We use an empirical approach to characterize the effect of charge-transfer efficiency (CTE) losses in images taken with the Wide-Field Channel of the Advanced Camera for Surveys. The study is based on profiles of warm pixels in 168 dark exposures taken between September and October 2009. The dark exposures allow us to explore charge traps that affect electrons when the background is extremely low. We develop a model for the readout process that reproduces the observed trails out to 70 pixels. We then invert the model to convert the observed pixel values in an image into an estimate of the original pixel values. We find that when we apply the image-restoration process to science images with a variety of stars on a variety of background levels, it restores flux, position, and shape. This means that the observed trails contain essentially all of the flux lost to inefficient CTE. The Space Telescope Science Institute is currently evaluating this algorithm with the aim of optimizing it and eventually providing enhanced data products. The empirical procedure presented here should also work for other epochs (eg., pre-SM4), though the parameters may have to be recomputed for the time when ACS was operated at a higher temperature than the current -81 C. Finally, this empirical approach may also hold promise for other instruments, such as WFPC2, STIS, the ACS's HRC, and even WFC3/UVIS.
We analyze the correlations between central dark matter (DM) content of early-type galaxies and their sizes and ages, using a sample of intermediate-redshift (z ~ 0.2) gravitational lenses from the SLACS survey, and by comparing them to a larger sample of z ~ 0 galaxies. We decompose the deprojected galaxy masses into DM and stellar components using combinations of strong lensing, stellar dynamics, and stellar populations modeling. For a given stellar mass, we find that for galaxies with larger sizes, the DM fraction increases and the mean DM density decreases, consistently with the cuspy halos expected in cosmological formation scenarios. The DM fraction also decreases with stellar age, which can be partially explained by the inverse correlation between size and age. The residual trend may point to systematic dependencies on formation epoch of halo contraction or stellar initial mass functions. These results are in agreement with recent findings based on local galaxies by Napolitano, Romanowsky & Tortora (2010) and suggest negligible evidence of galaxy evolution over the last ~ 2.5 Gyr other than passive stellar aging.
We present limits on the molecular gas content of Lyman Break Galaxies (LBGs) at z~5 from observations targetting redshifted CO(1-0) and CO(2-1) line emission. We observed a single field containing eight spectroscopically-confirmed z~5 LBGs, seven of which are contained within a narrow (z=4.95\pm 0.08) redshift range and the eighth is at z=5.2. No source was individually detected. Assuming the CO to H2 conversion factor for vigorous starbursts, we place upper limits on the molecular gas content of individual z~5 LBGs of M(H2)<~10^10 Msun. From a stacking analysis combining all of the non-detections, the typical z~5 LBG has an H2 mass limit comparable to their stellar mass, < 3.1 x 10^9 Msun. This limit implies that, given the star formation rates of these systems (measured from their UV emission), star formation could be sustained for at most ~100Myr, similar to the typical ages of their stellar populations. The lack of a substantially larger reservoir of cold gas argues against the LBGs being UV luminous super starbursts embedded in much larger UV-dark systems and as a result increases the likelihood that at least those LBGs with multiple components are starbursts triggered by mergers. The sources responsible for reionization are expected to be starbursts similar to these systems, but with lower luminosities, masses and consequently with star formation timescales far shorter than the recombination timescale. If so, the ionized bubbles expected in the IGM during the reionization era will infrequently have UV-luminous sources at their centres.
We describe the application of non-negative matrix factorisation to generate compact reconstructions of quasar spectra from the Sloan Digital Sky Survey (SDSS), with particular reference to broad absorption line quasars (BALQSOs). BAL properties are measured for SiIV lambda1400, CIV lambda1550, AlIII lambda1860 and MgII lambda2800, resulting in a catalogue of 3547 BALQSOs. Two corrections, based on extensive testing of synthetic BALQSO spectra, are applied in order to estimate the intrinsic fraction of CIV BALQSOs. First, the probability of an observed BALQSO spectrum being identified as such by our algorithm is calculated as a function of redshift, signal-to-noise ratio and BAL properties. Second, the different completenesses of the SDSS target selection algorithm for BALQSOs and non-BAL quasars are quantified. Accounting for these selection effects the intrinsic CIV BALQSO fraction is 41+/-5 per cent. Our analysis of the selection effects allows us to measure the dependence of the intrinsic CIV BALQSO fraction on luminosity and redshift. We find a factor of 3.5+/-0.4 decrease in the intrinsic fraction from the highest redshifts, z~4.0, down to z~2.0. The redshift dependence implies that an orientation effect alone is not sufficient to explain the presence of BAL troughs in some but not all quasar spectra. Our results are consistent with the intrinsic BALQSO fraction having no strong luminosity dependence, although with 3-sigma limits on the rate of change of the intrinsic fraction with luminosity of -6.9 and 7.0 per cent dex^-1 we are unable to rule out such a dependence.
We have imaged the disk surrounding the nearby (D~73 pc), ~12 Myr, classical T Tauri binary system V4046 Sgr with the Submillimeter Array (SMA) at an angular resolution of ~2". We detect a rotating disk in 12CO(2-1) and 13CO(2-1) emission, and resolve the continuum emission at 1.3 mm. We infer disk gas and dust masses of ~110 and ~40 Earth masses, respectively. Fits to a power-law disk model indicate that the molecular disk extends to ~370 AU and is viewed at an inclination of between ~33 and ~39 degrees for dynamical stellar masses ranging from 1.8 $M_\odot$ down to 1.5 $M_\odot$ (the range of total mass previously determined for the central, 2.4 day spectroscopic binary). This range of disk inclination is consistent with that assumed in deducing the central binary mass (i.e., 35 degrees), suggesting that the V4046 Sgr binary system and its circumbinary, molecular disk are coplanar. In light of the system's age and binarity, the presence of an extensive molecular disk orbiting V4046 Sgr provides constraints on the timescales of processes related to Jovian planet formation, and demonstrates that circumbinary Jovian planets potentially could form around close binary systems.
We construct a numerical model of emission from minijets, localized flows driven by magnetic reconnection inside Poynting-flux-dominated jets proposed to explain the ultrafast variability of blazars. The geometrical structure of the model consists of two wedge-like regions of relativistically flowing gas, separated by a stationary shock. The dynamics is based on solutions of relativistic magnetic reconnection with a guide field from Lyubarsky (2005). Electron distributions in each region are chosen to the match the pressure and density of the local plasma. Synchrotron emission from both regions is used to calculate Compton scattering, Compton drag and photon-photon opacity effects, with exact treatment of anisotropy and the Klein-Nishina regime. Radiative effects on plasma are taken into account, including the dependence of pressure on electron radiative losses and adiabatic heating of the flow decelerating under Compton drag. The results are applied to the July 2006 flare in the BL Lac object PKS 2155-304, with the aim of matching TeV flux measurements by H.E.S.S. with models that satisfy the variability constraints, while keeping X-ray emission below simultaneous Chandra observations. We find that models of isolated minijets with a significant guide field overproduce X-ray emission, and that we must take into account the radiative interaction of oppositely-oriented minijets in order to achieve a high enough dominance by Comptonized TeV radiation. We argue that such interactions are likely to occur in a jet where there is substantial internal reconnection, producing a large number of misaligned minijets. Finally, we show that large jet magnetizations are indeed required to satisfy all observational constraints and that the effective Lorentz factor of the minijet plasma has to be larger than 50, in agreement with earlier one-zone estimates.
IRAS04325+2402 (herafter IRAS04325) is a complex protostellar system hosting two young stellar objects (AB and C in the following) at a separation of 1250AU. Here we present new deep Gemini imaging and spectroscopy for the system covering the wavelength regime from 1-12mu as well as Sub-Millimeter Array interferometry at 870mu, in combination with Spitzer and literature data. Object AB is a low-mass star with a disk/envelope system and an outflow cavity, which is prominently seen in infrared images. Object C, previously suspected to be a brown dwarf, is likely a very low mass star, with an effective temperature of ~3400K. It features an edge-on disk and an elongated envelope, and shows strong indications for accretion and ejection activity. Both objects are likely to drive parsec-scale molecular outflows. The two objects are embedded in an isolated, dense molecular cloud core. High extinction, lack of X-ray emission, and relatively high bolometric luminosity argue for a very young age below 1Myr. The disk/outflow systems of AB and C are misaligned by ~60deg against each other and by 80 and 40deg against the orbital plane of the binary. The system might be a good case for primordial misalignment, as opposed to misalignment caused by dynamical interactions, because the outflow direction is constant and the realignment timescale is likely larger than the system age. This favours turbulent fragmentation, rather than rotational fragmentation, as the formation scenario. We show that the spectral energy distributions and images for the two objects can be reproduced with radiative transfer models for disk/envelope systems. Our analysis provides reassurance in the established paradigm for the structure and early evolution of YSOs, but stresses the importance of developing 3D models with sophisticated dust chemistry (abridged).
There have been suggestions that the abundance of Extremely Metal-Poor (EMP) stars can be reproduced by Hypernovae (HNe), not by normal supernovae (SNe). However, recently it was also suggested that if the innermost neutron-rich or proton-rich matter is ejected, the abundance patterns of ejected matter are changed, and normal SNe may also reproduce the observations of EMP stars. In this letter, we calculate explosive nucleosynthesis with various Ye and entropy, and investigate whether normal SNe with this innermost matter, which we call "hot-bubble" component, can reproduce the abundance of EMP stars. We find that neutron-rich (Ye = 0.45-0.49) and proton-rich (Ye = 0.51-0.55) matter can increase Zn/Fe and Co/Fe ratios as observed, but tend to overproduce other Fe-peak elements. In addition to it, we find that if slightly proton-rich matter with 0.50 <= Ye < 0.501 with s/kb ~ 15-40 is ejected as much as ~ 0.06 Msolar, even normal SNe can reproduce the abundance of EMP stars, though it requires fine-tuning of Ye. On the other hand, HNe can more easily reproduce the observations of EMP stars without fine-tuning. Our results imply that HNe are the most possible origin of the abundance pattern of EMP stars.
Using the Sloan Digital Sky Survey (SDSS) data release 4 (DR 4), we investigate the spatial distribution of low and high surface brightness galaxies (LSBs and HSBs, respectively). In particular, we focus our attention on the influence of interactions between galaxies on the star formation strength in the redshift range $0.01 < z < 0.1$. With cylinder counts and projected distance to the first and fifth-nearest neighbor as environment tracers, we found that LSBs tend to have a lack of companions compared to HSBs at small scales ($<2$ Mpc). Regarding the interactions, we have evidence that the fraction of LSBs with strong star formation activity increases when the neighbor is closer than $r_{p}/r_{90} \sim 4$. The intensity of the effect of the interaction on the star formation strength, measured by the average value of the birthrate parameter $b$, seems to be stronger for HSBs than for LSBs. The analysis of our population of LSBs and HSBs hosting an AGN show that, regardless of the mass range, the fraction of LSBs having an AGN is lower than the corresponding fraction of HSBs with an AGN. This result, and those concerning the star-forming properties of LSBs as a function of the environment, fit with the scenario proposed by some authors where, below a given threshold of mass density, LSB disks are unable to propagate instabilities, preventing the massive central black hole of galaxies from being fed and activated. Our results suggest that, rather than being a condition for their survival and evolution, isolation of LSBs is more connected with their formation scenario.
Neutron-rich isotopes with masses near that of iron are produced in type Ia and II supernovae. Traces of such nucleosynthesis are found in primitive meteorites in the form of variations in the isotopic abundance of 54Cr, the most neutron-rich stable isotope of chromium. The hosts of these isotopic anomalies must be presolar grains that condensed in the outflows of supernovae, offering the opportunity to study the nucleosynthesis of iron-peak nuclei in ways that complement spectroscopic observations and can inform models of stellar evolution. However, despite almost two decades of extensive search, the carrier of 54Cr anomalies is still unknown, presumably because it is fine-grained and is chemically labile. Here we identify in the primitive meteorite Orgueil the carrier of 54Cr-anomalies as nanoparticles, most likely spinels that show large enrichments in 54Cr relative to solar composition (54Cr/52Cr ratio >3.6xsolar). Such large enrichments in 54Cr can only be produced in supernovae. The mineralogy of the grains supports condensation in the O/Ne-O/C zones of a type II supernova, although a type Ia origin cannot be excluded. We suggest that planetary materials incorporated different amounts of these nanoparticles, possibly due to late injection by a nearby supernova that also delivered 26Al and 60Fe to the solar system. This idea explains why the relative abundance of 54Cr and other neutron-rich isotopes vary between planets and meteorites. We anticipate that future isotopic studies of the grains identified here will shed new light on the birth of the solar system and the conditions insupernovae.
An innovative approach to map the large-scale structure in the Universe sidesteps the conventional need to observe millions of galaxies individually, and holds promise for both astrophysical and cosmological studies.
Blue horizontal-branch (BHB) stars with $T_{\rm eff}$ approximately larger than 11500 K show several observational anomalies. In globular clusters, they exhibit low rotational velocities, abundance anomalies (as compared to cluster abundances), photometric jumps and gaps and spectroscopic gravities lower than predicted by canonical models. It is commonly believed that the low rotational velocities of these stars permit atomic diffusion to be efficient in their atmosphere thereby causing the observed anomalies. Recent detections of vertical stratification of iron (and some other chemical elements) in several BHB stars concur with this framework. In this paper, improved model atmospheres that include the vertical stratification of the elements are applied to BHB stars to verify if they can explain their observational anomalies. The results from theoretical model atmospheres are consistent with the photometric jumps and gaps observed for BHB stars in globular clusters. It is found that iron stratification in the theoretical models and that obtained from observations have similar tendancies. Our results also show that the spectroscopic gravities obtained while using chemically homogeneous model atmospheres to fit observations are underestimated. These results significantly strengthen the belief that atomic diffusion is responsible for these BHB-star anomalies.
Self-gravitating accretion disks collapse to star-forming(SF) regions extending to the inner edge of the dusty torus in active galactic nuclei (AGNs). A full set of equations including feedback of star formation is given to describe the dynamics of the regions. We explore the role of supernovae explosion (SNexp), acting to excite turbulent viscosity, in the transportation of angular momentum in the regions within 1pc scale. We find that accretion disks with typical rates in AGNs can be driven by SNexp in the regions and metals are produced spontaneously. The present model predicts a metallicity--luminosity relationship consistent with that observed in AGNs. As relics of SF regions, a ring (or belt) consisting of old stars remains for every episode of supermassive black hole activity. We suggest that multiple stellar rings with random directions interact and form a nuclear star cluster after episodes driven by star formation.
The Hipparcos orbiting observatory has revealed a large number of helium-core-burning "clump" stars in the Galactic field. These low-mass stars exhibit signatures of extra-mixing processes that require modeling beyond the first dredge-up of standard models. The 12C/13C ratio is the most robust diagnostic of deep mixing, because it is insensitive to the adopted stellar parameters. In this work we present 12C/13C determinations in a sample of 34 Galactic clump stars as well as abundances of nitrogen, carbon and oxygen. Abundances of carbon were studied using the C2 Swan (0,1) band head at 5635.5 A. The wavelength interval 7980-8130 A with strong CN features was analysed in order to determine nitrogen abundances and 12C/13C isotope ratios. The oxygen abundances were determined from the [O I] line at 6300 A. Compared with the Sun and dwarf stars of the Galactic disk, mean abundances in the investigated clump stars suggest that carbon is depleted by about 0.2 dex, nitrogen is enhanced by 0.2 dex and oxygen is close to abundances in dwarfs. Comparisons to evolutionary models show that the stars fall into two groups: the one is of first ascent giants with carbon isotope ratios altered according to the first dredge-up prediction, and the other one is of helium-core-burning stars with carbon isotope ratios altered by extra mixing. The stars investigated fall to these groups in approximately equal numbers.
Four newest CCD eclipse timings of the white dwarf for polar UZ Fornacis and Six updated CCD mid-eclipse times for SW Sex type nova-like V348 Puppis are obtained. The detailed O-C analyses for both CVs inside period gap are made. Orbital period increases at a rate of $2.63(\pm0.58)\times10^{-11} s\;s^{-1}$ for UZ Fornacis and of $5.8(\pm1.9)\times10^{-12} s\;s^{-1}$ for V348 Puppis, respectively, are discovered in their new O-C diagrams. However, the conservative mass transfer from the secondary to the massive white dwarf cannot explain the observed orbital period increases for both CVs, which are regarded as part of modulations at longer periods. Moreover, the O-C diagram of UZ Fornacis shows a possible cyclical change with a period of $\sim23.4(\pm5.1)yr$. For explaining the observed cyclical period changes in UZ Fornacis, both mechanisms of magnetic activity cycles in the late-type secondary and the light travel-time effect are regarded as two probable causes. Not only does the modulation period 23.4yr obey the empirical correlation derived by \cite{lan99}, but also the estimated fractional period change $\Delta P/P\sim7.3\times10^{-7}$ displays a behavior similar to that of the CVs below the period gap. On the other hand, a calculation for the light travel-time effect implies that the tertiary component in UZ Fornacis may be a brown dwarf with a high confidence level, when the orbital inclination of the third body is larger than $16^{\circ}$.
We demonstrate that the comparison of Tully-Fisher relations (TFRs) derived from global HI line widths to TFRs derived from the circular velocity profiles of dynamical models (or stellar kinematic observations corrected for asymmetric drift) is vulnerable to systematic and uncertain biases introduced by the different measures of rotation used. We therefore argue that to constrain the relative locations of the TFRs of spiral and S0 galaxies, the same tracer and measure must be used for both samples. Using detailed near-infrared imaging and the circular velocities of axisymmetric Jeans models of 14 nearby edge-on Sa-Sb spirals and 14 nearby edge-on S0s drawn from a range of environments, we find that S0s lie on a TFR with the same slope as the spirals, but are on average 0.53\pm 0.15 mag fainter at Ks-band at a given rotational velocity. This is a significantly smaller offset than that measured in earlier studies of the S0 TFR, which we attribute to our elimination of the bias associated with using different rotation measures and our use of earlier type spirals as a reference. Since our measurement of the offset avoids systematic biases, it should be preferred to previous estimates. A spiral stellar population in which star formation is truncated would take \approx 1 Gyr to fade by 0.53 mag at Ks-band. If S0s are the products of a simple truncation of star formation in spirals, then this finding is difficult to reconcile with the observed evolution of the spiral/S0 fraction with redshift. Recent star formation could explain the observed lack of fading in S0s, but the offset of the S0 TFR persists as a function of both stellar and dynamical mass. We show that the offset of the S0 TFR could therefore be explained by a systematic difference between the total mass distributions of S0s and spirals, in the sense that S0s need to be smaller or more concentrated than spirals.
The formation scenario for massive stars is still under discussion. To further constrain current theories, it is vital to spatially resolve the structures from which material accretes onto massive young stellar objects (MYSOs). Due to the small angular extent of MYSOs, one needs to overcome the limitations of conventional thermal infrared imaging, regarding spatial resolution, in order to get observational access to the inner structure of these objects.We employed mid - infrared interferometry, using the MIDI instrument on the ESO /VLTI, to investigate the Kleinmann - Wright Object, a massive young stellar object previously identified as a Herbig Be star precursor. Dispersed visibility curves in the N- band (8 - 13 {\mu}m) have been obtained at 5 interferometric baselines. We show that the mid - infrared emission region is resolved. A qualitative analysis of the data indicates a non - rotationally symmetric structure, e.g. the projection of an inclined disk. We employed extensive radiative transfer simulations based on spectral energy distribution fitting. Since SED - only fitting usually yields degenerate results, we first employed a statistical analysis of the parameters provided by the radiative transfer models. In addition, we compared the ten best - fitting self - consistent models to the interferometric observations. Our analysis of the Kleinmann - Wright Object suggests the existence of a circumstellar disk of 0.1M\odot at an intermediate inclination of 76\circ, while an additional dusty envelope is not necessary for fitting the data. Furthermore, we demonstrate that the combination of IR interferometry with radiative transfer simulations has the potential to resolve ambiguities arising from the analysis of spectral energy distributions alone.
Aims: We formulate an improved time series analysis method for the analysis
of photometry of active stars. This new Continuous Period Search (CPS) method
is applied to 12 years of V band photometry of the young solar analogue HD
116956 (NQ UMa).
Methods: The new method is developed from the previous Three Stage Period
Analysis (TSPA) method. Our improvements are the use of a sliding window in
choosing the modelled datasets, a criterion applied to select the best model
for each dataset and the computation of the time scale of change of the light
curve. We test the performance of CPS with simulated and real data.
Results: The CPS has a much improved time resolution which allows us to
better investigate fast evolution of stellar light curves. We can also separate
between the cases when the data is best described by periodic (i.e. rotational
modulation of brightness) and aperiodic (e.g. constant brightness) models. We
find, however, that the performance of the CPS has certain limitations. It does
not determine the correct model complexity in all cases, especially when the
underlying light curve is constant and the number of observations too small.
Also the sensitivity in detecting two close light curve minima is limited and
it has a certain amount of intrinsic instability in its period estimation.
Using the CPS, we find persistent active longitudes in the star HD 116956 and a
"flip-flop" event that occurred at 1999. We also find some signs of an activity
cycle with a period of about 3 years. Assuming that the surface differential
rotation of the star causes observable period variations in the stellar light
curve, we determine the differential rotation coefficient to be |k| > 0.11. The
mean timescale of change of the light curve during the whole 12 year observing
period was T C = 44.1 d, which is of the same order as the predicted convective
turnover time of the star.
The MeerKAT UltraDeep HI Survey aims to observe the 21 cm emission line of neutral hydrogen gas out to a redshift of z=1 and beyond. From both direct detections and stacked signal, we will address the HI mass function, the cosmic neutral gas density of the Universe (Omega_HI) and their evolution over cosmic times, as well as galaxy evolution via e.g., the Tully-Fisher relation, the relation between HI mass and Hubble Type or stellar mass, and the Schmidt-Kennicutt star-formation law. We propose to observe two fields, the COSMOS and Chandra Deep Field South (CDF-S) for 1000 hours each, adding an additional 4000 hours to one of these fields in 2015 when the full instantaneous bandwidth of MeerKAT (0.58-2.5 GHz) will be realised.
New high resolution spectra of the short period (P~1.76 days) young detached binary LT CMa are reported for the first time. By combining the results from the analysis of new radial velocity curves and published light curves, we determine values for the masses, radii and temperatures as follows: M_1= 5.59 (0.20) M_o, R_1=3.56 (0.07) R_o and T_eff1= 17000 (500) K for the primary and M_2=3.36 (0.14) M_o, R_2= 2.04 (0.05) R_o and T_eff2= 13140 (800) K for the secondary. Static absorbtion features apart from those coming from the close binary components are detected in the several spectral regions. If these absorbtion features are from a third star, as the light curve solutions support, its radial velocity is measured to be RV_3=70(8) km s^-1. The orbit of the binary system is proved to be eccentric (e=0.059) and thus the apsidal motion exists. The estimated linear advance in longitude of periastron corresponds to an apsidal motion of U=694+/-5 yr for the system. The average internal structure constant log k_2,obs=-2.53 of LT CMa is found smaller than its theoretical value of log k_2,theo=-2.22 suggesting the stars would have more central concentration in mass. The photometric distance of LT CMa (d=535+/-45 pc) is found to be much smaller than the distance of CMa OB1 association (1150 pc) which rules out membership. A comparison with current stellar evolution models for solar metallicity indicates that LT CMa (35 Myr) is much older than the CMa OB1 association (3 Myr), confirming that LT CMa is not a member of CMa OB1. The kinematical and dynamical analysis indicate LT CMa is orbiting the Galaxy in a circular orbit and belongs to the young thin-disk population.
Numerical models of disc galaxy formation predict the existence of extended, hot ( T~10^6 K) gas haloes around present day spirals. The X-ray luminosity of these haloes is predicted to increase strongly with galaxy mass. However, searches for their X-ray emission have not been successful so far. We calculate the all sky O VII column density distributions for the haloes of three Milky Way like disc galaxies, resulting from cosmological high-resolution, N-body/gasdynamical simulations. We perform calculations both including the disc gas and without it, so the disc contribution to the column density is quantified. It is found that the column densities estimated for Milky Way-like galaxies are just below the observational upper limit, making a test of the hot halo paradigm likely within observational reach.
Molecular FeH provides a large number of sharp and isolated absorption lines that can be used to measure radial velocity, rotation, or magnetic field strength with high accuracy. Our aim is to provide an FeH atlas for M-type stars in the spectral region from 986 nm to 1077 nm (Wing-Ford band). To identify these lines in CRIRES spectra of the magnetically inactive, slowly rotating, M5.5 dwarf GJ1002, we calculated model spectra for the selected spectral region with theoretical FeH line data. In general this line list agrees with the observed data, but several individual lines differ significantly in position or in line strength. After identification of as many as possible FeH lines, we correct the line data for position and line strength to provide an accurate atlas of FeH absorption lines for use in high precision spectroscopy of low mass stars. For all lines, we use a Voigt function to obtain their positions and equivalent widths. Identification with theoretical lines is done by hand. For confirmation of the identified lines, we use statistical methods, cross- correlation techniques, and line intensities. Eventually, we were able to identify FeH lines from the (0, 0), (1, 0), (1, 1), (2, 1), (2, 2), (3, 2), and (4, 3) vibrational bands in the observed spectra and correct the positions of the lines if necessary. The deviations between theoretical and observed positions follow a normal distribution approximately around zero. In order to empirically correct the line strength, we determined Teff, instrumental broadening (rotational broadening) and a van der Waals enhancement factor for FeH lines in GJ1002. We also give scaling factors for the Einstein A values to correct the line strengths. With the identified lines, we derived rotational temperatures from line intensities for GJ1002. ... .
We derive the dense core structure and the water abundance in four massive star-forming regions which may help understand the earliest stages of massive star formation. We present Herschel-HIFI observations of the para-H2O 1_11-0_00 and 2_02-1_11 and the para-H2-18O 1_11-0_00 transitions. The envelope contribution to the line profiles is separated from contributions by outflows and foreground clouds. The envelope contribution is modelled using Monte-Carlo radiative transfer codes for dust and molecular lines (MC3D and RATRAN), with the water abundance and the turbulent velocity width as free parameters. While the outflows are mostly seen in emission in high-J lines, envelopes are seen in absorption in ground-state lines, which are almost saturated. The derived water abundances range from 5E-10 to 4E-8 in the outer envelopes. We detect cold clouds surrounding the protostar envelope, thanks to the very high quality of the Herschel-HIFI data and the unique ability of water to probe them. Several foreground clouds are also detected along the line of sight. The low H2O abundances in massive dense cores are in accordance with the expectation that high densities and low temperatures lead to freeze-out of water on dust grains. The spread in abundance values is not clearly linked to physical properties of the sources.
Experiments designed to measure the redshifted 21~cm line from the Epoch of Reionization (EoR) are challenged by strong astrophysical foreground contamination, ionospheric distortions, complex instrumental response and other different types of noise (e.g. radio frequency interference). The astrophysical foregrounds are dominated by diffuse synchrotron emission from our Galaxy. Here we present a simulation of the Galactic emission used as a foreground module for the LOFAR- EoR key science project end-to-end simulations. The simulation produces total and polarized intensity over $10^\circ \times 10^\circ$ maps of the Galactic synchrotron and free-free emission, including all observed characteristics of the emission: spatial fluctuations of amplitude and spectral index of the synchrotron emission, together with Faraday rotation effects. The importance of these simulations arise from the fact that the Galactic polarized emission could behave in a manner similar to the EoR signal along the frequency direction. As a consequence, an improper instrumental calibration will give rise to leakages of the polarized to the total signal and mask the desired EoR signal. In this paper we address this for the first time through realistic simulations.
We analyse a DGP brane filled with a k-essence field and assume the k-field evolving linearly with the cosmic time of the brane. We then solve analytically the Friedmann equation and deduce the different behaviour of the brane at the low and the high energy regimes. The asymptotic behaviour can be quite different involving accelerating branes, big bangs, big crunches, big rips or quiescent singularities. The latter correspond to a type of sudden singularity.
We present new mm interferometric and optical integral-field unit (IFU) observations and construct a sample of 12 E and S0 galaxies with molecular gas which have both CO and optical maps. The galaxies contain 2 x 10^7 to 5 x 10^9 M\odot of molecular gas distributed primarily in central discs or rings (radii 0.5 to 4 kpc). The molecular gas distributions are always coincident with distributions of optically-obscuring dust that reveal tightly-wound spiral structures in many cases. The ionised gas always approximately corotates with the molecular gas, evidencing a link between these two gas components, yet star formation is not always the domi- nant ionisation source. The galaxies with less molecular gas tend to have [O III]/H{\beta} emission-line ratios at high values not expected for star formation. Most E/S0s with molecular gas have young or intermediate age stellar populations based on optical colours, ultraviolet colours and absorption linestrengths. The few that appear purely old lie close to the limit where such populations would be undetectable based on the mass fractions of expected young to observed old stars. The 8{\mu}m polycyclic aromatic hydrocarbon (PAH) and 24{\mu}m emission yield similar star formation rate estimates of E/S0s, but the total infrared overpredicts the rate due to a contribution to dust heating from older stars. The radio-far infrared relation also has much more scatter than for other star-forming galaxies. However, despite these biases and additional scatter, the derived star formation rates locate the E/S0 galaxies within the large range of the Schmidt-Kennicutt and constant efficiency star formation laws. Thus the star formation process in E/S0s is not overwhelmingly different than in other star-forming galaxies, although one of the more reliable tracers (24{\mu}m) points to a possible lower star-formation efficiency at a given gas surface density.
We hypothesise that planets are made by tidal downsizing of migrating giant planet embryos. The proposed scheme for planet formation consists of these steps: (i) a massive young protoplanetary disc fragments at R ~ several tens to hundreds of AU on gaseous clumps with masses of a few Jupiter masses; (ii) the clumps cool and contract, and simultaneously migrate closer in to the parent star; (iii) as earlier suggested by Boss (1998), dust sediments inside the gas clumps to form terrestrial mass solid cores; (iv) if the solid core becomes more massive than ~ 10 Earth masses, a massive gas atmosphere collapses onto the solid core; (v) when the gas clumps reach the inner few AU from the star, tidal shear and evaporation due to stellar irradiation peel off the outer metal-poor envelope of the clump. If tidal disruption occurs quickly, while the system is still in stage (iii), a terrestrial planet core is left. If it happens later, in stage (iv), a metal rich gas giant planet with a solid core emerges from the envelope.
The merger of a binary system composed of a black hole and a neutron star may leave behind a torus of hot, dense matter orbiting around the black hole. While numerical-relativity simulations are necessary to simulate this process accurately, they are also computationally expensive and unable at present to cover the large space of possible parameters, which include the relative mass ratio, the stellar compactness and the black hole spin. To mitigate this and provide a first reasonable coverage of the space of parameters, we have developed a method for estimating the mass of the remnant torus from black hole-neutron star mergers. The toy model makes use of the relativistic affine model to describe the tidal deformations of an extended tri-axial ellipsoid orbiting around a Kerr black hole and measures the mass of the remnant torus by considering which of the fluid particles composing the star are on bound orbits at the time of the tidal disruption. We tune the toy model by using the results of fully general-relativistic simulations obtaining relative precisions of few a percent and use it to investigate the space of parameters extensively. In this way we find that the torus mass is largest for systems with highly spinning black holes, small stellar compactnesses and large mass ratios. As an example, tori as massive as $M_{b,\text{tor}} \simeq 1.33\,M_{\odot}$ can be produced for a very extended star with compactness $C\simeq 0.1$ inspiralling around a black hole with dimensionless spin $a=0.85$ and mass ratio $q\simeq 0.3$. However, for a more astrophysically reasonable mass ratio $q \simeq 0.14$ and a canonical value of the stellar compactness $C\simeq 0.145$, the toy model sets a considerably smaller upper limit of $M_{b,\text{tor}} \lesssim 0.34\,M_{\odot}$.
In the context of massive fragmenting protoplanetary discs, Boss (1998) suggested that grains can grow and sediment inside giant planet embryos formed at R ~ 5 AU away from the star. Several authors since then criticised the suggestion. Convection may prevent grain sedimentation, and the embryos cannot even form so close to the parent star as cooling is too inefficient at these distances. Here we reconsider the grain sedimentation process suggested by Boss (1998) but inside an embryo formed, as expected in the light of the cooling constraints, at R ~ 100 AU. Such embryos are much less dense and are also cooler. We make analytical estimates of the process and also perform simple spherically symmetric radiation hydrodynamics simulations to test these ideas. We find that convection in our models does not become important before a somewhat massive (~ an Earth mass, this is clarified in a followup paper) solid core is built. Turbulent mixing slows down dust sedimentation but is overwhelmed by grain sedimentation when the latter grow to a centimetres size. The minimum time required for dust sedimentation to occur is a few thousand years, and is a strong function of the embryo's mass, dust content and opacity. An approximate analytical criterion is given to delineate conditions in which a giant embryo contracts and heats up faster than dust can sediment. As Boss et al (2002), we argue that core formation through grain sedimentation inside the giant planet embryos may yield an unexplored route to form giant gas and giant ice planets. The present model also stands at the basis of paper III, where we study the possibility of forming terrestrial planet cores by tidal disruption and photoevaporation of the planetary envelope.
Giant planet embryos are believed to be spawned by gravitational instability in massive extended (R ~ 100 AU) protostellar discs. In a recent paper we have shown that dust can sediment inside the embryos, as argued earlier by Boss (1998) in a slightly different model. Here we study numerically the next stage of this process -- the formation of a solid core. If conditions are conducive to solid core formation, the centre of the gas cloud goes through the following sequence of phases: (i) becomes grain (and metal) rich; (ii) forms a terrestrial mass solid core via a rapid collapse driven by self-gravity of the grains; (iii) starts to accrete a gaseous atmosphere when the solid core reaches mass of a few to 10 Earth masses. This sequence of events may build either terrestrial planet cores or metal rich giant planets inside the larger gas reservoir of the giant planet embryo. In a companion Letter we argue that tidal and irradiation effects from the parent star should disrupt the outer metal poor layers of the embryo, releasing nearly "ready to use" planets. We propose this as an alternative way to build planets.
We consider the effects of uncertainties in nuclear reaction rates on the cosmological constraints on the decays of unstable particles during or after Big-Bang nucleosynthesis (BBN). We identify the nuclear reactions due to non-thermal hadrons that are the most important in perturbing standard BBN, then quantify the uncertainties in these reactions and in the resulting light-element abundances. These results also indicate the key nuclear processes for which improved cross section data would allow different light-element abundances to be determined more accurately, thereby making possible more precise probes of BBN and evaluations of the cosmological constraints on unstable particles. Applying this analysis to models with unstable gravitinos decaying into neutralinos, we calculate the likelihood function for the light-element abundances measured currently, taking into account the current experimental errors in the determinations of the relevant nuclear reaction rates. We find a region of the gravitino mass and abundance in which the abundances of deuterium, He4 and Li7 may be fit with chi^2 = 5.5, compared with chi^2 = 31.7 if the effects of gravitino decays are unimportant. The best-fit solution is improved to chi^2 ~ 2.0 when the lithium abundance is taken from globular cluster data. Some such re-evaluation of the observed light-element abundances and/or nuclear reaction rates would be needed if this region of gravitino parameters is to provide a complete solution to the cosmological Li7 problem.
The Galactic Center is a prominent source in X-rays and gamma-rays and the study of its high-energy emission is crucial in understanding the physical phenomena taking place in its dense and extreme environment, phenomena that are possibly common to other galactic nuclei. However this emission is also very complex and consists of both thermal and non thermal radiation produced by compact and extended sources, surrounded by more diffuse components. In spite of the fundamental advances obtained in the last ten years with Chandra, XMM-Newton, INTEGRAL, HESS and Suzaku several questions remain open to investigations. I will review here the main results and the open issues on the high-energy diagnostic of the galactic nuclear activity.
In early 2008, the young low-mass star EX Lupi, the prototype of the EXor class of eruptive variables, optically brightened by over five magnitudes for a period of 7 months. The previous time a change of such amplitude had been observed in EX Lup was over 50 years ago. In this Letter we present new optical and near-IR high resolution spectroscopy of EX~Lup during the 2008 outburst. We investigate the physical characteristics of the outburst both soon after it began and some four months later, and consider the energetics and kinematics observed. Emission line strengths, widths, and profiles changed significantly between the two observations. Also, modeling of the 2.2935 um CO overtone bandhead emission suggests that an inner gap in the circumstellar gas disk around the star may be present and it is from the inner edge of the gas disk that the CO overtone emission probably arises. We derive a mass accretion luminosity and rate during the extreme outburst of ~2+-0.5~Lsun and ~2+-0.5x10^-7 Msun yr^-1, respectively, which suggests that this outburst was indeed one of the strongest witnessed in EX Lup, yet not as strong as those observed in FU Orionis stars.
We present a SINFONI integral field kinematical study of 33 galaxies at z~3 from the AMAZE and LSD projects which are aimed at studying metallicity and dynamics of high-redshift galaxies. The number of galaxies analyzed in this paper constitutes a significant improvement compared to existing data in the literature and this is the first time that a dynamical analysis is obtained for a relatively large sample of galaxies at z~3. 11 galaxies show ordered rotational motions ($\sim 30\%$ of the sample), in these cases we estimate dynamical masses by modeling the gas kinematics with rotating disks and exponential mass distributions. We find dynamical masses in the range 2 10^9 Msun -2 10^11 Msun with a mean value of ~2\ 10^10 Msun. By comparing observed gas velocity dispersion with that expected from models, we find that most rotatin objects are dynamically "hot", with intrinsic velocity dispersions of the order of ~90 km/s. The median value of the ratio between the maximum disk rotational velocity and the intrinsic velocity dispersion for the rotating objects is 1.6, much lower than observed in local galaxies value (~10) and slightly lower than the z~2 value (2-4). Finally we use the maximum rotational velocity from our modeling to build a baryonic Tully-Fisher relation at z~3. Our measurements indicate that z~3 galaxies have lower stellar masses (by a factor of ten on average compared to local galaxies with the same dynamical mass. However, the large observed scatter suggests that the Tully-Fisher relation is not yet "in place" at these early cosmic ages, possibly due to the young age of galaxies.
The Advanced CCD Imaging Spectrometer (ACIS) is one of two focal-plane instruments on the Chandra X-ray Observatory. During initial radiation-belt passes, the exposed ACIS suffered significant radiation damage from trapped soft protons scattering off the x-ray telescope's mirrors. The primary effect of this damage was to increase the charge-transfer inefficiency (CTI) of the ACIS 8 front-illuminated CCDs. Subsequently, the Chandra team implemented procedures to remove the ACIS from the telescope's focus during high-radiation events: planned protection during radiation-belt transits; autonomous protection triggered by an on-board radiation monitor; and manual intervention based upon assessment of space-weather conditions. However, as Chandra's multilayer insulation ages, elevated temperatures have reduced the effectiveness of the on-board radiation monitor for autonomous protection. Here we investigate using the ACIS CCDs themselves as a radiation monitor. We explore the 10-year database to evaluate the CCDs' response to particle radiation and to compare this response with other radiation data and environment models.
We have observed warm molecular hydrogen in two nearby edge-on disk galaxies, NGC 4565 and NGC 5907, using the Spitzer high-resolution infrared spectrograph. The 0-0 S(0) 28.2 micron and 0-0 S(1) 17.0 micron pure rotational lines were detected out to 10 kpc from the center of each galaxy on both sides of the major axis, and in NGC 4565 the S(0) line was detected at r = 15 kpc on one side. This location lies beyond a steep drop in the radio continuum emission from cosmic rays in the disk. Despite indications that star formation activity decreases with radius, the H2 excitation temperature and the ratio of the H2 line and the far-IR luminosity surface densities, Sigma_L(H2}/Sigma_L(TIR}, change very little as a function of radius, even into the diffuse outer region of the disk of NGC 4565. This suggests that the source of excitation of the H2 operates over a large range of radii, and is broadly independent of the strength and relative location of UV emission from young stars. Although excitation in photodissociation regions is the most common explanation for the widespread H2 emission, cosmic ray heating or shocks cannot be ruled out. The inferred mass surface densities of warm molecular hydrogen in both edge-on galaxies differ substantially, being 4(-60) M_solar/pc^2 and 3(-50) M_solar/pc^2 at r = 10 kpc for NGC 4565 and NGC 5907, respectively. The higher values represent very unlikely point-source upper limits. The point source case is not supported by the observed emission distribution in the spectral slits. These mass surface densities cannot support the observed rotation velocities in excess of 200 km/s. Therefore, warm molecular hydrogen cannot account for dark matter in these disk galaxies, contrary to what was implied by a previous ISO study of the nearby edge-on galaxy NGC 891.
We study the correction to the scale invariant power spectrum of a scalar field on de Sitter space from small black holes that formed during a pre-inflationary matter dominated era. The formation probability of such black holes is estimated from primordial Gaussian density fluctuations. We determine the correction to the spectrum by first deriving the Keldysh propagator for a massless scalar field on Schwarzschild-de Sitter space. Our results suggest that the effect is strong enough to be tested -- and possibly even ruled out -- by observations.
We construct the most general effective Lagrangian coupling gravity and electromagnetism up to mass dimension 6 by enumerating all possible non-minimal coupling terms respecting both diffeomorphism and gauge invariance. In all, there are only two unique terms after field re-definitions; one is known to arise from loop effects in QED while the other is a parity violating term which may be generated by weak interactions within the standard model of particle physics. We show that neither the cosmological propagation of light nor, contrary to earlier claims, solar system tests of General Relativity are useful probes of these terms. These non-minimal couplings of gravity and electromagnetism may remain a mystery for the foreseeable future.
Have been calculated the differential cross section and mean free path of neutrino of neutrino interaction in dense matter.
It is well known that there is a Hawking temperature on the cosmological horizon of the de-sitter spacetime, and the de-sitter spacetime can be a special case of a FRW universe. Therefore, there may be a corresponding Hawking temperature in a FRW universe. Indeed, there have been several clues showing that there is a Hawking temperature on the apparent horizon of a FRW universe. In our paper, however, after finding the corresponding cosmological horizon of a FRW universe, and then investigating the behavior of a Klein-Gordon field near the cosmological horizon, we find that there is a Hawking temperature on the cosmological horizon. Moreover, we also find that the Hawking temperature on the apparent horizon of a FRW universe in some previous work is just a special case in our results, where the variation rate of cosmological horizon $\overset{.}{r}_{H}$ is zero.
We consider the three dimensional gravitational Vlasov Poisson system which is a canonical model in astrophysics to describe the dynamics of galactic clusters. A well known conjecture is the stability of spherical models which are nonincreasing radially symmetric steady states solutions. This conjecture was proved at the linear level by several authors in the continuation of the breakthrough work by Antonov in 1961. In a previous work (arXiv:0904.2443), we derived the stability of anisotropic models under {\it spherically symmetric perturbations} using fundamental monotonicity properties of the Hamiltonian under suitable generalized symmetric rearrangements first observed in the physics litterature. In this work, we show how this approach combined with a {\it new generalized} Antonov type coercivity property implies the orbital stability of spherical models under general perturbations.
We present a new methodology for calculating the electromagnetic radiation from accelerated charged particles. Our formulation - the `endpoint formulation' - combines numerous results developed in the literature in relation to particular radiation processes using a complete, and completely general, treatment. We do this by describing particle motion via a series of discrete, instantaneous acceleration events, or `endpoints', with each such event being treated as a source of emission. This method implicitly allows for particle creation/destruction, and is suited to direct numerical implementation in either the time- or frequency-domains. In this paper, we demonstrate the complete generality of our method for calculating the radiated field from charged particle motion, and show how it reduces to the classical named radiation processes such as synchrotron, Vavilov-Cherenkov, and transition radiation under appropriate limits. Using this formulation, we are immediately able to answer outstanding questions regarding the phenomenology of radio emission from ultra-high-energy particle interactions in both the Earth's atmosphere and the Moon. In particular, our formulation makes it apparent that the dominant emission component of the Askaryan Effect (coherent radio-wave radiation from high-energy particle cascades in dense media) comes from coherent `bremsstrahlung' from particle acceleration, rather than coherent Vavilov-Cherenkov radiation.
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We carry out fully 3-dimensional simulations of evolution from self-similar, spherically symmetric linear perturbations of a Cold Dark Matter dominated Einstein-de Sitter universe. As a result of the radial orbit instability, the haloes which grow from such initial conditions are triaxial with major-to-minor axis ratios of order 3:1. They nevertheless grow approximately self-similarly in time. In all cases they have power-law density profiles and near-constant velocity anisotropy in their inner regions. Both the power-law index and the value of the velocity anisotropy depend on the similarity index of the initial conditions, the former as expected from simple scaling arguments. Halo structure is thus not "universal" but remembers the initial conditions. On larger scales the density and anisotropy profiles show two characteristic scales, corresponding to particles at first pericentre and at first apocentre after infall. They are well approximated by the NFW model only for one value of the similarity index. In contrast, at all radii within the outer caustic the pseudo phase-space density can be fit by a single power law with an index which depends only very weakly on the similarity index of the initial conditions. This behaviour is very similar to that found for haloes formed from LCDM initial conditions and so can be considered approximately universal.
We present results of a study of the virial state of high redshift dark matter haloes in an N-body simulation. We find that the majority of collapsed, bound haloes are not virialized at any redshift slice in our study ($z=15-6$) and have excess kinetic energy. At these redshifts, merging is still rampant and the haloes cannot strictly be treated as isolated systems. To assess if this excess kinetic energy arises from the environment, we include the surface pressure term in the virial equation explicitly and relax the assumption that the density at the halo boundary is zero. Upon inclusion of the surface term, we find that the haloes are much closer to virialization, however, they still have some excess kinetic energy. We report trends of the virial ratio including the extra surface term with three key halo properties: spin, environment, and concentration. We find that haloes with closer neighbors depart more from virialization, and that haloes with larger spin parameters do as well. We conclude that except at the lowest masses ($M < 10^6 \Msun$), dark matter haloes at high redshift are not fully virialized. This finding has interesting implications for galaxy formation at these high redshifts, as the excess kinetic energy will impact the subsequent collapse of baryons and the formation of the first disks.
We present a systematic study of the physical properties of late-M dwarfs based on high-quality dynamical mass measurements and near-infrared (NIR) spectra. We use astrometry from Keck NGS and LGS AO imaging to determine orbits for late-M binaries. We find that LP 349-25 (M7.5+M8) is a pair of young brown dwarfs (Mtot = 0.120 Msun) for which Lyon and Tucson evolutionary models jointly predict an age of 140+/-30 Myr. This is consistent with the age of the Pleiades, but at least LP 349-25A defies the empirical Pleiades lithium depletion boundary, implying that the system is in fact older and that evolutionary models underpredict the component luminosities. We find that LHS 1901AB (M6.5+M6.5) is a pair of very low-mass stars (Mtot = 0.194 Msun) with model-derived ages consistent with limits from its lack of activity (> 6 Gyr). Our improved orbit for Gl 569Bab (M8.5+M9) results in a higher mass for this binary (Mtot = 0.140 Msun) compared to previous work (0.125 Msun). We use these masses along with our published results for 2MASS J2206-2047AB (M8+M8) to test four sets of ultracool model atmospheres currently in use. Fitting these models to our NIR integrated-light spectra provides temperature estimates warmer by ~250 K than those derived independently from Dusty evolutionary models given the measured masses and luminosities. We propose that model atmospheres are more likely to be the source of this discrepancy, as it would be difficult to explain a uniform temperature offset over such a wide range of masses, ages, and activity levels in the context of evolutionary models. Our results contrast those of Konopacky et al. as we find an opposite and smaller mass discrepancy from what they report when we adopt their model-testing approach since our Teff estimates from fitting spectra are ~650 K higher than from their fitting of broadband photometry alone.
We present the results of a comprehensive Keck/DEIMOS spectroscopic survey of the ultra-faint Milky Way satellite galaxy Segue 1. We have obtained velocity measurements for 99.1% of the stars within 67 pc (2.3 half-light radii) of the center of Segue 1 that have colors and magnitudes consistent with membership, down to a magnitude limit of r=21.7. Based on photometric, kinematic, and metallicity information, we identify 71 stars as probable Segue 1 members, including some as far out as 87 pc. After correcting for the influence of binary stars using repeated velocity measurements, we determine a velocity dispersion of 3.7^{+1.4}_{-1.1} km/s, with a corresponding mass within the half-light radius of 5.8^{+8.2}_{-3.1} x 10^5 Msun. The stellar kinematics of Segue 1 require very high mass-to-light ratios unless it is far from dynamical equilibrium, even if the period distribution of unresolved binary stars is skewed toward implausibly short periods. With a total luminosity less than that of a single bright red giant and a V-band mass-to-light ratio of 3400 Msun/Lsun, Segue 1 is the darkest galaxy currently known. We critically re-examine recent claims that Segue 1 is a tidally disrupting star cluster and that kinematic samples are contaminated by the Sagittarius stream. The extremely low metallicities ([Fe/H] < -3) of two Segue 1 stars and the large metallicity spread among the members demonstrate conclusively that Segue 1 is a dwarf galaxy, and we find no evidence in favor of tidal effects. We also show that contamination by the Sagittarius stream has been overestimated. Segue 1 has the highest measured dark matter density of any known galaxy and will therefore be a prime testing ground for dark matter physics and galaxy formation on small scales.
We use new kinematic data from the ultra-faint Milky Way satellite Segue 1 to model its dark matter distribution and derive upper limits on the dark matter annihilation cross-section. Using gamma-ray flux upper limits from the Fermi satellite and MAGIC, we determine cross-section exclusion regions for dark matter annihilation into a variety of different particles including charged leptons. We show that these exclusion regions are beginning to probe the regions of interest for a dark matter interpretation of the electron and positron fluxes from PAMELA, Fermi, and HESS, and that future observations of Segue 1 have strong prospects for testing such an interpretation. We additionally discuss prospects for detecting annihilation with neutrinos using the IceCube detector, finding that in an optimistic scenario a few neutrino events may be detected. Finally we use the kinematic data to model the Segue 1 dark matter velocity dispersion and constrain Sommerfeld enhanced models.
The excursion set theory based on spherical or ellipsoidal gravitational collapse provides an elegant analytic framework for calculating the mass function and the large-scale bias of dark matter haloes. This theory assumes that the perturbed density field evolves stochastically with the smoothing scale and exhibits Markovian random walks in the presence of a density barrier. Here we derive an analytic expression for the halo bias in a new theoretical model that incorporates non-Markovian extension of the excursion set theory with a stochastic barrier. This model allows us to handle non-Markovian random walks and to calculate perturbativly these corrections to the standard Markovian predictions for the halo mass function and halo bias. Our model contains only two parameters: kappa, which parameterizes the degree of non-Markovianity and whose exact value depends on the shape of the filter function used to smooth the density field, and a, which parameterizes the degree of stochasticity of the barrier. Appropriate choices of kappa and a in our new model can lead to a closer match to both the halo mass function and halo bias in the latest N-body simulations than the standard excursion set theory.
The spin of black holes in black hole-neutron star (BHNS) binaries can have a strong influence on the merger dynamics and the postmerger state; a wide variety of spin magnitudes and orientations are expected to occur in nature. In this paper, we report the first simulations in full general relativity of BHNS mergers with misaligned black hole spin. We vary the spin magnitude from a/m=0 to a/m=0.9 for aligned cases, and we vary the misalignment angle from 0 to 80 degrees for a/m=0.5. We restrict our study to 3:1 mass ratio systems and use a simple Gamma-law equation of state. We find that the misalignment angle has a strong effect on the mass of the postmerger accretion disk, but only for angles greater than ~ 40 degrees. Although the disk mass varies significantly with spin magnitude and misalignment angle, we find that all disks have very similar lifetimes ~ 100ms. Their thermal and rotational profiles are also very similar. For a misaligned merger, the disk is tilted with respect to the final black hole's spin axis. This will cause the disk to precess, but on a timescale longer than the accretion time. In all cases, we find promising setups for gamma-ray burst production: the disks are hot, thick, and hyperaccreting, and a baryon-clear region exists above the black hole.
Future astrophysical datasets promise to strengthen constraints on models of inflation, and extracting these constraints requires methods and tools commensurate with the quality of the data. In this paper we describe ModeCode, a new, publicly available code that computes the primordial scalar and tensor power spectra for single field inflationary models. ModeCode solves the inflationary mode equations numerically, avoiding the slow roll approximation. It is interfaced with CAMB and CosmoMC to compute cosmic microwave background angular power spectra and perform likelihood analysis and parameter estimation. ModeCode is easily extendable to additional models of inflation, and future updates will include Bayesian model comparison. Errors from ModeCode contribute negligibly to the error budget for analyses of data from Planck or other next generation experiments. We constrain representative single field models (phi^n with n=2/3, 1, 2, and 4, natural inflation, and "hilltop" inflation) using current data, and provide forecasts for Planck. From current data, we obtain weak but nontrivial limits on the post-inflationary physics, which is a significant source of uncertainty in the predictions of inflationary models, while we find that Planck will dramatically improve these constraints. In particular, Planck will link the inflationary dynamics with the post-inflationary growth of the horizon, and thus begin to probe the "primordial dark ages" between TeV and GUT scale energies.
(abbreviated) We perform hydrodynamical simulations of minor-merger induced gas sloshing and the subsequent formation of cold fronts. Using the Virgo cluster as a test case, we show for the first time that the sloshing scenario can reproduce the radii and the contrasts in X-ray brightness, pro jected temperature, and metallicity across the observed cold fronts quantitatively. We identify several new features typical for sloshing cold fronts: an alternating distribution of cool, metal enriched X-ray brightness excess regions and warm brightness deficit regions of reduced metallicity; a constant or radially decreasing temperature accompanied by a plateau in metallicity inside the cold fronts; a warm rim outside the CFs; and a large-scale brightness excess towards the responsible subcluster, which will be helpful for its identification. We can trace these new features not only in Virgo, but also in other clusters exhibiting sloshing cold fronts. By comparing synthetic and real observations, we estimate that the causative minor merger event took place about 1 Gyr ago when a subcluster of 2-4 x 10 13 Msun passed the Virgo core at 100 to 400 kpc distance, where a smaller mass corresponds to a smaller pericentre distance, and vice versa. Our line-of-sight is approximately perpendicular to the orbital plane of the subcluster. The most likely candidate is the galaxy group around NGC 4365, currently located about 5 degree (1.6 Mpc) south of the Virgo centre. Additionally, for the first time we quantify the metal redistribution by sloshing and discuss its importance. Finally, we demonstrate that the bow shock of a fast galaxy passing the Virgo cluster at ~ 400 kpc distance also causes sloshing and leads to very similar cold front structures. The responsible galaxy would be located about 2.2 Mpc north of the Virgo centre.
Photometry of the unique pre-main sequence binary system KH 15D is presented, spanning the years 2005-2010. This system has exhibited photometric variations and eclipses over the last 50 years caused by a precessing circumbinary disk. Advancement of the occulting edge across the binary orbit has continued and the photospheres of both stars are now completely obscured at all times. The system is now visible only by scattered light, and yet it continues to show a periodic variation on the orbital cycle with an amplitude exceeding two magnitudes. This variation, which depends only on the binary phase, has likely been present in the data since at least 1995. It can, by itself, account for shoulders on the light curve prior to ingress and following egress, obviating the need for components of extant models such as a scattering halo around star A or forward scattering from a fuzzy disk edge. A plausible source for the variable scattering component is reflected light from the far side of a warped occulting disk. We have detected color changes in V-I of several tenths of a magnitude to both the blue and red that occur during times of minima. These may indicate the presence of a third source of light (faint star) within the system, or a change in the reflectance properties of the disk as the portion being illuminated varies with the orbital motion of the stars. The data support a picture of the circumbinary disk as a geometrically thin, optically thick layer of perhaps mm or cm-sized particles that has been sculpted by the binary stars and possibly other components into a decidedly nonplanar configuration. A simple (infinitely sharp) knife-edge model does a good job of accounting for all of the recent (2005-2010) occultation data.
We have obtained deep near infrared J- and K-band observations of 14 BL Herculis and 5 W Virginis SMC stars from the OGLE III survey with the ESO New Technology Telescope equipped with the SOFI infrared camera. From these observations, period-luminosity (P-L) relations in the J and Ks 2MASS bands were derived. The slopes of the K and J band relations of -2.15 +- 0.19 and -1.95 +- 0.24, respectively, agree very well with the corresponding slopes derived previously for population II Cepheids in globular clusters, Galactic bulge and in the Large Magellanic Cloud. The distance modulus to the SMC obtained from our data using P-L relation derived for globular cluster Cepheids equals 18.85 +- 0.07 (statistical) +- 0.07 (systematic without including potential metallicity effect), which within the uncertainties agrees well with the results obtained with other methods.
The 6.7 GHz maser transition of methanol has been found exclusively towards massive star forming regions. A majority of the masers have been found to lack the presence of any associated radio continuum. This could be due to the maser emission originating prior to the formation of an HII region around the central star, or from the central object being too cool to produce a HII region. One way to distinguish between the two scenarios is to determine and model the spectral energy distributions (SEDs) of the masers. We observed a sample of 20 6.7 GHz methanol masers selected from the blind Arecibo survey, from centimeter to submillimeter wavelengths. We combined our observations with existing data from various Galactic plane surveys to determine SEDs from centimeter to near-infrared wavelengths. We find that 70% of the masers do not have any associated radio continuum, with the rest of the sources being associated with hypercompact and ultracompact HII regions. Modeling the SEDs shows them to be consistent with rapidly accreting massive stars, with accretion rates well above 10^{-3} M_sun/yr. The upper limits on the radio continuum are also consistent with any ionized region being confined close to the stellar surface. This confirms the paradigm of 6.7 GHz methanol masers being signposts of early phases of massive star formation, mostly prior to the formation of a hypercompact HII region.
We present observations of twelve rotational transitions of H2O-16, H2O-18,
and H2O-17 toward the massive star-forming region NGC 6334 I, carried out with
Herschel/HIFI as part of the guaranteed time key program Chemical HErschel
Surveys of Star forming regions (CHESS). We analyze these observations to
obtain insights into physical processes in this region.
We identify three main gas components (hot core, cold foreground, and
outflow) in NGC 6334 I and derive the physical conditions in these components.
The hot core, identified by the emission in highly excited lines, shows a
high excitation temperature of 200 K, whereas water in the foreground component
is predominantly in the ortho- and para- ground states. The abundance of water
varies between 4 10^-5 (outflow) and 10^-8 (cold foreground gas). This
variation is most likely due to the freeze-out of water molecules onto dust
grains. The H2O-18/H2O-17 abundance ratio is 3.2, which is consistent with the
O-18/O-17 ratio determined from CO isotopologues. The ortho/para ratio in water
appears to be relatively low 1.6(1) in the cold, quiescent gas, but close to
the equilibrium value of three in the warmer outflow material (2.5(0.8)).
High-resolution N-body simulations of dark matter halos indicate that the Milky Way contains numerous subhalos. When a dark matter subhalo passes in front of a star, the light from that star will be deflected by gravitational lensing, leading to a small change in the star's apparent position. This astrometric microlensing signal depends on the inner density profile of the subhalo and can be greater than a few microarcseconds for an intermediate-mass subhalo (Mvir > 10000 solar masses) passing within arcseconds of a star. Current and near-future instruments could detect this signal, and we evaluate SIM's, Gaia's, and ground-based telescopes' potential as subhalo detectors. We develop a general formalism to calculate a subhalo's astrometric lensing cross section over a wide range of masses and density profiles, and we calculate the lensing event rate by extrapolating the subhalo mass function predicted by simulations down to the subhalo masses potentially detectable with this technique. We find that, although the detectable event rates are predicted to be low on the basis of current simulations, lensing events may be observed if the central regions of dark matter subhalos are more dense than current models predict (>1 solar mass within 0.1 pc of the subhalo center). Furthermore, targeted astrometric observations can be used to confirm the presence of a nearby subhalo detected by gamma-ray emission. We show that, for sufficiently steep density profiles, ground-based adaptive optics astrometric techniques could be capable of detecting intermediate-mass subhalos at distances of hundreds of parsecs, while SIM could detect smaller and more distant subhalos.
We develop analytic solutions for the linear evolution of metric perturbations in the DGP braneworld modified gravity scenario including near-horizon and superhorizon modes where solutions in the bulk are required. These solutions apply to both the self-accelerating and normal branch and elucidate the nature of coordinate singularities and initial data in the bulk as well as their effect on perturbation evolution on the brane. Even on superhorizon scales, the evolution of metric perturbations is no longer necessarily scale free due to multiple resonances in the bulk. Based on these analytic solutions, we devise convenient fitting functions for the evolution that bridge the various spatial and temporal regimes. Compared with a direct numerical integration of the bulk equations, the fits are accurate at the percent level and are sufficient for current and upcoming observational tests.
In this short review on stellar convection dynamics I address the following, currently very topical, issues: (1) the surface effects of the Reynolds stresses and nonadiabaticity on solar-like pulsation frequencies, and (2) oscillation mode lifetimes of stochastically excited oscillations in red giants computed with different time-dependent convection formulations.
Polarization has been detected at early times for all types of supernova, indicating that such systems result from or quickly develop some form of asymmetry. In addition, the detection of strong line polarization in supernovae is suggestive of chemical inhomogeneities ("clumps") in the layers above the photosphere, which may reflect hydrodynamical instabilities during the explosion. We have developed a fast, flexible, approximate semi-analytic code for modeling polarized line radiative transfer within 3-D inhomogeneous rapidly-expanding atmospheres. Given a range of model parameters, the code generates random sets of clumps in the expanding ejecta and calculates the emergent line profile and Stokes parameters for each configuration. The ensemble of these configurations represents both the effects of various host geometries and of different viewing angles. We present results for the first part of our survey of model geometries, specifically the effects of the number and size of clumps (and the related effect of filling factor) on the emergent spectrum and Stokes parameters. Our simulations show that random clumpiness can produce line polarization in the range observed in SNe Ia (~1-2%), as well as the Q-U loops that are frequently seen in all SNe. We have also developed a method to connect the results of our simulations to robust observational parameters such as maximum polarization and polarized equivalent width in the line. Our models, in connection with spectropolarimetric observations, can constrain the 3-D structure of supernova ejecta and offer important insight into the SN explosion physics and the nature of their progenitor systems.
Using a detailed Galactic model in which we consider distinct contributions from the bulge, thin disc, thick disc, and halo, and a population synthesis approach, we determined the birth rates, numbers, and period distributions of double white dwarfs (DWDs) within each component. In the Galaxy as a whole, our model predicts the current birth rate of DWDs to be 3.21x10^{-2} yr^{-1}, the local density to be 2.2x10^{-4} pc^{-3} and the total number to be 2.76x10^{8}. Assuming SNIa are formed from the merger of two CO white dwarfs, the SNIa rate should be 0.0013 yr^{-1}. The frequency spectra of DWD strain amplitude and number distribution are presented as a function of galactic component, DWD type, formation channel, and metallicity. We confirm that CO+He and He+He white dwarf (WD) pairs should dominate the GW signal at very high frequencies (log f Hz^{-1} > -2.3), while CO+CO and ONeMg WD pairs have a dominant contribution at log f Hz^{-1} < -2.3. Formation channels involving two common-envelope (CE) phases or a stable Roche lobe overflow phase followed by a CE phase dominate the production of DWDs detectable by LISA at log f Hz^{-1} > -4.5. DWDs with the shortest orbital periods will come from the CE+CE channel. The Exposed Core plus CE channel is a minor channel. A number of resolved DWDs would be detected, making up 0.012% of the total number of DWDs in the Galaxy. The majority of these would be CO+He and He+He pairs formed through the CE+CE channel.
We calculate the scale dependence of the bispectrum and trispectrum in (quasi) local models of non-Gaussian primordial density perturbations, and characterize this scale dependence in terms of new observable parameters. They can help to discriminate between models of inflation, since they are sensitive to properties of the inflationary physics that are not probed by the standard observables. We find consistency relations between these parameters in certain classes of models. We apply our results to a scenario of modulated reheating, showing that the scale dependence of non-Gaussianity can be significant. We also discuss the scale dependence of the bispectrum and trispectrum, in cases where one varies the shape as well as the overall scale of the figure under consideration. We conclude providing a formulation of the curvature perturbation in real space, which generalises the standard local form by dropping the assumption that f_NL and g_NL are constants.
We study the mass and spin evolution in a symbiotic system consisting of a black hole with magnetosphere and jets, surrounded by a steady-state, thin accretion disk. We analyze how the limiting value of the spin parameter and the conversion efficiency of accreted mass into radiation depend on the interplay of electromagnetic radiation reaction, magnetosphere characteristics and jet cross-section. As a main result, we find that the presence of the jets increases the spin limit (basically obstructing the reverse effect of radiation in the innermost region of the accretion disk) and enhances the energy conversion efficiency.
We present the first light commissioning results from the Physical Research Laboratory (PRL) optical fiber-fed high resolution cross-dispersed Echelle Spectrograph. It is capable of a single- shot spectral coverage of 3700A to 8600A at R ~ 63,000 and is under very stable conditions of temperature (0.04{\deg}C at 23{\deg}C). In the very near future pressure control will also be achieved by enclosing the entire spectrograph in a low-pressure vacuum chamber (~0.01mbar). It is attached to a 1.2m telescope using two 50micron core optical fibers (one for the star and another for simultaneous Th-Ar spectral calibration). The 1.2m telescope is located at Mt. Abu, India, and we are guaranteed about 80 to 100 nights a year for observations with the spectrograph. The instrument will be ultimately used for radial-velocity searches of exoplanets around 1000 dwarf stars, brighter than 10th magnitude, for the next 5 years with a precision of 3 to 5m/s using the simultaneous Th-Ar spectral lamp reference technique. The spectrograph has already achieved a stability of 3.7m/s in short-term time scale and in the near future we expect the stability to be at 1m/s once we install the spectrograph inside the vacuum chamber.
The brightest events in a time series of cosmological transients obey an observation time dependence which is often overlooked. This dependence can be exploited to probe the global properties of electromagnetic and gravitational wave transients (Howell et al. 2007a, Coward & Burman 2005). We describe a new relation based on a peak flux--observation time distribution and show that it is invariant to the luminosity distribution of the sources (Howell et al. 2007b). Applying this relation, in combination with a new data analysis filter, to \emph{Swift} gamma-ray burst data, we demonstrate that it can constrain their rate density.
We identify 231 objects in the newly released Cycle 0 dataset from the Kepler Mission as double-lined, detached eclipsing binary systems with Teff < 5500 K and orbital periods shorter than ~32 days. We model each light curve using the JKTEBOP code to obtain precise values for each system. For each binary we provide their Kepler ID, effective temperature, Kepler magnitude, orbital period, time of primary minimum, inclination, eccentricity, longitude of periastron, surface brightness ratio, sum of the fractional radii, ratio of the radii, and luminosity ratio. Of these binaries, we identify 142 as systems that contain two main-sequence stars with at least one component having a mass M < 1.0 M_sun, and provide the estimated effective temperature, mass, and radius of each component. 91 systems have eclipse depths of at least 0.1 magnitude, and thus are suitable for ground-based follow-up, with 79 having both components with masses < 1.0 M_sun. Of these 79 systems, 11 have periods less than 1.0 day, 43 have periods between 1.0 and 10.0 days, and 25 have periods greater than 10.0 days. This new sample of low-mass, double-lined, detached eclipsing binary candidates more than doubles the number of previously known systems, and extends the sample into the completely heretofore unexplored P > 10.0 day period regime. We find preliminary evidence from these systems that the radii of low-mass stars in binary systems decrease with period, with 40.0% of systems with P > 10.0 days agreeing to within 5% of theoretical models, compared to only 9.0% of systems with P < 1.0 day. This supports the theory that binary spin-up is the primary cause of inflated radii in low-mass binary systems. With follow-up radial-velocity and multi-color light curves, it will be possible to more precisely determine the mass-radius-temperature relation for the lower main-sequence and fully explore this hypothesis.
We describe a new finite element method (FEM) to construct continuous equilibrium distribution functions of stellar systems. The method is a generalization of Schwarzschild's orbit superposition method from the space of discrete functions to continuous ones. In contrast to Schwarzschild's method, FEM produces a continuous distribution function (DF) and satisfies the intra element continuity and Jeans equations. The method employs two finite-element meshes, one in configuration space and one in action space. The DF is represented by its values at the nodes of the action-space mesh and by interpolating functions inside the elements. The Galerkin projection of all equations that involve the DF leads to a linear system of equations, which can be solved for the nodal values of the DF using linear or quadratic programming, or other optimization methods. We illustrate the superior performance of FEM by constructing ergodic and anisotropic equilibrium DFs for spherical stellar systems (Hernquist models). We also show that explicitly constraining the DF by the Jeans equations leads to smoother and/or more accurate solutions with both Schwarzschild's method and FEM.
We review feasibility studies, technological developments and astrophysical prospects for Laue lenses devoted to unprecedented hard X-/gamma-ray astronomy observations.
With the development of extreme high contrast ground-based adaptive optics instruments and space missions aimed at detecting and characterizing Jupiter- and terrestrial-mass planets, it is critical that each target star be thoroughly vetted to determine whether it is a viable target given both the instrumental design and scientific goals of the program. With this in mind, we have conducted a high contrast imaging survey of mature AFGKM stars with the PALAO/PHARO instrument on the Palomar 200 inch telescope. The survey reached sensitivities sufficient to detect brown dwarf companions at separations of > 50 AU. The results of this survey will be utilized both by future direct imaging projects such as GPI, SPHERE and P1640 and indirect detection missions such as SIM Lite. Out of 84 targets, all but one have no close-in (0.45-1") companions and 64 (76%) have no stars at all within the 25" field-of-view. The sensitivity contrasts in the Ks passband ranged from 4.5 to 10 for this set of observations. These stars were selected as the best nearby targets for habitable planet searches owing to their long-lived habitable zones (> 1 billion years). We report two stars, GJ 454 and GJ 1020, with previously unpublished proper motion companions. In both cases, the companions are stellar in nature and are most likely M dwarfs based on their absolute magnitudes and colors. Based on our mass sensitivities and level of completeness, we can place an upper limit of ~17% on the presence of brown dwarf companions with masses >40 MJ at separations of 1 arcsecond. We also discuss the importance of including statistics on those stars with no detected companions in their field of view for the sake of future companion searches and an overall understanding of the population of low-mass objects around nearby stars.
A novel mechanism for explaining the matter-antimatter asymmetry of the universe is considered. The mechanism does not require the baryon number violating interactions or CP violation at a microscopic level. Our analysis of the matter-antimatter asymmetry is in the context of salient experimental results obtained in the condensed matter physics.
We perform a numerical simulation of the corona of the young, rapidly rotating K0 dwarf AB Doradus using a global MHD model. The model is driven by a surface map of the radial magnetic field constructed using Zeeman-Doppler Imaging. We find that the global structure of the stellar corona is dominated by strong azimuthal tangling of the magnetic field due to the rapid rotation. The MHD solution enables us to calculate realistic Alfv\'en surfaces and we can therefore estimate the stellar mass loss rate and angular momentum loss rate without making undue theoretical simplifications. We consider three cases, parametrized by the base density of the corona, that span the range of possible solutions for the system. We find that overall, the mass and angular-momentum loss rates are higher than in the solar case; the mass loss rates are 10 to 500 times higher, and the angular momentum loss rate can be up to $3\times{10}^4$ higher than present day solar values. Our simulations show that this model can be use to constrain the wide parameter space of stellar systems. It also shows that an MHD approach can provide more information about the physical system over the commonly used potential field extrapolation.
We present results of numerical modeling made for the galactic stellar and stellar-gas disk embedded in the spherical halo and bulge. The stellar disk is simulated by N-body system, the equations of hydrodynamics are solved by TVD-method. We used TREEcode-algorithm for calculation of a self-gravity in stellar and gaseous components. The possibility of bars birth in a hot stellar disk because of gravitational instability of a cold gas component is investigated. The conditions of occurrence lopsided-galaxies from a axisymmetric disk as a result of gravitational instability are explored. The self-consistent models of double bars are constructed and the dynamical stability of these structures is discussed.
Wolf-Rayet stars have been identified as objects in their final phase of massive star evolution. It has been suggested that Wolf-Rayet stars are the progenitors of long-duration gamma ray bursts in low metallicity environments. However, this deduction has yet to be proven. Here we report on our initial results from a VLT/FORS linear spectropolarimetry survey of Wolf-Rayet stars in the Magellanic Clouds, which is intended to constrain the physical criteria - such as weaker stellar winds, rapid rotation, and associated asymmetry - of the collapsar model. Finally, we provide an outlook for polarisation studies with an extremely large telescope.
We review compare and extend recent studies searching for evidence for a preferred cosmological axis. We start from the Union2 SnIa dataset and use the hemisphere comparison method to search for a preferred axis in the data. We find that the hemisphere of maximum accelerating expansion rate is in the direction (l,b)=(306^\circ, 15^\circ) (\Omega_m=0.19) while the hemisphere of minimum acceleration is in the opposite direction (l,b)=(126^\circ, -15^\circ) (\Omega_m=0.30). The level of anisotropy is described by the normalized difference of the best fit values of \Omega_m between the two hemispheres in the context of \lcdm fits. We find a maximum anisotropy level in the Union2 data of \frac{\Delta \Omega_m_max}{\Omega_m}=0.42. This level does not necessarily correspond to statistically significant anisotropy because it is reproduced by about 30% of simulated isotropic data mimicking the best fit Union2 dataset. However, when combined with the axes directions of other cosmological observations (bulk velocity flow axis, three axes of CMB low multipole moments and quasar optical polarization alignment axis), the statistical evidence for a cosmological anisotropy increases dramatically. We estimate the probability that the above independent six axes directions would be so close in the sky to be less than 1%. Thus either the relative coincidence of these six axes is a very large statistical fluctuation or there is an underlying physical or systematic reason that leads to their correlation.
We present an extended analysis of deep Chandra HETG observations of the WR+OB binary system WR 147 that was resolved into a double X-ray source (Zhekov & Park, 2010, ApJ, 709, L119). Our analysis of the profiles of strong emission lines shows that their centroids are blue-shifted in the spectrum of the northern X-ray source. We find no suppressed forbidden line in the He-like triplets which indicates that the X-ray emitting region is not located near enough to the stars in the binary system to be significantly affected by their UV radiation. The most likely physical picture that emerges from the entire set of HETG data suggests that the northern X-ray source can be associated with the colliding stellar wind region in the wide WR+OB binary system, while the X-rays of its southern counterpart, the WN8 star, are result from stellar wind shocking onto a close companion (a hypothesized third star in the system).
We present a set-up called TIANSHAN Radio Experiment for Neutrino Detection (TREND), being presently deployed on the site of the 21 cm array (21CMA) radio telescope, in XinJiang, China. We describe here its detection performances as well as the analysis method we applied to the data recorded with a small scale prototype. We demonstrate the ability of the TREND set-up for an autonomous radio-detection of extended air showers induced by cosmic rays. The full set-up will consist of 80 antennas deployed over a 4 km2 area, and could result in a very attractive and unequalled radio-detection facility for the characterisation of showers induced by ultra-high energy neutrinos with energies around 10^17 eV.
A two-component hydrodynamic model is constructed of the global superfluid flow induced by two-component Ekman pumping during the recovery stage of a glitch. The model successfully accounts for the quasi-exponential recovery observed in pulsars like Vela and the "overshoot" observed in pulsars like the Crab. By fitting the model to high-resolution timing data, three important constitutive coefficients in bulk nuclear matter can be extracted: the shear viscosity, the mutual friction parameter, and the charged fluid fraction. The fitted coefficients for the Crab and Vela are compared with theoretical predictions for several equations of state, including the color-flavor locked and two-flavor color superconductor phases of quark matter.
Early results from the Herschel Space Observatory revealed the water cation H2O+ to be an abundant ingredient of the interstellar medium. Here we present new observations of the H2O and H2O+ lines at 1113.3 and 1115.2 GHz using the Herschel Space Observatory toward a sample of high-mass star-forming regions to observationally study the relation between H2O and H2O+ . Nine out of ten sources show absorption from H2O+ in a range of environments: the molecular clumps surrounding the forming and newly formed massive stars, bright high-velocity outflows associated with the massive protostars, and unrelated low-density clouds along the line of sight. Column densities per velocity component of H2 O+ are found in the range of 10^12 to a few 10^13 cm-2 . The highest N(H2O+) column densities are found in the outflows of the sources. The ratios of H2O+/H2O are determined in a range from 0.01 to a few and are found to differ strongly between the observed environments with much lower ratios in the massive (proto)cluster envelopes (0.01-0.1) than in outflows and diffuse clouds. Remarkably, even for source components detected in H2O in emission, H2O+ is still seen in absorption.
U 2206+54 is a wind-fed high mass X-ray binary with a main-sequence donor star. The nature of its compact object was recently identified as a slow-pulsation magnetized neutron star. INTEGRAL/IBIS observations have a long-term hard X-ray monitoring of 4U 2206+54 and detected a hard X-ray outburst around 15 December 2005 combined with the RXTE/ASM data.The hard X-ray outburst had a double-flare feature with a duration of $\sim$ 2 days. The first flare showed a fast rise and long time decaying light curve about 15 hours with a peak luminosity of $\sim 4\times 10^{36}$ erg s$^{-1}$ from 1.5 -- 12 keV and a hard spectrum (only significantly seen above 5 keV). The second one had the mean hard X-ray luminosity of $1.3\times 10^{36}$ erg s$^{-1}$ from 20 -- 150 keV with a modulation period at $\sim 5550$ s which is the pulse period of the neutron star in 4U 2206+54; its hard X-ray spectrum from 20 -- 300 keV can be fitted with a broken power-law model with the photon indexes $\Gamma_1 \sim 2.3,\ \Gamma_2 \sim 3.3$, and the break energy is $E_b \sim 31$ keV or a bremsstrahlung model of $kT\sim 23$ keV. We suggest that the hard X-ray flare could be induced by suddenly enhanced accretion dense materials from stellar winds hitting the polar cap region of the neutron star. This hard X-ray outburst may be a link to supergiant fast X-ray transients though 4U 2206+54 has a different type of companion.
We present observations of seven transits and seven eclipses of the transiting planet system HD 189733 taken with Spitzer IRAC at 8 microns. We use a new correction for the detector ramp variation with a double-exponential function. Our main findings are: (1) an upper limit on the variability of the day-side planet flux of 2.7% (68% confidence); (2) the most precise set of transit times measured for a transiting planet, with an average accuracy of 3 seconds; (3) a lack of transit-timing variations, excluding the presence of second planets in this system above 20% of the mass of Mars in low-order mean-motion resonance at 95% confidence; (4) a confirmation of the planet's phase variation, finding the night side is 64% as bright as the day side, as well as an upper limit on the night-side variability of 17% (68% confidence); (5) a better correction for stellar variability at 8 micron causing the phase function to peak 3.5 hrs before secondary eclipse, confirming that the advection and radiation timescales are comparable at the 8 micron photosphere; (6) variation in the depth of transit, which possibly implies variations in the surface brightness of the portion of the star occulted by the planet, posing a fundamental limit on non-simultaneous multi-wavelength transit absorption measurements of planet atmospheres; (7) a measurement of the infrared limb-darkening of the star, in agreement with stellar atmosphere models; (8) an offset in the times of secondary eclipse of 69 sec, which is mostly accounted for by a 31 sec light travel time delay and 33 sec delay due to the shift of ingress and egress by the planet hot spot; this confirms that the phase variation is due to an offset hot spot on the planet; (9) a retraction of the claimed eccentricity of this system due to the offset of secondary eclipse; and (10) high precision measurements of the parameters of this system.
We investigate the prospects for discovering blazars at very high-redshifts (z>6) with the Fermi Gamma-Ray Space Telescope (Fermi), employing a model for the evolving gamma-ray luminosity function (GLF) of the blazar population. Our previous GLF model is used as a basis, which features luminosity-dependent density evolution implied from X-ray data on active galactic nuclei, as well as the blazar sequence paradigm for their spectral energy distribution, and which is consistent with EGRET and current Fermi observations of blazars.Here we augment the high-redshift evolution of this model by utilizing the luminosity function of quasars from the Sloan Digital Sky Survey (SDSS), which is well-constrained up to z~5. We find that Fermi may discover a few blazars up to z~6 in the entire sky during its 5-year survey. We further discuss how such high-redshift blazar candidates may be efficiently selected in future Fermi data.
We pick out the 35 brightest galaxies from Goto's E+A galaxies catalogue which are selected from the Sloan Digital Sky Survey Data Release 5. The spectra of E+As are prominently characterized by the strong Balmer absorption lines but little [Oii] or H_alpha emission lines. In this work we study the stellar populations of the sample galaxies by fitting their spectra using ULySS, which is a robust full spectrum fitting method. We fit each of the sample with 1-population (a single stellar population-a SSP) and 3-population (3 SSPs) models, separately. By 1-population fits, we obtain SSP-equivalent ages and metallicities which correspond to the `luminosity-weighted' averages. By 3-population fits, we divide components into three groups in age (old stellar population-OSP, intermediate-age stellar population-ISP, and young stellar population-YSP), and then get the optimal age, metallicity and population fractions in both mass and light for OSP, ISP and YSP. During the fits, both Pegase.HR/Elodie3.1 and Vazdekis/Miles are used as two independent population models. The two models result in generally consistent conclusions as follows: for all the sample galaxies, YSPs (< 1Gyr) make important contributions to the light. However, the dominant contributors to mass are OSPs. We also reconstruct the smoothing star formation histories (SFHs) by giving star formation rate (SFR) versus evolutionary age. In addition, we fit the E+A sample and 34 randomly selected elliptical galaxies with 2-population (2 SSPs) model. We obtain the equivalent age of old components for each of the E+A sample and elliptical galaxies. By comparison, the old components of E+As are statistically much younger than those of ellipticals. From the standpoint of the stellar population age, this probably provides an evidence for the proposed evolutionary link from E+As to early-types (E/S0s).
We have carried out multi-epoch VLBI observations with VERA (VLBI Exploration of Radio Astrometry) of the 22~GHz H$_{2}$O masers associated with a Class 0 protostar L1448C in the Perseus molecular cloud. The maser features trace the base of collimated bipolar jet driven by one of the infrared counter parts of L1448C named as L1448C(N) or L1448-mm A. We detected possible evidences for apparent acceleration and precession of the jet according to the three-dimensional velocity structure. Based on the phase-referencing VLBI astrometry, we have successfully detected an annual parallax of the H$_{2}$O maser in L1448C to be 4.31$\pm$0.33~milliarcseconds (mas) which corresponds to a distance of 232$\pm$18~pc from the Sun. The present result is in good agreement with that of another H$_{2}$O maser source NGC~1333 SVS13A in the Perseus molecular cloud, 235~pc. It is also consistent with the photometric distance, 220~pc. Thus, the distance to the western part of the Perseus molecular cloud complex would be constrained to be about 235~pc rather than the larger value, 300~pc, previously reported.
To account for the non-thermal emission from the classical nova V2491 Cygni, we perform a series of numerical calculations of radiative transfer of gamma-ray photons from the radioactive isotope $^{22}$Na in the matter ejected from a white dwarf. Using a simple wind model for the dynamical evolution of the ejecta and a monte-carlo code, we calculate radiative transfer of the gamma-ray photons in the ejecta. Repeated scattering of the gamma-ray photons by electrons in the ejecta, i.e., Compton degradation, results in an extremely flat spectrum in the hard X-ray range, which successfully reproduces the observed spectrum of the X-ray emission from V2491 Cygni. The amount of the isotope $^{22}$Na synthesized in the ejecta is required to be $3/times 10^{-5}/ M_/odot$ to account for the flux of the hard X-ray emission. Our model indicates that the ejecta become transparent to the gamma-ray photons within several tens days. Using the results, we discuss the detectability of the gamma-ray line emission by the INTEGRAL gamma-ray observatory and the Fermi Gamma-ray Space Telescope.
X-ray emission from the supernova remnant N23 in the Large Magellanic Cloud (LMC) is studied using the X-ray Imaging Spectrometer (XIS) onboard Suzaku. Thanks to superior energy resolution of the XIS in the soft X-ray band, we resolved H-like and He-like Oxygen K\alpha emission lines from N23 with unprecedentedly high quality, and as a result, identified a new optically thin thermal emission component with a temperature ~0.2 keV, as well as that with a temperature of ~0.5-0.7 keV previously known. This alters the estimate of the ionization timescale net from ~10^{10-11} cm^-3s to >~10^{12} cm^{-3}s. Under the assumption that N23 is still in the Sedov phase, its age evaluated from the newly discovered low temperature component is ~8000 yr, although it is possible that N23 has already moved into the radiative phase. The abundances of the heavy elements are found to be roughly consistent with those of the LMC average, which indicates that the origin of the X-ray emission of N23 is swept-up ambient material, as expected from its ionization timescale.
From observations collected with the ESPaDOnS & NARVAL spectropolarimeters at
CFHT and TBL, we report the detection of Zeeman signatures on the prototypical
classical TTauri star AATau, both in photospheric lines and accretion-powered
emission lines. Using time series of unpolarized and circularly polarized
spectra, we reconstruct at two epochs maps of the magnetic field, surface
brightness and accretion-powered emission of AATau. We find that AATau hosts a
2-3kG magnetic dipole tilted at ~20deg to the rotation axis, and of presumably
dynamo origin. We also show that the magnetic poles of AATau host large cool
spots at photospheric level and accretion regions at chromospheric level.
The logarithmic accretion rate at the surface of AATau at the time of our
observations is strongly variable, ranging from -9.6 to -8.5 and equal to -9.2
in average (in Msun/yr); this is an order of magnitude smaller than the disc
accretion rate at which the magnetic truncation radius (below which the disc is
disrupted by the stellar magnetic field) matches the corotation radius (where
the Keplerian period equals the stellar rotation period) - a necessary
condition for accretion to occur. It suggests that AATau is largely in the
propeller regime, with most of the accreting material in the inner disc regions
being expelled outwards and only a small fraction accreted towards the surface
of the star. The strong variability in the observed surface mass-accretion rate
and the systematic time-lag of optical occultations (by the warped accretion
disc) with respect to magnetic and accretion-powered emission maxima also
support this conclusion.
Our results imply that AATau is being actively spun-down by the star-disc
magnetic coupling and appears as an ideal laboratory for studying angular
momentum losses of forming Suns in the propeller regime.
Despite the low elemental deuterium abundance in the Galaxy, enhanced molecular D/H ratios have been found in the environments of low-mass star forming regions, and in particular the Class 0 protostar IRAS 16293-2422. The CHESS (Chemical HErschel Surveys of Star forming regions) Key Program aims at studying the molecular complexity of the interstellar medium. The high sensitivity and spectral resolution of the HIFI instrument provide a unique opportunity to observe the fundamental 1,1,1 - 0,0,0 transition of the ortho-D2O molecule, inaccessible from the ground, and to determine the ortho-to-para D2O ratio. We have detected the fundamental transition of the ortho-D2O molecule at 607.35 GHz towards IRAS 16293-2422. The line is seen in absorption with a line opacity of 0.62 +/- 0.11 (1 sigma). From the previous ground-based observations of the fundamental 1,1,0 - 1,0,1 transition of para-D2O seen in absorption at 316.80 GHz we estimate a line opacity of 0.26 +/- 0.05 (1 sigma). We show that the observed absorption is caused by the cold gas in the envelope of the protostar. Using these new observations, we estimate for the first time the ortho to para D2O ratio to be lower than 2.6 at a 3 sigma level of uncertainty, to be compared with the thermal equilibrium value of 2:1.
The RAdial Velocity Experiment (RAVE) is a spectroscopic survey of the Milky
Way. We use the subsample of spectra with spectroscopically determined values
of stellar parameters to determine the distances to these stars. The list
currently contains 235,064 high quality spectra which show no peculiarities and
belong to 210,872 different stars. The numbers will grow as the RAVE survey
progresses. The public version of the catalog will be made available through
the CDS services along with the ongoing RAVE public data releases.
The distances are determined with a method based on the work by Breddels et
al.~(2010). Here we assume that the star undergoes a standard stellar evolution
and that its spectrum shows no peculiarities. The refinements include: the use
of either of the three isochrone sets, a better account of the stellar ages and
masses, use of more realistic errors of stellar parameter values, and
application to a larger dataset. The derived distances of both dwarfs and
giants match within ~21% to the astrometric distances of Hipparcos stars and to
the distances of observed members of open and globular clusters. Multiple
observations of a fraction of RAVE stars show that repeatability of the derived
distances is even better, with half of the objects showing a distance scatter
of \simlt 11%.
RAVE dwarfs are ~300 pc from the Sun, and giants are at distances of 1 to 2
kpc, and up to 10 kpc. This places the RAVE dataset between the more local
Geneva-Copenhagen survey and the more distant and fainter SDSS sample. As such
it is ideal to address some of the fundamental questions of Galactic structure
and evolution in the pre-Gaia era. Individual applications are left to separate
papers, here we show that the full 6-dimensional information on position and
velocity is accurate enough to discuss the vertical structure and kinematic
properties of the thin and thick disks.
Gamma-ray bursts (GRBs) are the most energetic events after the Big Bang and they have been observed up to very high redshift. By means of measures of chemical abundances now available for the galaxies hosting such events,thought to originate from the explosion of very powerful supernovae (Type Ib/c), we have the opportunity to study the nature of these host galaxies. The aim of this paper is to identify the hosts of Long GRBs (LGRBs) observed both at low and high redshift to see whether the hosts can be galaxies of the same type observed at different cosmic epochs. We adopt detailed chemical evolution models for galaxies of different morphological type (ellipticals, spirals, irregulars) which follow the time evolution of the abundances of several chemical elements (H, He, $\alpha$-elements, Fe), and compare the results with the observed abundances and abundance ratios in galaxies hosting LGRBs. We find that the abundances and abundance ratios predicted by models devised for typical irregular galaxies can well fit the abundances in the hosts both at high and low redshift. We also find that the predicted Type Ib/c supernova rate for irregulars is in good agreement with observations. Models for spirals and particularly ellipticals do not fit the high-redshift hosts of LGRBs (DLA systems) nor the low redshift hosts: in particular, ellipticals cannot possibly be the hosts of gamma-ray-bursts at low redshift since they do not show any star formation, and therefore no supernovae Ib/c. We conclude that the observed abundance and abundance ratios in LGRBs hosts suggest that these hosts are irregular galaxies both at high and low redshift thus showing that the host galaxies belong to in an evolutionary sequence.
Since the detection of the asymptotic properties of the dipole gravity modes in the Sun, the quest to find the individual gravity modes has continued. A deeper analysis of the GOLF/SoHO data unveils the presence of a pattern of peaks that could be interpreted as individual dipole gravity modes. The computed collapsed spectrum -around these candidate modes- uncovers the presence of a quasi constant frequency splitting, in contrast with regions where no g modes are expected in which the collapsogram gives random results. Besides, the same technique applied to VIRGO/SoHO unveils some common signals between both power spectra. Thus, we can identify and characterize the modes, for example, with their central frequency and splittings. This would open the path towards new investigations to better constrain the solar core.
We find a significant number of massive and compact galaxies in clusters from the ESO Distant Clusters Survey (EDisCS) at 0.4<z<1. They have similar stellar masses, ages, sizes and axial ratios to local z~0.04 compact galaxies in WINGS clusters, and to z=1.4-2 massive and passive galaxies found in the general field. If non-BCG cluster galaxies of all densities, morphologies and spectral types are considered, the median size of EDisCS galaxies is only a factor 1.18 smaller than in WINGS. We show that for morphologically selected samples, the morphological evolution taking place in a significant fraction of galaxies during the last Gyrs may introduce an apparent, spurious evolution of size with redshift, which is actually due to intrinsic differences in the selected samples. We conclude that the median mass-size relation of cluster galaxies does not evolve significantly from z~0.7 to z~0.04. In contrast, the masses and sizes of BCGs and galaxies with M*>4x10^11 Msun have significantly increased by a factor of 2 and 4, respectively, confirming the results of a number of recent works on the subject. Our findings show that progenitor bias effects play an important role in the size-growth paradigm of massive and passive galaxies.
The Scorpius-Centaurus association is the most-nearby group of massive and young stars. As nuclear-fusion products are ejected by massive stars and supernovae into the surrounding interstellar medium, the search for characteristic gamma-rays from radioactivity is one way to probe the history of activity of such nearby massive stars on a My time scale through their nucleosynthesis. 26Al decays within ~1 My, 1809 keV gamma-rays from its decay can be measured with current gamma-ray telescopes, such as INTEGRAL's gamma-ray spectrometer SPI. Following earlier 26Al gamma-ray mapping with NASA's Compton observatory, we test spatial emission skymaps of 26Al for a component which could be attributed to ejecta from massive stars in the Scorpius-Centaurus group of stars. Such a model fit of spatial distributions for large-scale and local components is able to discriminate 26Al emission associated with Scorpius-Centaurus, in spite of the strong underlying nucleosynthesis signal from the Galaxy at large. We find an 26Al signal above 5 sigma significance, which we associate with the Sco-Cen group. The observed flux of 6 *10^{-5}ph cm^{-2} s^{-1} corresponds to 1.1 *10^{-4} M_sol of 26Al. This traces the nucleosynthesis ejecta of several massive stars within the past several million years. We confirm through direct detection of radioactive 26Al the recent ejection of massive-star nucleosynthesis products from the Sco-Cen association. Its youngest subgroup in Upper Scorpius appears to dominate 26Al contributions from this association. Our 26Al signal can be interpreted as a measure of the age and richness of this youngest subgroup. We also estimate a kinematic imprint of these nearby massive-star ejecta from the bulk motion of 26Al and compare this to other indications of Scorpius-Centaurus massive-star activity .
We present the Chandra discovery of soft diffuse X-ray emission in NGC 4151 (L[0.5-2keV]~10^{39} erg s$^{-1}$), extending ~2 kpc from the active nucleus and filling in the cavity of the HI material. The best fit to the X-ray spectrum requires either a kT~0.25 keV thermal plasma or a photoionized component. In the thermal scenario, hot gas heated by the nuclear outflow would be confined by the thermal pressure of the HI gas and the dynamic pressure of inflowing neutral material in the galactic disk. In the case of photoionization, the nucleus must have experienced an Eddington limit outburst. For both scenarios, the AGN-host interaction in NGC 4151 must have occured relatively recently (some 10^4 yr ago). This very short timescale to the last episode of high activity phase may imply such outbursts occupy $\gtrsim$1% of AGN lifetime.
We present the results of the fourth Optical/IR Interferometry Imaging Beauty Contest. The contest consists of blind imaging of test data sets derived from model sources and distributed in the OI-FITS format. The test data consists of spectral data sets on an object "observed" in the infrared with spectral resolution. There were 4 different algorithms competing this time: BSMEM the Bispectrum Maximum Entropy Method by Young, Baron & Buscher; RPR the Recursive Phase Reconstruction by Rengaswamy; SQUEEZE a Markov Chain Monte Carlo algorithm by Baron, Monnier & Kloppenborg; and, WISARD the Weak-phase Interferometric Sample Alternating Reconstruction Device by Vannier & Mugnier. The contest model image, the data delivered to the contestants and the rules are described as well as the results of the image reconstruction obtained by each method. These results are discussed as well as the strengths and limitations of each algorithm.
We discuss Green's-function solutions of the equation for a geometrically thin, axisymmetric Keplerian accretion disc with a viscosity prescription "\nu ~ R^n". The mathematical problem was solved by Lynden-Bell & Pringle (1974) for the special cases with boundary conditions of zero viscous torque and zero mass flow at the disc center. While it has been widely established that the observational appearance of astrophysical discs depend on the physical size of the central object(s), exact time-dependent solutions with boundary conditions imposed at finite radius have not been published for a general value of the power-law index "n". We derive exact Green's-function solutions that satisfy either a zero-torque or a zero-flux condition at a nonzero inner boundary R_{in}>0, for an arbitrary initial surface density profile. Whereas the viscously dissipated power diverges at the disc center for the previously known solutions with R_{in}=0, the new solutions with R_{in}>0 have finite expressions for the disc luminosity that agree, in the limit t=>infinity, with standard expressions for steady-state disc luminosities. The new solutions are applicable to the evolution of the innermost regions of thin accretion discs.
We present the results of the study of the substructure and galaxy content of ten rich clusters of galaxies in three different superclusters of the Sloan Great Wall. We determine the substructure in clusters using the 'Mclust' package from the 'R' statistical environment and analyse their galaxy content. We analyse the distribution of the peculiar velocities of galaxies in clusters and calculate the peculiar velocity of the first ranked galaxy. We show that clusters in our sample have more than one component; in some clusters different components also have different galaxy content. We find that in some clusters with substructure the peculiar velocities of the first ranked galaxies are large. All clusters in our sample host luminous red galaxies. They can be found both in the central areas of clusters as well as in the outskirts, some of them have large peculiar velocities. About 1/3 of red galaxies in clusters are spirals. The scatter of colours of red ellipticals is in most clusters larger than that of red spirals. The presence of substructure in rich clusters, signs of possible mergers and infall, as well as the large peculiar velocities of the first ranked galaxies suggest that the clusters in our sample are not yet virialized. We present merger trees of dark matter haloes in an N-body simulation to demonstrate the formation of present-day dark matter haloes via multiple mergers during their evolution. In simulated dark matter haloes we find a substructure similar to that in observed clusters.
The planets magnetic field has been explained based on the dynamo theory, which presents as many difficulties in mathematical terms as well as in predictions. It proves to be extremely difficult to calculate the dipolar magnetic moment of the extrasolar planets using the dynamo theory. The aim is to find an empirical relationship (justifying using first principles) between the planetary magnetic moment, the mass of the planet, its rotation period and the electrical conductivity of its most conductive layer. Then this is applied to Hot Jupiters. Using all the magnetic planetary bodies of the solar system and tracing a graph of the dipolar magnetic moment versus body mass parameter, the rotation period and electrical conductivity of the internal conductive layer is obtained. An empirical, functional relation was constructed, which was adjusted to a power law curve in order to fit the data. Once this empirical relation has been defined, it is theoretically justified and applied to the calculation of the dipolar magnetic moment of the extra solar planets known as Hot Jupiters. Almost all data calculated is interpolated, bestowing confidence in terms of their validity. The value for the dipolar magnetic moment, obtained for the exoplanet Osiris (HD209458b), helps understand the way in which the atmosphere of a planet with an intense magnetic field can be eroded by stellar wind. The relationship observed also helps understand why Venus and Mars do not present any magnetic field.
Aims. Current and upcoming space missions may be able to detect moons of transiting extra-solar planets. In this context it is important to understand if exomoons are expected to exist and what their possible properties are. Methods. Using estimates for the stability of exomoon orbits from numerical studies, a list of 87 known transiting exoplanets is tested for the potential to host large exomoons. Results. For 92% of the sample, moons larger than Luna can be excluded on prograde orbits, unless the parent exoplanet's internal structure is very different from the gas-giants of the solar system. Only WASP-24b, OGLE2-TR-L9, CoRoT-3b and CoRoT-9b could have moons above 0.4 m\oplus, which is within the likely detection capabilities of current observational facilities. Additionally, the range of possible orbital radii of exomoons of the known transiting exoplanets, with two exceptions, is below 8 Jupiter-radii and therefore rather small.
The deconfinement phase transition from hadronic matter to quark matter in the interior of compact stars is investigated. The hadronic phase is described in the framework of relativistic mean-field (RMF) theory, when also the scalar-isovector delta-meson effective field is taken into account. The MIT bag model for describing a quark phase is used. The changes of the parameters of phase transition caused by the presence of delta-meson field are explored. Finally, alterations in the integral and structural parameters of hybrid stars due to both deconfinement phase transition and inclusion of delta-meson field are discussed.
The population of debris discs on the main sequence is well constrained, however very little is known about debris discs around evolved stars. In this work we provide a theoretical framework that considers the effects of stellar evolution on debris discs; firstly considering the evolution of an individual disc from the main sequence through to the white dwarf phase, then extending this to the known population of debris discs around main sequence A stars. This population is determined from Spitzer observations and the steady state collisional models of Wyatt et al 2007, extended to include realistic emission properties of grains using a relationship between the realistic and blackbody disc radius. It is found that discs around evolved stars are harder to detect than on the main sequence. In the context of our models discs should be detectable with Herschel or Alma on the giant branch. However this is subject to the uncertain effect of sublimation on debris discs, which such observations should help to constrain. It is found that the evolved main sequence population of debris discs are hard to detect around white dwarfs and this fits with the only such detection being the WD2226-120, the white dwarf at the centre of the helix nebula. If our models under predicted the disc flux, this observation is at the optimum age and distance to be detected. Observations of hot dusty white dwarf discs with radii less than 0.01AU are not explained by our models, however a potential source of material to replenish these discs is suggested; material that has left the disc due to stellar wind drag, but is not accreted onto the star before the end of the AGB.
We carry out a series of high-resolution (1024 X 1024) hydrodynamic simulations to investigate the orbital evolution of a Saturn-Jupiter pair embedded in a gaseous disk. This work extends the results of our previous work by exploring a different orbital configuration---Jupiter lies outside Saturn (q<1, where q= M_i/M_o is the mass ratio of the inner planet and the outer one). We focus on the effects of different initial separations (d) between the two planets and the various surface density profiles of the disk, where \sigma \propto r^{-\alpha}. We also compare the results of different orbital configurations of the planet pair. Our results show that: (1) when the initial separation is relatively large(d>d_{iLr}, where d_{iLr} is the distance between Jupiter and its first inner Lindblad resonance), the two planets undergo divergent migration. However, the inward migration of Saturn could be halted when Jupiter compresses the inner disk in which Saturn is embedded. (2) Convergent migration occurs when the initial separation is smaller (d<d_{iLr}) and the density slope of the disk is nearly flat (\alpha<1/2). Saturn is then forced by Jupiter to migrate inward when the two planets are trapped into mean motion resonances (MMRs), and Saturn may get very close to the central star. (3) In the case of q<1, the eccentricity of Saturn could be excited to a very high value (e_{S}~0.4-0.5) by the MMRs and the system could maintain stability. These results explain the formation of MMRs in the exoplanet systems where the outer planet is more massive than the inner one. It also helps us to understand the origin of the "hot Jupiter/Saturn" undergoing high eccentric orbit.
Amino acids in solar system bodies may have played a key role in the chemistry that led to the origin of life on Earth. We present laboratory studies testing the stability of amino acids against gamma radiation photolysis. All the 20 chiral amino acids in the levo form used in the proteins of the current terrestrial biochemistry have been irradiated in the solid state with gamma radiation to a dose of 3.2 MGy which is the dose equivalent to that derived by radionuclide decay in comets and asteroids in 1.05x109 years. For each amino acid the radiolysis degree and the radioracemization degree was measured by differential scanning calorimetry (DSC) and by optical rotatory dispersion (ORD) spectroscopy. From these measurements a radiolysis rate constant kdsc and a radioracemization rate constant krac have been determined for each amino acid and extrapolated to a dose of 14 MGy which corresponds to the expected total dose delivered by the natural radionuclides decay to all the organic molecules present in comets and asteroids in 4.6x109 years, the age of the Solar System. It is shown that all the amino acids studied can survive a radiation dose of 14 MGy in significant quantity although part of them are lost in radiolytic processes. Similarly, also the radioracemization process accompanying the radiolysis does not extinguish the chirality. The knowledge of the radiolysis and radioracemization rate constants may permit the calculation of the original concentration of the amino acids at the times of the formation of the Solar System starting from the concentration found today in carbonaceous chondrites. For some amino acids the concentration in the presolar nebula could have been up to 6 times higher than currently observed in meteorites.
For a long time, the well-known supercritically accreting binary SS433 is being proposed as a prototype for a class of hypothetical bright X-ray sources that may be identified with the so-called Ultraluminous X-ray sources (ULXs) in nearby galaxies or at least with part of them. Like SS433, these objects should be associated with optical nebulae, powered by both radiation of the central source and its wind or jet activity. Indeed, around many ULXs, bright optical nebulae (ULX Nebulae, ULXNe) are found. Here, we use SS433 as a prototype for the power source creating the nebulae around ULXs. Though many factors are important such as the structure of the host star-forming region and the possible supernova remnant formed together with the accreting compact object, we show that most of the properties of ULXNe may be explained by an SS433-like system evolving for up to about one million years in a constant density environment. The basic stages of evolution of a ULX Nebula include a non-spherical HII-region with a central cavity created by non-radiative shock waves, an elongated or bipolar shock-powered nebula created by jet activity and a large-scale quasi-spherical bubble.
The cosmic microwave background radiation defines a preferred cosmic rest frame, and inflationary cosmological theories predict that the microwave background temperature fluctuations should be statistically isotropic in this rest frame. For observers moving with respect to the rest frame, the temperature fluctuations will no longer be isotropic, due to the preferred direction of motion. The most prominent effect is a dipole temperature variation, which has long been observed with an amplitude of a part in a thousand of the mean temperature. An observer's velocity with respect to the rest frame will also induce changes in the angular correlation function and creation of non-zero off-diagonal correlations between multipole moments. We calculate both of these effects, which are part-in-a-thousand corrections to the rest frame power spectrum and correlation function. Both should be detectable in future full-sky microwave maps from the Planck satellite. These signals will constrain cosmological models in which the cosmic dipole arises partly from large-scale isocurvature perturbations, as suggested by recent observations.
Using a population synthesis technique, we have calculated detailed models of the present-day field population of objects that have resulted from the merger of a giant primary and a main-sequence or brown dwarf secondary during common-envelope evolution. We used a grid of 116 stellar and 32 low-mass/brown dwarf models, a crude model of the merger process, and followed the angular momentum evolution of the binary orbit and the primary's rotation prior to merger, as well as the merged object's rotation after the merger. We find that present-day merged objects that are observable as giant stars or core-helium burning stars in our model population constitute between 0.24% and 0.33% of the initial population of ZAMS binaries, depending upon the input parameters chosen. The median projected rotational velocity of these merged objects is ~16 km/sec, an order of magnitude higher than the median projected rotational velocity in a model population of normal single stars calculated using the same stellar models and initial mass function. The masses of the merged objects are typically less than ~2 solar masses, with a median mass of 1.28 solar masses, which is slightly more than, but not significantly different from, their normal single star counterparts. The luminosities in our merged object population range from ~10-100 solar luminosities, with a strong peak in the luminosity distribution at ~60 solar luminosities, since the majority of the merged objects (57%) lie on the horizontal branch at the present epoch. The results of our population synthesis study are discussed in terms of possible observational counterparts either directly involving the high rotational velocity of the merger product or indirectly, via the effect of rotation on envelope abundances and on the amount and distribution of circumstellar matter.
We present intermediate-resolution optical spectrophotometry of 65 galaxies obtained in support of the Spitzer Infrared Nearby Galaxies Survey (SINGS). For each galaxy we obtain a nuclear, circumnuclear, and semi-integrated optical spectrum designed to coincide spatially with mid- and far-infrared spectroscopy from the Spitzer Space Telescope. We make the reduced, spectrophotometrically calibrated one-dimensional spectra, as well as measurements of the fluxes and equivalent widths of the strong nebular emission lines, publically available. We use optical emission-line ratios measured on all three spatial scales to classify the sample into star-forming, active galactic nuclei (AGN), and galaxies with a mixture of star formation and nuclear activity. We find that the relative fraction of the sample classified as star-forming versus AGN is a strong function of the integrated light enclosed by the spectroscopic aperture. We supplement our observations with a large database of nebular emission-line measurements of individual HII regions in the SINGS galaxies culled from the literature. We use these ancillary data to conduct a detailed analysis of the radial abundance gradients and average HII-region abundances of a large fraction of the sample. We combine these results with our new integrated spectra to estimate the central and characteristic (globally-averaged) gas-phase oxygen abundances of all 75 SINGS galaxies. We conclude with an in-depth discussion of the absolute uncertainty in the nebular oxygen abundance scale.
We investigate particle production near extra species loci (ESL) in a higher dimensional field space and derive a speed limit in moduli space at weak coupling. This terminal velocity is set by the characteristic ESL-separation and the coupling of the extra degrees of freedom to the moduli, but it is independent of the moduli's potential if the dimensionality of the field space is considerably larger than the dimensionality of the loci, D >> d. Once the terminal velocity is approached, particles are produced at a plethora of nearby ESLs, preventing a further increase in speed via their backreaction. It is possible to drive inflation at the terminal velocity, providing a generalization of trapped inflation with attractive features: we find that more than sixty e-folds of inflation for sub-Planckian excursions in field space are possible if ESLs are ubiquitous, without fine tuning of initial conditions and less tuned potentials. We construct a simple, observationally viable model with a slightly red scalar power-spectrum and suppressed gravitational waves; we comment on the presence of additional observational signatures originating from IR-cascading and individual massive particles. We also show that moduli-trapping at an ESL is suppressed for D >> d, hindering dynamical selection of high-symmetry vacua on the landscape based on this mechanism.
We present status and results of AstroGrid-D, a joint effort of astrophysicists and computer scientists to employ grid technology for scientific applications. AstroGrid-D provides access to a network of distributed machines with a set of commands as well as software interfaces. It allows simple use of computer and storage facilities and to schedule or monitor compute tasks and data management. It is based on the Globus Toolkit middleware (GT4). Chapter 1 describes the context which led to the demand for advanced software solutions in Astrophysics, and we state the goals of the project. We then present characteristic astrophysical applications that have been implemented on AstroGrid-D in chapter 2. We describe simulations of different complexity, compute-intensive calculations running on multiple sites, and advanced applications for specific scientific purposes, such as a connection to robotic telescopes. We can show from these examples how grid execution improves e.g. the scientific workflow. Chapter 3 explains the software tools and services that we adapted or newly developed. Section 3.1 is focused on the administrative aspects of the infrastructure, to manage users and monitor activity. Section 3.2 characterises the central components of our architecture: The AstroGrid-D information service to collect and store metadata, a file management system, the data management system, and a job manager for automatic submission of compute tasks. We summarise the successfully established infrastructure in chapter 4, concluding with our future plans to establish AstroGrid-D as a platform of modern e-Astronomy.
Iodine is distinguished from other elements used in dark matter direct detection experiments both by its large mass as well as its large magnetic moment. Inelastic dark matter utilizes the large mass of iodine to allay tensions between the DAMA annual modulation signature and the null results from other experiments. We explore models of inelastic dark matter that also take advantage of the second distinct property of iodine, namely its large magnetic moment. In such models the couplings are dominated by magnetic, rather than electric, interactions. These models provide simple examples where the DAMA signal is compatible with all existing limits. We consider dipole moments for the WIMP, through conventional magnetism as well as ``dark'' magnetism, including both magnetic-magnetic and magnetic-electric scattering. We find XENON100 and CRESST should generically see a signal, although significantly suppressed compared with electric inelastic dark matter models, while KIMS should see a large signal.
We study symmetry restoration at finite temperature in the standard model during the electroweak phase transition in the presence of a weak magnetic field. We compute the finite temperature effective potential up to the contribution of ring diagrams, using the broken phase degrees of freedom, and keep track of the gauge parameter dependence of the results. We show that under these conditions, the phase transition becomes stronger first order.
The next generation of ground-based gravitational wave detectors may detect a few mergers of comparable-mass M\simeq 100-1000 Msun ("intermediate-mass'', or IMBH) spinning black holes. Black hole spin is known to have a significant impact on the orbit, merger signal, and post-merger ringdown of any binary with non-negligible spin. In particular, the detection volume for spinning binaries depends significantly on the component black hole spins. We provide a fit to the single-detector and isotropic-network detection volume versus (total) mass and arbitrary spin for equal-mass binaries. Our analysis assumes matched filtering to all significant available waveform power (up to l=6 available for fitting, but only l<= 4 significant) estimated by an array of 64 numerical simulations with component spins as large as S_{1,2}/M^2 <= 0.8. We provide a spin-dependent estimate of our uncertainty, up to S_{1,2}/M^2 <= 1. For the initial (advanced) LIGO detector, our fits are reliable for $M\in[100,500]M_\odot$ ($M\in[100,1600]M_\odot$). In the online version of this article, we also provide fits assuming incomplete information, such as the neglect of higher-order harmonics. We briefly discuss how a strong selection bias towards aligned spins influences the interpretation of future gravitational wave detections of IMBH-IMBH mergers.
We study time evolution of the $Q$ ball in thermal logarithmic potential using lattice simulations. As the temperature decreases due to the cosmic expansion, the thermal logarithmic term in the potential is eventually overcome by a mass term, and we confirm that the $Q$ ball transforms from the thick-wall type to the thin-wall type for a positive coefficient of radiative corrections to the mass term, as recently suggested. Moreover, we find that the $Q$ ball finally ``melts down'' when the $Q$-ball solution disappears. We also discuss the effects of this phenomenon on the detectability of gravitational waves from the $Q$-ball formation.
A neutral dark matter particle may possess an electric dipole moment (EDM) or a magnetic dipole moment (MDM), so that its scattering with nuclei is governed by electromagnetic interactions. If the moments are induced by dimension-5 operators, they may be detectable in direct search experiments. We calculate complete expressions of the scattering cross sections and the recoil energy spectra for dark matter with these attributes. We also provide useful formulae pertinent to dark matter that interacts via a charge form factor (CFF) which is related to the charge radius defined by an effective dimension-6 operator. We show that a 7 GeV dark matter particle with an EDM, MDM or CFF easily reproduces the CoGeNT excess while remaining consistent with null searches.
We study in detail static spherically symmetric solutions of non linear Pauli-Fierz theory. We obtain a numerical solution with a constant density source. This solution shows a recovery of the corresponding solution of General Relativity via the Vainshtein mechanism. This result has already been presented by us in a recent letter, and we give here more detailed information on it as well as on the procedure used to obtain it. We give new analytic insights upon this problem, in particular for what concerns the question of the number of solutions at infinity. We also present a weak field limit which allows to capture all the salient features of the numerical solution, including the Vainshtein crossover and the Yukawa decay.
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We analyze the linear stability of a dilute, hot plasma, taking into account the effects of stratification and anisotropic thermal conduction. The work is motivated by attempts to understand the dynamics of the intracluster medium in galaxy clusters. We show that magnetic field configurations that nominally stabilize either the heat-flux driven buoyancy instability (associated with a positive thermal gradient) or the magnetothermal instability (negative thermal gradient) can lead to previously unrecognized g-mode overstabilities. The driving source of the overstability is either radiative cooling (positive temperature gradient) or the heat flux itself (negative temperature gradient). While the implications of these overstabilities have yet to be explored, we speculate that the cold fronts observed in many relaxed galaxy clusters may be related to their non-linear evolution.
(Abridged) We present a molecular survey of the outflows powered by L1448-mm and IRAS 04166+2706, two sources with prominent wing and extremely high velocity (EHV) components in their CO spectra. The molecular composition of the two outflows presents systematic changes with velocity that we analyze by dividing the outflow in three chemical regimes, two of them associated with the wing component and the other the EHV gas. The analysis of the two wing regimes shows that species like H2CO and CH3OH favor the low-velocity gas, while SiO and HCN are more abundant in the fastest gas. We also find that the EHV regime is relatively rich in O-bearing species, as is not only detected in CO and SiO (already reported elsewhere), but also in SO, CH3OH, and H2CO (newly reported here), with a tentative detection in HCO+. At the same time, the EHV regime is relatively poor in C-bearing molecules like CS and HCN. We suggest that this difference in composition arises from a lower C/O ratio in the EHV gas. The different chemical compositions of the wing and EHV regimes suggest that these two outflow components have different physical origins. The wing component is better explained by shocked ambient gas, although none of the existing shock models explains all observed features. The peculiar composition of the EHV gas may reflect its origin as a dense wind from the protostar or its surrounding disk.
We compare sensitive HI data from The HI Nearby Galaxy Survey (THINGS) and deep far UV (FUV) data from GALEX in the outer disk of M83. The FUV and HI maps show a stunning spatial correlation out to almost 4 optical radii (r25), roughly the extent of our maps. This underscores that HI traces the gas reservoir for outer disk star formation and it implies that massive (at least low level) star formation proceeds almost everywhere HI is observed. Whereas the average FUV intensity decreases steadily with increasing radius before leveling off at ~1.7 r25, the decline in HI surface density is more subtle. Low HI columns (<2 M_solar/pc^2) contribute most of the mass in the outer disk, which is not the case within r25. The time for star formation to consume the available HI, inferred from the ratio of HI to FUV intensity, rises with increasing radius before leveling off at ~100 Gyr, i.e., many Hubble times, near ~1.7 r25. Assuming the relatively short H2 depletion times observed in the inner parts of galaxies hold in outer disks, the conversion of HI into bound, molecular clouds seems to limit star formation in outer galaxy disks. The long consumption times suggest that most of the extended HI observed in M83 will not be consumed by in situ star formation. However, even these low star formation rates are enough to expect moderate chemical enrichment in a closed outer disk.
We present the early UV and optical light curve of Type IIP supernova (SN) 2010aq at z=0.0862, and compare it to analytical models for thermal emission following supernova shock breakout in a red supergiant star. SN 2010aq was discovered in joint monitoring between the GALEX Time Domain Survey in the NUV and the Pan-STARRS1 Medium Deep Survey in the g, r, i, and z bands. The GALEX and Pan-STARRS1 observations detect the SN less than 1 day after shock breakout, measure a diluted blackbody temperature of 31,000 +/- 6,000 K 1 day later, and follow the rise in the UV/optical light curve over the next 2 days caused by the expansion and cooling of the SN ejecta. The high signal-to-noise ratio of the simultaneous UV and optical photometry allows us to fit for a progenitor star radius of 700 +/- 200 R_sun, the size of a red supergiant star. An excess in UV emission two weeks after shock breakout compared to SNe well fitted by model atmosphere-code synthetic spectra with solar metallicity, is best explained by suppressed line blanketing due to a lower metallicity progenitor star in SN 2010aq. Continued monitoring of Pan-STARRS1 Medium Deep Survey fields by the GALEX Time Domain Survey will increase the sample of early UV detections of Type II SNe by an order of magnitude, and probe the diversity of SN progenitor star properties.
We report radial velocity measurements of the G-type subgiants 24 Sextanis (=HD90043) and HD200964. Both are massive, evolved stars that exhibit periodic variations due to the presence of a pair of Jovian planets. Photometric monitoring with the T12 0.80m APT at Fairborn Observatory demonstrates both stars to be constant in brightness to <= 0.002 mag, thus strengthening the planetary interpretation of the radial velocity variations. 24 Sex b,c have orbital periods of 453.8 days and 883~days, corresponding to semimajor axes 1.333 AU and 2.08 AU, and minimum masses (Msini) 1.99 Mjup and 0.86 Mjup, assuming a stellar mass 1.54 Msun. HD200964 b,c have orbital periods of 613.8 days and 825 days, corresponding to semimajor axes 1.601 AU and 1.95 AU, and minimum masses 1.85 Mjup and 0.90 Mjup, assuming M* = 1.44 Msun. We also carry out dynamical simulations to properly account for gravitational interactions between the planets. Most, if not all, of the dynamically stable solutions include crossing orbits, suggesting that each system is locked in a mean motion resonance that prevents close encounters and provides long-term stability. The planets in the 24 Sex system likely have a period ratio near 2:1, while the HD200964 system is even more tightly packed with a period ratio close to 4:3. However, we caution that further radial velocity observations and more detailed dynamical modelling will be required to provide definitive and unique orbital solutions for both cases, and to determine whether the two systems are truly resonant.
Studies of distant galaxies show correlations between their SFRs and stellar masses, implying that their star-formation histories (SFHs) are highly similar. Moreover, observations show that the UV luminosities and stellar masses grow from z=8 to z=3, implying that the SFRs increase with time. We study this evolution in galaxies at 3 < z < 8 selected at constant comoving number density, n = 2 x 10^-4 Mpc^-3. Studying galaxies at constant comoving number density tracks the evolution of stellar mass and star formation in the predecessors and descendants of these galaxies. We show that the SFRs of these galaxies increase from z=8 to 3 as SFR(t) ~ t^alpha with alpha = 1.7 +/- 0.2. This conflicts with previous assumptions that the SFR is either constant or declines exponentially in time, but consistent with expectations from theory. Furthermore, we show that the stellar mass growth in these galaxies is consistent with this derived SFH. This provides evidence that the slope of the high-mass end of the IMF is approximately Salpeter unless the duty cycle of star formation is much less than unity. We argue that these relations follow from gas accretion (either through accretion or delivered by mergers) coupled with galaxy disk growth, where the SFR depends on the gas surface density. This implies increasing gas masses with time but declining gas fractions, where the gas fraction decreases from z=8 to z=3 as f_gas ~ (1 + z)^0.9 for galaxies with this number density. Comparing the gas accretion rate to the SFR we find that at z > 4 galaxies acquire gas faster than it can be converted into stars. This is the "gas accretion epoch". At z < 4 the SFR overtakes the gas accretion rate, indicating a period where galaxies consume gas faster than it is acquired. At z < 3, galaxies with this number density depart from these relations implying that gas accretion is slowed at later times.
We report the detection of a giant planet in a 6.4950 day orbit around the 1.7 Msun subgiant HD102956. The planet has a semimajor axis a = 0.081 AU and minimum mass Msini = 0.96 Mjup. HD102956 is the most massive star known to harbor a hot Jupiter, and its planet is only the third known to orbit within 0.6 AU of a star more massive than 1.5 Msun. Based on our sample of 137 subgiants with M* > 1.45 Msun we find that 0.5-2.3% of A-type stars harbor a close-in planet (a < 0.1 AU) with Msini > 1 Mjup, consistent with hot-Jupiter occurrence for Sun-like stars. Thus, the paucity of planets with 0.1 < a/AU < 1.0 around intermediate-mass stars may be an exaggerated version of the "period valley" that is characteristic of planets around Sun-like stars.
We argue that the decomposition of gamma-ray maps in spherical harmonics is a sensitive tool to study dark matter (DM) annihilation or decay in the main Galactic halo of the Milky Way. Using the harmonic decomposition in a window excluding the Galactic plane, we show for one year of Fermi data that adding a spherical template (such as a line-of-sight DM profile) to an astrophysical background significantly reduces chi^2. In some energy bins the significance of this "DM" fraction is above three sigma. Assuming a power-law energy spectrum for the backgrounds and the DM component, we find that sources following the stellar mass density or an NFW annihilation profile are preferred to an NFW decay or a bivariate Gaussian profile. We check that the dependence of the DM fraction on the data analysis choices, such as the window size, the pixel size etc. is not significant. We also calculate the contribution from point sources to the variance matrix. Based on the analysis of the angular power spectrum, we indirectly find the average number of photons coming from the multi-photon sources in energy bins above 3 GeV.
We explore the kinematics of continuum clumps in the Perseus molecular cloud, derived from C18O J=3-2 data. Two populations are examined, identified using the automated algorithms CLFIND and GAUSSCLUMPS on existing SCUBA data. The clumps have supersonic linewidths with distributions which suggest the C18O line probes a lower-density 'envelope' rather than a dense inner core. Similar linewidth distributions for protostellar and starless clumps implies protostars do not have a significant impact on their immediate environment. The proximity to an active young stellar cluster seems to affect the linewidths: those in NGC1333 are greater than elsewhere. In IC348 the proximity to the old IR cluster has little influence, with the linewidths being the smallest of all. A virial analysis suggests that the clumps are bound and close to equipartition. In particular, the starless clumps occupy the same parameter space as the protostars, suggesting they are true stellar precursors and will go on to form stars. We also search for ordered C18O velocity gradients across the face of each core, usually interpreted as rotation. We note a correlation between the directions of the identified gradients and outflows across protostars, indicating we may not have a purely rotational signature. The fitted gradients are larger than found in previous work, probably as a result of the higher resolution of our data and/or outflow contamination. These gradients, if interpreted solely in terms of rotation, suggest that rotation is not dynamically significant. Furthermore, derived specific angular momenta are smaller than observed in previous studies, centred around j~0.001 km/s pc, which indicates we have identified lower levels of rotation, or that the C18O J=3-2 line probes conditions significantly denser and/or colder than n~10^5 per cc and T~10 K.
The Galactic globular cluster omega Centauri is a prime candidate for hosting an intermediate mass black hole. Recent measurements lead to contradictory conclusions on this issue. We use VLT-FLAMES to obtain new integrated spectra for the central region of omega Centauri. We combine these data with existing measurements of the radial velocity dispersion profile taking into account a new derived center from kinematics and two different centers from the literature. The data support previous measurements performed for a smaller field of view and show a discrepancy with the results from a large proper motion data set. We see a rise in the radial velocity dispersion in the central region to 22.8+-1.2 km/s, which provides a strong sign for a central black hole. Isotropic dynamical models for omega Centauri imply black hole masses ranging from 3.0 to 5.2x10^4 solar masses depending on the center. The best-fitted mass is 4.7+-1.0x10^4 solar masses.
We present the first high spectral resolution observations of Orion KL in the frequency ranges 1573.4 - 1702.8 GHz (band 6b) and 1788.4 - 1906.8 GHz (band 7b) obtained using the HIFI instrument on board the Herschel Space Observatory. We characterize the main emission lines found in the spectrum, which primarily arise from a range of components associated with Orion KL including the hot core, but also see widespread emission from components associated with molecular outflows traced by H2O, SO2, and OH. We find that the density of observed emission lines is significantly diminished in these bands compared to lower frequency Herschel/HIFI bands.
I have shown that if we assume that the Standard Model of particle physics and Feynman-Weinberg quantum gravity holds at all times, then in the very early universe, the Cosmic Background Radiation (CBR) cannot couple to right handed electrons and quarks. If this property of CBR has persisted to the present day, the Ultra HIgh Energy Cosmic Rays (UHECR) can propagate a factor of ten further than they could if the CBR were an electromagnetic field, since most of the cross section for pion production when a UHECR hits a CBR photon is due to a quark spin flip, and such a flip cannot occur if the CBR photon cannot couple to right handed quarks. The GZM effect will still reduce the number of UHECR, but UHECR can arrive from a distance of a redshift of up to $z=0.1$. I show that taking this additional propagation distance into account allows us to identify the sources of 4 of the 6 UHECR which the Pierre Auger Collaboration could not identify, and also identify the source of the 320 EeV UHECR seen by the Fly's Eye instrument. I suggest an experiment to test this hypothesis about the CBR.
A metal-rich environment facilitates planet formation, making metal-rich stars the most favorable targets for surveys seeking to detect new exoplanets. Using this advantage to identify likely low-mass planet hosts, however, has been difficult: until now, methods to determine M-dwarf metallicities required observationally expensive data (such as parallaxes and high-resolution spectra), and were limited to a few bright cool stars. We have obtained moderate (R~2700) resolution K-band spectra of 17 M-dwarfs with metallicity estimates derived from their FGK companions. Analysis of these spectra, and inspection of theoretical synthetic spectra, reveal that an M-dwarf's metallicity can be inferred from the strength of its Na I doublet (2.206 {\mu}m & 2.209 {\mu}m) and Ca I triplet (2.261 {\mu}m, 2.263 {\mu}m & 2.265 {\mu}m) absorption lines. We use these features, and a temperature-sensitive water index, to construct an empirical metallicity indicator applicable for M-dwarfs with near-solar metallicities (-0.5<[Fe/H]<+0.5). This indicator has an accuracy of +/- 0.15 dex, comparable to that of existing techniques for estimating M-dwarf metallicities, but is more observationally accessible, requiring only a moderate resolution K-band spectrum. Applying this method to 8 known M-dwarf planet hosts, we estimate metallicities ([Fe/H]) in excess of the mean metallicity of M-dwarfs in the solar neighborhood, consistent with the metallicity distribution of FGK planet hosts.
New absolute spectrophotometry of the Kitt Peak night sky has been obtained in 2009/10, which we compare to previously published data obtained in 1988 and 1999, allowing us to look for changes over the past two decades. A comparison of the data between 1988, 1999 and 2009/10 reveals that the sky brightness of Kitt Peak has stayed remarkably constant over the past 20 years. Compared to 1988, the 2009/10 data show no change in the sky brightness at Zenith though, as expected, the sky glow has increased most dramatically in the direction of Tucson. Comparisons between the 1999 and 2009/10 data suggest that the sky has actually decreased in brightness compared to 10 years ago. However, the older data were both taken during times of increased solar activity. When we correct the measurements for the solar irradiance fluctuations, we find that compared to 20 years ago, the sky is ~0.1 magnitude brighter at Zenith and ~0.3 magnitudes brighter towards Tucson. But even after these corrections, we still find that the sky over Kitt Peak is comparable to what it was 10 years ago at Zenith and ~0.1 magnitude darker towards Tucson. This suggests that the strengthened lighting ordinances Tucson and Pima County established in the early 2000s have been quite effective. With some care, the Kitt Peak night sky will remain this dark many years into the future.
Random surface deviations in a reflector antenna reduce the aperture efficiency. This communication presents a method for estimating the mean surface deviation of a parabolic reflector from a set of measured points. The proposed method takes into account systematic measurement errors, such as the offset between the origin of reference frame and the vertex of the surface, and the misalignment between the surface rotation axis and the measurement axis. The results will be applied to perform corrections to the surface of one of the 30 m diameter radiotelescopes at the Instituto Argentino de Radioastronom\'ia (IAR).
Nowadays, science has been coming into a new paradigm, called data-intensive science. While current studies of the new phenomenon focused on building up infrastructure for this new paradigm, yet a few studies concern users of scientific data, particularly their usage practices in the newly emerging paradigm, even though the importance of understanding users' work flow and practices has been summoned. This study endeavors to improve our understanding of users' data usage behavior through a content analysis of publications in a frequently cited new paradigm-related project, Sloan Digital Sky Survey (SDSS). We found that (1) nearly half studies used one data source only. A few studies exploited three or more data sources; (2) the number of objects that were analyzed in SDSS publications is in all scales from one digit to millions; (3) different paper types may affect the data usage patterns; (4) Users are not only consumers of scientific data. They are producers too; (5) studies that can use multiple large scale data sources are relative rare. Issues of data provenance, trust, and usability may prevent researchers from doing this kind of research.
The mystery of where and how Nature accelerates the cosmic rays is still unresolved a century after their discovery. Gamma ray bursts (GRBs) have been proposed as one of the more plausible sources of extragalactic cosmic rays. A positive observation of neutrinos in coincidence with a GRB would identify these objects as sources of the highest-energy cosmic rays and provide invaluable information about the processes occurring inside these phenomena. Calculations show that a kilometer-scale neutrino telescope is necessary for this task. The idea of such a detector is now becoming reality as IceCube at the South Pole nears completion. The contribution reviews the status of the construction and operation of IceCube and summarize the results from searches for neutrinos from GRBs and similar phenomena with IceCube and its predecessor, AMANDA. At the end, an outline of future plans and perspectives for IceCube is given.
The interaction between emerging magnetic flux and the pre-existing ambient field has become a "hot" topic for both numerical simulations and high-resolution observations of the solar atmosphere. The appearance of brightenings and surges during episodes of flux emergence is believed to be a signature of magnetic reconnection processes. We present an analysis of a small-scale flux emergence event in NOAA 10971, observed simultaneously with the Swedish 1-m Solar Telescope on La Palma and the \emph{Hinode} satellite during a joint campaign in September 2007. Extremely high-resolution G-band, H$\alpha$, and \ion{Ca}{2} H filtergrams, \ion{Fe}{1} and \ion{Na}{1} magnetograms, EUV raster scans, and X-ray images show that the emerging region was associated with chromospheric, transition region and coronal brightenings, as well as with chromospheric surges. We suggest that these features were caused by magnetic reconnection at low altitude in the atmosphere. To support this idea, we perform potential and linear force-free field extrapolations using the FROMAGE service. The extrapolations show that the emergence site is cospatial with a 3D null point, from which a spine originates. This magnetic configuration and the overall orientation of the field lines above the emerging flux region are compatible with the structures observed in the different atmospheric layers, and remain stable against variations of the force-free field parameter. Our analysis supports the predictions of recent 3D numerical simulations that energetic phenomena may result from the interaction between emerging flux and the pre-existing chromospheric and coronal field.
We study cell count moments up to fifth order of the distributions of haloes, of halo substructures as a proxy for galaxies, and of mass in the context of the halo model and compare theoretical predictions to the results of numerical simulations. On scales larger than the size of the largest cluster, we present a simple point cluster model in which results depend only on cluster-cluster correlations and on the distribution of the number of objects within a cluster, or cluster occupancy. The point cluster model leads to expressions for moments of galaxy counts in which the volume-averaged moments on large scales approach those of the halo distribution and on smaller scales exhibit hierarchical clustering with amplitudes $S_k$ determined by moments of the occupancy distribution. In this limit, the halo model predictions are purely combinatoric, and have no dependence on halo profile, concentration parameter, or potential asphericity. The full halo model introduces only two additional effects: on large scales, haloes of different mass have different clustering strengths, introducing relative bias parameters; and on the smallest scales, halo structure is resolved and details of the halo profile become important, introducing shape-dependent form factors. Because of differences between discrete and continuous statistics, the hierarchical amplitudes for galaxies and for mass behave differently on small scales even if galaxy number is exactly proportional to mass, a difference that is not necessarily well described in terms of bias.
In this work, we study and quantify properties of strong-field small-scale convection and compare observed properties with those predicted by numerical simulations. We analyze spectropolarimetric 630.25 nm data from a unipolar ephemeral region near sun center. We use line-of-sight velocities and magnetic field measurements obtained with Milne-Eddington inversion techniques along with measured continuum intensities and Stokes V amplitude asymmetry at a spatial resolution of 0.15 arcseconds to establish statistical relations between the measured quantities. We also study these properties for different types of distinct magnetic features, such as micropores, bright points, ribbons, flowers and strings. We present the first direct observations of a small-scale granular magneto-convection pattern within extended regions of strong (more than 600 G average) magnetic field. Along the boundaries of the flux concentrations we see mostly downflows and asymmetric Stokes V profiles, consistent with synthetic line profiles calculated from MHD simulations. We note the frequent occurrence of bright downflows along these boundaries. In the interior of the flux concentrations, we observe an up/down flow pattern that we identify as small-scale magnetoconvection, appearing similar to that of field-free granulation but with scales 4 times smaller. Measured RMS velocities are 70% of those of nearby field-free granulation, even though the average radiative flux is not reduced. The interiors of these flux concentrations are dominated by upflows.
In the past decade, much progress has been made in characterising the processes leading to the enhanced deuterium fractionation observed in the ISM and in particular in the cold, dense parts of star forming regions such as protostellar envelopes. Very high molecular D/H ratios have been found for saturated molecules and ions. However, little is known about the deuterium fractionation in radicals, even though simple radicals often represent an intermediate stage in the formation of more complex, saturated molecules. The imidogen radical NH is such an intermediate species for the ammonia synthesis in the gas phase. Herschel/HIFI represents a unique opportunity to study the deuteration and formation mechanisms of such species, which are not observable from the ground. We searched here for the deuterated radical ND in order to determine the deuterium fractionation of imidogen and constrain the deuteration mechanism of this species. We observed the solar-mass Class 0 protostar IRAS16293-2422 with the heterodyne instrument HIFI as part of the Herschel key programme CHESS (Chemical HErschel Surveys of Star forming regions). The deuterated form of the imidogen radical ND was detected and securely identified with 2 hyperfine component groups of its fundamental transition in absorption against the continuum background emitted from the nascent protostar. The 3 groups of hyperfine components of its hydrogenated counterpart NH were also detected in absorption. We derive a very high deuterium fractionation with an [ND]/[NH] ratio of between 30 and 100%. The deuterium fractionation of imidogen is of the same order of magnitude as that in other molecules, which suggests that an efficient deuterium fractionation mechanism is at play. We discuss two possible formation pathways for ND, by means of either the reaction of N+ with HD, or deuteron/proton exchange with NH.
The non-linear dynamics of bending instability and vertical structure of a galactic stellar disc embedded into a spherical halo are studied with N-body numerical modelling. Development of the bending instability in stellar galactic disc is considered as the main factor that increases the disc thickness. Correlation between the disc vertical scale height and the halo-to-disc mass ratio is predicted from the simulations. The method of assessment of the spherical-to-disc mass ratio for edge-on spiral galaxies with small bulges is considered. Modelling of eight edge-on galaxies: NGC 891, NGC 4738, NGC 5170, UGC 6080, UGC 7321, UGC 8286, UGC 9422 and UGC 9556 is performed. Parameters of stellar discs, dark haloes and bulges are estimated. The lower limit of the dark-to-luminous mass ratio in our galaxies is of the order of 1 within the limits of their stellar discs. The dark haloes dominate by mass in the galaxies with very thin stellar discs (NGC 5170, UGC 7321 and UGC 8286).
The study of total ozone columns above Kiev and variations of ozone concentrations in the troposphere at different altitudes above Kiev was carried out using ground-based Fourier Transform InfraRed (FTIR) spectrometric observations that are taken on a routine basis at the Main Astronomical Observatory of the National Academy of Sciences of Ukraine (MAO NASU). This study was performed within the framework of the international ESA-NIVR-KNMI OMI-AO project no.2907 entitled OMI validation by ground-based remote sensing: ozone columns and atmospheric profiles during the time frame 2005-2008. The infrared FTIR spectral observations of direct solar radiation in the wavelength range of 2-12 micron as transmitted through the Earth's atmosphere were performed during the months of April-October of each year. The aim of the project was the validation of total ozone columns and vertical ozone profiles as obtained by the Ozone Monitoring Instrument (OMI)) onboard of the NASA EOS-Aura scientific satellite platform. The modeling of the ozone spectral band shape near 9.6 microns was performing with the MODTRAN code and a molecular band model based on the HITRAN-2004 molecular database. The a-priori information for the spectral modeling consisted of water vapor and temperature profiles from the NASA EOS-Aqua-AIRS satellite instrument, stratospheric ozone profiles from the NASA EOS-Aura-MLS satellite instrument, TEMIS-KNMI climatological ozone profiles and surface ozone concentration measurements performed at the specific times of infrared spectra observations. The troposphere ozone variability was analyzed for two typical episodes: the spring episode of enhanced total ozone columns and the summer episode of enhanced surface ozone concentrations.
We have studied the molecular hydrogen energetics of the edge-on spiral galaxy NGC\,891, using a 34-position map in the lowest three pure rotational H$_2$ lines observed with the Spitzer Infrared Spectrograph. The S(0), S(1), and S(2) lines are bright with an extinction corrected total luminosity of $\sim2.8 \times 10^{7}$ L$_{\odot}$, or 0.09\% of the total-infrared luminosity of NGC\,891. The H$_2$ line ratios are nearly constant along the plane of the galaxy -- we do not observe the previously reported strong drop-off in the S(1)/S(0) line intensity ratio in the outer regions of the galaxy, so we find no evidence for the very massive cold CO-free molecular clouds invoked to explain the past observations. The H$_2$ level excitation temperatures increase monotonically indicating more than one component to the emitting gas. More than 99\% of the mass is in the lowest excitation (T$_{ex}$ $\sim$125 K) ``warm'' component. In the inner galaxy, the warm H$_2$ emitting gas is $\sim$15\% of the CO(1-0)-traced cool molecular gas, while in the outer regions the fraction is twice as high. This large mass of warm gas is heated by a combination of the far-UV photons from stars in photo-dissociation regions (PDRs) and the dissipation of turbulent kinetic energy. Including the observed far-infrared [OI] and [CII] fine-structure line emission and far-infrared continuum emission in a self-consistent manner to constrain the PDR models, we find essentially all of the S(0) and most (70\%) of the S(1) line arises from low excitation PDRs, while most (80\%) of the S(2) and the remainder of the S(1) line emission arises from low velocity microturbulent dissipation.
FS CMa type stars are a recently described group of objects with the B[e] phenomenon that exhibit strong emission-line spectra and strong IR excesses. In this paper we report the first attempt for a detailed modeling of IRAS 00470+6429, for which we have the best set of observations. Our modeling is based on two key assumptions: the star has a main-sequence luminosity for its spectral type (B2) and the circumstellar envelope is bimodal, composed of a slowly outflowing disk-like wind and a fast polar wind. Both outflows are assumed to be purely radial. We adopt a novel approach to describe the dust formation site in the wind that employs timescale arguments for grain condensation and a self-consistent solution for the dust destruction surface. With the above assumptions we were able to reproduce satisfactorily many observational properties of IRAS 00470+6429, including the H line profiles and the overall shape of the spectral energy distribution. Our adopted recipe for dust formation proved successful in reproducing the correct amount of dust formed in the circumstellar envelope. Possible shortcomings of our model, as well as suggestions for future improvements, are discussed.
I summarize in this paper the results and perspectives of representative ground experiments for the observation of very high energy cosmic rays.
The cooling rate of young neutron stars gives direct insight into their internal makeup. Although the temperatures of several young neutron stars have been measured, until now a young neutron star has never been observed to decrease in temperature over time. We fit 9 years of archival Chandra ACIS spectra of the likely neutron star in the ~330 years old Cassiopeia A supernova remnant with our non-magnetic carbon atmosphere model. Our fits show a relative decline in the surface temperature by 4% (5.4 sigma, from 2.12+-0.01*10^6 K in 2000 to 2.04+-0.01*10^6 K in 2009) and observed flux (by 21%). Using a simple model for neutron star cooling, we show that this temperature decline could indicate that the neutron star became isothermal sometime between 1965 and 1980, and constrains some combinations of neutrino emission mechanisms and envelope compositions. However, the neutron star is likely to have become isothermal soon after formation, in which case the temperature history suggests episodes of additional heating or more rapid cooling. Observations over the next few years will allow us to test possible explanations for the temperature evolution.
Interior to the gaseous envelopes of Saturn, Uranus, and Neptune, there are high-density cores with masses larger than 10 Earth masses. According to the conventional sequential accretion hypothesis, such massive cores are needed for the onset of efficient accretion of their gaseous envelopes. However, Jupiter's gaseous envelope is more massive and core may be less massive than those of Saturn. In order to account for this structural diversity and the super-solar metallicity in the envelope of Jupiter and Saturn, we investigate the possibility that they may have either merged with other gas giants or consumed several Earth-mass proto-planetary embryos during or after the rapid accretion of their envelope. In general, impinging sub-Earth-mass planetesimals disintegrate in gas giants' envelopes deposit heavy elements well outside the cores and locally suppress the convection. Consequently, their fragments sediment to promote the growth of cores. Through a series of numerical simulations, we show that it is possible for colliding super-Earth-mass embryos to reach the cores of gas giants. Direct parabolic collisions also lead to the coalescence of gas giants and merging of their cores. In these cases, the energy released from the impact leads to vigorous convective motion throughout the envelope and the erosion of the cores. This dichotomy contributes to the observed dispersion in the internal structure and atmospheric composition between Jupiter and Saturn and other gas giant planets and elsewhere.
In the solar corona, several mechanisms of the drift wave instability can make the mode growing up to amplitudes at which particle acceleration and stochastic heating by the drift wave take place. The stochastic heating, well known from laboratory plasma physics where it has been confirmed in numerous experiments, has been completely ignored in past studies of coronal heating. However, in the present study and in our very recent works it has been shown that the inhomogeneous coronal plasma is, in fact, a perfect environment for fast growing drift waves. As a matter of fact, the large growth rates are typically of the same order as the plasma frequency. The consequent heating rates may exceed the required values for a sustained coronal heating by several orders of magnitude. Some aspects of these phenomena are investigated here. In particular the analysis of the particle dynamics within the growing wave is compared with the corresponding fluid analysis. While both of them predict the stochastic heating, the threshold for the heating obtained from the single particle analysis is higher. The explanation for this effect is given.
In this paper, we test the consistence of Gamma Ray Bursts (GRBs) Data-set and Supernovae Union2 (SNU2) via the so-called {\it multi-dimensional consistence test} under the assumption that $\Lambda$CDM model is a potentially correct cosmological model. We find that the probes are inconsistent with $1.456\sigma$.
We investigate the stability of strange quark matter and the properties of the cor- responding strange stars, within a wide range of quark mass scaling. The calculation shows that the resulting maximum mass always lies between 1.5M_{sun} and 1.8M_{sun} for all the scalings chosen here. Strange star sequences with a linear scaling would sup- port less gravitational mass, and a change (increase or decrease) of the scaling around the linear scaling would lead to a higher maximum mass. Radii invariably decrease with the mass scaling. Then the larger the scaling, the faster the star might spin. In addition, the variation of the scaling would cause an order of magnitude change of the strong electric field on quark surface, which is essential to support possible crusts of strange stars against gravity and may then have some astrophysical implications.
Supermassive black holes (SMBHs) are common in local galactic nuclei, and SMBHs as massive as several billion solar masses already exist at redshift z=6. These earliest SMBHs may arise by the combination of Eddington-limited growth and mergers of stellar-mass seed BHs left behind by the first generation of metal-free stars, or by the rapid direct collapse of gas in rare special environments where the gas can avoid fragmenting into stars. In this contribution, I review these two competing scenarios. I also briefly mention some more exotic ideas and how the different models may be distinguished in the future by LISA and other instruments.
Pulsars, or more generally rotation powered neutron stars, are excellent factories of antimatter in the Galaxy, in the form of pairs of electrons and positrons. Electrons are initially extracted from the surface of the star by the intense rotation induced electric fields and later transformed into electron-positron pairs through electromagnetic cascading. Observations of Pulsar Wind Nebulae (PWNe) show that cascades in the pulsar magnetosphere must ensure pair multiplicities of order $10^{4}-10^{5}$. These pairs finally end up as part of the relativistic magnetized wind emanating from the pulsar. The wind is slowed down, from its highly relativistic bulk motion, at a termination shock, which represents the reverse shock due to its interaction with the surrounding ejecta of the progenitor supernova. At the (relativistic) termination shock, acceleration of the pairs occurs, as part of the dissipation process, so that the cold wind is transformed into a plasma of relativistic non-thermal particles, plus a potential thermal component, which however has never been observed. As long as the pulsar wind is embedded in the supernova remnant these pairs are forced to escavate a bubble and lose energy adiabatically (because of the expansion) and radiatively (because of magnetic and radiation fields). We discuss here the observational constraints on the energy and number content of such pairs and discuss the scenarios that may allow for the pairs to escape in the interstellar medium and possibly contribute to the positron excess that has recently been detected by the PAMELA satellite. Special attention is dedicated to the case of Pulsar Bow Shock Nebulae. The pairs produced in these objects may be effectively carried out of the Supernova Remnant and released in the Interstellar Medium. As a result, Bow Shock Pulsar Wind Nebulae might be the main contributors to the positron excess in the Galaxy.
We investigate a massive ($\varSigma \sim 10000 g cm^{-2}$ at 1 AU) protoplanetary disc model by means of 3D radiation magnetohydrodynamics simulations. The vertical structure of the disc is determined self-consistently by a balance between turbulent heating caused by the MRI and radiative cooling. Concerning the vertical structure, two different regions can be distinguished: A gas-pressure dominated, optically thick midplane region where most of the dissipation takes place, and a magnetically dominated, optically thin corona which is dominated by strong shocks. At the location of the photosphere, the turbulence is supersonic ($M \sim 2$), which is consistent with previous results obtained from the fitting of spectra of YSOs. It is known that the turbulent saturation level in simulations of MRI-induced turbulence does depend on numerical factors such as the numerical resolution and the box size. However, by performing a suite of runs at different resolutions (using up to 64x128x512 grid cells) and with varying box sizes (with up to 16 pressure scaleheights in the vertical direction), we find that both the saturation levels and the heating rates show a clear trend to converge once a sufficient resolution in the vertical direction has been achieved.
Recent discovery of several overluminous type Ia supernovae (SNe Ia) indicates that the explosive masses of white dwarfs may significantly exceed the canonical Chandrasekhar mass limit. Rapid differential rotation may support these massive white dwarfs. Based on the single-degenerate scenario, and assuming that the white dwarfs would differentially rotate when the accretion rate $\dot{M}>3\times 10^{-7}M_{\odot}\rm yr^{-1}$, employing Eggleton's stellar evolution code we have performed the numerical calculations for $\sim$ 1000 binary systems consisting of a He star and a CO white dwarf (WD). We present the initial parameters in the orbital period - helium star mass plane (for WD masses of $1.0 M_{\odot}$ and $1.2 M_{\odot}$, respectively), which lead to super-Chandrasekhar mass SNe Ia. Our results indicate that, for an initial massive WD of $1.2 M_{\odot}$, a large number of SNe Ia may result from super-Chandrasekhar mass WDs, and the highest mass of the WD at the moment of SNe Ia explosion is 1.81 $M_\odot$, but very massive ($>1.85M_{\odot}$) WDs cannot be formed. However, when the initial mass of WDs is $1.0 M_{\odot}$, the explosive masses of SNe Ia are nearly uniform, which is consistent with the rareness of super-Chandrasekhar mass SNe Ia in observations.
Aims. To determine the effect of the Hall term in the generalised Ohm's law
on the damping and phase mixing of Alfv\'en waves in the ion cyclotron range of
frequencies in uniform and non-uniform equilibrium plasmas.
Methods. Wave damping in a uniform plasma is treated analytically, whilst a
Lagrangian remap code (Lare2d) is used to study Hall effects on damping and
phase mixing in the presence of an equilibrium density gradient.
Results. The magnetic energy associated with an initially Gaussian field
perturbation in a uniform resistive plasma is shown to decay algebraically at a
rate that is unaffected by the Hall term to leading order in k^2di^2 where k is
wavenumber and di is ion skin depth. A similar algebraic decay law applies to
whistler perturbations in the limit k^2di^2>>1. In a non-uniform plasma it is
found that the spatially-integrated damping rate due to phase mixing is lower
in Hall MHD than it is in MHD, but the reduction in the damping rate, which can
be attributed to the effects of wave dispersion, tends to zero in both the weak
and strong phase mixing limits.
The 511 keV positron annihilation emission remains a mysterious component of the high energy emission of our Galaxy. Its study was one of the key scientific objective of the SPI spectrometer on-board the INTEGRAL satellite. In fact, a lot of observing time has been dedicated to the Galactic disk with a particular emphasis on the central region. A crucial issue in such an analysis concerns the reduction technique used to treat this huge quantity of data, and more particularly the background modeling. Our method, after validation through a variety of tests, is based on detector pattern determination per ~6 month periods, together with a normalisation variable on a few hour timescale. The Galactic bulge is detected at a level of ~70 sigma allowing more detailed investigations. The main result is that the bulge morphology can be modelled with two axisymmetric Gaussians of 3.2 deg. and 11.8 deg. FWHM and respective fluxes of 2.5 and 5.4 x 10^-4 photons/(cm^2.s^1). We found a possible shift of the bulge centre towards negative longitude at l=-0.6 +/- 0.2 degrees. In addition to the bulge, a more extended structure is detected significantly with flux ranging from 1.7 to 2.9 x10^-3 photons/(cm^2.s^1) depending on its assumed geometry (pure disk or disk plus halo). The disk emission is also found to be symmetric within the limits of the statistical errors.
Accretion models predict that fluorescence lines broadened by relativistic effects should arise from reflection of X-ray emission onto the inner region of the accretion disc surrounding the central black hole of active galactic nuclei (AGN). The theory behind the origin of relativistic lines is well established, and observational evidence from a moderate number of sources seems to support the existence of these lines. The aim of this work is to establish the fraction of AGN with relativistic Fe Kalpha lines, and study possible correlations with source physical properties. An XMM-Newton collection of 149 radio-quiet Type 1 AGN has been systematically and uniformly analyzed in order to search for significant evidence of a relativistically broadened Fe Kalpha line. To enable statistical studies, an almost complete, flux-limited subsample of 31 sources has been defined. The 2-10 keV spectra of the FERO sources have been compared with a complex model including most of the physical components observed in the X-ray spectra of Seyfert galaxies: a power law primary continuum modified by non-relativistic Compton reflection and warm absorption, plus a series of narrow Fe line reflection features. The observed fraction of sources in the flux-limited sample that show significant evidence of a relativistic Fe Kalpha line is 36%. The average line Equivalent Width (EW) is of the order of 100 eV, while the average disc inclination angle is 28+/-5 deg and the average power-law index of the radial disc emissivity law is 2.4+/-0.4. The spin value is well constrained only in 2 cases (MCG-6-30-15 and MRK509), and in the rest of the cases, whenever a constraint can be placed, it always implies the rejection of the static black hole solution. The Fe Kalpha line EW does not correlate with disc parameters or with system physical properties, such as black hole mass, accretion rate and hard X-ray luminosity.
We have discovered an accreting black hole (BH) in a spectroscopically confirmed globular cluster (GC) in NGC 1399 through monitoring of its X-ray activity. The source, with a peak luminosity of L_x=2x10^39 ergs/s, reveals an order of magnitude change in the count rate within ~10 ks in a Chandra observation. The BH resides in a metal-rich [Fe/H]~0.2 globular cluster. After RZ2109 in NGC 4472 this is only the second black-hole X-ray source in a GC confirmed via rapid X-ray variability. Unlike RZ2109, the X-ray spectrum of this BH source did not change during the period of rapid variability. In addition to the short-term variability the source also exhibits long-term variability. After being bright for at least a decade since 1993 within a span of 2 years it became progressively fainter, and eventually undetectable, or marginally detectable, in deep Chandra and XMM observations. The source also became harder as it faded. The characteristics of the long term variability in itself provide sufficient evidence to identify the source as a BH. The long term decline in the luminosity of this object was likely not recognized in previous studies because the rapid variability within the bright epoch suppressed the average luminosity in that integration. The hardening of the spectrum accompanying the fading would also make this black hole source indistinguishable from an accreting neutron star in some epochs. Therefore some low mass X-ray binaries identified as NS accretors in snapshot studies of nearby galaxies may also be BHs. Thus the discovery of the second confirmed BH in an extragalactic GC through rapid variability at the very least suggests that accreting BHs in GCs are not exceedingly rare occurences.
Context: Multiwavelength observations of gamma-ray burst prompt and afterglow emission are a key tool to disentangle the various possible emission processes and scenarios proposed to interpret the complex gamma-ray burst phenomenology. Aims: We collected a large dataset on GRB060908 in order to carry out a comprehensive analysis of the prompt emission as well as the early and late afterglow. Methods: Data from Swift-BAT, -XRT and -UVOT together with data from a number of different ground-based optical/NIR and millimeter telescopes allowed us to follow the afterglow evolution from about a minute from the high-energy event down to the host galaxy limit. We discuss the physical parameters required to model these emissions. Results: The prompt emission of GRB060908 was characterized by two main periods of activity, spaced by a few seconds of low intensity, with a tight correlation between activity and spectral hardness. Observations of the afterglow began less than one minute after the high-energy event, when it was already in a decaying phase, and it was characterized by a rather flat optical/NIR spectrum which can be interpreted as due to a hard energy-distribution of the emitting electrons. On the other hand, the X-ray spectrum of the afterglow could be fit by a rather soft electron distribution. Conclusions: GRB060908 is a good example of a gamma-ray burst with a rich multi-wavelength set of observations. The availability of this dataset, built thanks to the joint efforts of many different teams, allowed us to carry out stringent tests for various interpretative scenarios showing that a satisfactorily modeling of this event is challenging. In the future, similar efforts will enable us to obtain optical/NIR coverage comparable in quality and quantity to the X-ray data for more events, therefore opening new avenues to progress gamma-ray burst research.
We present deep UBVI photometry for Trumpler 20, a rich, intermediate-age open cluster located at l=301.47, b=+2.22 (RA=12:39:34, DEC=-60:37:00, J2000.0) in the fourth Galactic quadrant. In spite of its interesting properties, this cluster has received little attenti on, probably because the line of sight to it crosses twice the Carina spiral arm, which causes a significant contamination of its color-magnitude diagram (CMD) by field stars, therefore complicating seriously its interpretation. We provide more robust estimates of the fundamental parameters of Trumpler 20, and investigate the most prominent features of its CMD: a rich He-burning star clump, and a vertical sequence of stars above the turnoff, which can be either blue stragglers or field stars. Our precise photometry has allowed us to derive updated values of the age and heliocentric distance of Trumpler 20, which we estimate to be 1.4 $\pm$ 0.2 Gyr and 3.0 $\pm$ 0.3 kpc, respectively. As predicted by models, at this age the clump has a tail towards fainter magnitudes and bluer colors, thus providing further confirmation of the evolutionary status of stars in this particular phase. The derived heliocentric distance places the cluster in the inter-arm region between the Carina and Scutum arms, which naturally explains the presence of the vertical sequence of stars (which was originally interpreted as the cluster itself) observed in the upper part of the CMD.Most of these stars would therefore belong to the general galactic field, while only a few of themwould be bona fide cluster blue stragglers. Our data suggest that the cluster metallicity is solar, and that its reddening is \textit{E(B-V)} = 0.35 $\pm$ 0.04.
Recent discoveries of several transiting planets with clearly non-zero eccentricities and some large inclinations started changing the simple picture of close-in planets having circular and low-inclination orbits. Two major scenarios to form such planets are planet migration in a disk, and planet--planet interactions combined with tidal dissipation. The former scenario can naturally produce a circular and low-inclination orbit, while the latter implicitly assumes an initially highly eccentric and possibly high-inclination orbit, which are then circularized and aligned via tidal dissipation. We investigate the tidal evolution of transiting planets on eccentric orbits. We show that the current and future orbital evolution of these systems is likely dominated by tidal dissipation, and not by a more distant companion. Although most of these close-in planets experience orbital decay all the way to the Roche limit, there are two characteristic evolution paths for them, depending on the relative efficiency of tidal dissipation inside the star and the planet. We point out that the current observations may be consistent with one of them. Our results suggest that at least some of the close-in planets with non-zero orbital eccentricity may have been formed by tidally circularizing an initially eccentric orbit. We also find that even when the stellar spin-orbit misalignment is observed to be small at present, some systems could have had a highly misaligned orbit in the past. Finally, we also re-examine the recent claim by Levrard et. al., who found that all orbital and spin parameters evolve on a similar timescale to orbital decay.
We present the Australia Telescope Compact Array (ATCA) observations of the SiO masers in the Galactic center in transitions of v=1, J=2--1 at 86 GHz and v=1, J=1--0 at 43 GHz. Two 86-GHz SiO masers were detected within the central parsec, and they are associated with IRS 10EE and IRS 15NE, respectively. We detected eighteen 43-GHz SiO masers within a projected separation of <2 pc from Sagittarius A* (Sgr A*), among which seven masers are newly discovered from our observations. This raises the total number of 43-GHz SiO masers within the central 4 parsecs of the GC region to 22. Simultaneous observations at 86 and 43 GHz showed that the intensity of 43-GHz SiO maser is ~3 times higher than that of 86-GHz maser in IRS 10EE (an OH/IR star), while the integrated flux of the SiO maser emission at 43 GHz is comparable with that at 86~GHz in IRS~15NE (an ordinary Mira variable). These results are consistent with previous observations of massive late-type stars in the Galaxy in which the 86-GHz SiO maser is in general weaker than the 43-GHz SiO maser in OH/IR stars, while the two transitions are comparably strong in Mira stars.
During post-main-sequence evolution, radial expansion of the primary star, accompanied by intense winds, can significantly alter the binary orbit via tidal dissipation and mass loss. The fate of a given binary system is determined by the initial masses of the primary and companion, the initial orbit (taken to be circular), the Reimers mass-loss parameter, and the tidal prescription employed. For a range of these parameters, we determine whether the orbit expands due to mass loss or decays due to tidal torques. Where a common envelope (CE) phase ensues, we estimate the final orbital separation based on the energy required to unbind the envelope. These calculations predict period gaps for planetary and brown dwarf companions to white dwarfs. In particular, the lower end of the gap is the longest period at which companions survive their CE phase while the upper end of the gap is the shortest period at which a CE phase is avoided. For binary systems with 1 $M_\odot$ progenitors, we predict no Jupiter-mass companions with periods $\lesssim$270 days. For binary systems consisting of a 1 $M_\odot$ progenitor with a 10 Jupiter-mass companion, we predict a close, post-CE population with periods $\lesssim$0.1 days and a far population with periods $\gtrsim$380 days. These results are consistent with the detection of a $\sim$50 $M_{\rm J}$ brown dwarf in a $\sim$0.08 day orbit around the white dwarf WD 0137-349 and the tentative detection of a $\sim$2 $M_{\rm J}$ planet in a $\sim$4 year orbit around the white dwarf GD66.
We demonstrate that an extremely small but positive quantum correction, or the Casimir energy, to the cosmological constant can arise from a massive bulk fermion field in the Randall-Sundrum model. Specifically, a cosmological constant doubly descended from the Planck-electroweak hierarchy and as minute as the observed dark energy scale can be naturally achieved without fine-tuning of the bulk fermion mass. To ensure the stabilization of the system, we discuss two stabilization mechanisms under this setup. It is found that the Goldberger-Wise mechanism can be successfully introduced in the presence of a massive bulk fermion, without spoiling the smallness of the quantum correction.
In the collapsar scenario of the long duration Gamma-Ray Bursts (GRBs), multi-TeV neutrino emission is predicted as the jet makes its way through the stellar envelope. Such a neutrino signal is also expected for more general ``failed'' GRBs in which a putative jet is ``choked'' by a heavy envelope. If the \nu_e \rightarrow \nu_\mu neutrino oscillation parameters are in the atmospheric neutrino oscillation range, we show that the resonant oscillation of \nu_e\leftrightarrow\nu_{\mu,\tau} can take place within the inner high density region of the choked jet progenitor with a heavy envelope, altering the neutrino flavor ratio on its surface to \Phi^s_{\nu_e}:\Phi^s_{\nu_\mu}:\Phi^s_{\nu_\tau}=5:11:2. Considering vacuum oscillation of these neutrinos on their way to Earth, the final flavor ratio detected on Earth is further modified to either $1:1.095:1.095$ for the large mixing angle solution to the solar neutrino data, or 1:1.3:1.3 for maximal mixing among the muon and tau neutrinos in vacuum.
Recently, in the series of works a new effect of acceleration of particles by black holes was found. Under certain conditions, the energy in the centre of mass frame can become infinitely large. The essential ingredient of such effect is the rotation of a black hole. In the present Letter, we argue that the similar effect exists for a nonrotating but charged black hole even for the simplest case of radial motion of particles in the Reissner-Nordstr\"om background. All main features of the effect under discussion due to rotating black holes have their counterpart for the nonrotating charged ones.
We have considered that the universe is the inhomogeneous $(n+2)$ dimensional quasi-spherical Szekeres space-time model. We consider the universe as a thermodynamical system with the horizon surface as a boundary of the system. To study the generalized second law (GSL) of thermodynamics through the universe, we have assumed the trapped surface is the apparent horizon. Next we have examined the validity of the generalized second law of thermodynamics (GSL) on the apparent horizon by two approaches: (i) using first law of thermodynamics on the apparent horizon and (ii) without using the first law. In the first approach, the horizon entropy have been calculated by the first law. In the second approach, first we have calculated the surface gravity and temperature on the apparent horizon and then horizon entropy have found from area formula. The variation of internal entropy have been found by Gibb's law. Using these two approaches separately, we find the conditions for validity of GSL in $(n+2)$ dimensional quasi-spherical Szekeres model.
We measured the decay time of the scintillation pulses produced by electron and nuclear recoils in CaF2(Eu) by a new fitting method. In the recoil energy region 5-30 keVee, we found differences of the decay time between electron and nuclear recoil events. In the recoil energy region above 20 keVee, we found that the decay time is independent of the recoil energy.
Within the Closed Time Path (CTP) framework, we derive kinetic equations for particle distribution functions that describe leptogenesis in the presence of several lepton flavours. These flavours have different Standard-Model Yukawa couplings, which induce flavour-sensitive scattering processes and thermal dispersion relations. Kinetic equilibrium, which is rapidly established and maintained via gauge interactions, allows to simplify these equations to kinetic equations for the matrix of lepton charge densities. In performing this simplification, we notice that the rapid flavour-blind gauge interactions damp the flavour oscillations of the leptons. Leptogenesis turns out to be in the parametric regime where the flavour oscillations are overdamped and flavour decoherence is mainly induced by flavour sensitive scatterings. We solve the kinetic equations for the lepton number densities numerically and show that they interpolate between the unflavoured and the fully flavoured regimes within the intermediate parametric region, where neither of these limits is applicable.
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We report the discovery of a tight substellar companion to the young solar analog PZ Tel, a member of the Beta Pictoris moving group observed with high contrast adaptive optics imaging as part of the Gemini NICI Planet-Finding Campaign. The companion was detected at a projected separation of 16.4 +/- 1.0 AU (0.33 +/- 0.01") in April 2009. Second-epoch observations in May 2010 demonstrate that the companion is physically associated and shows significant orbital motion. Monte Carlo modeling constrains the orbit of PZ Tel B to eccentricities > 0.6. The near-IR colors of PZ Tel B indicate a spectral type of M7+/-2 and thus this object will be a new benchmark companion for studies of ultracool, low-gravity photospheres. Adopting an age of 12 +8 -4 Myr for the system, we estimate a mass of 36 +/- 6 Mjup based on the Lyon/DUSTY evolutionary models. PZ Tel B is one of few young substellar companions directly imaged at orbital separations similar to those of giant planets in our own solar system. Additionally, the primary star PZ Tel A shows a 70 um emission excess, evidence for a significant quantity of circumstellar dust that has not been disrupted by the orbital motion of the companion.
The halo-galaxy lensing correlation function or the average tangential shear profile over sampled halos is a very powerful means of measuring the halo masses, the mass profile, and the halo-mass correlation function of very large separations in the linear regime. We reformulate the halo-galaxy lensing correlation in harmonic space. We find that, counter-intuitively, errors in the conventionally used flat-sky approximation remain at a % level even at very small angles. The errors increase at larger angles and for lensing halos at lower redshifts: the effect is at a few % level at the baryonic acoustic oscillation scales for lensing halos of $z\sim 0.2$, and comparable with the effect of primordial non-Gaussianity with $f_{\rm NL}\sim 10$ at large separations. Our results allow to readily estimate/correct for the full-sky effect on a high-precision measurement of the average shear profile available from upcoming wide-area lensing surveys.
We combine GALEX (ultra-violet; UV) and SDSS (optical) photometry to study the recent star formation histories of ~100 field galaxies on the optical red sequence, a large fraction of which exhibit widespread signs of disturbed morphologies in deep optical imaging that are consistent with recent merging events. More than 70% of bulge-dominated galaxies in this sample show tidal features at a surface brightness limit of 28 mag arcsec^-2. We find that, while they inhabit the optical red sequence, they show a wide spread in their UV colours (~4 mags), akin to what has been discovered recently in the general early-type population. A strong correlation is found between UV colour and the strength of the tidal distortions, such that the bluest galaxies are more distorted. This strongly suggests that the blue UV colours seen in many nearby early-types are driven by (low-level) merger-induced star formation within the last 3 Gyrs, contributing less than 10% of the stellar mass. If the ongoing mergers in this sample, which have a median mass ratio of 1:4, are representative of the nearby red merger population, then less than 25% of the new stellar mass in the remnants is typically added through merger-induced star formation. While the dust extinction in the inter-stellar medium (ISM) in these galaxies is small [E(B-V)<0.1], the local dust content of the star-forming regions is, on average, a factor of 3 higher. Finally, we use our theoretical machinery to provide a recipe for calculating the age of the most recent star formation event (t2) in nearby (z<0.1) red early-type galaxies: Log (t2) [Gyrs] ~ 0.6.[(NUV-u)-(g-z)-1.73], where NUV, u, g and z are the observed photometric magnitudes of the galaxies in the GALEX/SDSS filtersets.
Strong gravitational lensing by groups or clusters of galaxies provides a powerful technique to measure the dark matter properties of individual lens galaxies. We study in detail the mass distribution of the satellite lens galaxy in the group-scale lens SL2S J08544-0121 by modelling simultaneously the spatially extended surface brightness distribution of the source galaxy and the lens mass distribution using Markov chain Monte Carlo methods. In particular, we measure the dark matter halo size of the satellite lens galaxy to be 6.0^{+2.9}_{-2.0} kpc with a fiducial velocity dispersion of 127^{+21}_{-12} km/s. This is the first time the size of an individual galaxy halo in a galaxy group has been measured using strong gravitational lensing without assumptions of mass following light. We verify the robustness of our halo size measurement using mock data resembling our lens system. Our measurement of the halo size is compatible with the estimated tidal radius of the satellite galaxy, suggesting that halos of galaxies in groups experience significant tidal stripping, a process that has been previously observed on galaxies in clusters. Our mass model of the satellite galaxy is elliptical with its major axis misaligned with that of the light by ~50 deg. The major axis of the total matter distribution is oriented more towards the centre of the host halo, exhibiting the radial alignment found in N-body simulations and observational studies of satellite galaxies. This misalignment between mass and light poses a significant challenge to modified Newtonian dynamics.
The rising amount of polarized observations of relativistic sources requires the correct theory for proper model fitting. The equations for general relativistic (GR) polarized radiative transfer are derived starting from the Boltzmann equation and basic ideas of general relativity. The derivation is aimed at providing a practical guide to reproducing the synchrotron part of radio & sub-mm emission from low luminosity active galactic nuclei (LLAGNs), in particular Sgr A*, and jets. The recipe for fast exact calculation of cyclo-synchrotron emissivities, absorptivities, Faraday rotation and conversion coefficients is given for isotropic particle distributions. The multitude of physical effects influencing simulated spectrum is discussed. The application of the prescribed technique is necessary to determine the black hole (BH) spin in LLAGNs, constraining it with all observations of total flux, linear and circular polarization fractions, and electric vector position angle as functions of the observed frequency.
The constraints on Sgr A* black hole (BH) and accretion flow parameters are found by fitting polarized sub-mm observations. The observations from 29 papers are averaged into a quasi-quiescent set. We run three-dimensional general relativistic magnetohydrodynamical (3D GRMHD) simulations for dimensionless spins a=0,0.5,0.7,0.9,0.98 till 20000M, construct an averaged dynamical model, perform GR polarized radiative transfer, and explore the parameter space of spin $a$, inclination angle \theta, position angle (PA), accretion rate \dot{M}, and electron temperature $T_e$ at 6M radius. The best-fitting model for spin a=0.9 gives \chi^2=0.99 with \theta=59deg, \dot{M}=1.3*10^{-8}M_sun/year, T_e=3.2*10^{10}K at 6M, the best-fitting model for spin a=0.5 gives \chi^2=0.84 with \theta=70deg, \dot{M}=7.0*10^{-8}M_sun/year, and T_p/T_e=22 at 6M with T_e=3.50*10^{10}K. We identify the physical phenomena leading to the matched linear polarization (LP), circular polarization (CP), and electric vector position angle (EVPA). Our statistical analysis reveals the most probable spin is a=0.9. The spin a=0.5 solutions are 10 times less probable despite giving lower minimum \chi^2 and spin a=0 is excluded as having probability P(a)<1%. Polarized data allows us to tightly constrain some quantities. Inclination angle, electron temperature, and position angle have ranges \theta=59+/-9deg, T_e=(3.4+1.2/-0.9)*10^{10}K, and PA=96+/-30deg with 90% confidence. The total range of accretion rate is large, but assuming spin a=0.9 we get \dot{M}(0.9)=(13+4/-3)*10^{-9}M_sun/year interval with 90% confidence. The emission region sizes at 230GHz of the best-fitting models are found to be marginally consistent with the observed by VLBI technique.
The Magellanic Stream (MS) is the nearest example of a gaseous trail formed by interacting galaxies. While the substantial gas masses in these kinds of circumgalactic structures are postulated to represent important sources of fuel for future star formation, the mechanisms whereby this material might be accreted back into galaxies remain unclear. Recent neutral hydrogen (HI) observations have demonstrated that the northern portion of the MS, which probably has been interacting with the Milky Way's hot gaseous halo for close to 1000~Myr, has a larger spatial extent than previously recognized, while also containing significant amounts of small-scale structure. After a brief consideration of the large-scale kinematics of the MS as traced by the recently-discovered extension of the MS, we explore the aging process of the MS gas through the operation of various hydrodynamic instabilities and interstellar turbulence. This in turn leads to consideration of processes whereby MS material survives as cool gas, and yet also evidently fails to form stars. Parallels between the MS and extragalactic tidal features are briefly discussed with an emphasis on steps toward establishing what the MS reveals about the critical role of local processes in determining the evolution of these kinds of systems.
We examine the absolute magnitudes and light-curve shapes of 14 nearby(redshift z = 0.004--0.027) Type Ia supernovae (SNe~Ia) observed in the ultraviolet (UV) with the Swift Ultraviolet/Optical Telescope. Colors and absolute magnitudes are calculated using both a standard Milky Way (MW) extinction law and one for the Large Magellanic Cloud that has been modified by circumstellar scattering. We find very different behavior in the near-UV filters (uvw1_rc covering ~2600-3300 A after removing optical light, and u ~3000--4000 A) compared to a mid-UV filter (uvm2 ~2000-2400 A). The uvw1_rc-b colors show a scatter of ~0.3 mag while uvm2-b scatters by nearly 0.9 mag. Similarly, while the scatter in colors between neighboring filters is small in the optical and somewhat larger in the near-UV, the large scatter in the uvm2-uvw1 colors implies significantly larger spectral variability below 2600 A. We find that in the near-UV the absolute magnitudes at peak brightness of normal SNe Ia in our sample are correlated with the optical decay rate with a scatter of 0.4 mag, comparable to that found for the optical in our sample. However, in the mid-UV the scatter is larger, ~1 mag, possibly indicating differences in metallicity. We find no strong correlation between either the UV light-curve shapes or the UV colors and the UV absolute magnitudes. With larger samples, the UV luminosity might be useful as an additional constraint to help determine distance, extinction, and metallicity in order to improve the utility of SNe Ia as standardized candles.
We report the discovery of two new transiting extrasolar planets. HAT-P-18b orbits the V=12.759 K2 dwarf star GSC 2594-00646, with a period P=5.508023+-0.000006 d, transit epoch Tc=2454715.02174+-0.00020 (BJD), and transit duration 0.1131+-0.0009 d. The host star has a mass of 0.77+-0.03 Msun, radius of 0.75+-0.04 Rsun, effective temperature 4803+-80 K, and metallicity [Fe/H]=+0.10+-0.08. The planetary companion has a mass of 0.197+-0.013 Mjup, and radius of 0.995+-0.052 Rjup yielding a mean density of 0.25+-0.04 g cm-3. HAT-P-19b orbits the V=12.901 K1 dwarf star GSC 2283-00589, with a period P=4.008778+-0.000006 d, transit epoch Tc=2455091.53417+-0.00034 (BJD), and transit duration 0.1182+-0.0014 d. The host star has a mass of 0.84+-0.04 Msun, radius of 0.82+-0.05 Rsun, effective temperature 4990+-130 K, and metallicity [Fe/H]=+0.23+-0.08. The planetary companion has a mass of 0.292+-0.018 Mjup, and radius of 1.132+-0.072 Rjup yielding a mean density of 0.25+-0.04 g cm-3. The radial velocity residuals for HAT-P-19 exhibit a linear trend in time, which indicates the presence of a third body in the system. Comparing these observations with theoretical models, we find that HAT-P-18b and HAT-P-19b are each consistent with a hydrogen-helium dominated gas giant planet with negligible core mass. HAT-P-18b and HAT-P-19b join HAT-P-12b and WASP-21b in an emerging group of low-density Saturn-mass planets, with negligible inferred core masses. However, unlike HAT-P-12b and WASP-21b, both HAT-P-18b and HAT-P-19b orbit stars with super-solar metallicity. This calls into question the heretofore suggestive correlation between the inferred core mass and host star metallicity for Saturn-mass planets.
Compact stars made of quark matter rather than confined hadronic matter, are expected to form a color superconductor. This superconductor ought to be threaded with rotational vortex lines within which the star's interior magnetic field is confined. The vortices (and thus magnetic flux) would be expelled from the star during stellar spin-down, leading to magnetic reconnection at the surface of the star and the prolific production of thermal energy. In this Letter, we show that this energy release can re-heat quark stars to exceptionally high temperatures, such as observed for Soft Gamma Repeaters (SGRs), Anomalous X-Ray pulsars (AXPs), and X-ray dim isolated neutron stars (XDINs). Moreover, our numerical investigations of the temperature evolution, spin-down rate, and magnetic field behavior of such superconducting quark stars suggest that SGRs, AXPs, and XDINs may be linked ancestrally. Finally, we discuss the possibility of a time delay before the star enters the color superconducting phase, which can be used to estimate the density at which quarks deconfine. We find this density to be five times that of nuclear saturation.
As very high energy (~100 GeV) gamma rays travel over cosmological distances, their flux is attenuated through interactions with the extragalactic background light. Observations of distant gamma ray sources at energies between ~200 GeV and a few TeV by ground-based gamma ray telescopes such as HESS, however, suggest that the universe is more transparent to very high energy photons than had been anticipated. One possible explanation for this is the existence of axion-like-particles (ALPs) which gamma rays can efficiently oscillate into, enabling them to travel cosmological distances without attenuation. In this article, we use data from the Fermi Gamma Ray Space Telescope to calculate the spectra at 1-100 GeV of two gamma ray sources, 1ES1101-232 at redshift z=0.186 and H 2356-309 at z=0.165, and use this in conjunction with the measurements of ground-based telescopes to test the ALP hypothesis. We find that the observations can be well-fit by an intrinsic power-law source spectrum with indices of -2.01 and -2.77 for 1ES1101-232 and H 2356-309, respectively, and that no ALPs or other exotic physics is necessary to explain the observed degree of attenuation.
Diffuse X-rays from the Galactic center (GC) region were found to exhibit many K-shell lines from iron and nickel atoms in the 6--9 keV band. The strong emission lines seen in the spectrum are neutral iron K$\alpha$ at 6.4~keV, He-like iron K$\alpha$ at 6.7~keV, H-like iron Ly$\alpha$ at 6.9~keV, and He-like iron K$\beta$ at 7.8~keV. Among them, the 6.4~keV emission line is a probe of non-thermal phenomena. We have detected strong 6.4~keV emission in several giant molecular clouds, some of which were newly discovered by Suzaku. All the spectra exhibit large equivalent widths of 1-2~keV and absorption columns of $2-10\times 10^{23}\{\rm H\ cm}^{-2}$. We found time variability of diffuse 6.4~keV emission in the Sgr B2 region comparing the maps and spectra obtained from 1994 to 2005 with ASCA, Chandra, XMM-Newton and Suzaku. We also report discovery of K$\alpha$ lines of neutral argon, calcium, chrome, and manganese atoms in the Sgr~A region. We show that the equivalent width of the 6.4~keV emission line detected in X-ray faint region against the 6.4 keV-associated continuum (power-law component) is $\sim 800\ {\rm eV}$. These features are naturally explained by the X-ray reflection nebula scenario rather than the low energy cosmic-ray electrons scenario. On the other hand, a 6.4~keV clump, G~0.162$-$0.217, discovered at the south end of the Radio Arc has a small equivalent width of 6.4~keV emission line of $\sim200\ {\rm eV}$. The Radio Arc is a site of relativistic electrons. Thus, it is conceivable that the X-rays of G~0.162$-$0.217 are due to low energy cosmic-ray electrons
Recently, gamma-ray telescopes AGILE and Fermi observed several middle-aged supernova remnants (SNRs) interacting with molecular clouds. It is likely that their gamma rays arise from the decay of neutral pions produced by the inelastic collision between cosmic rays (CRs) and nucleons, which suggests that SNRs make the bulk of Galactic CRs. In this letter, we provide the analytical solution of the distribution of CRs that have escaped from a finite-size region, which naturally explains observed broken power-law spectra of the middle-aged SNRs. In addition, the typical value of the break energy of the gamma-ray spectrum, 1-10 GeV, is naturally explained from the fact that the stellar wind dynamics shows the separation between the molecular clouds and the explosion center of about 10 pc. We find that a runaway-CR spectrum of the four middle-aged SNRs (W51C, W28, W44 and IC 443) interacting with molecular clouds could be the same, even though it leads to different gamma-ray spectra. This result is consistent with that of recent studies of the Galactic CR propagation, and supports that SNRs are indeed the sources of Galactic CRs.
We have conducted VLBA phase-referencing monitoring of H2O masers around the red supergiant, S Persei, for six years. We have fitted maser motions to a simple expanding-shell model with a common annual parallax and stellar proper motion, and obtained the annual parallax as 0.413+/-0.017 mas, and the stellar proper motion as (-0.49+/-0.23 mas/yr, -1.19+/-0.20 mas/yr) in right ascension and declination, respectively. The obtained annual parallax corresponds to the trigonometric distance of 2.42+0.11-0.09 kpc. Assuming the Galactocentric distance of the Sun of 8.5 kpc, the circular rotational velocity of the LSR at the distance of the Sun of 220 km/s, and a flat Galactic rotation curve, S Persei is suggested to have a non-circular motion deviating from the Galactic circular rotation for 15 km/s, which is mainly dominated by the anti rotation direction component of 12.9+/-2.9 km/s. This red supergiant is thought to belong to the OB association, Per OB1, so that this non-circular motion is representative of a motion of the OB association in the Milky Way. This non-circular motion is somewhat larger than that explained by the standard density-wave theory for a spiral galaxy, and is attributed to either a cluster shuffling of the OB association, or to non-linear interactions between non-stationary spiral arms and multi-phase interstellar media. The latter comes from a new view of a spiral arm formation in the Milky Way suggested by recent large N-body/smoothed particle hydrodynamics numerical simulations.
Predicting the severity of the solar eruptive phenomena like flares and Coronal Mass Ejections (CMEs) remains a great challenge despite concerted efforts for several decades. The advent of high quality vector magnetograms obtained from Hinode (SOT/SP) has increased the possibility of meeting this challenge. In particular, the Spatially Averaged Signed Shear Angle (SASSA) seems to be an unique parameter to quantify the non-potentiality of the active regions. We demonstrate the usefulness of SASSA for predicting the flare severity. For this purpose we present case studies of the evolution of magnetic non-potentiality using 115 vector magnetograms of four active regions namely ARs NOAA 10930, 10960, 10961 and 10963 during December 08-15, 2006, June 03-10, 2007, June 28-July 5, 2007 and July 10-17, 2007 respectively. The NOAA ARs 10930 and 10960 were very active and produced X and M class flares respectively, along with many smaller X-ray flares. On the other hand, the NOAA ARs 10961 and 10963 were relatively less active and produced only very small (mostly A and B-class) flares. For this study we have used a large number of high resolution vector magnetograms obtained from Hinode (SOT/SP). The analysis shows that the peak X-ray flux of the most intense solar flare emanating from the active regions depends on the magnitude of the SASSA at the time of the flare. This finding of the existence of a lower limit of SASSA for a given class of X-ray flare will be very useful for space weather forecasting. We have also studied another non-potentiality parameter called mean weighted shear angle (MWSA) of the vector magnetograms along with SASSA. We find that the MWSA does not show such distinction as the SASSA for upper limits of GOES X-Ray flux of solar flares, however both the quantities show similar trends during the evolution of all active regions studied.
Context: The $\gamma$-ray blazar PKS 2155-304 has attracted considerable attention because of its extreme TeV variability characteristics during an exceptional flaring period in 2006. Among the observed key findings are (i) a minimum variability timescale as short as $\sim 200$ sec and (ii) highly variable TeV emission, which in the frequency interval [$10^{-4}$ Hz, $10^{-2}$ Hz] can be described by a log-normal distribution and suggests an underlying multiplicative (and not additive) process. Aims: Simultaneously accounting for these findings appears difficult within conventional approaches. Following earlier suggestions for the TeV blazar Mkn 501, we explore a possible scenario where PKS 2155-304 is supposed to harbor a supermassive binary black hole system and where the observed TeV variability is dominated by emission from the less massive black hole. Methods: We analyze the constraints on the very high energy (VHE) source imposed by the observed variability characteristics and the integrated VHE luminosity output, and discuss its implications for a binary black hole system. Results: We show that for a secondary mass of $m_{\rm BH} \sim 10^7 M_{\odot}$, fluctuations in the disk accretion rate that feed the jet could account for the observed red-noise type variability process down to frequencies of $\sim 10^{-2}$ Hz. Jet curvature induced by orbital motion, on the other hand, could further relax constraints on the intrinsic jet speeds. Conclusions: Because a binary system can lead to different (yet not independent) periodicities in different energy bands, a longterm (quasi-) periodicity analysis could offer important insights into the real nature of the central engine of PKS~2155-304.
We investigate whether or nor it is possible to find a scalar field model or models that are capable of explaining simultaneously the observed $N$-$z$ relation given by the 2dF Galaxy Redshift Survey, which still seems to exhibit a spatial periodicity of the galaxy distribution(the 'picket-fence structure'), and the CMB spectrum obtained by the WMAP experiments. It is found that both the observed size of the spatial periodicity and the amplitude of the 2dF $N$-$z$ relation can be fairly well fitted by the theoretical computations based on the scalar field models with $-20\le \xi\le -10$, and $140\le m_{\rm s} \le 160$, where $\xi$ is the gravitational coupling parameter, and $m_{\rm s}$ the normalized mass of the scalar field, respectively. To reproduce the CMB spectrum of the WMAP, we find that it is very crucial to have a null state of the scalar field in the early epochs of evolution of the universe.
Traditionally runaway stars are O and B type stars with large peculiar velocities.We want to extend this definition to young stars (up to ~50 Myr) of any spectral type and identify those present in the Hipparcos catalogue applying different selection criteria such as peculiar space velocities or peculiar one-dimensional velocities. Runaway stars are important to study the evolution of multiple star systems or star clusters as well as to identify origins of neutron stars. We compile distances, proper motions, spectral types, luminosity classes, V magnitudes and B-V colours and utilise evolutionary models from different authors to obtain star ages and study a sample of 7663 young Hipparcos stars within 3 kpc from the Sun. Radial velocities are obtained from the literature. We investigate the distributions of the peculiar spatial velocity, the peculiar radial velocity as well as the peculiar tangential velocity and its one-dimensional components and obtain runaway star probabilities for each star in the sample. In addition, we look for stars that are situated outside any OB association or OB cluster and the Galactic plane as well as stars of which the velocity vector points away from the median velocity vector of neighbouring stars or the surrounding local OB association/ cluster although the absolute velocity might be small. We find a total of 2547 runaway star candidates (with a contamination of normal Population I stars of 20 per cent at most). Thus, after subtraction of those 20 per cent, the runaway frequency among young stars is about 27 per cent. We compile a catalogue of runaway stars which will be available via VizieR.
In this short communication we consider the possibility that stars less evolved than the polluters are the source of the dilution needed to explain the observed composition of second-generation globular cluster (GC) stars and the Na-O and Mg-Al anticorrelations. If these stars can lose 0.5-1% of their mass during the relevant epochs, there is enough diluting material to produce the observed anticorrelations. In this case, the original mass of proto-GCs was several tens times higher than the current mass of GCs. While not strictly impossible, this is a stringent hypothesis that needs more support. Should this scenario be found true, then the link between the primordial (first-generation) population in GC and the field population would be very strong.
Using Herschel PACS and SPIRE observations of Lockman Hole-North and GOODS-N as part of the HerMES project, we explore the far-IR properties of a sample of mid-IR selected starburst dominated ultra-luminous infrared galaxies (ULIRGs) at z ~ 2. The selection of the sample is based on the detection of the stellar bump that appears in the SED of star-forming galaxies at 1.6um. We derive robust estimates of infrared luminosities (L_IR) and dust temperatures (T_d) of the population and find that while the luminosities in our sample span less than an order of magnitude (12.24< log(L_IR/Lo) < 12.94), they cover a wide range of dust temperatures (25< T_d < 62 K). Galaxies in our sample range from those that are as cold as high-z sub-millimeter galaxies (SMGs) to those that are as warm as optically faint radio galaxies (OFRGs) and local ULIRGs. Nevertheless, our sample has median T_d=42.3 K, filling the gap between SMGs and OFRGs, bridging the two populations. We demonstrate that a significant fraction of our sample would be missed from ground based (sub)mm surveys (850-1200um) showing that the latter introduce a bias towards the detection of colder sources. We conclude that Herschel} observations, confirm the existence of high-z ULIRGs warmer than SMGs, show that the mid-IR selection of high-z ULIRGs is not T_d-dependent, reveal a large dispersion in T_d of high-z ULIRGs, and provide the means to characterize the bulk of the ULIRG population, free from selection biases introduced by ground based (sub)mm surveys.
We present a wide-field IFS survey on the nearby face-on Sbc galaxy NGC 628,
comprising 11094 individual spectra, covering a nearly circular field-of-view
of ~6 arcmin in diameter, with a sampling of ~2.7 arcsec per spectrum in the
optical wavelength range (3700--7000 AA). This galaxy is part of the PPAK IFS
Nearby Galaxies Survey, (PINGS, Rosales-Ortega et al. 2009). To our knowledge,
this is the widest spectroscopic survey ever made in a single nearby galaxy. A
detailed flux calibration was applied, granting a spectrophotometric accuracy
of $\sim$\,0.2 mag.
The age of the stellar populations shows a negative gradient from the inner
(older) to the outer (younger) regions. We found an inversion of this gradient
in the central ~1 kpc region, where a somewhat younger stellar population is
present within a ring at this radius. This structure is associated with a
circumnuclear star-forming region at ~ 500 pc, also found in similar spiral
galaxies. From the study of the integrated and spatially resolved ionized gas
we found a moderate SFR of ~ 2.4 Msun yr$^{-1}$. The oxygen abundance shows a a
clear gradient of higher metallicity values from the inner part to the outer
part of the galaxy, with a mean value of 12~+~log(O/H) ~ 8.7. At some specific
regions of the galaxy, the spatially resolved distribution of the physical
properties show some level of structure, suggesting real point-to-point
variations within an individual \hh region. Our results are consistent with an
inside-out growth scheme, with stronger star formation at the outer regions,
and with evolved stellar populations in the inner ones.
The final state of turbulent magnetic relaxation in a reversed field pinch is well explained by Taylor's hypothesis. However, recent resistive-magnetohydrodynamic simulations of the relaxation of braided solar coronal loops have led to relaxed fields far from the Taylor state, despite the conservation of helicity. We point out the existence of an additional topological invariant in any flux tube with non-zero field: the topological degree of the field line mapping. We conjecture that this constrains the relaxation, explaining why only one of three example simulations reaches the Taylor state.
We present an extended scheme for the calculation of the profiles of emission lines from accretion discs around rotating black holes. The scheme includes discs with angular momenta which are parallel and antiparallel with respect to the black hole's angular momentum, as both configurations are assumed to be stable (King et al., 2005). We discuss line shapes for such discs and present a code for modelling observational data with this scheme in X-ray data analysis programs. Based on a Green's function approach, an arbitrary radius dependence of the disc emissivity and arbitrary limb darkening laws can be easily taken into account, while the amount of precomputed data is significantly reduced with respect to other available models.
We explore the feasibility and limitations of using the 1.6um bump as a photometric redshift indicator and selection technique and use it to study the rest-frame H-band galaxy luminosity and stellar mass functions at redshift z~2. We use publicly available Spitzer/IRAC images in the GOODS fields and find that color selection in the IRAC bandpasses alone is comparable in completeness and contamination to BzK selection. We find that the shape of the 1.6um bump is robust, and photometric redshifts are not greatly affected by choice of model parameters. Comparison with spectroscopic redshifts shows photometric redshifts to be reliable. We create a rest-frame NIR selected catalog of galaxies at z~2 and construct a galaxy stellar mass function (SMF). Comparisons with other SMFs at approximately the same redshift but determined using shorter wavelengths show good agreement. This agreement suggests that selection at bluer wavelengths does not miss a significant amount of stellar mass in passive galaxies. Comparison with SMFs at other redshifts shows evidence for the downsizing scenario of galaxy evolution. We conclude by pointing out the potential for using the 1.6um technique to select high-redshift galaxies with the JWST, whose lambda > 0.6 um coverage will not be well suited to selecting galaxies using techniques that require imaging at shorter wavelengths.
Lorentz Invariance Violation (LIV) may be a good observational window on Quantum Gravity physics. Within last few years, all major Gamma-ray experiments have published results from the search for LIV with variable astrophysical sources: Gamma-ray Bursts with detectors on-board satellites and Active Galactic Nuclei with ground-based experiments. In this paper, the recent time-of-flight studies with unpolarized photons published from the space and ground based observations are reviewed. Various methods used in the time delay searches are described, and their performance discussed. Since no significant time-lag value was found within experimental precision of the measurements, the present results consist of 95% Confidence Level limits on the Quantum Gravity scale on the linear and quadratic terms in the standard photon dispersion relations.
Using Herschel's HIFI instrument we have observed [C II] along a cut through S140 and high-J transitions of CO and HCO+ at two positions on the cut, corresponding to the externally irradiated ionization front and the embedded massive star forming core IRS1. The HIFI data were combined with available ground-based observations and modeled using the KOSMA-tau model for photon dominated regions. Here we derive the physical conditions in S140 and in particular the origin of [C II] emission around IRS1. We identify three distinct regions of [C II] emission from the cut, one close to the embedded source IRS1, one associated with the ionization front and one further into the cloud. The line emission can be understood in terms of a clumpy model of photon-dominated regions. At the position of IRS1, we identify at least two distinct components contributing to the [C II] emission, one of them a small, hot component, which can possibly be identified with the irradiated outflow walls. This is consistent with the fact that the [C II] peak at IRS1 coincides with shocked H2 emission at the edges of the outflow cavity. We note that previously available observations of IRS1 can be well reproduced by a single-component KOSMA-tau model. Thus it is HIFI's unprecedented spatial and spectral resolution, as well as its sensitivity which has allowed us to uncover an additional hot gas component in the S140 region.
The traditional generalized Ohm's law in MHD do not explicitly present the
relation of electric currents and electric fields in fully ionized plasma, and
lead to some unexpected concepts, such as "the magnetic frozen-in plasma",
magnetic reconnection etc. In the present paper, we solve the balance equation
can give exact solution of the velocities of electrons and ions, and then
derived the electric current in fully ionized plasma. In the case ignoring
boundary condition, there is no electric current in the plane perpendicular to
the magnetic field when external forces are ignored. The electric field in the
plane perpendicular to magnetic field do not contribute to the electric
currents, so do the induced electric field from the motion of the plasma across
magnetic field. The lack of induced electric current will keep magnetic field
in space unaffected. The velocity of the bulk velocity of the plasma
perpendicular to magnetic field is not free, it is decided by electromagnetic
field and the external forces. We conclude that the bulk velocity of the fully
ionized plasma is not coupled with the magnetic field. The motion of the plasma
do not change the magnetic field in space, but the plasma will be confined by
magnetic field.
Due to the confinement of magnetic field, the plasma kinetic energy will be
transformed into plasma thermal energy by the Lamor motion and collisions
between the same species of particles inside plasma. Because the electric field
perpendicular to magnetic field do not contribute electric current, the
variation of magnetic field will transfer energy directly into the plasma
thermal energy by induced electric field. The heating of plasma could be from
the kinetic energy and the variation of magnetic field.
The high-frequency quasi-periodic oscillations (HF QPOs) that appear in the X-ray fluxes of low-mass X-ray binaries remain an unexplained phenomenon. Among other ideas, it has been suggested that a non-linear resonance between two oscillation modes in an accretion disc orbiting either a black hole or a neutron star plays a role in exciting the observed modulation. Several possible resonances have been discussed. A particular model assumes resonances in which the disc-oscillation modes have the eigenfrequencies equal to the radial and vertical epicyclic frequencies of geodesic orbital motion. This model has been discussed for black hole microquasar sources as well as for a group of neutron star sources. Assuming several neutron (strange) star equations of state and Hartle-Thorne geometry of rotating stars, we briefly compare the frequencies expected from the model to those observed. Our comparison implies that the inferred neutron star radius "RNS" is larger than the related radius of the marginally stable circular orbit "rms" for nuclear matter equations of state and spin frequencies up to 800Hz. For the same range of spin and a strange star (MIT) equation of state, the inferrred radius RNS is roughly equal to rms. The Paczynski modulation mechanism considered within the model requires that RNS < rms. However, we find this condition to be fulfilled only for the strange matter equation of state, masses below one solar mass, and spin frequencies above 800Hz. This result most likely falsifies the postulation of the neutron star 3:2 resonant eigenfrequencies being equal to the frequencies of geodesic radial and vertical epicyclic modes. We suggest that the 3:2 epicyclic modes could stay among the possible choices only if a fairly non-geodesic accretion flow is assumed, or if a different modulation mechanism operates.
We use deep Hubble Space Telescope images taken with the Advanced Camera for Surveys (ACS) in the F475W and F814W filters to investigate the globular cluster systems in four edge-on Sa spiral galaxies covering a factor of 4 in luminosity. The specific frequencies of the blue globular clusters in the galaxies in our sample fall in the range 0.34 -- 0.84, similar to typical values found for later-type spirals. The number of red globular clusters associated with the bulges generally increases with the bulge luminosity, similar to what is observed for elliptical galaxies, although the specific frequency of bulge clusters is a factor of 2-3 lower for the lowest luminosity bulges than for the higher luminosity bulges. We present a new empirical relation between the fraction of red globular clusters and total bulge luminosity based on the elliptical galaxies studied by ACSVCS (ACS Virgo Cluster Survey), and discuss how this diagram can be used to assess the importance that dissipative processes played in building spiral bulges. Our results suggest a picture where dissipative processes, which are expected during gas-rich major mergers, were more important for building luminous bulges of Sa galaxies, whereas secular evolution may have played a larger role in building lower-luminosity bulges in spirals.
We study the effects of diffusion on the non-linear corotation torque, or horseshoe drag, in the two-dimensional limit, focusing on low-mass planets for which the width of the horseshoe region is much smaller than the scale height of the disc. In the absence of diffusion, the non-linear corotation torque saturates, leaving only the Lindblad torque. Diffusion of heat and momentum can act to sustain the corotation torque. In the limit of very strong diffusion, the linear corotation torque is recovered. For the case of thermal diffusion, this limit corresponds to having a locally isothermal equation of state. We present some simple models that are able to capture the dependence of the torque on diffusive processes to within 20% of the numerical simulations.
We present a new software pipeline -- PyMorph -- for automated estimation of structural parameters of galaxies. Both parametric fits through a two dimensional bulge disk decomposition as well as structural parameter measurements like concentration, asymmetry etc. are supported. The pipeline is designed to be easy to use yet flexible; individual software modules can be replaced with ease. A find-and-fit mode is available so that all galaxies in a image can be measured with a simple command. A parallel version of the Pymorph pipeline runs on computer clusters and a Virtual Observatory compatible web enabled interface is under development.
We present the third release of the AMBER data reduction software by the JMMC. This software is based on core algorithms optimized after several years of operation. An optional graphic interface in a high level language allows the user to control the process step by step or in a completely automatic manner. Ongoing improvement is the implementation of a robust calibration scheme, making use of the full calibration sets available during the night. The output products are standard OI-FITS files, which can be used directly in high level software like model fitting or image reconstruction tools. The software performances are illustrated on a full data set of calibrators observed with AMBER during 5 years taken in various instrumental setup.
The solar atmosphere is structured and inhomogeneous both horizontally and vertically. The omnipresence of coronal magnetic loops implies gradients of the equilibrium plasma quantities like the density, magnetic field and temperature. These gradients are responsible for the excitation of drift waves that grow both within the two-component fluid description (in the presence of collisions and without it) and within the two-component kinetic descriptions (due to purely kinetic effects). In the present work the effects of the density gradient in the direction perpendicular to the magnetic field vector are investigated within the kinetic theory, in both electrostatic and electromagnetic regimes. The electromagnetic regime implies the coupling of the gradient-driven drift wave with the Alfven wave. The growth rates for the two cases are calculated and compared. It is found that, in general, the electrostatic regime is characterized by stronger growth rates, as compared with the electromagnetic perturbations. Also discussed is the stochastic heating associated with the drift wave. The released amount of energy density due to this heating should be more dependent on the magnitude of the background magnetic field than on the coupling of the drift and Alfven waves. The stochastic heating is expected to be much higher in regions with a stronger magnetic field. On the whole, the energy release rate caused by the stochastic heating can be several orders of magnitude above the value presently accepted as necessary for a sustainable coronal heating.
We present deep 3.6 cm radio continuum observations of the HII region W40 obtained using the Very Large Array in its A and B configurations. We detect a total of 20 compact radio sources in a region of 4 x 4 arcmin, with 11 of them concentrated in a band with 30 arcsec of extent. We also present JHK photometry of the W40 cluster taken with the QUIRC instrument on the University of Hawaii 2.2 meter telescope. These data reveal that 15 of the 20 VLA sources have infrared counterparts, and 10 show radio variability with periods less than 20 days. Based on these combined radio and IR data, we propose that 8 of the radio sources are candidate ultracompact HII regions, 7 are likely to be young stellar objects, and 2 may be shocked interstellar gas.
We present here a new observational technique, Phase Closure Nulling (PCN), which has the potential to obtain very high contrast detection and spectroscopy of faint companions to bright stars. PCN consists in measuring closure phases of fully resolved objects with a baseline triplet where one of the baselines crosses a null of the object visibility function. For scenes dominated by the presence of a stellar disk, the correlated flux of the star around nulls is essentially canceled out, and in these regions the signature of fainter, unresolved, scene object(s) dominates the imaginary part of the visibility in particular the closure phase. We present here the basics of the PCN method, the initial proof-of-concept observation, the envisioned science cases and report about the first observing campaign made on VLTI/AMBER and CHARA/MIRC using this technique.
We use the parallax measurements of RE J 0317-853 in order to determine its mass, radius and cooling age and thereby obtain constraints on the possible evolutionary origins. We observed RE J 0317-853 with Hubble Space Telescope's Fine Guidance System in order to measure the parallax of RE J 0317-853 and its binary companion, the non-magnetic white dwarf LB 9802; spectra of comparison stars were taken with the Boller & Chivens spectrograph of the SMARTS telescope in order to correct the parallax zero point. For the corrected parallax we determine the radius, mass and the cooling age with the help of evolutionary models from the literature. The properties of RE J 0317-853 were constrained by the parallax information. Different cases of the core composition and the uncertain effective temperature were discussed. We confirm that RE J 0317-853 is close to Chandrasekhar mass in all cases and almost as old as its companion LB 9802. The precise evolutionary history of RE J 0317-853 depends on the knowledge of the effective temperature. A single star progenitor is possible if we assume that the effective temperature is at the cooler end of the possible range from 30 000 to 50 000 K; if T_eff is rather at the hotter end, a binary-merger scenario for RE J 0317-853 becomes more plausible.
Being fast rotating objects, Isolated Neutron Stars (INSs) are natural targets for high-time resolution observations across the whole electromagnetic spectrum. With the number of objects detected at optical (plus ultraviolet and infrared) wavelengths now increased to 24, high-time resolution observations of INSs at these wavelengths are becoming more and more important. While classical rotation-powered radio pulsars, like the Crab and Vela pulsars, have been the first INSs studied at high-time resolution in the optical domain, observations performed in the last two decades have unveiled potential targets in other types of INSs which are not rotation powered, although their periodic variability is still related to the neutron star rotation. In this paper I review the current status of high-time resolution observations of INSs in the optical domain for different classes of objects: rotation-powered pulsars, magnetars, thermally emitting neutron stars, and rapid radio transients, I describe their timing properties, and I outline the scientific potentials of their optical timing studies.
I discuss four key questions about Galactic Center dynamics, their implications for understanding both the environment of the Galactic MBH and galactic nuclei in general, and the progress made in addressing them. The questions are (1) Is the stellar system around the MBH relaxed? (2) Is there a "dark cusp" around the MBH? (3) What is the origin of the stellar disk(s)?, and (4) What is the origin of the S-stars?
We study the backreaction of free quantum fields on a flat Robertson-Walker spacetime. Apart from renormalization freedom, the vacuum energy receives contributions from both the trace anomaly and the thermal nature of the quantum state. The former represents a dynamical realisation of dark energy, while the latter mimics an effective dark matter component. The semiclassical dynamics yield two classes of asymptotically stable solutions. The first reproduces the concordance model in a suitable regime. The second lacks a classical counterpart, but is in excellent agreement with recent observations.
We combine variability information from the MAssive Compact Halo Objects (MACHO) survey of the Large Magellanic Cloud (LMC) with infrared photometry from the Spitzer Space Telescope Surveying the Agents of a Galaxy's Evolution (SAGE) survey to create a dataset of ~30 000 variable red sources. We photometrically classify these sources as being on the first ascent of the Red Giant Branch (RGB), or as being in one of three stages along the Asymptotic Giant Branch (AGB): oxygen-rich, carbon-rich, or highly reddened with indeterminate chemistry ("extreme" AGB candidates). We present linear period-luminosity relationships for these sources using 8 separate infrared bands (J, H, K, 3.6, 4.5, 5.8, 8.0, and 24 micron) as proxies for the luminosity. We find that the wavelength dependence of the slope of the period-luminosity relationship is different for different photometrically determined classes of AGB stars. Stars photometrically classified as O-rich show the least variation of slope with wavelength, while dust enshrouded extreme AGB stars show a pronounced trend toward steeper slopes with increasing wavelength. We find that O-rich AGB stars pulsating in the fundamental mode obey a period-magnitude relation with a slope of -3.41 +/- 0.04 when magnitude is measured in the 3.6 micron band, in contrast to C-rich AGB stars, which obey a relation of slope -3.77 +/- 0.05.
We present a parameterized model of the intra-cluster medium that is suitable for jointly analysing pointed observations of the Sunyaev-Zel'dovich (SZ) effect and X-ray emission in galaxy clusters. The model is based on assumptions of hydrostatic equilibrium, the Navarro, Frenk and White (NFW) model for the dark matter, and a softened power law profile for the gas entropy. We test this entropy-based model against high and low signal-to-noise mock observations of a relaxed and recently-merged cluster from N-body/hydrodynamic simulations, using Bayesian hyper-parameters to optimise the relative statistical weighting of the mock SZ and X-ray data. We find that it accurately reproduces both the global values of the cluster temperature, total mass and gas mass fraction (fgas), as well as the radial dependencies of these quantities outside of the core (r > kpc). For reference we also provide a comparison with results from the single isothermal beta model. We confirm previous results that the single isothermal beta model can result in significant biases in derived cluster properties.
Very massive stars preferentially reside in the cores of their parent clusters and form binary or multiple systems. We study the role of tight very massive binaries in the origin of the field population of very massive stars. We performed numerical simulations of dynamical encounters between single (massive) stars and a very massive binary with parameters similar to those of the most massive known Galactic binaries, WR 20a and NGC 3603-A1. We found that these three-body encounters could be responsible for the origin of high peculiar velocities ($\geq$ 70 km/s) observed for some very massive ($\geq$ 60-70 Msun) runaway stars in the Milky Way and the Large Magellanic Cloud (e.g., $\lambda$ Cep, BD+43 3654, Sk-67 22, BI 237, 30 Dor 016), which can hardly be explained within the framework of the binary-supernova scenario. The production of high-velocity massive stars via three-body encounters is accompanied by the recoil of the binary in the opposite direction to the ejected star. We show that the relative position of the very massive binary R145 and the runaway early B-type star Sk-69 206 on the sky is consistent with the possibility that both objects were ejected from the central cluster, R136, of the star-forming region 30 Doradus via the same dynamical event -- a three-body encounter.
We address the infrared(IR) divergence problem during inflation that appears in the loop corrections to the primordial perturbations. In our previous paper, we claimed that, at least in single field models, the IR divergence is originating from the gauge artifact. Namely, diverging IR corrections should not appear in genuine gauge-invariant observables. We propose here one simple but explicit example of such gauge-invariant quantities. Then, we explicitly calculate such a quantity to find that the IR divergence is absent at the leading order in the slow-roll approximation for the usual scale invariant vacuum state. At the same time we notice that there is a subtle issue on the gauge-invariance in how to specify the initial vacuum state.
Grand unified theories of fundamental forces predict that magnetic monopoles are inevitable in the Universe because the second homotopy group of the order parameter manifold is $\mathbb{Z}$. We point out that monopoles can annihilate in pairs due to an influence of Alice strings. As a consequence, a monopole charge is charactarized by $\mathbb{Z}_2$ rather than $\mathbb{Z}$ if the Universe can accommodate Alice strings, which is the case of certain grand unified theories.
We derive the field equations and the equations of motion for massive test particles in modified theories of gravity with an arbitrary coupling between geometry and matter by using the Palatini formalism. We show that the independent connection can be expressed as the Levi-Civita connection of an auxiliary, matter Lagrangian dependent metric, which is related with the physical metric by means of a conformal transformation. Similarly to the metric case, the field equations impose the non-conservation of the energy-momentum tensor. We derive the explicit form of the equations of motion for massive test particles in the case of a perfect fluid, and the expression of the extra-force is obtained in terms of the matter-geometry coupling functions and of their derivatives. Generally, the motion is non-geodesic, and the extra force is orthogonal to the four-velocity.
We examine the dark matter phenomenology in supersymmetric light higgs boson scenarios, adapting nonuniversal Higgs masses at the gauge coupling unification scale. The correct relic density is obtained mostly through the annihilation into a pseudoscalar $A$, which gives high values for the self-annihilation cross-section at present times. Our analysis shows that most part of the $A$ pole region can produce detectable gamma-rays and antiproton signals, and still be compatible with with recent direct detection data from XENON100 and CDMS-II.
We continue the study of covariant power-counting renormalizable gravity constrained by scalar Lagrange multiplier. Lorentz symmetry breaking is investigated in such a theory in comparison with the one in ghost condensation model. Covariant power-counting renormalizable vector gravity which is invariant under $U(1)$ gauge symmetry is proposed. Several forms of vector Lagrange multiplier in this theory are discussed. It is shown that covariant scalar/vector gravity under consideration may have power-law or de Sitter accelerating cosmological solution corresponding to inflationary era. Simplest black hole solution is obtained and dispersion relations for graviton are presented.
In the previous paper (Part~1), we have verified that the SK assumption on the direction does not hold in the analysis of neutrino events occurred inside the SK detector. We have made four possible L/E analyses, L_nu/E_nu, L_nu/E_mu, L_mu/E_nu and L_mu/E_mu. Among four kinds of L/E analyses, we have shown that only L_nu/E_nu analysis can give the signature of maximum oscillations clearly, while the L_mu/E_mu analysis which are really done by Super-Kamiokande Collaboration cannot give the maximum oscillation at all. It is thus concluded that Super-Kamiokande type experiment cannot find the maximum oscillation from L/E analysis. Therefore, we would suggest Super-Kamiokande Collaboration to re-analyze the zenith angle distribution of the neutrino events which occur inside the detector carefully.
We consider a scenario in which primordial scalar perturbations are generated when complex conformal scalar field rolls down its negative quartic potential. Initially, these are the perturbations of the phase of this field; they are converted into the adiabatic perturbations at a later stage. A potentially dangerous feature of this scenario is the existence of perturbations in the radial field direction, which have red power spectrum. We show, however, that the infrared effects are harmless, as they can be absorbed into field redefinition. We also evaluate the statistical anisotropy inherent in the model due to the existence of the long-ranged radial perturbations.
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We present radio and X-ray observations, as well as optical light curves, for a subset of 26 BL Lac candidates from the Sloan Digital Sky Survey (SDSS) lacking strong radio emission and with z<2.2. Half of these 26 objects are shown to be stars, galaxies, or absorbed quasars. We conclude that the other 13 objects are Active Galactic Nuclei (AGN) with abnormally weak emission features; ten of those 13 are definitively radio-quiet, and, for those with available optical light curves, their level of optical flux variability is consistent with radio-quiet quasars. We cannot exclude the possibility that some of these 13 AGN lie on the extremely radio-faint tail of the BL Lac distribution, but our study generally supports the notion that all BL Lac objects are radio-loud. These radio-quiet AGN appear to have intrinsically weak or absent broad emission line regions, and, based on their X-ray properties, we argue that some are low-redshift analogs to weak line quasars (WLQs). SDSS BL Lac searches are so far the only systematic surveys of the SDSS database capable of recovering such exotic low-redshift WLQs. There are 71 more z<2.2 radio-quiet BL Lac candidates already identified in the SDSS not considered here, and many of those might be best unified with WLQs as well. Future studies combining low- and high-redshift WLQ samples will yield new insight on our understanding of the structure and formation of AGN broad emission line regions.
(abridged) We report a study of the relation between dust and gas over a 100deg^2 area in the Taurus molecular cloud. We compare the H2 column density derived from dust extinction with the CO column density derived from the 12CO and 13CO J= 1-0 lines. We derive the visual extinction from reddening determined from 2MASS data. The comparison is done at an angular size of 200", corresponding to 0.14pc at a distance of 140pc. We find that the relation between visual extinction Av and N(CO) is linear between Av~3 and 10 mag in the region associated with the B213--L1495 filament. In other regions the linear relation is flattened for Av > 4 mag. We find that the presence of temperature gradients in the molecular gas affects the determination of N(CO) by ~30--70% with the largest difference occurring at large column densities. Adding a correction for this effect and accounting for the observed relation between the column density of CO and CO2 ices and Av, we find a linear relationship between the column of carbon monoxide and dust for observed visual extinctions up to the maximum value in our data 23mag. We have used these data to study a sample of dense cores in Taurus. Fitting an analytical column density profile to these cores we derive an average volume density of about 1.4e4 cm^-3 and a CO depletion age of about 4.2e5 years. We estimate the H2 mass of Taurus to be about 1.5e4 M_sun, independently derived from the Av and N(CO) maps. We derive a CO integrated intensity to H2 conversion factor of about 2.1e20 cm^-2 (K km/s)^-1, which applies even in the region where the [CO]/[H_2] ratio is reduced by up to two orders of magnitude. The distribution of column densities in our Taurus maps resembles a log--normal function but shows tails at large and low column densities.
Circumstellar disks are an essential ingredient of the formation of low-mass stars. It is unclear, however, whether the accretion-disk paradigm can also account for the formation of stars more massive than about 10 solar masses, in which strong radiation pressure might halt mass infall. Massive stars may form by stellar merging, although more recent theoretical investigations suggest that the radiative-pressure limit may be overcome by considering more complex, nonspherical infall geometries. Clear observational evidence, such as the detection of compact dusty disks around massive young stellar objects, is needed to identify unambiguously the formation mode of the most massive stars. Here we report near-infrared interferometric observations that spatially resolve the astronomical unit-scale distribution of hot material around a high-mass (approx. 20 solar masses) young stellar object. The image shows an elongated structure with a size of about 13 x 19 astronomical units, consistent with a disk seen at an inclination angle of 45 degree. Using geometric and detailed physical models, we found a radial temperature gradient in the disk, with a dust-free region less than 9.5 astronomical units from the star, qualitatively and quantitatively similar to the disks observed in low-mass star formation. Perpendicular to the disk plane we observed a molecular outflow and two bow shocks, indicating that a bipolar outflow emanates from the inner regions of the system.
We present the results of a Spitzer photometric investigation into the IR excesses of close binary systems. In a sample of 10 objects, excesses in IRAC and MIPS24 bands implying the presence of warm dust are found for 3. For 2 objects we do not find excesses reported in earlier IRAS studies. We discuss the results in the context of the scenario suggested by Rhee and co-workers, in which warm dust is continuously created by destructive collisions between planetary bodies. A simple numerical model for the steady-state distribution of dust in one IR excess system shows a central clearing of radius 0.22 AU caused by dynamical perturbations from the binary star. This is consistent with the size of the central clearing derived from the Spitzer spectral energy distribution. We conclude that close binaries could be efficient "destroyers of worlds", lead to destabilize the orbits of their planetary progeny by magnetically-driven angular momentum loss and secular shrinkage of the binary separation.
The red clump is found to be split into two components along several sightlines toward the Galactic Bulge. This split is detected with high significance toward the areas (-3.5<l<1,b<-5) and (l,b)=(0,+5.2), i.e., along the Bulge minor axis and at least 5 degrees off the plane. The fainter (hereafter ``main'') component is the one that more closely follows the distance-longitude relation of the Bulge red clump. The main component is ~0.5 magnitudes fainter than the secondary component and with an overall approximately equal population. For sightlines further from the plane, the difference in brightness increases, and more stars are found in the secondary component than in the main component. The two components have very nearly equal (V-I) color.
The [CII] fine--structure line at 158um is an excellent tracer of the warm diffuse gas in the ISM and the interfaces between molecular clouds and their surrounding atomic and ionized envelopes. Here we present the initial results from Galactic Observations of Terahertz C+ (GOTC+), a Herschel Key Project devoted to study the [CII] fine structure emission in the galactic plane using the HIFI instrument. We use the [CII] emission together with observations of CO as a probe to understand the effects of newly--formed stars on their interstellar environment and characterize the physical and chemical state of the star-forming gas. We collected data along 16 lines--of--sight passing near star forming regions in the inner Galaxy near longitudes 330 degrees and 20 degrees. We identify fifty-eight [CII] components that are associated with high--column density molecular clouds as traced by 13CO emission. We combine [CII], 12CO, and 13CO observations to derive the physical conditions of the [CII]--emitting regions in our sample of high--column density clouds based on comparison with results from a grid of Photon Dominated Region (PDR) models. From this unbiased sample, our results suggest that most of [CII] emission originates from clouds with H2 volume densities between 10e3.5 and 10e5.5 cm^-3 and weak FUV strength (CHI_0=1-10). We find two regions where our analysis suggests high densities >10e5 cm^-3 and strong FUV fields (CHI=10e4-10e6), likely associated with massive star formation. We suggest that [CII] emission in conjunction with CO isotopes is a good tool to differentiate between regions of massive star formation (high densities/strong FUV fields) and regions that are distant from massive stars (lower densities/weaker FUV fields) along the line--of--sight
We present new results from a significant extension of our previous high angular resolution (0.3" = 40 AU) Submillimeter Array survey of the 880 um continuum emission from dusty circumstellar disks in the ~1 Myr-old Ophiuchus star-forming region. An expanded sample is constructed to probe disk structures that emit significantly lower millimeter luminosities (hence dust masses), down to the median value for T Tauri stars. Using a Monte Carlo radiative transfer code, the millimeter visibilities and broadband spectral energy distribution for each disk are simultaneously reproduced with a two-dimensional parametric model for a viscous accretion disk. We find wide ranges of characteristic radii (14-198 AU) and disk masses (0.004-0.143 M_sun), but a narrow distribution of surface density gradients (0.4-1.1) that is consistent with a uniform value $\gamma$ = 0.9 +/- 0.2 and independent of mass (or millimeter luminosity). In this sample, we find a correlation between the disk luminosity/mass and characteristic radius, such that fainter disks are both smaller and less massive. We suggest that this relationship is an imprint of the initial conditions inherited by the disks at their formation epoch, compare their angular momenta with those of molecular cloud cores, and speculate on how future observations can help constrain the distribution of viscous evolution timescales. No other correlations between disk and star properties are found. The inferred disk structures are briefly compared with theoretical models for giant planet formation, although resolution limitations do not permit us to directly comment on material inside R = 20 AU. However, there is some compelling evidence for dust evolution in the planet formation region: 4/17 disks in the sample show resolved regions of significantly reduced optical depths within ~20-40 AU of their central stars.
The Milky Way System and the Andromeda galaxy experienced radically different evolutionary histories. Nevertheless, it is found that these two galaxies ended up with globular cluster systems in which individual clusters have indistinguishable distributions of half-light radii. Furthermore globulars in both M31 and the Galaxy are found to have radii that are independent of their luminosities. In this respect globular clusters differ drastically from early-type galaxies in which half-light radius and luminosity are tightly correlated. Metal-rich globular clusters in M31 occupy a slightly larger volume than do those in the Galaxy. The specific globular cluster frequency in the Andromeda galaxy is found to he significantly higher than it is in the Milky Way System. The present discussion is based on the 107 Galactic globular clusters, and 200 putative globulars in M31, for which UBV photometry was available.
Two dimensional modeling of collisionless shocks has been of tremendous importance in understanding the physics of the non-linear evolution, momentum transfer and particle acceleration, but current computer capacities have now reached a point where three dimensional modeling is becoming feasible. We present the first three dimensional model of a fully developed and relaxed relativistic ion-electron shock, and analyze and compare it to similar 2D models. Quantitative and qualitative differences are found with respect to the two-dimensional models. The shock jump conditions are of course different, because of the extra degree of freedom, but in addition it is found that strong parallel electric fields develop at the shock interface, the level of magnetic field energy is lower, and the non-thermal particle distribution is shallower with a powerlaw index of ~2.2.
We present the results of an extensive observational study of the active star-forming complex W51 that was observed in the J=2-1 transition of the 12CO and 13CO molecules over a 1.25 deg x 1.00 deg region with the University of Arizona Heinrich Hertz Submillimeter Telescope. We use a statistical equilibrium code to estimate physical properties of the molecular gas. We compare the molecular cloud morphology with the distribution of infrared (IR) and radio continuum sources, and find associations between molecular clouds and young stellar objects (YSOs) listed in Spitzer IR catalogs. The ratios of CO lines associated with HII regions are different from the ratios outside the active star-forming regions. We present evidence of star formation triggered by the expansion of the HII regions and by cloud-cloud collisions. We estimate that about 1% of the cloud mass is currently in YSOs.
Observations of HDO are an important complement for studies of water, because they give strong constraints on the formation processes -- grain surfaces versus energetic process in the gas phase, e.g. in shocks. The HIFI observations of multiple transitions of HDO in Sgr~B2(M) presented here allow the determination of the HDO abundance throughout the envelope, which has not been possible before with ground-based observations only. The abundance structure has been modeled with the spherical Monte Carlo radiative transfer code RATRAN, which also takes radiative pumping by continuum emission from dust into account. The modeling reveals that the abundance of HDO rises steeply with temperature from a low abundance ($2.5\times 10^{-11}$) in the outer envelope at temperatures below 100~K through a medium abundance ($1.5\times 10^{-9}$) in the inner envelope/outer core, at temperatures between 100 and 200~K, and finally a high abundance ($3.5\times 10^{-9}$) at temperatures above 200~K in the hot core.
To investigate the accretion and feedback processes in massive star formation, we analyze the shapes of emission lines from hot molecular cores, whose asymmetries trace infall and expansion motions. The high-mass star forming region SgrB2(M) was observed with Herschel/HIFI (HEXOS key project) in various lines of HCN and its isotopologues, complemented by APEX data. The observations are compared to spherically symmetric, centrally heated models with density power-law gradient and different velocity fields (infall or infall+expansion), using the radiative transfer code RATRAN. The HCN line profiles are asymmetric, with the emission peak shifting from blue to red with increasing J and decreasing line opacity (HCN to H$^{13}$CN). This is most evident in the HCN 12--11 line at 1062 GHz. These line shapes are reproduced by a model whose velocity field changes from infall in the outer part to expansion in the inner part. The qualitative reproduction of the HCN lines suggests that infall dominates in the colder, outer regions, but expansion dominates in the warmer, inner regions. We are thus witnessing the onset of feedback in massive star formation, starting to reverse the infall and finally disrupting the whole molecular cloud. To obtain our result, the THz lines uniquely covered by HIFI were critically important.
Spectroscopic observations of the low-mass eclipsing binary NSVS 11868841 have been obtained and the radial velocities were derived for both components. The masses and radii determined for the components are $M_1$ =0.870$\pm$0.074\Msun, $M_2$=0.607$\pm$0.053\Msun and $R_1$ =0.983 $\pm$0.030 \Rsun, $R_2$ =0.901$\pm$0.026 \Rsun. Both the primary and secondary stars' radii are 10 \% and 57\% larger than those of zero-age-main-sequence stars with the same masses. This discrepancy may be arisen from the large spot coverage of both stars. We collected absolute parameters of 21 low mass double-lined eclipsing binaries and compared their positions in the mass-radius and mass-effective temperature panels. The large radii and lower effective temperatures are solved neither with difference in metallicity nor in mixing length parameters. These discrepancies in the low mass stars may be originated by magnetic fields causing inhibition convective energy transport which leads to large magnetic spot coverage on the surface of a low mass star.
We describe a Phased Array Feed (PAF) system, called Apertif, which will be installed in the Westerbork Synthesis Radio Telescope (WSRT). The aim of Apertif is, at frequencies from 1.0 to 1.7 GHz, to increase the instantaneous field of view of the WSRT 8 deg^2 and its observing bandwidth to 300 MHz with high spectral resolution. This system will turn the WSRT into an effective survey telescope with scientific applications ranging from deep surveys of the northern sky of HI and OH emission and polarised continuum to efficient searches for pulsars and transients. We present results obtained with a prototype PAF installed in one of the WSRT dishes. These results demonstrate that at decimetre wavelengths PAFs have excellent performance and that even for a single beam on the sky they outperform single feed radio dishes. PAFs turn radio telescopes into very effective survey instruments. Apertif is now fully funded and the community is invited to express their interest in using Apertif (this http URL )
Aims. We report results of an X-ray study of the supernova remnant (SNR) G344.7-0.1 and the point-like X-ray source located at the geometrical center of the SNR radio structure. Methods. The morphology and spectral properties of the remnant and the central X-ray point-like source were studied using data from the XMM-Newton and Chandra satellites. Archival radio data and infrared Spitzer observations at 8 and 24 $\mu$m were used to compare and study its multi-band properties at different wavelengths. Results. The XMM-Newton and Chandra observations reveal that the overall X-ray emission of G344.7-0.1 is extended and correlates very well with regions of bright radio and infrared emission. The X-ray spectrum is dominated by prominent atomic emission lines. These characteristics suggest that the X-ray emission originated in a thin thermal plasma, whose radiation is represented well by a plane-parallel shock plasma model (PSHOCK). Our study favors the scenario in which G344.7-0.1 is a 6 x 10^3 year old SNR expanding in a medium with a high density gradient and is most likely encountering a molecular cloud on the western side. In addition, we report the discovery of a soft point-like X-ray source located at the geometrical center of the radio SNR structure. The object presents some characteristics of the so-called compact central objects (CCO). However, its neutral hydrogen absorption column (N_{H}) is inconsistent with that of the SNR. Coincident with the position of the source, we found infrared and optical objects with typical early-K star characteristics. The X-ray source may be a foreground star or the CCO associated with the SNR. If this latter possibility were confirmed, the point-like source would be the farthest CCO detected so far and the eighth member of the new population of isolated and weakly magnetized neutron stars.
We investigate the scale-dependence of f_NL in the self-interacting curvaton model. We show that the scale-dependence, encoded in the spectral index n_{f_NL}, can be observable by future cosmic microwave background observations, such as CMBpol, in a significant part of the parameter space of the model. We point out that together with information about the trispectrum g_NL, the self-interacting curvaton model parameters could be completely fixed by observations. We also discuss the scale-dependence of g_NL and its implications for the curvaton model, arguing that it could provide a complementary probe in cases where the theoretical value of n_{f_NL} is below observational sensitivity.
A sensitive (1{\sigma} rms at 1 MHz resolution ~3 mK) 1 mm spectral line survey (214.5-285.5 GHz) of VY Canis Majoris (VY CMa) and IRC+10216 has been conducted to compare the chemistries of oxygen and carbon-rich circumstellar envelopes. This study was carried out using the Submillimeter Telescope (SMT) of the Arizona Radio Observatory (ARO) with a new ALMA-type receiver. This survey is the first to chemically characterize an O-rich circumstellar shell at millimeter wavelengths. In VY CMa, 128 emission features were detected arising from 18 different molecules, and in IRC+10216, 720 lines were observed, assigned to 32 different species. The 1 mm spectrum of VY CMa is dominated by SO2 and SiS; in IRC +10216, C4H and SiC2 are the most recurrent species. Ten molecules were common to both sources: CO, SiS, SiO, CS, CN, HCN, HNC, NaCl, PN, and HCO+. Sulfur plays an important role in VY CMa, but saturated/unsaturated carbon dominates the molecular content of IRC+10216, producing CH2NH, for example. Although the molecular complexity of IRC+10216 is greater, VY CMa supports a unique "inorganic" chemistry leading to the oxides PO, AlO, and AlOH. Only diatomic and triatomic compounds were observed in VY CMa, while species with 4 or more atoms are common in IRC+10216, reflecting carbon's ability to form strong multiple bonds, unlike oxygen. In VY CMa, a new water maser (v_2=2) has been found, as well as vibrationally-excited NaCl. Toward IRC+10216, vibrationally-excited CCH was detected for the first time.
TMR-1 (IRAS~04361+2547) is a class~I proto-stellar source located in the nearby Taurus star-forming region. Its circumstellar environment is characterized by extended dust emission with complex structures and conspicuous filaments. A faint companion, called TMR-1C, located near the proto-star had been detected in previous studies, but its nature as a very young substellar object remained inconclusive. To improve the constraints on the nature of TMR-1C, and to investigate the process of very low-mass star formation in the TMR-1 system we use very sensitive infrared imaging observations as well as NIR spectroscopy. We construct the SED of TMR-1C over a much larger wavelength range as had been possible in previous work and compare it with models of extincted background stars, young sub-stellar objects, and very low-mass stars with circumstellar disk and envelope emission. We also search for additional low-luminosity objects in the immediate environment of the TMR-1, study the surrounding NIR dust morphology, and analyse the emission line spectrum of a filamentary structure in the physical context of a bow-shock model. We find that the observed SED of TMR-1C is inconsistent with an extincted background star, nor can be fitted with available models for a young extremely low-mass (<12M_Jup) object. Our near-IR spectrum indicates an effective temperature of at least ~3000K. Based on a good match of TMR-1C's SED with radiation transfer models of young stellar objects with circumstellar disks, we propose that TMR-1C is most likely a very low-mass star with M~0.1-0.2M_sun surrounded by a circumstellar disk with high inclination, i>80deg. Moreover, we detect an additional very faint source, which we call TMR-1D, and that shows a quite striking symmetry in position with TMR-1C. TMR-1C and TMR-1D may have been formed from a common triggered star-formation event, caused by... (abstract abridged)
Deep, wide, near-infrared imaging surveys provide an opportunity to study the clustering of various galaxy populations at high redshift on the largest physical scales. We have selected $1<z<2$ extremely red objects (EROs) and $1<z<3$ distant red galaxies (DRGs) in SA22 from the near-infrared photometric data of the UKIDSS Deep eXtragalactic Survey (DXS) and $gri$ optical data from CTIO covering 3.3~deg$^2$. This is the largest contiguous area studied to sufficient depth to select these distant galaxies to date. The angular two-point correlation functions and the real space correlation lengths of each population are measured and show that both populations are strongly clustered and that the clustering cannot be parameterised with a single power law. The correlation function of EROs shows a double power law with the inflection at $\sim$ 0.6$'$--1.2$'$ (0.6--1.2~h$^{-1}$~Mpc). The bright EROs ($K<18.8$) show stronger clustering on small scales but similar clustering on larger scales, whereas redder EROs show stronger clustering on all scales. Clustering differences between EROs that are old passively evolved galaxies (OGs) and dusty star-forming galaxies (DGs), on the basis of their $J-K$ colour, are also investigated. The clustering of $r-K$ EROs are compared with that of $i-K$ EROs and the differences are consistent with their expected redshift distributions. The correlation function of DRGs is also well described by a double power law and consistent with previous studies once the effects of the broader redshift distribution our selection of DRGs returns are taken into account. We also perform the same analysis on smaller sub-fields to investigate the impact of cosmic variance on the derived clustering properties. Currently this study is the most representative measurement of the clustering of massive galaxies at $z>1$ on large scales.
The opening-up of the magnetic field during solar eruptive events is often accompanied by a dimming of the local coronal emission. From observations of filament eruptions recorded with the Extreme-Ultraviolet Imager on STEREO during 2008-2009, it is evident that these dimmings are much more pronounced in 19.5 nm than in the lower-temperature line 17.1 nm, as viewed either on the disk or above the limb. We conclude that most of the cooler coronal plasma is not ejected but remains gravitationally bound when the loops open up. This result is consistent with Doppler measurements by Imada and coworkers, who found that the upflow speeds in a transient coronal hole increased dramatically above a temperature of 1 MK; it is also consistent with the quasistatic behavior of polar plumes, as compared with the hotter interplume regions that are the main source of the fast solar wind. When the open flux reconnects and closes down again, the trapped plasma is initially heated to such high temperatures that it is no longer visible at Fe IX 17.1 nm. Correspondingly, 17.1 nm images show a dark ribbon or ``heat wave'' propagating away from the polarity inversion line and coinciding with the brightened Fe XV 28.4 nm and Fe XII 19.5 nm post-eruptive loops and their footpoint areas. Such dark ribbons provide a clear example of dimmings that are not caused by a density depletion. The propagation of the ``heat wave'' is driven by the closing-down, not the opening-up, of flux and can be observed both off-limb and on-disk.
We discuss black hole spin measurements employing the relativistic iron line profiles in the X-ray domain. We investigate the iron line band for two representative sources -- MCG -6-30-15 (active galaxy) and GX 339-4 (X-ray binary). We compare two models of the broad iron line, LAOR and KYRLINE. We realise that the spin is currently determined entirely from the position of the marginally stable orbit while the effect of the spin on the overall line shape would be resolvable with higher resolution X-ray missions. We show that the precision of the spin measurements depends on an unknown angular distribution of the disc emission. We study how sensitive the spin determination is to the assumptions about the intrinsic angular distribution of the emitted photons. We find that the uncertainty of the directional emission distribution translates to 20% uncertainty in the determination of the radius of marginally stable orbit. We perform radiation transfer computations of an X-ray irradiated disc atmosphere (NOAR code) to determine the directionality of outgoing X-rays in the 2-10 keV energy band. Based on these computations, we find that from the simple formulae for the directionality, the isotropic case reproduces the simulated data with the best accuracy. The most frequently used limb-darkening law favours higher values of spin and, in addition, a steeper radial emissivity profile. Furthermore, we present a spectral analysis of an XMM-Newton observation of a Seyfert 1.5 galaxy IRAS 05078+1626 being the first X-ray spectroscopic study of this source. The lack of the significant relativistic blurring of the reflection model component suggests the accretion disc to be truncated at a farther radius.
We present dynamical models of NGC 4494, which we built using our iterative method presented in a previous paper. These models are live N-body models consisting of equal mass particles, and they are steady state as confirmed by a fully self-consistent evolution. Our goals were twofold. The first one -- namely to test whether our iterative method could indeed be used to construct galactic models following given observational constraints, both photometric and kinematic -- was fully achieved. Our method allowed us to go beyond a simple spherical model and to make full sets of rotating, axisymmetric models without any limitations to the velocity distribution. Our second goal was to understand better the structure of NGC 4494, and more specifically to set constraints on its halo mass. For this we tried three families of models: without halo, with a light halo and with a heavy halo, respectively. Our models reproduce well the photometry and the kinematics, the latter except specific regions where some non-equilibrium or non-axisymmetric structure could be present in the galaxy (e.g. the kinematically decoupled core). However, the lower order moments of the velocity distribution (up to and including the second order) do not allow us to discriminate between the three halos. On the other hand, when we extend the comparison to the higher order moments of the velocity distribution obtained from the long-slit data, we find that our light halo model fits the data better than the no halo, or the heavy halo models. They also reproduce the shape of the angular dependence of the PNe velocity dispersion in the outermost parts of the galaxy, but not the amplitude of its azimuthal variation. This may imply that a yet more general class of models, such as triaxial, may be necessary for a yet better fit.
We investigate the thermonuclear bursting behaviour of IGR J17473-2721, an X-ray transient that in 2008 underwent a six month long outburst, starting (unusually) with an X-ray burst. We detected a total of 57 thermonuclear bursts throughout the outburst with AGILE, Swift, RXTE, and INTEGRAL. The wide range of inferred accretion rates (between <1% and about 20% of the Eddington accretion rate m-dot_Edd) spanned during the outburst allows us to study changes in the nuclear burning processes and to identify up to seven different phases. The burst rate increased gradually with the accretion rate until it dropped (at a persistent flux corresponding to about 15% of m-dot_Edd) a few days before the outburst peak, after which bursts were not detected for a month. As the persistent emission subsequently decreased, the bursting activity resumed with a much lower rate than during the outburst rise. This hysteresis may arise from the thermal effect of the accretion on the surface nuclear burning processes, and the timescale is roughly consistent with that expected for the neutron star crust thermal response. On the other hand, an undetected superburst, occurring within a data gap near the outburst peak, could have produced a similar quenching of burst activity.
The goal of this work is to investigate the Faraday rotation measure (RM) of radio galaxies in hot galaxy clusters in order to establish a possible connection between the magnetic field strength and the gas temperature of the intracluster medium. We performed Very Large Array observations at 3.6 cm and 6 cm of two radio galaxies located in A401 and Ophiuchus, a radio galaxy in A2142, and a radio galaxy located in the background of A2065. All these galaxy clusters are characterized by high temperatures. We obtained detailed RM images at an angular resolution of 3'' for most of the observed radio galaxies. The RM images are patchy and reveal fine substructures of a few kpc in size. Under the assumption that the radio galaxies themselves have no effect on the measured RMs, these structures indicate that the intracluster magnetic fields fluctuate down to such small scales. These new data are compared with RM information present in the literature for cooler galaxy clusters. For a fixed projected distance from the cluster center, clusters with higher temperature show a higher dispersion of the RM distributions (sigmaRM), mostly because of the higher gas density in these clusters. Although the previously known relation between the clusters X-ray surface brightness (Sx) at the radio galaxy location and sigmaRM is confirmed, a possible connection between the sigmaRM-Sx relation and the cluster temperature, if present, is very weak. Therefore, in view of the current data, it is impossible to establish a strict link between the magnetic field strength and the gas temperature of the intracluster medium.
GRS 1915+105 is a prominent black hole system exhibiting variability over a wide range of time scales and its observed light curves have been classified into 12 temporal states. Here we undertake a complete analysis of these light curves from all the states using various quantifiers from nonlinear time series analysis, such as, the correlation dimension (D_2), the correlation entropy (K_2), singular value decomposition (SVD) and the multifractal spectrum ($f(\alpha)$ spectrum). An important aspect of our analysis is that, for estimating these quantifiers, we use algorithmic schemes which we have proposed recently and tested successfully on synthetic as well as practical time series from various fields. Though the schemes are based on the conventional delay embedding technique, they are automated so that the above quantitative measures can be computed using conditions prescribed by the algorithm and without any intermediate subjective analysis. We show that nearly half of the 12 temporal states exhibit deviation from randomness and their complex temporal behavior could be approximated by a few (3 or 4) coupled ordinary nonlinear differential equations. These results could be important for a better understanding of the processes that generate the light curves and hence for modelling the temporal behavior of such complex systems. To our knowledge, this is the first complete analysis of an astrophysical object (let alone a black hole system) using various techniques from nonlinear dynamics.
I briefly review recent observations of regions forming low mass stars. The discussion is cast in the form of seven questions that have been partially answered, or at least illuminated, by new data. These are the following: where do stars form in molecular clouds; what determines the IMF; how long do the steps of the process take; how efficient is star formation; do any theories explain the data; how are the star and disk built over time; and what chemical changes accompany star and planet formation. I close with a summary and list of open questions.
We use CFHTLS deep optical data, WIRCam Deep Survey (WIRDS) NIR data and XMM data to identify z>1.1 clusters in the CFHTLS D1 and D4 fields. Counterparts to such clusters can not be identified without deep NIR data and as such the total of =1deg2 of J , H & Ks band imaging provided by WIRDS is an indispensable tool in such work. Using public XMM X-ray data, we identify extended X-ray sources in the two fields. The resulting catalogue of extended X-ray sources was analyzed for optical/NIR counterparts, using a red-sequence algorithm. Redshifts of candidate groups and clusters were estimated using the median photometric redshifts of detected counterparts and where available spectroscopic data. Additionally, we surveyed X-ray point sources for potential group systems at the limit of our detection range in the X-ray data. A catalogue of z > 1.1 cluster candidates in the two fields has been compiled and cluster masses, radii and temperatures have been estimated using the scaling relations. The catalogue consists of 15 z > 1.1 candidates. Three of the detections are previously published extended X-ray sources. Of note is JKSC 041 for which we identify possible structures at z = 0.8, z = 0.96, z = 1.13 and z = 1.49. We also make an independent detection of the massive cluster, XMMXCS J2215.9-1738. We use the z > 1.1 catalogue to compare the cluster number counts in these fields with models based on WMAP 7-year cosmology and find that the models slightly over-predict the observations, whilst at z>1.5 we do not detect any clusters. We note that cluster number counts at z > 1.1 are highly sensitive to the cosmological model, however a significant reduction in present statistical (due to available survey area) and systematic (due to cluster scaling relations) uncertainties is required in order to confidently constrain cosmological parameters using cluster number counts at high redshift.
The newly installed Wide Field Camera 3 (WFC3) on the Hubble Space Telescope has been used to obtain multi-band images of the nearby spiral galaxy M83. These new observations are the deepest and highest resolution images ever taken of a grand-design spiral, particularly in the near ultraviolet, and allow us to better differentiate compact star clusters from individual stars and to measure the luminosities of even faint clusters in the U band. We find that the luminosity function for clusters outside of the very crowded starburst nucleus can be approximated by a power law, dN/dL \propto L^{alpha}, with alpha = -2.04 +/- 0.08, down to M_V ~ -5.5. We test the sensitivity of the luminosity function to different selection techniques, filters, binning, and aperture correction determinations, and find that none of these contribute significantly to uncertainties in alpha. We estimate ages and masses for the clusters by comparing their measured UBVI,Halpha colors with predictions from single stellar population models. The age distribution of the clusters can be approximated by a power-law, dN/dt propto t^{gamma}, with gamma=-0.9 +/- 0.2, for M > few x 10^3 Msun and t < 4x10^8 yr. This indicates that clusters are disrupted quickly, with ~80-90% disrupted each decade in age over this time. The mass function of clusters over the same M-t range is a power law, dN/dM propto M^{beta}, with beta=-1.94 +/- 0.16, and does not have bends or show curvature at either high or low masses. Therefore, we do not find evidence for a physical upper mass limit, M_C, or for the earlier disruption of lower mass clusters when compared with higher mass clusters, i.e. mass-dependent disruption. We briefly discuss these implications for the formation and disruption of the clusters.
Knowledge of the population of radio sources in the range ~2-200 GHz is important for understanding their effects on measurements of the Cosmic Microwave Background power spectrum. We report measurements of the 30 GHz flux densities of 605 radio sources from the Combined Radio All-sky Targeted Eight-GHz Survey (CRATES), which have been made with the One Centimetre Receiver Array prototype (OCRA-p) on the Torun 32-m telescope. The flux densities of sources that were also observed by WMAP and previous OCRA surveys are in broad agreement with those reported here, however a number of sources display intrinsic variability. We find a good correlation between the 30 GHz and Fermi gamma-ray flux densities for common sources. We examine the radio spectra of all observed sources and report a number of Gigahertz-peaked and inverted spectrum sources. These measurements will be useful for comparison to those from the Low Frequency Instrument of the Planck satellite, which will make some of its most sensitive observations in the region covered here.
We obtained JHK images and low-resolution JH spectra in the embedded young cluster in the Serpens cloud Main core (also known as Serpens North). We determined spectral types for 15 previously identified cluster members (for 5 of them for the first time), 1 new candidate, and 11 stars that appear to be field interlopers. Extinction, for which we derived an analytical expression, was obtained by taking SpT and near-IR excess into account. The location on the Hertzsprung-Russell diagram indicates that we probed a low-mass population of the cloud (0.05 - 1.5 Msol), including 1 - 3 brown dwarfs. We used our individually determined photospheric parameters to analyze the ISO and the Spitzer determined spectral energy distribution classes. The latter were correlated with the age and location of the sources in the cloud. We find that most flat objects from our study (4 out of 5) have SEDs consistent with reddened classical T Tau stars; however, when comparing to the thick disk SEDs of lower mass M-type objects, we find that the flat ones show more excess, perhaps indicating an earlier evolutionary stage. We determined a median age for the cluster to be 1 Myr for distance of 380 pc, and 3 Myr for a less likely distance of 260 pc. The core of the cluster is on average younger than the rest of the cluster. We do not find objects with disks past 5 Myr. We do find diskless, X-ray bright objects younger than 1 Myr, as was also noted in the study of Winston et al (2009). We find two groups of young objects associated with dark filaments, indicating that star formation was not always confined to the core.
We investigate the consequences of non-minimal gravitational coupling to matter and study how it differs from the case of minimal coupling by choosing certain simple forms for the nature of coupling, The values of the parameters are specified at $z=0$ (present epoch) and the equations are evolved backwards to calculate the evolution of cosmological parameters. We find that the Hubble parameter evolves more slowly in non-minimal coupling case as compared to the minimal coupling case. In both the cases, the universe accelerates around present time, and enters the decelerating regime in the past. Using the latest Union2 dataset for supernova Type Ia observations as well as the data for baryon acoustic oscillation (BAO) from SDSS observations, we constraint the parameters of Linder exponential model in the two different approaches. We find that there is a upper bound on model parameter in minimal coupling. But for non-minimal coupling case, there is range of allowed values for the model parameter.
Recent measurements performed with some direct dark matter detection experiments, e.g. CDMS-II and CoGENT (after DAMA/LIBRA), have unveiled a few events compatible with WIMP-nuclei interactions. The preferred mass range is around 10 GeV, with a quite large spin-independent cross section of $10^{-43}-10^{-41}\,{\rm cm^2}$. In this letter, we recall that a light WIMP with dominant couplings to quarks should also generate cosmic-ray antiprotons. Taking advantage of recent works constraining the Galactic dark matter mass profile on the one hand and on cosmic-ray propagation on the other hand, we point out that considering a thermal annihilation cross section for such low mass candidates unavoidably results in an antiproton flux in tension with the current data, leading either to exclusion or to observable features. This should be taken into account for a consistent interpretation of direct detection signals.
We report on extragalactic sources detected in a 455 square-degree map of the southern sky made with data at a frequency of 148 GHz from the Atacama Cosmology Telescope 2008 observing season. We provide a catalog of 157 sources with flux densities spanning two orders of magnitude: from 15 to 1500 mJy. Comparison to other catalogs shows that 98% of the ACT detections correspond to sources detected at lower radio frequencies. Three of the sources appear to be associated with the brightest cluster galaxies of low redshift X-ray selected galaxy clusters. Estimates of the radio to mm-wave spectral indices and differential counts of the sources further bolster the hypothesis that they are nearly all radio sources, and that their emission is not dominated by re-emission from warm dust. In a bright (>50 mJy) 148 GHz-selected sample with complete cross-identifications from the Australia Telescope 20 GHz survey, we observe an average steepening of the spectra between 5, 20, and 148 GHz with median spectral indices of $\alpha_{\rm 5-20} = -0.07 \pm 0.06$, $\alpha_{\rm 20-148} = -0.39 \pm0.04$, and $\alpha_{\rm 5-148} = -0.20 \pm 0.03$. When the measured spectral indices are taken into account, the 148 GHz differential source counts are consistent with previous measurements at 30 GHz in the context of a source count model dominated by flat spectrum radio sources. Extrapolating with an appropriately rescaled model for the radio source counts, the Poisson contribution to the spatial power spectrum from synchrotron-dominated sources with flux density less than 20 mJy is $C^{\rm Sync} = (2.8 \pm 0.3) \times 10^{-6} \micro\kelvin^2$.
We present new SMA and PdBI observations of the intermediate-mass object IRAS 22198+6336 in the millimeter continuum and in several molecular line transitions. The millimeter continuum emission reveals a strong and compact source with a mass of around 5 Msun and with properties of Class 0 objects. CO emission shows an outflow with a quadrupolar morphology centered on the position of the dust condensation. The CO outflow emission seems to come from two distinct outflows, one of them associated with SiO outflow emission. A large set of molecular lines has been detected toward a compact dense core clearly coincident with the compact millimeter source, and showing a velocity gradient perpendicular to the outflow traced by CO and SiO. The chemically rich spectrum and the rotational temperatures derived from CH$_3$CN and CH$_3$OH (100-150 K) indicate that IRAS 22198+6336 is harbouring one the few intermediate-mass hot cores known at present.
We discuss the application of a likelihood ratio technique to a new data-set comprising 6621 sources selected at 250um from the Herschel-Astrophysical Terahertz Large Area Survey science demonstration observations. We show that this likelihood ratio technique can effectively identify the optical/near-infrared counterparts to these objects. We identify 2423 counterparts to these sources with reliability R >= 0.8, and briefly discuss our method for determining photometric redshifts. We show that 59.3 percent of the 250um-selected galaxies have counterparts in our catalogue down to an r-band magnitude limit of 22.4 mag in data from the Sloan Digital Sky Survey seventh data release, and we confidently identify 61.8 percent of these (approximately 36.6 percent of the >5 sigma 250um sources). We derive the counterpart identification completeness as a function of redshift, and show that 250um-selected Herschel-ATLAS sources have a peak in their redshift distribution which is lower than that of SDSS DR7 galaxies. Combined with an analysis of their sub-mm photometric redshift distribution, this suggests a bimodal n(z) for 250um selected sources at S(250um) > 32 mJy. We also suggest a new method for efficiently selecting populations of strongly-lensed galaxies residing at high redshifts. Our identifications are matched to UV-NIR photometry and spectroscopic redshifts from the GAMA survey, and these data are available as part of the Herschel-ATLAS public data release.
Optical long baseline interferometry is a technique that has generated almost 850 refereed papers to date. The targets span a large variety of objects from planetary systems to extragalactic studies and all branches of stellar physics. We have created a database hosted by the JMMC and connected to the Optical Long Baseline Interferometry Newsletter (OLBIN) web site using MySQL and a collection of XML or PHP scripts in order to store and classify these publications. Each entry is defined by its ADS bibcode, includes basic ADS informations and metadata. The metadata are specified by tags sorted in categories: interferometric facilities, instrumentation, wavelength of operation, spectral resolution, type of measurement, target type, and paper category, for example. The whole OLBIN publication list has been processed and we present how the database is organized and can be accessed. We use this tool to generate statistical plots of interest for the community in optical long baseline interferometry.
Recently, an extension of the geodesic equations of motion using the Dark Energy length scale was proposed. Here, we apply this extension to the analyzing the motion of test particles at the galactic scale and longer. A cosmological check of the extension is made using the observed rotational velocity curves and core sizes of 1393 spiral galaxies. We derive the density profile of a model galaxy using this extension, and with it, we calculate $\sigma_8$ to be $0.73_{\pm 0.12}$; this is within experimental error of the WMAP value of $0.761_{-0.048}^{+0.049}$. We then calculate $R_{200}$ to be $206_{\pm 53}$ kpc, which is in reasonable agreement with observations.
We present ultraviolet (UV) and optical photometry of 26 Type Ia supernovae (SNe~Ia) observed from March 2005 to March 2008 with the NASA {\it Swift} Ultraviolet and Optical Telescope (UVOT). The dataset consists of 2133 individual observations, making it by far the most complete study of the UV emission from SNe~Ia to date. Grouping the SNe into three subclasses as derived from optical observations, we investigate the evolution of the colors of these SNe, finding a high degree of homogeneity within the normal subclass, but dramatic differences between that group and the subluminous and SN 2002cx-like groups. For the normal events, the redder UV filters on UVOT ($u$, $uvw1$) show more homogeneity than do the bluer UV filters ($uvm2$, $uvw2$). Searching for purely UV characteristics to determine existing optically based groupings, we find the peak width to be a poor discriminant, but we do see a variation in the time delay between peak emission and the late, flat phase of the light curves. The UV light curves peak a few days before the $B$ band for most subclasses (as was previously reported by Jha et al. 2006a), although the SN 2002cx-like objects peak at a very early epoch in the UV. That group also features the bluest emission observed among SNe~Ia. As the observational campaign is ongoing, we discuss the critical times to observe, as determined by this study, in order to maximize the scientific output of future observations.
In a previous communication [Phys. Rev. D 77, 083504 (2008)] we have studied the observational viability of a class of cosmological models in which the vacuum energy density decays linearly with the Hubble parameter, resulting in a production of cold dark matter particles at late times. Similarly to the flat $\Lambda$CDM case, there are only two free parameters to be adjusted by the data in this class of $\Lambda(t)$CDM scenarios, namely, the Hubble and the matter density parameters. In the present paper, we update our previous analysis by using three of the most recent SNe Ia compilations sets along with the current measurements of distance to the BAO peaks at $z = 0.2$ and $z = 0.35$ and the position of the first acoustic peak of the CMB power spectrum. We show that in terms of $\chi^2$ statistics both models provide good fits to the data and very similar results. A quantitative analysis discussing the differences in parameter estimates due to SNe light-curve fitting methods (SALT2 and MLCS2k2) is also performed using the current SDSS SNe Ia compilation.
We present the discovery of photometric variations in the carbon-dominated atmosphere (hot DQ) white dwarf star SDSS J133710.19-002643.6. We find evidence for two low-amplitude, harmonically-related periodicities at 169 s and 339 s, making it the fastest and smallest amplitude of the four known hot DQ variables and the only variable whose spectrum suggests the presence of hydrogen. The star's fundamental and harmonic amplitudes are roughly equal, and its pulse shape is similar to the other two members of the class with detected harmonics. Like the other variables, it appears relatively stable in frequency and amplitude.
Bulk dark energy properties are determined by the redshift evolution of its pressure-to-density ratio, $w_{de}(z)$. An experimental goal is to decide if the dark energy is dynamical, as in the quintessence (and phantom) models treated here. We show that a three-parameter approximation $w_{de}(z; \epsilon_s, \epsilon_{\phi\infty}, \zeta_s)$ fits well the ensemble of trajectories for a wide class of late-inflaton potentials $V(\phi)$. Markov Chain Monte Carlo probability calculations are used to confront our $w_{de}(z)$ trajectories with current observational information on Type Ia supernova, Cosmic Microwave Background, galaxy power spectra, weak lensing and the Lyman-${\alpha}$ forest. We find the best constrained parameter is a low redshift slope parameter, $\epsilon_s \propto (\partial \ln V / \partial \phi)^2$ when the dark energy and matter have equal energy densities. A tracking parameter $\epsilon_{\phi\infty}$ defining the high-redshift attractor of $1+w_{de}$ is marginally constrained. Poorly determined is $\zeta_s$, characterizing the evolution of $\epsilon_s$, and a measure of $\partial^2 \ln V / \partial \phi^2$ . The constraints we find already rule out some popular quintessence and phantom models, or restrict their potential parameters. We also forecast how the next generation of cosmological observations improve the constraints: by a factor of about five on $\epsilon_s$ and $\epsilon_{\phi\infty}$, but with $\zeta_s$ remaining unconstrained (unless the true model significantly deviates from $\Lambda$CDM). Thus potential reconstruction beyond an overall height and a gradient is not feasible for the large space of late-inflaton models considered here.
Context. With the latest infrared surveys, the number of massive protostellar candidates has increased significantly. New studies have posed additional questions on important issues about the formation, evolution, and other phenomena related to them. Complementary to infrared data, radio observations are a good tool to study the nature of these objects, and to diagnose the formation stage. Aims. Here we study the far-infrared source IRAS 16353-4636 with the aim of understanding its nature and origin. In particular, we search for young stellar objects (YSOs), possible outflow structure, and the presence of non-thermal emission. Methods. Using high-resolution, multi-wavelength radio continuum data obtained with the Australia Telescope Compact Array, we image IRAS 16353-4636 and its environment from 1.4 to 19.6 GHz, and derive the distribution of the spectral index at maximum angular resolution. We also present new JHKs photometry and spectroscopy data obtained at ESO NTT. 13 CO and archival HI line data, and infrared databases (MSX, GLIMPSE, MIPSGal) are also inspected. Results. The radio continuum emission associated with IRAS 16353-4636 was found to be extended (~10 arcsec), with a bow-shaped morphology above 4.8 GHz, and a strong peak persistent at all frequencies. The NIR photometry led us to identify ten near-IR sources and classify them according to their color. We used the HI line data to derive the source distance, and analyzed the kinematical information from the CO and NIR lines detected. Conclusions. We have identified the source IRAS 16353-4636 as a new protostellar cluster. In this cluster we recognized three distinct sources: a low-mass YSO, a high-mass YSOs, and a mildly confined region of intense and non-thermal radio emission. We propose the latter corresponds to the terminal part of an outflow.
We present the first chemical composition study of two unevolved stars in the globular cluster NGC 2808, obtained with the spectrograph X-shooter@VLT. NGC 2808 shows three discrete, well separated main sequences. The most accepted explanation for this phenomenon is that their stars have different helium contents. We observed one star on the bluest main sequence, (bMS, claimed to have high helium content, Y~0.4), and one on the reddest main sequence (rMS, consistent with a canonical helium content, Y=0.245). We analyzed features of NH, CH, Na, Mg, Al, and Fe. While Fe, Ca, and other elements have the same abundances in the two stars, the bMS star shows a huge enhancement of N, a depletion of C, an enhancement of Na and Al, and small depletion of Mg with respect to the rMS star. This is exactly what is expected if stars on the bMS formed from the ejecta produced by an earlier stellar generation in the complete CNO and MgAl cycles whose main product is helium. The elemental abundance pattern differences in these two stars are consistent with the differences in helium content suggested by the color-magnitude diagram positions of the stars.
We report on a large stellar flare from the nearby dMe flare star EV Lac observed by the Swift and Konus-Wind satellites and the Liverpool Telescope. It is the first large stellar flare from a dMe flare star to result in a Swift trigger based on its hard X-ray intensity. Its peak f_X from 0.3--100 keV of 5.3x10^-8 erg/cm2/s is nearly 7000 times larger than the star's quiescent coronal flux, and the change in magnitude in the white filter is >4.7. This flare also caused a transient increase in EV Lac's bolometric luminosity (L_bol) during the early stages of the flare, with a peak estimated L_X/L_bol ~3.1. We apply flare loop hydrodynamic modeling to the plasma parameter temporal changes to derive a loop semi-length of l/Rstar =0.37 +/-0.07. The soft X-ray spectrum of the flare reveals evidence of iron Kalpha emission at 6.4 keV. We model the Kalpha emission as fluorescence from the hot flare source irradiating the photospheric iron, and derive loop heights of h/Rstar=0.1, consistent within factors of a few with the heights inferred from hydrodynamic modeling. The Kalpha emission feature shows variability on time scales of ~200 s which is difficult to interpret using the pure fluorescence hypothesis. We examine Kalpha emission produced by collisional ionization from accelerated particles, and find parameter values for the spectrum of accelerated particles which can accommodate the increased amount of Kalpha flux and the lack of observed nonthermal emission in the 20-50 keV spectral region.
We present the abundance analysis of a sample of more than 120 red giants in the globular cluster (GC) NGC 1851, based on FLAMES spectra. We find a small but detectable metallicity spread. This spread is compatible with the presence of two different groups of stars with a metallicity difference of 0.06-0.08 dex, in agreement with earlier photometric studies. If stars are divided into these two groups according to their metallicity, both components show a Na-O anticorrelation (signature of a genuine GC nature) of moderate extension. The metal-poor stars are more concentrated than the metal-rich ones. We tentatively propose the hypothesis that NGC 1851 formed from a merger of two individual GCs with a slightly different Fe and alpha-element content, and possibly an age difference up to 1 Gyr. This is supported also by number ratios of stars on the split subgiant and on the bimodal horizontal branches. The distribution of n-capture process elements in the two components also supports the idea that the enrichment must have occurred in each of the structures separately, and not as a continuum of events in a single GC. The most probable explanation is that the proto-clusters formed into a (now dissolved) dwarf galaxy and later merged to produce the present GC.
We present a discussion of two-dimensional magneto-hydrodynamics (MHD) configurations, concerning the equilibria of accretion disks of a strongly magnetized astrophysical object. We set up a viscoresistive scenario which generalizes previous two-dimensional analyses by reconciling the ideal MHD coupling of the vertical and the radial equilibria within the disk with the standard mechanism of the angular momentum transport, relying on dissipative properties of the plasma configuration. The linear features of the considered model are analytically developed and the non-linear configuration problem is addressed, by fixing the entire disk profile at the same order of approximation. Indeed, the azimuthal and electron force balance equations are no longer automatically satisfied when poloidal currents and matter fluxes are included in the problem. These additional components of the equilibrium configuration induce a different morphology of the magnetic flux surface, with respect to the ideal and simply rotating disk.
In the time-ordered data (TOD) files of the WMAP CMB observations, there is an undocumented timing offset of -25.6 ms between the spacecraft attitude and radio flux density timestamps. If the offset induced an error during calibration of the raw TOD, then this would add variance per pixel. This variance would be present in the calibrated TOD. Low-resolution map-making as a function of timing offset should show a minimum variance for the correct timing offset. Three years of the calibrated, filtered WMAP 3-year TOD are compiled into sky maps at HEALPix resolution N_side=8, individually for each of the K, Ka, Q, V and W band differencing assemblies (DA's), as a function of timing offset. The median per map of the temperature fluctuation variance per pixel is calculated and minimised against timing offset, over a range of +- 5 exposure times. Minima are clearly present. The timing offsets that minimise the median variance are -38 +- 9 ms (K, Ka), -30 +- 4 ms (Q), -27 +- 10 ms (V), and -29 +- 550 ms (W), i.e. an average of -31 +- 3 ms, where the WMAP collaboration's preferred offset is 0 +- 1.7 ms. Hence, the latter is rejected at a significance of 8.5 sigma. The hypothesis of a -25.6 ms offset, suggested by Liu, Xiong & Li from the TOD file timing offset, is consistent with these minima at 1.4 sigma. It is difficult to avoid the conclusion that the WMAP calibrated TOD and inferred maps are wrongly calibrated. CMB quadrupole estimates (3/pi)C_2 based on the incorrectly calibrated TOD are overestimated by roughly (17 +- 2) % (KQ85 mask) to (58 +- 5) % (KQ75 mask). Ideally, the WMAP map-making pipelines should be redone starting from the uncalibrated TOD and using the -25.6 ms timing offset correction.
The interaction of black holes with ambient magnetic fields is important for a variety of highly energetic astrophysical phenomena. We study this interaction within the force-free approximation in which a tenuous plasma is assumed to have zero inertia. Blandford and Znajek (BZ) used this approach to demonstrate the conversion of some of the black hole's energy into electromagnetic Poynting flux in stationary and axisymmetric single black hole systems. We adopt this approach and extend it to examine asymmetric and, most importantly, dynamical systems by implementing the fully nonlinear field equations of general relativity coupled to Maxwell's equations. For single black holes, we study in particular the dependence of the Poynting flux and show that, even for misalignments between the black hole spin and the direction of the asymptotic magnetic field, a Poynting flux is generated with a luminosity dependent on such misalignment. For binary black hole systems, we show both in the head-on and orbiting cases that the moving black holes generate a Poynting flux.
The ${\cal F}$-lipped $SU(5)\times U(1)_X$ Grand Unified Theory (GUT) supplemented by TeV-scale vector-like particles from ${\cal F}$-theory, together dubbed ${\cal F}$-$SU(5)$, offers a natural multi-phase unification process which suggests an elegant implementation of the No-Scale Supergravity boundary conditions at the unification scale $M_{\cal F} \simeq 7 \times 10^{17}$~GeV. Enforcing the No-Scale boundary conditions, including $B_\mu(M_{\cal F})=0$ on the Higgs bilinear soft term, with the precision 7-year WMAP value on the dark matter relic density isolates a highly constrained ``golden point'' located near $M_{1/2} = 455$~GeV and $\tan \beta = 15$ in the $\tan\beta-M_{1/2}$ plane, which simultaneously satisfies all known experiments, and moreover corresponds to an imminently observable proton decay rate. Because the universal gaugino mass is actually determined from established low energy data via Renormalization Group Equation (RGE) running, there are no surviving arbitrary scale parameters in the present model.
It is now a well established fact based on several observations that we live in a Universe dominated by dark energy. The most natural candidates for dark energy are fields in curved space-time. We develop the formalism to study the gravitational collapse of fields given any general potential. We apply this formalism to models of dark energy motivated by particle physics considerations. We solve the resulting evolution equations which determine the time evolution of field configurations as well as the dynamics of spacetime.
This article reviews basic construction and cosmological implications of a power-counting renormalizable theory of gravitation recently proposed by Horava. We explain that (i) at low energy this theory does not exactly recover general relativity but instead mimic general relativity plus dark matter; that (ii) higher spatial curvature terms allow bouncing and cyclic universes as regular solutions; and that (iii) the anisotropic scaling with the dynamical critical exponent z=3 solves the horizon problem and leads to scale-invariant cosmological perturbations even without inflation. We also comment on issues related to an extra scalar degree of freedom called scalar graviton. In particular, for spherically-symmetric, static, vacuum configurations we prove non-perturbative continuity of the lambda->1+0 limit, where lambda is a parameter in the kinetic action and general relativity has the value lambda=1. We also derive the condition under which linear instability of the scalar graviton does not show up.
With the discovery of Dark Energy, $\Lambda_{DE}$, there is now a universal length scale, $\ell_{DE}=c/(\Lambda_{DE} G)^{1/2}$, associated with the universe that allows for an extension of the geodesic equations of motion. In this paper, we will study a specific class of such extensions, and show that contrary to expectations, they are not automatically ruled out by either theoretical considerations or experimental constraints. In particular, we show that while these extensions affect the motion of massive particles, the motion of massless particles are not changed; such phenomena as gravitational lensing remain unchanged. We also show that these extensions do not violate the equivalence principal, and that because $\ell_{DE}=14010^{800}_{820}$ Mpc, a specific choice of this extension can be made so that effects of this extension are not be measurable either from terrestrial experiments, or through observations of the motion of solar system bodies. A lower bound for the only parameter used in this extension is set.
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