instrument of the Herschel observatory. Using simulated and real observations, we show that the hyperparameters and instrument parameters are correctly estimated, which opens up many perspectives for imaging in astrophysics.
We performed multifrequency multiepoch Very Long Baseline Array (VLBA) observations of the blazar CTA 102 during its 2006 radio flare, the strongest ever reported for this source. These observations provide an excellent opportunity to investigate the evolution of the physical properties of blazars, especially during these flaring events. We want to study the kinematic changes in the source during the strong radio outburst in April 2006 and test the assumption of a shock-shock interaction. This assumption is based on the analysis and modeling of the single-dish observations of CTA\,102 (Paper I). In this paper we study the kinematics of CTA 102 at several frequencies using VLBI observations. From the modeled jet features we derived estimates for the evolution of the physical parameters, such as the particle density and the magnetic field. Furthermore, we combined our observations during the 2006 flare with long-term VLBA monitoring of the source at 15 GHz and 43 GHz. We cross-identified seven features throughout our entire multifrequency observations and find evidence of two possible recollimation shocks around 0.1 mas (deprojected 18 pc at a viewing angle of 2.6 degrees) and 6.0 mas (deprojected 1 kpc) from the core. The 43 GHz observations reveal a feature ejected at epoch $t_\mathrm{ej}=2005.9\pm0.2$, which could be connected to the 2006 April radio flare. Furthermore, this feature might be associated with the traveling component involved in the possible shock-shock interaction, which gives rise to the observed double peak structure in the single-dish light curves reported in Paper I.
There are many occasions when one does not have complete information in order to classify objects into different classes, and yet it is important to do the best one can since other decisions depend on that. In astronomy, especially time-domain astronomy, this situation is common when a transient is detected and one wishes to determine what it is in order to decide if one must follow it. We propose to use the Difference Boosting Neural Network (DBNN) which can boost differences between feature vectors of different objects in order to differentiate between them. We apply it to the publicly available data of the Catalina Real-Time Transient Survey (CRTS) and present preliminary results. We also describe another use with a stellar spectral library to identify spectra based on a few features. The technique itself is more general and can be applied to a varied class of problems.
Context. Supernova Remnants (SNRs) are thought to be the primary candidates for the sources of Galactic cosmic rays. According to Diffusive Shock Acceleration theory, SNR shocks produce a power-law spectrum with index s = 2, perhaps non-linearly modified to harder spectra at high energy. Observations of SNRs often indicate particle spectra that are softer than that and show features not expected from classical theory. Known drawbacks of the standard approach are the assumption that SNRs evolve in a uniform environment, and that the reverse shock does not accelerate particles. Relaxing those assumptions increases the complexity of the problem, because one needs reliable hydrodynamical data for the plasma flow as well as good estimates for the magnetic field at the reverse shock. Aims. We show that these two factors are especially important when modeling young core-collapse SNRs that evolve in a complicated circumstellar medium shaped by the winds of progenitor stars. Methods. We use high-resolution numerical simulations for the hydrodynamical evolution of the SNR. Instead of parametrizations of the magnetic-field profiles inside the SNR, we follow the advection of frozen-in magnetic field inside the SNR, and thus obtain the B-field value at all locations, in particular at the reverse shock. To model cosmic-ray acceleration we solve the cosmic-ray transport equation in test-particle approximation. Results. We find that the complex plasma-flow profiles of core-collapse SNRs significantly modify the particle spectra. Additionally, the reverse shock strongly affects the emission spectra and the surface brightness.
NGC 4921 and 7049 are two spiral galaxies presenting narrow, distinct dust features. A detailed study of the morphology of those features has been carried out using Hubble Space Telescope archival images. NGC 4921 shows a few but well-defined dust arms midway to its centre while NGC 7049 displays many more dusty features, mainly collected within a ring-shaped formation. Numerous dark and filamentary structures, called outgrowths, are found to protrude from the dusty arms in both galaxies. The outgrowths point both outwards and inwards in the galaxies. Mostly they are found to be V-shaped or Y-shaped with the branches connected to dark arm filaments. Often the stem of the Y appears to consist of intertwined filaments. Remarkably, the outgrowths show considerable similarities to elephant trunks in H II regions. A model of the outgrowths, based on magnetized filaments, is proposed. The model provides explanations of both the shapes and orientations of the outgrowths. Most important, it can also give an account for their intertwined structures. It is found that the longest outgrowths are confusingly similar to dusty spiral arms. This suggests that some of the outgrowths can develop into such arms. The time-scale of the development is estimated to be on the order of the rotation period of the arms or shorter. Similar processes may also take place in other spiral galaxies. If so, the model of the outgrowths can offer a new approach to the old winding problem of spiral arms.
We investigate the dependence of the He/H8 emission ratio on kinetic temperature and total Balmer brightness. The line pair He\,{\sc i}\,3888\,\AA{} and H$_8$\,3889 has been observed simultaneously with the Ca II 8498 line in a number of quiescent prominences. The He/H8 emission ratio R is found to cover defined parts of a general anti-relation with the total H8 emission, depending on the kinetic temperature, T_kin, of the individual prominence: High H8 brightness is related to small R and T_kin values, and preferably occurs in prominences with a less significant fine-structure.
The non-thermal particle spectra responsible for the emission from many astrophysical systems are thought to originate from shocks via a first order Fermi process otherwise known as diffusive shock acceleration. The same mechanism is also widely believed to be responsible for the production of high energy cosmic rays. With the growing interest in collisionless shock physics in laser produced plasmas, the possibility of reproducing and detecting shock acceleration in controlled laboratory experiments should be considered. The various experimental constraints that must be satisfied are reviewed. It is demonstrated that several currently operating laser facilities may fulfil the necessary criteria to confirm the occurrence of diffusive shock acceleration of electrons at laser produced shocks. Successful reproduction of Fermi acceleration in the laboratory could open a range of possibilities, providing insight into the complex plasma processes that occur near astrophysical sources of cosmic rays.
We present the analysis of the multicolour CCD observations in the 2010 season of the Blazhko RRc star TV Boo. TV Boo shows a complex Blazhko modulation dominated by two independent modulations with P_{fm1}=9.74 d and P_{fm2}=21.43 d long periods. Both modulation components appear in the frequency spectra as multiplet structures around the harmonics of the pulsation. The positive value of the asymmetry parameter (Q=+0.51) of the primary modulation suggests that it is similar in its character to the Blazhko effect of most of the modulated RRab stars. Interestingly, the secondary, lower-amplitude modulation exhibits a negative asymmetry parameter (Q=-0.22), which is an unusually low value when compared to the Blazhko-modulated RRab stars. Apart from the two modulation frequencies, the spectra also show an additional frequency f' and its linear combinations with the pulsation and the primary modulation f_{1}+f' and f_{1}-f'-f_{m1}. We conclude that the additional frequency most probably belongs to a non-radial mode.
We observe simultaneously the Ca II K, Ca II 8542 and H-beta emissions in solar prominences at high spatial and spectral resolution. We confirm a branching in the emission relations of Ca II and H-beta, which correlates with the non-thermal line broadening.
Accreting black holes (BHs) produce intense radiation and powerful relativistic jets, which are affected by the BH's spin magnitude and direction. While thin disks might align with the BH spin axis via the Bardeen-Petterson effect, this does not apply to jet systems with thick disks. We used fully three-dimensional general relativistic magnetohydrodynamical simulations to study accreting BHs with various BH spin vectors and disk thicknesses with magnetic flux reaching saturation. Our simulations reveal a "magneto-spin alignment" mechanism that causes magnetized disks and jets to align with the BH spin near BHs and further away to reorient with the outer disk. This mechanism has implications for the evolution of BH mass and spin, BH feedback on host galaxies, and resolved BH images for SgrA* and M87.
Following previous investigations by Giordano and Mancuso [1] and Mancuso and Giordano [2, 3] on the differential rotation of the solar corona as obtained through the analysis of the intensity time series of the O VI 1032 Ang. spectral line observed by the UVCS/SOHO telescope during solar cycle 23, we analysed the possible influence of projection effects of extended coronal structures on the observed differential rotation rate in the ultraviolet corona. Through a simple geometrical model, we found that, especially at higher latitudes, the differential rotation may be less rigid than observed, since features at higher latitudes could be actually linked to much lower coronal structures due to projection effects. At solar maximum, the latitudinal rigidity of the UV corona, with respect to the differential rotating photosphere, has thus to be considered as an upper limit of the possible rigidity. At solar minimum and near the equatorial region throughout the solar cycle, projection effects are negligible.
We present in this article the use of probabilistic background constraints in astronomical image deconvolution to approach to a solution as an interval estimate. We elaborate our objective -- the interval estimate of the unknown object from observed data and our approach -- monte-carlo experiment and analysis of marginal distributions of image values. One-dimensional observation and deconvolution using proposed approach are simulated. Confidence intervals reveal the uncertainties due to the background constraint are calculated and significance levels for sources retrieved from restored images are provided.
We present a candidate for the most distant galaxy known to date with a photometric redshift z = 10.7 +0.6 / -0.4 (95% confidence limits; with z < 9.5 galaxies of known types ruled out at 7.2-sigma). This J-dropout Lyman Break Galaxy, named MACS0647-JD, was discovered as part of the Cluster Lensing and Supernova survey with Hubble (CLASH). We observe three magnified images of this galaxy due to strong gravitational lensing by the galaxy cluster MACSJ0647.7+7015 at z = 0.591. The images are magnified by factors of ~8, 7, and 2, with the brighter two observed at ~26th magnitude AB (~0.15 uJy) in the WFC3/IR F160W filter (~1.4 - 1.7 um) where they are detected at >~ 12-sigma. All three images are also confidently detected at >~ 6-sigma in F140W (~1.2 - 1.6 um), dropping out of detection from 15 lower wavelength HST filters (~0.2 - 1.4 um), and lacking bright detections in Spitzer/IRAC 3.6um and 4.5um imaging (~3.2 - 5.0 um). We rule out a broad range of possible lower redshift interlopers, including some previously published as high redshift candidates. Our high redshift conclusion is more conservative than if we had neglected a Bayesian photometric redshift prior. Given CLASH observations of 17 high mass clusters to date, our discoveries of MACS0647-JD at z ~ 10.8 and MACS1149-JD1 at z ~ 9.6 are consistent with a lensed luminosity function extrapolated from lower redshifts. This would suggest that low luminosity galaxies could have reionized the universe. However given the significant uncertainties based on only two galaxies, we cannot yet rule out the sharp drop off in number counts at z >~ 10 suggested by field searches.
The caustic technique measures the mass of galaxy clusters in both their virial and infall regions and, as a byproduct, yields the list of cluster galaxy members. Here we use 100 galaxy clusters with mass M200>=1E14 Msun/h extracted from a cosmological N-body simulation of a LambdaCDM universe to test the ability of the caustic technique to identify the cluster galaxy members. We identify the true three-dimensional members as the gravitationally bound galaxies. The caustic technique uses the caustic location in the redshift diagram to separate the cluster members from the interlopers. We apply the technique to mock catalogues containing 1000 galaxies in the field of view of 12 Mpc/h on a side at the cluster location. On average, this sample size roughly corresponds to 180 real galaxy members within 3r200, similar to recent redshift surveys of cluster regions. The caustic technique yields a completeness, the fraction of identified true members, fc=0.95 (+- 0.03) within 3r200. The contamination increases from fi=0.020 (+0.046;-0.015) at r200 to fi=0.08 (+0.11;-0.05) at 3r200. No other technique for the identification of the members of a galaxy cluster provides such large completeness and small contamination at these large radii. The caustic technique assumes spherical symmetry and the asphericity of the cluster is responsible for most of the spread of the completeness and the contamination. By applying the technique to an approximately spherical system obtained by stacking the individual clusters, the spreads decrease by at least a factor of two. We finally estimate the cluster mass within 3r200 after removing the interlopers: for individual clusters, the mass estimated with the virial theorem is unbiased and within 30 per cent of the actual mass; this spread decreases to less than 10 per cent for the spherically symmetric stacked cluster.
In this work we set observational constraints of the Superfluid Chaplygin gas model, which gives a unified description of the dark sector of the Universe as a Bose-Einstein condensate (BEC) that behaves as dark energy (DE) while it is in the ground state and as dark matter (DM) when it is in the excited state. We first show and perform the various steps leading to a form of the equations suitable for the observational tests to be carried out. Then, by using a Markov Chain Monte Carlo (MCMC) code, we constrain the model with a sample of cosmology-independent long gamma-ray bursts (LGRBs) calibrated using their Type I Fundamental Plane, as well as the Union2.1 set and observational Hubble parameter data. In this analysis, using our cosmological constraints, we sketch the effective equation of state parameter and deceleration parameter, and we also obtain the redshift of the transition from deceleration to acceleration: $z_t$.
The future Cherenkov Telescope Array (CTA) will consist of several tens of telescopes of different mirror sizes. CTA will provide next generation sensitivity to very high energy photons from few tens of GeV to >100 TeV. Several focal plane instrumentation options are currently being evaluated inside the CTA consortium. In this paper, the current status of the FlashCam prototyping project is described. FlashCam is based on a fully digital camera readout concept and features a clean separation between photon detector plane and signal digitization/triggering electronics.
Since its launch on 22 September 2006, the EUV Imaging Spectrometer onboard the Hinode satellite has exhibited a gradual decay in sensitivity. Using spectroheliograms taken in the Fe VIII 185.21 Angstrom and Si VII 275.35 Angstrom emission lines in quiet regions near Sun center we characterize that decay. For the period from December 2006 to March 2012, the decline in the sensitivity can be characterized as an exponential decay with an average time constant of 7358 +/- 1030 days (20.2 +/- 2.8 years). Emission lines formed at temperatures >10^6.1 K in the quiet-Sun data exhibit solar-cycle effects.
The Kepler satellite has discovered a number of transiting planets around close binary stars. These circumbinary systems have highly aligned planetary and binary orbits. In this paper, we explore how the mutual inclination between the planetary and binary orbits may reflect the physical conditions of the assembly of protoplanetary disks and the interaction between protostellar binaries and circumbinary disks. Given the turbulent nature of star-forming molecular clouds, it is possible that the gas falling onto the outer region of a circumbinary disk and the central protostellar binary have different axes of rotation. Thus, the newly assembled circumbinary disk can be misaligned with respect to the binary. However, the gravitational torque from the binary produces a warp and twist in the disk, and the back-reaction torque tends to align the disk and the binary orbital plane. We present a new, analytic calculation of this alignment torque, and show that the binary-disk inclination angle can be reduced appreciably after the binary accretes a few percent of its mass from the disk. Our calculation suggests that in the absence of other disturbances, circumbinary disks and planets around close (sub-AU) stellar binaries, for which mass accretion onto the proto-binary is very likely to have occurred, are expected to be highly aligned with the binary orbits, while disks and planets around wide binaries can be misaligned.
The 2nd Fermi-LAT pulsar catalog includes 117 gamma-ray pulsars, of which roughly one third are millisecond pulsars (MSPs) while the remaining two thirds split evenly into young radio-loud and radio-quiet pulsars. Although this large population will enable future, detailed studies of emission mechanisms and the evolution of the underlying neutron star population, some nearly-universal properties are already clear and unequivocal. We discuss some of these aspects below, including the altitude of the gamma-ray emission site and the shape of the gamma-ray spectrum and its implications for the radiation mechanism.
After introduction we focus on: the transport of charged particles, the acceleration of ions at shocks, and the acceleration of electrons at shocks. Chapter 2 studies the propagation of solar energetic particles(SEPs) in turbulent magnetic fields. Particle trajectories in turbulent magnetic fields are numerically integrated. The turbulence includes a Kolmogorov-like power spectrum containing a broad range of scales. Small-scale variations in particle intensities(dropouts) and velocity dispersions can be reproduced. The result gives a constraint on the error of onset analysis for inferring SEP informations. We find that dropouts are rarely produced using the two-component model(Matthaeus et al., 1990). The result questions the turbulence model. Chapter 3 studies the acceleration of ions. We use 3-D hybrid simulations to study the acceleration of low-energy particles at parallel shocks. We find that particles gain energy by reflection at the shock. The protons can move off field lines in 3-D electric and magnetic fields. We also use a stochastic integration method to study diffusive shock acceleration including large-scale magnetic variations. The results can explain the observations of anomalous cosmic rays by Voyager 1. Chapter 4 studies electron acceleration at a shock in a turbulent magnetic field by combining hybrid simulations and test-particle simulations. The acceleration is enhanced by including large-scale turbulence. Since electrons mainly follow field lines, the field-line braiding allows electrons interacting with shock many times. Ripples also contribute to acceleration by mirroring electrons. The process favors perpendicular shocks. We discuss the implication to SEPs by comparing the acceleration of electrons with that of protons. The intensity correlation of electrons and ions in SEPs implies perpendicular shocks play important roles in accelerating particles.
In this letter we discuss de Sitter vacua in maximal gauged supergravity in 4 dimensions. We show that, using the newly deformed theories introduced in arxiv:hep-th/12090760, we can obtain de Sitter vacua with arbitrarily flat tachyonic directions in the SO(4,4)c models.
When electric-type flux threads compact extra dimensions, a quantum nucleation event can break a flux line and initiate a cascade that unwinds many units of flux. Here, we present a novel mechanism for inflation based on this phenomenon. From the 4D point of view, the cascade begins with the formation of a bubble containing an open Friedmann-Robertson-Walker cosmology, but the vacuum energy inside the bubble is initially only slightly reduced, and subsequently decreases gradually throughout the cascade. If the initial flux number Q_0 ~ O(100), during the cascade the universe can undergo N ~ 60 efolds of inflationary expansion with gradually decreasing Hubble constant, producing a nearly scale-invariant spectrum of adiabatic density perturbations with amplitude and tilt consistent with observation, and a potentially observable level of non-Gaussianity and tensor modes. The power spectrum has a small oscillatory component that does not decay away during inflation, with a period set approximately by the light-crossing time of the compact dimension(s). Since the ingredients are fluxes threading compact dimensions, this mechanism fits naturally into the string landscape, but does not appear to suffer from the eta problem or require fine-tuning (beyond the usual anthropic requirement of small vacuum energy after reheating).
In some models dark energy is described by phantom scalar fields (scalar fields with "wrong" sign of the kinetic term in the lagrangian). In the current paper we study the effect of phantom scalar field and/or phantom electromagnetic field on gravitational lensing by black holes in the strong deflection regime. The black-hole solutions that we have studied have been obtained in the frame of the Einstein-(anti-)Maxwell-(anti-)dilaton theory. The obtained results show considerable effect of the phantom scalar and electromagnetic fields on the angular position, brightness and separation of the relativistic images.
We discuss the SUSY dark matter phenomenology in some simple and predictive models of nonuniversal gaugino masses at the GUT scale. Assuming the gaugino masses to transform as a sum of singlet and a nonsinglet representation of the GUT group SU(5), one can evade the LEP constraints to access the bulk annihilation region of the bino dark matter relic density. Besides, with this assumption one can also have a mixed gaugino-higgsino dark matter, giving the right relic density over large parts of the parameter space. We consider the model predictions for LHC and dark matter experiments in both the cases. Finally we consider the AMSB model prediction of wino dark matter giving the right relic density for TeV scale wino mass. Assuming this wino dark matter mass to be at the first Sommerfeld resonance of about 4 TeV one can simultaneously reproduce the right relic density as well as the hard positron spectrum observed by the PAMELA experiment.
Modified Chaplygin gas as an exotic fluid has been introduced in [34]. Essential features of the modified Chaplygin gas as a cosmological model are discussed. Observational constraints on the parameters of the model have been included. The relationship between the modified Chaplygin gas and a homogeneous minimally coupled scalar field are reevaluated by constructing its self-interacting potential. In addition, we study the role of the tachyonic field in the modified Chaplygin gas cosmological model and the mapping between scalar field and tachyonic field is also considered.
We propose a curvaton model in which the initial condition of the curvaton oscillation is determined by its attractor behavior during inflation. Assuming a chaotic inflation model, we find that the initial condition determined by the attractor behavior is appropriate to generate a sizable non-Gaussianity contribution to the curvature perturbation, which will be tested in the foreseeable future. Implications on the thermal history of the universe and on particle physics models are also discussed.
We use direct numerical simulations to compute turbulent transport coefficients for passive scalars in turbulent rotating flows. Effective diffusion coefficients in the directions parallel and perpendicular to the rotations axis are obtained by studying the diffusion of an imposed initial profile for the passive scalar, and calculated by measuring the scalar average concentration and average spatial flux as a function of time. The Rossby and Schmidt numbers are varied to quantify their effect on the effective diffusion. It is find that rotation reduces scalar diffusivity in the perpendicular direction. The perpendicular diffusion can be estimated from mixing length arguments using the characteristic velocities and lengths perpendicular to the rotation axis. Deviations are observed for small Schmidt numbers, for which turbulent transport decreases and molecular diffusion becomes more significant.
In this paper we investigate a steady accretion within the Einstein-Straus vacuole, in the presence of the cosmological constant. The dark energy damps the mass accretion rate and --- above certain limit --- completely stops the steady accretion onto black holes, which in particular is prohibited in the inflation era and after (roughly) $10^{12}$ years from Big Bang (assuming the presently known value of the cosmological constant). Steady accretion would not exist in the late phases of the Penrose's scenario - known as the Weyl curvature hypothesis - of the evolution of the Universe.
D\'ungal's letter to Charlemagne on the double solar eclipse in the year 810 is extremely interesting both for its form and for its subject matter. Part I of the present study deals with the epistula as a literary work (genre, language, sources), dealing in turn with vocabulary, morphology and syntax, rythmical prose and rhetorical figures, literary and Biblical references. If we compare it with D\'ungal's other works, the letter is cast in the canonical oratio structure similar to his later Responsa contra Claudium (ed. Zanna, Firenze 2002) and it is likewise based on lengthy quotations drawns from Macrobius' commentary In Somnium Scipionis. A possible echo of Vitruvius' astronomical presentation in book IX of his De architectura is suggested. Finally, we attempt to define how the author's persona as famulus et orator and reclusus at St-Denis relates to Charlemagne and to abbot Waldo in his pursuit of Chirstian wisdom based on the Bible rahter than of scholarship per se based on academic research. Part II is a thorough technical discussion of the astronomical issue presented to the Irish scholar by the Emperor, i.e. The frequency of solar eclipses and their visibility in the two emispheres in the year 810 (see maps provided). It assesses D\'ungal's case in terms of eclipse theory and reviews previous comments on his letter to Charlemagne by astronomer Ismael Bullialdus (1605-1694). It also introduces us to first-hand knowledge of eclipses in history and nowadays, providing a glimpse into the complex problems tackled by the Irishman and his sources in Late Antique and in the Early Middle Ages. Ample footnotes to the Italian translation of D\'ungal's work are an essential guiding tool for Latinists unfamiliar with astronomy.
Non-spherical systems described by MOND theories of modified gravity arising from generalizations of the Poisson equations are affected by a MONDian extra-quadrupolar potential \phi_M even if they are isolated and they are in deep Newtonian regime. In general MOND theories quickly approaching Newtonian dynamics for accelerations beyond A_0, \phi_M is proportional to a multiplicative scaling coefficient \alpha \sim 1, while in MOND models becoming Newtonian beyond \kappa A_0, \kappa >> 1, it is enhanced by \kappa^2. We analytically work out some orbital effects due to \phi_M in the framework of QUMOND, and compare them with the latest observational determinations of Solar System's planetary dynamics, exoplanets and double lined spectroscopic binary stars. The current admissible range for the anomalous perihelion precession of Saturn yields |\kappa| <= 2.5 x 10^5, while the radial velocity of \alpha Cen AB allows to infer |\kappa|<= 6.2 x 10^4 (A) and |\kappa|<= 4.2 x 10^4 (B). In evaluating such preliminary constraints it must be recalled that QUMOND is not the nonrelativistic limit of TeVeS.
Links to: arXiv, form interface, find, astro-ph, recent, 1211, contact, help (Access key information)