{\it Hubble Space Telescope} (\hst) Wide Field Planetary Camera 2 ({\it WFPC2}) images of the Virgo Cluster dwarf elliptical galaxy VCC 128 reveal an apparently double nucleus. The two components, which are separated by $\sim 32$ pc in projection, have the same magnitude and color. We present a spectrum of this double nucleus and show that it is inconsistent with one or both components being emission-line background objects or foreground stars. The most likely interpretation is that, as suggested by \citet{lauer_etal_96} for the double nucleus in NGC 4486B, we are seeing a nuclear disk surrounding a supermassive black hole. This is only the second time an early-type dwarf (dE/dSph) galaxy has been suggested to host a SMBH.
We explore and discount the hypothesis that the strong, continual H$\alpha$-emitting T dwarf 2MASS J12373919+6526148 can be explained as a young, low gravity, very low mass brown dwarf. The source is already known to have a marginally-fainter absolute magnitude than similar T dwarfs with trigonometric parallax measurements, and has a tangential velocity consistent with old disk kinematics. Applying the technique of Burgasser, Burrows & Kirkpatrick on new near infrared spectroscopy for this source, estimates of its {\teff}, $\log{g}$ and metallicity ([M/H]) are obtained. 2M 1237+6526 has a {\teff} $\approx$ 800-850 K. If [M/H] is solar, $\log{g}$ is as high as $\sim$5.5 (cgs) and this source is older than 10 Gyr. We find a more plausible scenario to be a modestly subsolar metallicity ([M/H] = -0.2) and moderate $\log{g}$ $\sim$ 5.0, implying an age older than 2 Gyr and a mass greater than 0.035 M$_{\sun}$. The alternative explanation of the unique emission of this source, involving an interacting, close, double degenerate system, should be investigated further. Indeed, there is some evidence of a {\teff} $<$ 500 K companion to 2M 1237+6526 on the basis of a possible $Spitzer IRAC$ [3.6]--[4.5] color excess. This excess may, however, be caused by a subsolar metallicity.
Technical libraries are currently experiencing very rapid change. In the near future their mission will change, their physical nature will change, and the skills of their employees will change. While some will not be able to make these changes, and will fail, others will lead us into a new era.
We derive expressions, in terms of "polar shapelets", for the image distortion operations associated with weak gravitational lensing. Shear causes galaxy shapes to become elongated, and is sensitive to the second derivative of the projected gravitational potential; flexion bends galaxy shapes into arcs, and is sensitive to the third derivative. Polar shapelets provide a natural representation, in which both shear and flexion transformations appear compact. Through this tool, we understand progress in several weak lensing methods. We then exploit various symmetries of shapelets to construct a range of shear estimators with useful properties. Through an analogous investigation, we also explore several flexion estimators. In particular, some of the estimators can be measured simultaneously and independently for every galaxy, and will provide unique checks for systematics in future weak lensing analyses. Using simulated images from the Shear TEsting Programme (STEP), we show that we can recover input shears with no significant bias. A complete software package to parametrize astronomical images in terms of polar shapelets, and to perform a full weak lensing analysis, is available from this http URL
We show that the luminosity of a star forming galaxy is capped by the
production and subsequent expulsion of cosmic rays from its interstellar
medium. By defining an Eddington luminosity in cosmic rays, we show that the
star formation rate of a given galaxy is limited by its mass content and the
cosmic ray mean free path. When the cosmic ray luminosity and pressure reaches
a critical value as a result of vigorous star formation, hydrostatic balance is
lost, a cosmic ray-driven wind develops, and star formation is choked off.
Cosmic ray pressure-driven winds are likely to produce wind velocities
significantly in excess of the galactic escape velocity.
It is possible that cosmic ray feedback results in the Faber-Jackson relation
for a plausible set of input parameters that describe cosmic ray production and
transport, which are calibrated by observations of the Milky Way's interstellar
cosmic rays.
Turbulent Comptonization, a potentially important damping and radiation mechanism in relativistic accretion flows, is discussed. Particular emphasis is placed on the physical basis, relative importance, and thermodynamics of turbulent Comptonization. The effects of metal-absorption opacity on the spectral component resulting from turbulent Comptonization is considered as well.
We simulate the early stages of the evolution of turbulent, virialized, high-mass protostellar cores, with primary attention to how cores fragment, and whether they form a small or large number of protostars. Our simulations use the Orion adaptive mesh refinement code to follow the collapse from ~0.1 pc scales to ~10 AU scales, for durations that cover the main fragmentation phase, using three-dimensional gravito-radiation hydrodynamics. We find that for a wide range of initial conditions radiation feedback from accreting protostars inhibits the formation of fragments, so that the vast majority of the collapsed mass accretes onto one or a few objects. Most of the fragmentation that does occur takes place in massive, self-shielding disks. These are driven to gravitational instability by rapid accretion, producing rapid mass and angular momentum transport that allows most of the gas to accrete onto the central star rather than forming fragments. In contrast, a control run using the same initial conditions but an isothermal equation of state produces much more fragmentation, both in and out of the disk. We conclude that massive cores with observed properties are not likely to fragment into many stars, so that, at least at high masses, the core mass function probably determines the stellar initial mass function. Our results also demonstrate that simulations of massive star forming regions that do not include radiative transfer, and instead rely on a barotropic equation of state or optically thin heating and cooling curves, are likely to produce misleading results.
Stable, hydrogen-burning, M dwarf stars comprise about 75% of all stars in the Galaxy. They are extremely long-lived and because they are much smaller in mass than the Sun (between 0.5 and 0.08 MSun), their temperature and stellar luminosity are low and peaked in the red. We have re-examined what is known at present about the potential for a terrestrial planet forming within, or migrating into, the classic liquid-surface-water habitable zone close to an M dwarf star. Observations of protoplanetary disks suggest that planet-building materials are common around M dwarfs, but N-body simulations differ in their estimations of the likelihood of potentially-habitable, wet planets residing within their habitable zones, which are only ~ 1/5 to 1/50 of the width of that for a G star. Particularly in light of the claimed detection of the planets with masses as small as 5.5 and 7.5 MEarth orbiting M stars, there seems no reason to exclude the possibility of terrestrial planets. Tidally locked synchronous rotation within the narrow habitable zone doesn't necessarily lead to atmospheric collapse, and active stellar flaring may not be as much of an evolutionarily disadvantageous factor as has previously been supposed. We conclude that M dwarf stars may indeed be viable hosts for planets on which the origin and evolution of life can occur. A number of planetary processes such as cessation of geothermal activity, or thermal and non-thermal atmospheric loss processes may limit the duration of planetary habitability to periods far shorter than the extreme lifetime of the M dwarf star. Nevertheless, it makes sense to include M dwarf stars in programs that seek to find habitable worlds and evidence of life.
Observations of two of the formaldehyde (H2CO) masers (A and D) in Sgr B2 using the VLBA+Y27 (resolution ~0.01") and the VLA (resolution ~9") are presented. The VLBA observations show compact sources (<10 milliarcseconds, <80 AU) with brightness temperatures >10^8 K. The maser sources are partially resolved in the VLBA observations. The flux densities in the VLBA observations are about 1/2 those of the VLA; and, the linewidths are about 2/3 of the VLA values. The applicability of a core-halo model for the emission distribution is demonstrated. Comparison with earlier H2CO absorption observations and with ammonia (NH3) observations suggests that H2CO masers form in shocked gas. Comparison of the integrated flux densities in current VLA observations with those in previous observations indicates that (1) most of the masers have varied in the past 20 years, and (2) intensity variations are typically less than a factor of two compared to the 20-year mean. No significant linear or circular polarization is detected with either instrument.
We examine the growth of eccentricities of a population of particles with initially circular orbits around a central massive body. Successive encounters between pairs of particles increase the eccentricities in the disk on average. As long as the epicyclic motions of the particles are small compared to the shearing motion between Keplerian orbits, there is no preferred scale for the eccentricities. The simplification due to this self-similarity allows us to find an analytic form for the distribution function; full numerical integrations of a disk with 200 planetesimals verify our analytical self-similar distribution. The shape of this non-equilibrium profile is identical to the equilibrium profile of a shear-dominated population whose mutual excitations are balanced by dynamical friction or Epstein gas drag.
We describe the statistical properties of narrowband drifting auroral kilometric radiation ('striated' AKR) based on observations from the Cluster wideband receiver during 2002-2005. We show that the observed characteristics, including frequency drift rate and direction, narrow bandwidth, observed intensity, and beaming angular sizes are all consistent with triggering by upward traveling ion solitary structures (`ion holes'). We calculate the expected perturbation of a horseshoe electron distribution function by an ion hole by integrating the resonance condition for a cyclotron maser instability (CMI) using the perturbed velocity distribution. We find that the CMI growth rate can be strongly enhanced as the horseshoe velocity distribution contracts inside the passing ion hole, resulting in a power gain increase greater than 100 dB. The gain curve is sharply peaked just above the R-mode cut-off frequency, with an effective bandwidth ~50 Hz, consistent with the observed bandwidth of striated AKR emission. Ion holes are observed in situ in the acceleration region moving upward with spatial scales and speeds consistent with the observed bandwidth and slopes of SAKR bursts. Hence, we suggest that SAKR bursts are a remote sensor of ion holes and can be used to determine the frequency of occurrence, locations in the acceleration region, and lifetimes of these structures.
We present and discuss correlations for optical and near-infrared (5500-10030 angstroms) line intensity measurements at many positions in the Crab Nebula. These correlations suggest the existence of gas produced by a range of nuclear processing, from material in which synthesis ended with the CNO-cycle, to some helium-burning and nitrogen depletion, to regions containing enriched products of oxygen-burning. The latter exhibit a gradual, linear rise of [Ni II] emission with increasing argon enrichment, whereas gas with less nuclear processing shows markedly different [Ni II] emission characteristics, including the highest derived abundances. This suggests two origins for stable, neutron-rich nickel in the nebula: a type of "alpha-rich freezeout" in the more highly processed material, and possibly removal of ions from the neutron star in other regions. In addition, the data indicate that anomalously strong observed [C I] emission comes from broad, low-ionization zones. Although the strongest He I emission could also be enhanced in similar low-ionization gas, correlations between relevant line ratios argue against that interpretation, strengthening the case for an exceptionally high helium mass fraction in some locations.
Howell et al. have reported the discovery of SN Ia SN 2003fg and conclude that SN 2003fg is very likely a super-Chandrasekhar-mass SN Ia perhaps with a mass of order 2 solar masses. Their work is the first strong evidence that has been presented for a super-Chandrasekhar SN Ia. We have performed an analysis of the SN 2003fg data using the Yoon & Langer binding energy formula for a rotating super-Chandrasekhar-mass white dwarf (also used by Howell et al.) included in a simple model of SNe Ia (which we call the SSC model for Simple Super-Chandrasekhar model for SNe Ia) which assumes spherically symmetric ejecta and relies on the approximations of an exponential density profile for SN Ia ejecta and of a sharp boundary of the SN Ia iron-peak-element core. Our results support the conclusion of Howell et al.: SN 2003fg is very probably super-Chandrasekhar and probably has mass of order 2 solar masses.
We have used the Submillimeter Array for the first interferometric CO imaging toward the starburst-Seyfert nucleus of the southern barred spiral galaxy NGC 1365, which is one of the four galaxies within 30 Mpc that have L_{8-1000micron} >= 10^{11} Lsun. Our mosaic maps of 12CO, 13CO, and C18O (J=2-1) emission at up to 2" (200 pc) resolutions have revealed a circumnuclear gas ring and several CO clumps in the central 3 kpc. The molecular ring shows morphological and kinematical signs of bar-driven gas dynamics, and the region as a whole is found to follow the star formation laws of Kennicutt. We have found that some of the gas clumps and peaks in CO brightness temperature, which we collectively call CO hotspots, coincide with the radio and mid-infrared sources previously identified as dust-enshrouded super star clusters. This hotspot-cluster association suggests that either the formation of the most massive clusters took place in large molecular gas concentrations (of Sigma_{mol} ~10^{3} Msun/pc^2 in 200 pc scales) or the clusters have heated their ambient gas to cause or enhance the CO hotspots. The active nucleus is in the region of weak CO emission and is not associated with distinctive molecular gas properties.
The key project HERLOGA to be proposed for the Herschel mission is aimed to provide an homogeneous data set on local active galaxies that could be the reference for further studies on the interplay between star formation processes and accretion onto massive black holes in galactic nuclei. The selected sample will be the overlap between the 12 micron sample and an all-sky hard-X ray selected sample of AGNs. The Herschel data will follow extensive observational work that is already available from radio to X-rays frequencies and will provide the baseline of zero-redshift objects for comparison with the high redshift Universe which will be revealed by the Herschel cosmological surveys.
The Oort Cloud, the Kuiper Belt and the Scattered Disk are dynamically distinct populations of small bodies evolving in the outer regions of the Solar System. Whereas their collisional activity is now quiet, gravitational interactions with giant planets may have shaped these populations both dynamically and collisionally during their formation. Using a hybrid approach (Charnoz & Morbidelli 2003), the present paper tries to couple the primordial collisional and dynamical evolution of these three populations in a self-consistent way. A critical parameter is the primordial size-distribution. We show that the initial planetesimal size distribution that allows an effective mass depletion of the Kuiper belt by collisional grinding, would decimate also the population of comet-size bodies that end in the Oort Cloud and, in particular, in the Scattered Disk. As a consequence, the Scattered Disk and the Oort Cloud would be too anemic, by a factor 20 to 100, relative to the estimates achieved from the observation of the fluxes of long period and Jupiter family comets, respectively. For these two reservoirs to have a sufficient number of comets, the initial size distribution in the planetesimal disk had to be such that the mass depletion by collisional erosion of in the Kuiper belt was negligible. Consequently, the current mass deficit of the Kuiper belt, needs to be explained by dynamical mechanisms.
The spectral energy distributions (SEDs) of some T Tauri stars display a deficit of near-IR flux that could be a consequence of an embedded Jupiter-mass planet partially clearing an inner hole in the circumstellar disc. Here, we use two-dimensional numerical simulations of the planet-disc interaction, in concert with simple models for the dust dynamics, to quantify how a planet influences the dust at different radii within the disc. We show that pressure gradients at the outer edge of the gap cleared by the planet act as a filter - letting particles smaller than a critical size through to the inner disc while holding back larger particles in the outer disc. The critical particle size depends upon the disc properties, but is typically of the order of 10 microns. This filtration process will lead to discontinuous grain populations across the planet's orbital radius, with small grains in the inner disc and an outer population of larger grains. We show that this type of dust population is qualitatively consistent with SED modelling of systems that have optically thin inner holes in their circumstellar discs. This process can also produce a very large gas-to-dust ratio in the inner disc, potentially explaining those systems with optically thin inner cavities that still have relatively high accretion rates.
Simulations of radio emission from extensive air showers we have published so far were performed with a Monte Carlo code using analytical parametrisations to describe the spatial, temporal, energy and angular particle distributions in the air shower. A new version of our simulation code, which replaces these parametrisations with precise, multi-dimensional histograms derived from per-shower CORSIKA simulations, is now available. The new code allows an independent selection between parametrisation and histogram for each of the relevant distributions, enabling us to study the changes arising from using a more realistic air shower model in detail. We describe the new simulation strategy, present some initial results and discuss the new possibilities.
Summary of Joint Discussion 13 of the 26th IAU General Assembly, Prague.
I consider various possibilities for making gamma--ray bursts, particularly from close binaries. In addition to the much--studied neutron star + neutron star and black hole + neutron star cases usually considered good candidates for short--duration bursts, there are other possibilities. In particular neutron star + massive white dwarf has several desirable features. These systems are likely to produce long--duration GRBs, in some cases definitely without an accompanying supernova, as observed recently. This class of burst would have a strong correlation with star formation, and occur close to the host galaxy. However rare members of the class need not be near star--forming regions, and could have any type of host galaxy. Thus a long--duration burst far from any star--forming region would also be a signature of this class. Estimates based on the existence of a known progenitor suggest that this type of GRB may be quite common, in agreement with the fact that the absence of a supernova can only be established in nearby bursts.
We consider the dynamical evolution of a disk of stars orbiting a central black hole. In particular, we focus on the effect of the stellar mass function on the evolution of the disk, using both analytic arguments and numerical simulations. We apply our model to the ring of massive stars at ~0.1pc from the Galactic Center, assuming that the stars formed in a cold, circular disk, and find that our model requires the presence of a significant population of massive (>100Msun) stars in order to explain the the observed eccentricities of 0.2-0.3. Moreover, in order to limit the damping of the heavier stars' eccentricities, we also require fewer low-mass stars than expected from a Salpeter mass function, giving strong evidence for a significantly ``top-heavy'' mass function in the rings of stars seen near to the Galactic Center. We also note that the maximum possible eccentricities attainable from circular initial conditions at ages of <10Myr are around 0.4-0.5, and suggest that any rings of stars found with higher eccentricities were probably not formed from circular disks.
We model the abundance gradients in the disk of the Milky Way for several chemical elements (O, Mg, Si, S, Ca, Sc, Ti, Co, V, Fe, Ni, Zn, Cu, Mn, Cr, Ba, La and Eu), and compare our results with the most recent and homogeneous observational data. We adopt a chemical evolution model able to well reproduce the main properties of the solar vicinity. We compute, for the first time, the abundance gradients for all the above mentioned elements in the galactocentric distance range 4 - 22 kpc. The comparison with the observed data on Cepheids in the galactocentric distance range 5-17 kpc gives a very good agreement for many of the studied elements. In addition, we fit very well the data for the evolution of Lanthanum in the solar vicinity for which we present results here for the first time. We explore, also for the first time, the behaviour of the abundance gradients at large galactocentric distances by comparing our results with data relative to distant open clusters and red giants and select the best chemical evolution model model on the basis of that. We find a very good fit to the observed abundance gradients, as traced by Cepheids, for most of the elements, thus confirming the validity of the inside-out scenario for the formation of the Milky Way disk as well as the adopted nucleosynthesis prescriptions.
The first three years of observation of the Wilkinson Microwave Anisotropy Probe (WMAP) have provided the most precise data on the anisotropies of the cosmic microwave background (CMB) to date. We investigate the impact of these results and their combination with data from other astrophysical probes on cosmological models with a dynamical dark energy component. By considering a wide range of such models, we find that the constraints on dynamical dark energy are significantly improved compared to the first year data.
We apply a matched-filter cluster detection algorithm to the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) i-band data for the Deep-1, Deep-2, Deep-3 and Deep-4 fields covering a total of 4square degrees. To test the implemented procedure we carry out simulations for assessing the frequency of noise peaks as well as estimate the recovery efficiency. We estimate that up to z~0.7 the catalogue is essentially complete for clusters of richness class R>~1. The recovered redshifts are in general overestimated by dz=0.1 with a scatter of sigma_dz~0.1, except at redshifts z>~1 where the estimated redshifts are systematically underestimated. The constructed cluster candidate catalogue contains 162 detections over an effective area of 3.112 square degrees corresponding to a density of ~52.1 per square degree. The median estimated redshift of the candidates is z=0.6. The estimated noise frequency is 16.9+-5.4 detections per square degree. From visual inspection we identify systems that show a clear concentration of galaxies with similar colour. These systems have a density of ~20 per square degree.
We consider essential mechanisms for orbit-shrinkage or "hardening" of compact binaries in globular clusters to the point of Roche-lobe contact and X-ray emission phase, focussing on the process of collisional hardening due to encounters between binaries and single stars in the cluster core. The interplay between this kind of hardening and that due to emission of gravitational radiation produces a characteristic scaling of the orbit-shrinkage time with the single-star binary encounter rate $\gamma$ in the cluster which we introduce, clarify, and explore. We investigate possible effects of this scaling on populations of X-ray binaries in globular clusters within the framework of a simple "toy" scheme for describing the evolution of pre-X-ray binaries in globular clusters. We find the expected qualitative trends sufficiently supported by data on X-ray binaries in galactic globular clusters to encourage us toward a more quantitative study.
We present a new speckle camera designed and built at Observatoire Midi-Pyr\'{e}n\'{e}es. This focal instrument has been used for four years with the 2-meter Bernard Lyot Telescope of Pic du Midi observatory. It can be set in various operating modes: full pupil imaging, masked-pupil imaging, spectroscopy, wave-front sensor and stellar coronagraphy, hence its name "PISCO" ("Pupil Interferometry Speckle COronagraph"). Restored images of double and triple stars have demonstrated its capabilities in providing close to diffraction limited images (0.06 arcsec in V). PISCO has been fully tested and is now ready to be used by the whole astronomical community.
Many lens surveys have hitherto used observations of large samples of background sources to select the small minority which are multiply imaged by lensing galaxies along the line of sight. Recently surveys such as SLACS and OLS have improved the efficiency of surveys by pre-selecting double-redshift systems from SDSS. We explore other ways to improve survey efficiency by optimum use of astrometric and morphological information in existing large-scale optical and radio surveys. The method exploits the small position differences between FIRST radio positions of lensed images and the SDSS lens galaxy positions, together with the marginal resolution of some larger gravitational lens systems by the FIRST beam. We present results of a small pilot study with the VLA and MERLIN, and discuss the desirable criteria for future surveys.
We present results from the first 2D and 3D simulations of the collapse of rotating stellar iron cores in general relativity employing a finite-temperature equation of state and an approximate treatment of deleptonization during collapse. We compare fully nonlinear and conformally flat spacetime evolution methods and find that the conformally flat treatment is sufficiently accurate for the core-collapse supernova problem. We focus on the gravitational wave (GW) emission from rotating collapse, core bounce, and early postbounce phases. Our results indicate that the GW signature of these phases is much more generic than previously estimated. In addition, we track the growth of a nonaxisymmetric instability of dominant m = 1 character in one of our models that leads to prolonged narrow-band GW emission at ~930 Hz over several tens of milliseconds.
The structure of the high galactic latitude Cometary Globule 12 (CG 12) has been investigated by means of radio molecular line observations. Detailed, high signal to noise ratio maps in C18O (1-0), C18O (2-1) and molecules tracing high density gas, CS (3-2), DCO+ (2-1) and H13CO+ (1-0), are presented. The C18O line emission is distributed in a 10' long North-South elongated lane with two strong maxima, CG12 N(orth) and CG12 S(outh). In CG12 S the high density tracers delineate a compact core, DCO+ core, which is offset by 15" from the C18O maximum. The observed strong C18O emission traces the surface of the DCO+ core or a separate, adjacent cloud component. The emission in high density tracers is weak in CG12 N and especially the H13CO+, DCO+ and N2H+ lines are +0.5 km/s offset in velocity with respect to the C18O lines. Evidence is presented that the molecular gas is highly depleted. The observed strong C18O emission towards CG12 N originates in the envelope of this depleted cloud component or in a separate entity seen in the same line of sight. The C18O lines in CG 12 were analyzed using Positive Matrix Factorization, PMF. The shape and the spatial distribution of the individual PMF factors fitted separately to the C18O (1-0) and (2-1) transitions were consistent with each other. The results indicate a complex velocity and line excitation structure in the cloud. Besides separate cloud velocity components the C18O line shapes and intensities are influenced by excitation temperature variations caused by e.g, the molecular outflow or by molecular depletion. Assuming a distance of 630 pc the size of the CG 12 compact head, 1.1 pc by 1.8 pc, and the C18O mass larger than 100 Msun are comparable to those of other nearby low/intermediate mass star formation regions.
We present an explanation of the Z-track phenomenon based on spectral fitting of RXTE observations of GX340+0 using the emission model previously shown to describe the dipping LMXB. In our Z-track model, the soft apex is a quiescent state of the source with lowest luminosity. Moving away from this point by ascending the normal branch the strongly increasing luminosity of the Accretion Disc Corona (ADC) Comptonized emission L_ADC provides substantial evidence for a large increase of mass accretion rate Mdot. There are major changes in the neutron star blackbody emission, kT increasing to high values, the blackbody radius R_BB decreasing, these changes continuing monotonically on both normal and horizontal branches. The blackbody flux increases by a factor of ten to three times the Eddington flux so that the physics of the horizontal branch is dominated by the high radiation pressure of the neutron star, which we propose disrupts the inner disc, and an increase of column density is detected. We further propose that the very strong radiation pressure is responsible for the launching of the jets detected in radio on the horizontal branch. On the flaring branch, we find that L_ADC is constant, suggesting no change in Mdot so that flaring must consist of unstable nuclear burning. At the soft apex, the mass accretion rate per unit area on the neutron star m_dot is minimum for the horizontal and normal branches and about equal to the theoretical upper limit for unstable burning. Thus it is possible that unstable burning begins as soon as the source arrives at this position, the onset being consistent with theory. The large increase in R_BB in flaring is reminiscent of radius expansion in X-ray bursts. Finally, in our model, Mdot does not increase monotonically along the Z-track as often previously thought.
We investigate the cosmological test based on the evolution of gas fraction in X-ray galaxy clusters and the stability of cosmological parameter derived from it. Using a sample of distant clusters observed by XMM-Newton and Chandra, and comparing their gas fraction at different radii to the gas fraction observed for nearby clusters, we have determined the likelihood functions for $\Omega_m$ in a flat universe and the confidence contours in the $\Omega_m-\Omega_{\Lambda}$ plane. Results obtained at the virial radius point to a high matter density Universe, while for inner radii the $\Omega_m$ parameter obtained tends to decrease, reaching values compatible with the concordance model. The analysis allows to conclude that this test provides ambiguous results due to the complex structure of the ICM that induce a dependence of the gas fraction with temperature, radius and redshift which cannot be accounted by a self similar argument expected in pure gravitational heating of the ICM. The use of gas fraction in X-ray clusters to constrain cosmological parameters seems therefore to be compromised until a better understanding of the ICM physics and the ability of observations of better quality up to the virial radius are achieved.
In order to constrain the physical processes that regulate and downsize the AGN population, the predictions of the MOdel for the Rise of GAlaxies aNd Active nuclei (MORGANA) are compared to luminosity functions (LFs) of AGNs in the optical, soft X-ray and hard X-ray bands, to the local BH-bulge mass relation, and to the observed X-ray number counts and background. We also give predictions on the accretion rate of AGNs in units of the Eddington rate and on the BH--bulge relation expected at high redshift. We find that it is possible to reproduce the downsizing of AGNs within the hierarchical LambdaCDM cosmogony, and that the most likely responsible for this downsizing is the stellar kinetic feedback that arises in star-forming bulges as a consequence of the high level of turbulence and leads to a massive removal of cold gas in small elliptical galaxies. At the same time, to obtain good fits to the number of bright quasars we need to require that quasar-triggered galactic winds self-limit the accretion onto BHs. In all cases, the predicted BH--bulge relation steepens considerably with respect to the observed one at bulge masses <10^{11} Msun; this problem is related to a known excess in the predicted number of small bulges, common to most similar models, so that the reproduction of the correct number of faint AGNs is done at the cost of underestimating their BH masses. This highlights an insufficient downsizing of elliptical galaxies, and hints for another feedback mechanism able to act on the compact discs that form and soon merge at high redshift. The results of this paper reinforce the need for direct investigations of the feedback mechanisms in active galaxies, that will be possible with the next generation of astronomical telescopes from sub-mm to X-rays.
Using a set of hydrodynamical simulations of 9 galaxy clusters with masses in the range 1.5 10^{14} M_sun < M_vir < 3.4 10^{15} M_sun, we have studied the density, temperature and X-ray surface brightness profiles of the intra-cluster medium in the regions around the virial radius. We have analyzed the profiles in the radial range well above the cluster core, the physics of which is still unclear and matter of tension between simulated and observed properties, and up to the virial radius and beyond, where present observations are unable to provide any constraints. We have modeled the radial profiles between 0.3 R_200 and 3 R_200 with power-laws with one index, two indexes and a rolling index. The simulated temperature and [0.5-2] keV surface brightness profiles well reproduce the observed behaviours outside the core. The shape of all these profiles in the radial range considered depends mainly on the activity of the gravitational collapse, with no significant difference among models including extra-physics. The profiles steepen in the outskirts, with the slope of the power-law fit that changes from -2.5 to -3.4 in the gas density, from -0.5 to -1.8 in the gas temperature, and from -3.5 to -5.0 in the X-ray soft surface brightness. We predict that the gas density, temperature and [0.5-2] keV surface brightness values at R_200 are, on average, 0.05, 0.60, 0.008 times the measured values at 0.3 R_200. At 2 R_200, these values decrease by an order of magnitude in the gas density and surface brightness, by a factor of 2 in the temperature, putting stringent limits on the detectable properties of the ICM in the virial regions.
We analyze high resolution spectroscopic observations of the optical afterglow of GRB050730, obtained with UVES@VLT about hours after the GRB trigger. The spectrum shows that the ISM of the GRB host galaxy at z = 3.967 is complex, with at least five components contributing to the main absorption system. We detect strong CII*, SiII*, OI* and FeII* fine structure absorption lines associated to the second and third component. For the first three components we derive information on the relative distance from the site of the GRB explosion. Component 1, which has the highest redshift, does not present any fine structure nor low ionization lines; it only shows very high ionization features, such as CIV and OVI, suggesting that this component is very close to the GRB site. From the analysis of low and high ionization lines and fine structure lines, we find evidences that the distance of component 2 from the site of the GRB explosion is 10-100 times smaller than that of component 3. We evaluated the mean metallicity of the z=3.967 system obtaining values about 0.01 of the solar metallicity or less. However, this should not be taken as representative of the circumburst medium, since the main contribution to the hydrogen column density comes from the outer regions of the galaxy while that of the other elements presumably comes from the ISM closer to the GRB site. Furthermore, difficulties in evaluating dust depletion correction can modify significantly these values. The mean [C/Fe] ratio agrees well with that expected by single star-formation event models. Interestingly the [C/Fe] of component 2 is smaller than that of component 3, in agreement with GRB dust destruction scenarios, if component 2 is closer than component 3 to the GRB site.
Ultra Luminous Infra-Red Galaxies (ULIRGs) -- gas-rich mergers harboring the most extreme star-forming conditions encountered in the local Universe -- are thought to re-enact the galaxy formation processes we are only barely able to glimpse in the distant Universe. Combining new single-dish molecular line observations of 12CO, 13CO, HCO+, HCN, and CS towards the two ULIRGs Arp220 and NGC6240 with existing data in the literature, we have compiled the most extensive molecular line data-sets to date of such galaxies. The data allow us to put strong constraints on the properties of the dense star forming gas in these two systems, and compare the relative usefulness of CS, HCN and HCO+ as tracers of dense gas. In addition, we have build molecular line templates based on our observations, and demonstrate that Herschel/HI-FI will be able to detect the high-J transitions of most of the above molecules in a large sample of ULIRGs out to z<=0.5, assuming Arp220 and NGC6240 are representative of the ULIRG population at these redshifts.
The origin of the particles in the highest energy end of the cosmic ray spectrum is discussed in the context of the wider problem of the origin of the whole cosmic radiation as observed at the Earth. In particular we focus our attention on the acceleration problem and on the transition from galactic to extragalactic cosmic rays.
We perform a self-consistent calculation of the thermal structure in the crust of a superbursting neutron star. In particular, we follow the nucleosynthetic evolution of an accreted element from deposition into the atmosphere down to neutron drip density. We include temperature-dependent continuum electron capture rates and realistic sources of heat loss by thermal neutrino emission from the crust and core. We show that, in contrast to previous calculations, electron captures to excited states and subsequent gamma-emission significantly reduces the local heat loss due to weak-interaction neutrinos. Furthermore, temperature-sensitive (gamma,n) rates trigger further energy deposition as the distribution of nuclei evolves toward a lower neutron separation energy. Depending on the initial composition these reactions release up to a factor of ten times more heat at densities <10^{11} g/cc than obtained previously. This heating reduces the ignition depth of superbursts. In particular, it reduces the discrepancy noted by Cumming et al. between the temperatures needed for unstable 12C ignition on timescales consistent with observations and the reduction in crust temperature from Cooper pair neutrino emission.
A number of trends among the properties of exoplanets have become evident in the years since the first one was announced in 1995. One particularly interesting trend began to emerge in 1997 -- the incidence of giant planets correlates with the metallicity of the host star. This has since been established with a high degree of statistical significance by several research groups. Other, more subtle, trends are beginning to appear as the sample size continues to grow and the statistics improve. I review the state of our knowledge concerning the observed compositional trends and their possible causes and suggest several research directions.
SPIRE, the Spectral and Photometric Imaging Receiver, is one of three instruments to fly on ESA's Herschel Space Observatory. It contains a three-band imaging photometer operating at 250, 360 and 520 microns, and an imaging Fourier Transform Spectrometer (FTS) covering 200-670 microns. It will be used for many extragalactic science programmes, a number of which will be implemented as Herschel Key Projects. The SPIRE consortium's Guaranteed Time (GT) programme will devote more than 1000 hours to Key Projects covering the high-z universe and local galaxies. It is also expected that substantial amounts of Herschel Open Time will be used for further extragalactic investigations. The high-z part of the SPIRE GT programme will focus on blank-field surveys with a range of depths and areas optimised to sample the luminosity-redshift plane and characterise the bolometric luminosity density of the universe at high z. Fields will be selected that are well covered at other wavelengths to facilitate source identifications and enable detailed studies of the redshifts, spectral energy distributions, and infrared properties of detected galaxies. The local galaxies programme will include a detailed spectral and photometric study of a sample of well resolved nearby galaxies, a survey of more than 300 local galaxies designed to provide a statistical survey of dust in the nearby universe, and a study of the ISM in low-metallicity environments, bridging the gap between the local universe and primordial galaxies.
In the course of the formation of cosmological structures, large shock waves are generated in the intra-cluster medium. In analogy to processes in supernova remnants, these shock waves may generate a significant population of relativistic electrons which, in turn, produce observable synchrotron emission. The extended radio relics found at the periphery of several clusters and possibly also a fraction of radio halo emission may have this origin. Here we derive an analytic expression for (i) the total radio power in the downstream region of a cosmological shock wave and (ii) the width of the radio-emitting region. These expressions predict a spectral slope close to -1 for strong shocks. Moderate shocks, such as those produced in mergers between clusters of galaxies, lead to a somewhat steeper spectrum. Moreover, we predict an upper limit for the radio power of cosmological shocks. Comparing our results to the radio relics in Abell115, 2256, and 3667, we conclude that the magnetic field in these relics is typically at a level of 0.1 mu G. Magnetic fields in the intra-cluster medium are presumably generated by the shocks themselves, this allows us to calculate the radio emission as a function of the cluster temperature. The resulting emissions agree very well with the radio power-temperature relation found for cluster halos. Finally, we show that cosmic accretion shocks generate less radio emission than merger shock waves. The latter may, however, be detected with upcoming radio telescopes.
Suzaku observed the molecular cloud MBM12 and a blank field less than 3
degrees away to separate the local and distant components of the diffuse soft
X-ray background. Towards MBM12, a local (D< 275 pc) O VII emission line was
clearly detected with an intensity of 3.5 ph cm^{-2} s^{-1} sr^{-1}$ (or line
units, LU), and the O VIII flux was <0.34 LU. The origin of this O VII emission
could be hot gas in the Local Hot Bubble (LHB), charge exchange between oxygen
ions in the solar wind (SWCX) and geocoronal or interplanetary material, or a
combination of the two. If entirely from the LHB, the implied temperature and
emission measure would predict 1/4 keV emission in excess of observations.
There is no evidence in the X-ray light curve or solar wind data for a
significant contribution from geocoronal SWCX. In any case, the observed O VII
flux represents an upper limit to both the LHB emission and interplanetary SWCX
in this direction.
The off-cloud observation was performed immediately following the on-cloud.
The net off-cloud O VII and O VIII intensities were (respectively) 2.34\pm0.33
and 0.77\pm0.16 LU, after subtracting the on-cloud foreground emission.
Assuming the LHB and SWCX components did not change, these increases can be
attributed to more distant Galactic disk, halo, or extragalactic emission. If
the distant O VII and O VIII emission is from a thermal plasma in collisional
equilibrium beyond the Galactic disk, a temperature of (2.1\pm0.1)\times10^6 K
with an emission measure of (4\pm0.6)\times10^-3} cm^{-6}pc is inferred.
Recently, the primordial non-Gaussianity in the curvaton model has been predicted assuming sudden decay of the curvaton. We extend the calculation to non-instantaneous decay by employing delta N -formalism. The difference between the sudden-decay approximation and our numerical result is larger than 1% only if the non-linearity parameter is small, -1.16 < f_NL < 60. Thus it is safe to use the sudden-decay approximation when deriving constraints for the curvaton model from WMAP3 (f_NL < 114), but with the Planck forecast |f_NL| <5 one should employ the fully numerical result. Often, the curvaton perturbations $\delta\sigma$ have been assumed to be small compared to the background value of the curvaton field $\sigma_0$. Consequently, the variance $\Delta^2 = <\delta\sigma^2> / \sigma_0^2$ has been assumed to be negligible. However, the measurements of CMB or large-scale structure perturbation amplitude do not constrain the variance if the main contribution to it comes from the ultraviolet (UV) scales, i.e., from smaller than observable scales. We discuss how, even in this case, observational constraints on non-Gaussianity set an upper bound to the small scale variance, Delta^2_UV < 90.
We describe Spitzer images of a sample of dwarf and low surface brightness galaxies, using the high sensitivity and spatial resolution to explore the morphologies of dust in these galaxies. For the starbursting dwarf UGC 10445, we present a complete infrared spectral energy distribution and modeling of its individual dust components. We find that its diffuse cold (T~19K) dust component extends beyond its near-infrared disk and speculate that the most plausible source of heating is ultraviolet photons from starforming complexes. We find that the mass of T~19K dust in UGC 10445 is surprisingly large, with a lower limit of 3 x 10^6 M_solar. We explore the implications of having such a high dust content on the nature and evolution of the galaxy.
We discuss a self-consistent unified model of the matter outflows from AGNs based on a theoretical approach and involving data on AGN evolution and structure. The model includes a unified geometry, two-phase gas dynamics, radiation transfer, and absorption spectrum calculations in the UV and X-ray bands. We briefly discuss several questions about the mass sources of the flows, the covering factors, and the stability of the narrow absorption details.
We report on the discovery of a pointlike source (CXOU J160103.1$-$513353) at the center of a Galactic supernova remnant (SNR) G330.2+1.0 with {\it Chandra X-Ray Observatory}. The X-ray spectrum fits a black-body (BB) model with $kT$ $\sim$ 0.49 keV, implying a small emission region of $R$ $\sim$ 0.4 km at the distance of 5 kpc. The estimated X-ray luminosity is $L_X$ $\sim$ 1 $\times$ 10$^{33}$ ergs s$^{-1}$ in the 1 $-$ 10 keV band. A power law model may also fit the observed spectrum, but the fit results in a very large photon index ($\Gamma$ $\sim$ 5). We find no counterparts at other wavelengths. The X-ray emission was steady over the $\sim$13 hr observation period, showing no variability. While we find marginal evidence for X-ray pulsations with $P$ $\approx$ 7.5 s, the presence of a pulsar at the position of this object is not conclusive with the current data, requiring an independent confirmation. These results are generally consistent with an interpretation of this object as a Central Compact Object associated with SNR G330.2+1.0.
We present the reconstructed real-space density and the predicted velocity fields from the Two Mass Redshift Survey (2MRS). The 2MRS is the densest all-sky redshift survey to date and includes about 23,200 galaxies with extinction corrected magnitudes brighter than K = 11.25. Our method is based on the expansion of these fields in Fourier-Bessel functions. Within this framework, the linear redshift distortions only affect the density field in the radial direction and can easily be deconvolved using a distortion matrix. Moreover, in this coordinate system, the velocity field is related to the density field by a simple linear transformation. The shot noise errors in the reconstructions are suppressed by means of a Wiener filter which yields a minimum variance estimate of the density and velocity fields. Using the reconstructed real-space density fields, we identify all major superclusters and voids. At 50 Mpc/h, our reconstructed velocity field indicates a back-side infall to the Great Attractor region of vi = (491 +/- 200)(beta/0.5) km/sec in the Local Group frame and v = (64 +/- 205)(beta/0.5) km/sec in the cosmic microwave background (CMB) frame and beta is the redshift distortion parameter. The direction of the reconstructed dipole agrees well with the dipole derived by Erdogdu et al. (2006). The misalignment between the reconstructed 2MRS and the CMB dipoles drops to 13 degrees at around 5000 km/sec but then increases at larger distances. A version of this paper with high resolution figures can be obtained from this http URL
(abridged) INTEGRAL has discovered large numbers of new hard X-ray sources, many of which are believed to be high mass X-ray binaries. However, for a significant fraction, their counterparts remain unidentified. We explore the use of photometric catalogues to find optical counterparts to high mass X-ray binaries. Candidates were selected from 2MASS photometry by means of a reddening free Q parameter. Sufficiently bright candidates were spectroscopically observed. Many of the candidates selected turned out to be moderately reddened late A or early F stars, but our method is able to identify the counterpart to IGR J16207-5129, confirmed by a Chandra localisation. We classify this object as a B0 supergiant. In the field of AX J1820.5-1434, we find a mid or early B-type star, but we cannot confirm it as the counterpart. For AX J1700.2-4220, we do not find any suitable candidate within the ASCA error circle. We classify HD 153295, a marginal candidate to be the counterpart, as B0.5IVe, and find a distance compatible with membership in Sco OB1. We derive a spectral type B0IIIe for HD100199, previously identified as the counterpart to IGR J11305-6256. In the case of IGR J17091-3624, the object associated with a variable radio source in the field is a late F star. The procedure used is able to correctly identify OB stars and, in about one third of the cases, may lead to the localisation of the correct counterpart. However, the majority of INTEGRAL error circles do not contain any suitable optically visible counterpart. Deep infrared searches are going to be necessary in order to locate the counterparts to these sources.
A new generation of CMB experiments will soon make sensitive high resolution maps of the microwave sky. At angular scales less than $\sim$10 arcminutes, most CMB anisotropies are generated at z $< 1000$, rather than at the surface of last scattering. Therefore, these maps potentially contain an enormous amount of information about the evolution of structure. Whereas spectral information can distinguish the thermal Sunyaev-Zeldovich (tSZ) effect from other anisotropies, the spectral form of anisotropies generated by the gravitational lensing and the kinetic Sunyaev-Zeldovich (kSZ) effects are identical. While spectrally identical, the statistical properties of these effects are different. We introduce a new real-space statistic, $<\theta (\hat{n})^3 \theta (\hat{m})>_c$, and show that it is identically zero for weakly lensed primary anisotropies and, therefore, allows a direct measurement of the kSZ effect. Measuring this statistic can offer a new tool for studing the reionization epoch. Models with the same optical depth, but different reionization histories, can differ by more than a factor of 3 in the amplitude of the kSZ-generated non-Gaussian signal.
The center of the galaxy cluster RX J0054.0-2823 at z = 0.292 is a dynamically active region which includes an interacting system of three galaxies surrounded by a large halo of intra-cluster light. We report here the discovery of an S-shaped feature of total length 11 arcsec in the central region of this cluster and discuss its physical nature. We test the gravitational lensing assumption by doing a mass modelling of the central part of the galaxy cluster. We very naturally reproduce position and form of this S-shape feature as a gravitationally lensed background object at redshift between 0.5 and 1.0. We conclude that the lensing nature is the very probable explanation for this S-shaped arc; the ultimate proof will be the spectroscopic confirmation by measuring the high redshift of this elongated feature with surface brightness V~24mag/arcsec2.
We have observed atmospheric gamma rays from 30GeV to 8TeV, using emulsion chambers at balloon altitudes, accumulating the largest total exposure in this energy range to date, SOT ~ 6.66m^2.sr.day. At very high altitudes, with residual overburden only a few g/cm^2, atmospheric gamma rays are mainly produced by a single interaction of primary cosmic rays with overlying atmospheric nuclei. Thus, we can use these gamma rays to study the spectrum of primary cosmic rays and their products in the atmosphere. From the observed atmospheric gamma ray spectrum, we deconvolved the primary cosmic-ray proton spectrum, assuming appropriate hadronic interaction models. Our deconvolved proton spectrum covers the energy range from 200GeV to 50TeV, which fills a gap in the currently available primary cosmic-ray proton spectra. We also estimated the atmospheric muon spectrum above 30GeV at high altitude from our gamma-ray spectrum, almost without reference to the primary cosmic rays, and compared the estimated flux with direct muon observations below 10GeV.
Recent observation to the afterglow of GRB051221A found a flat segment in the X-ray light curve around 0.1 day after the burst. This flat segment caused the flux increasing by a factor of 5 over the extension of a single power law decrease. It may be caused either by a strong energy injection or by contribution of a second outflow component. Such a two component jet could be formed if the initial ejecta launched in the double neutron stars merger or neutron star-black hole merger is neutron rich and magnetized. In this work we show that the multi-band afterglows of GRB051221A could be well fitted by a two component model, provided that the shock physics parameters in different components are much different. This result suggests that GRB051221A might be the first detection of two component jet in short gamma-ray burst outflow.
In the galaxy clusters SSDS J1004+411 and ACO 1689, a large number of multiply-imaged background objects have recently been observed. We use these data to map the projected mass distribution in the inner regions of these clusters. The source redshifts span a large range, which eliminates the degeneracies that plague nearly all lensing work. As a result the mass maps are very well-constrained, despite very weak prior assumptions. ACO 1689 lenses so many objects that we can afford to map it twice using disjoint sets of images, thus verifying our internal error estimates. We then deproject the mass maps (pretending for this purpose that they are spherical) and obtain inner profiles consistent with rho propto r^{-1} and indistinguishable from recent cold dark matter simulations. Assuming that baryons make only a small difference to the profile outside sim 10 kpc, these results support the prediction of a universal inner profile for dark matter structures, independent of any parametrization of that profile.
Aims: We have carried out an infrared study of the southern Galactic massive star forming region associated with IRAS 14416-5937. Methods: This star forming region has been mapped simultaneously in two far infrared bands at ~ 150 & 210 micron using the TIFR 1-m balloon borne telescope with ~ 1' angular resolution. We have used 2MASS JHK$_s$ as well as Spitzer-GLIMPSE data of this region to study the stellar populations of the embedded young cluster. This region comprises of two sources, designated as A & B and separated by ~ 2 pc. The spectrum of a region located close to the source A obtained using the Long Wavelength Spectrometer (LWS) on-board the Infrared Space Observatory (ISO), is presented. Emission from warm dust and from Unidentified Infrared Bands (UIBs) is estimated using the mid-infrared data of the MSX survey. Results: The spatial distributions of (1) the temperature of cool dust and (2) optical depth at 200 micron have been obtained taking advantage of the similar beams in both the TIFR bands. A number of atomic fine structure lines have been detected in the ISO-LWS spectrum, which have been used to estimate the electron density and the effective temperature of the ionising radiation in this region. From the near and mid infrared images, we identify a dust lane due north-west of source A. The dust lane is populated by Class I type sources. Class II type sources are found further along the dust lane as well as below it. Self consistent radiative transfer models of the two sources (A and B) are in good agreement with the observed spectral energy distributions. Conclusions: The spatial distribution of young stellar objects in and around the dust lane suggests that active star formation is taking place along the dust lane and is possibly triggered by the expanding HII regions of A and B.
We have performed soft X-ray spectroscopy of two hot white dwarfs with the Chandra observatory using the Low Energy Transmission Grating. The first target is the hot DA white dwarf LB1919 (Teff=69000 K). This star is representative of a small group of hot DAs whose metallicities lie well below predictions from radiative levitation theory. The Chandra spectrum shows a rich absorption line spectrum which may allow to find the origin of the low-metallicity nature of these DAs. The second target is PG1520+525, a very hot non-pulsating PG1159 star. We find that it is hotter (Teff=150 000 K) than the pulsating prototype PG1159-035 (Teff=140 000) and conclude that both stars confine the blue edge of the GW Vir instability strip.
We study the evolution of first star (Population III) binaries. Under specific conditions, these stars may produce high redshift gamma-ray bursts (GRBs). We demonstrate that the occurrence rate of GRBs does not depend sensitively on evolutionary parameters in the population synthesis models. We show that the first binaries may form a very small group (< 1%) of fast rotating stars through binary tidal interactions that make GRBs. This finding is contrary to the Bromm & Loeb assumption that all stars in close Population III binaries will be spun up by tides and produce a GRB. We find that there is simply not enough fast rotating stars in Population III binaries to expect detection with SWIFT. Predicted detection rates, even with very optimistic assumptions on binary fraction, evolutionary parameters and GRB detection, are very small: 0.1-0.01 per year.
We present integrated photometry and color-magnitude diagrams (CMDs) for 24 star clusters in M33, of which 12 were previously uncataloged. These results are based on Advanced Camera for Surveys observations from the Hubble Space Telescope of two fields in M33. Our integrated V magnitudes and V-I colors for the previously identified objects are in good agreement with published photometry. We are able to estimate ages for 21 of these clusters using features in the CMDs, including isochrone fitting to the main sequence turnoffs for 17 of the clusters. Comparisons of these ages with the clusters' integrated colors and magnitudes suggest that simple stellar population models perform reasonably well in predicting these properties.
We present in this paper a new three-dimensional galaxy classification system designed to account for the diversity of galaxy properties in the nearby universe. To construct this system we statistically analyse a sample of >22,000 galaxies at v<15,000 km/s (z<0.05) with Spearman rank and principal component analyses. Fourteen major galaxy properties are considered, including: Hubble type, size, colour, surface brightness, magnitude, stellar mass, internal velocities, HI gas content, and an index that measures dynamical disturbances. We find, to a high degree, that most galaxy properties are correlated, with in particular Hubble type, colour, and stellar mass all strongly related. We argue that this tight 3-way correlation is a result of evolutionary processes that depend on galaxy mass, as we show that the relation between colour and mass is independent of Hubble type. Various principal component analyses reveal that most of the variation in nearby galaxy properties can be accounted for by eigenvectors dominated by: (i) the scale of a galaxy, such as its stellar mass, (ii) the spectral type, and (iii) the degree of dynamical disturbances. We suggest that these three properties: mass, star formation, and interactions/mergers are the major features that determine a galaxy's physical state, and should be used to classify galaxies. As shown in Conselice (2003), these properties are measurable within the CAS (concentration, asymmetry, clumpiness) structural system, thus providing an efficient mechanism for classifying galaxies in optical light within a physical meaningful framework. We furthermore discuss the fraction and number density of galaxies in the nearby universe as a function of Hubble type, for comparison with higher redshift populations.
We present results of our detailed theoretical study of the observed orbital modulation of the radio emission in Cyg X-1. The modulation occurs due to free-free absorption in the wind from the companion star varying with the orbital phase, and our results put strong constraints on the spatial distribution of the jet radio emission at the frequencies of 2-15 GHz. A crucial role in enhancing the asymmetry of the wind absorption suffered by the jet emission is played by the irradiation by X-rays emitted in the vicinity of the black hole. This increases the wind temperature by more than order of magnitude with respect to that of the wind of an isolated supergiant. The observed phase lags of the minima of the radio emission with respect to the spectroscopic zero phase strongly imply the bulk of the mass of the jet is nonrelativistic (~5 x 10^8 cm/s) within the jet core. The jet can, however, become relativistic outside the core. Also, the jet can have a two-component structure, being slow on the outside and fast inside, in which case its synchrotron-emitting part may be relativistic already in the core. We also consider the observed superorbital modulation of the radio emission (with the period of ~150 d) and find it can be explained by a jet precession both causing variable wind absorption and changing the jet Doppler factor. Finally, we consider the case of Cyg X-3, and show that its lack of observable orbital radio modulation (in spite of strong modulation of X-rays) is explained by that system being both much more compact and much more luminous than Cyg X-1.
We report broadband UBV and/or BVRI CCD photometry for a total of 1857 stars
in the thick-disk and halo populations of the Galaxy. The majority of our
targets were selected as candidate field horizontal-branch or other A-type
stars (FHB/A, N = 576), or candidate low-metallicity stars (N = 1221), from the
HK and Hamburg/ESO objective-prism surveys. Similar data for a small number of
additional stars from other samples are also reported.
These data are being used for several purposes. In the case of the FHB/A
candidates they are used to accurately separate the lower-gravity FHB stars
from various higher-gravity A-type stars, a subsample that includes the
so-called Blue Metal Poor stars, halo and thick-disk blue stragglers,
main-sequence A-type dwarfs, and Am and Ap stars. These data are also being
used to derive photometric distance estimates to high-velocity hydrogen clouds
in the Galaxy and for improved measurements of the mass of the Galaxy.
Photometric data for the metal-poor candidates are being used to refine
estimates of stellar metallicity for objects with available medium-resolution
spectroscopy, to obtain distance estimates for kinematic analyses, and to
establish initial estimates of effective temperature for analysis of
high-resolution spectroscopy of the stars for which this information now
exists.
The DAO-type white dwarf LS V+4621 is the hydrogen-rich central star of the possible planetary nebula Sh 2-216. We have taken high-resolution, high-S/N ultraviolet spectra with STIS aboard the HST and FUSE in order to constrain its photospheric parameters. A detailed spectral analysis by means of state-of-the-art NLTE model-atmosphere techniques is presented which includes the determination the individual abundances of iron-group elements.
The far-ultraviolet spectrum of the DAO White Dwarf LS V+4621, the exciting
star of the possible planetary nebula Sh 2-216,is strongly contaminated by
absorption features from the interstellar medium (ISM). For an ongoing spectral
analysis, we aim to extract the pure photospheric spectrum in order to identify
and model metal lines of species which are not detectable in the
near-ultraviolet wavelength range.
We have modeled the interstellar absorption precisely and considered it for
the simulation of the FUSE (Far Ultraviolet Spectroscopic Explorer)
observation. A state-of-the-art NLTE model-atmosphere spectrum which includes
16 elements is combined with the ISM absorption and then compared with the FUSE
spectrum.
We show that even most massive initial solar composition stars hardly form black holes with mass exceeding about 100 solar mass.
Astrophysical space missions deliver invaluable information about our universe, stellar dynamics of our galaxy, and motion of celestial bodies in the solar system. Astrometric space missions SIM and Gaia will determine distances to stars and cosmological objects as well as their physical characteristics and positions on the celestial sphere with microarcsecond precision. These and other space missions dedicated to exploration of the solar system are invaluable for experimental testing of general relativity. Permanently growing accuracy of space and ground-based astronomical observations require corresponding development of relativistic theory of reference frames, motion of celestial bodies, and propagation of light/radio signals from a source of light/radio to observer. Such theory must be based on Einstein's general relativity and account for various relativistic effects both in the solar system and outside of its boundary. We describe a hierarchy of the relativistic frames adopted by the International Astronomical Union in 2000, and outline directions for its theoretical and practical extentions by matching the IAU 2000 reference frames in the solar system to the cosmological Friedman-Robertson-Walker reference frame and to the frames used in the parametrized post-Newtonian formalism.
Neutrino radiation takes a major role in the momentum, heat, and lepton transports in proto-neutron stars (PNSs). These diffusive processes affect the growth of magnetorotational instability (MRI) in PNSs. We perform a local linear analysis for the axisymmetric and nonaxisymmetric MRI including the effects of neutrino transports and ohmic dissipation. We find that the MRI can grow even in the multi-diffusive situations that are realized in neutrino loaded PNSs. When the toroidal magnetic component dominates over the poloidal one, nonaxisymmetric MRI modes grow much faster than axisymmetric modes. These results suggest the importance of the nonaxisymmetric MRI in PNSs. Thus the understandings of three-dimensional nonlinear evolutions of the MRI are necessary to reveal the explosion mechanism of core-collapse supernovae.
We studied extended X-ray emission from the Carina Nebula taken with the Suzaku CCD camera XIS on 2005 Aug. 29. The X-ray morphology, plasma temperature and absorption to the plasma are consistent with the earlier Einstein results. The Suzaku spectra newly revealed emission lines from various species including oxygen, but not from nitrogen. This result restricts the N/O ratio significantly low, compared with evolved massive stellar winds, suggesting that the diffuse emission is originated in an old supernova remnant or a super shell produced by multiple supernova remnants. The X-ray spectra from the north and south of Eta Carinae showed distinct differences between 0.3-2 keV. The south spectrum shows strong L-shell lines of iron ions and K-shell lines of silicon ions, while the north spectrum shows them weak in intensity. This means that silicon and iron abundances are a factor of 2-4 higher in the south region than in the north region. The abundance variation may be produced by an SNR ejecta, or relate to the dust formation around the star forming core.
The 3:1 mean-motion resonance of the planar elliptic restricted three body problem (Sun-Jupiter-asteroid) is considered. The double numeric averaging is used to obtain the evolutionary equations which describe the long-term behavior of the asteroid's argument of pericentre and eccentricity. The existence of the adiabatic chaos area in the system's phase space is shown.
This review summarizes recent attempts to reconstruct the expansion history of the Universe and to probe the nature of dark energy. Reconstruction methods can be broadly classified into parametric and non-parametric approaches. It is encouraging that, even with the limited observational data currently available, different approaches give consistent results for the reconstruction of the Hubble parameter $H(z)$ and the effective equation of state $w(z)$ of dark energy. Model independent reconstruction using current data allows for modest evolution of dark energy density with redshift. However, a cosmological constant (= dark energy with a constant energy density) remains an excellent fit to the data. Some pitfalls to be guarded against during cosmological reconstruction are summarized and future directions for the model independent reconstruction of dark energy are explored.
Galactic dust constitutes approximately half of the elements more massive than helium produced in stellar nucleosynthesis. Notwithstanding the formation of dust grains in the dense, cool atmospheres of late-type stars, there still remain huge uncertainties concerning the origin and fate of galactic stardust. In this paper, we identify the intergalactic medium (i.e. the region between gravitationally-bound galaxies) as a major sink for galactic dust. We discover a systematic shift in the colour of background galaxies viewed through the intergalactic medium of the nearby M81 group. This reddening coincides with atomic, neutral gas previously detected between the group members. The dust-to-HI mass ratio is high (1/20) compared to that of the solar neighborhood (1/120) suggesting that the dust originates from the centre of one or more of the galaxies in the group. Indeed, M82, which is known to be ejecting dust and gas in a starburst-driven superwind, is cited as the probable main source.
We have studied the UV spectral behavior of the recurrent nova T Pyx during 16 years of IUE observations. We examined both the IUE line-by-line images and the extracted spectra in order to understand the reality and the origin of the observed spectral variations. The UV continuum of T Pyx has remained nearly constant in slope and intensity over this time interval, without any indication of long-term trends. The reddening determined from the UV data is E(B-V}=0.25 \pm 0.02. The best single-curve fit to the dereddened UV continuum is a power-law distribution $\propto \lambda^{-2.33}$. The tail of this curve agrees well with the B, V, and J magnitudes of T Pyx, indicating that the contribution of the secondary star is negligible. One peculiar aspect of T Pyx is that most emission lines (the strongest ones being those of CIV 1550 and HeII 1640) show substantial changes both in intensity and detectability, in contrast to the near constancy of the continuum. Several individual spectra display emission features that are difficult to identify, suggesting a composite spectroscopic system. We tentatively ascribe the origin of these transient emission features either to loops and jets from the irradiated secondary or to moving knots of the surrounding nebula that are (temporarily) projected in front of the system. The inspection of all IUE line-by-line images has led to the detection of emission spikes outside the central strip of the spectrum, which in some cases seem associated to known emission features in the (main) spectrum. A comparison with other ex-novae reveals a surprising similarity to the spectrum of the very-slow nova HR Del, whose white dwarf primary has a mass that is allegedly about one half that of T Pyx.
The ANTARES neutrino telescope is being constructed in the Mediterranean Sea. It consists of a large three-dimensional array of photo-multiplier tubes. The data acquisition system of the detector takes care of the digitisation of the photo-multiplier tube signals, data transport, data filtering, and data storage. The detector is operated using a control program interfaced with all elements. The design and the implementation of the data acquisition system are described.
Context: Sticking of colliding dust particles through van der Waals forces is the first stage in the grain growth process in protoplanetary disks, eventually leading to the formation of comets, asteroids and planets. A key aspect of the collisional evolution is the coupling between dust and gas motions, which depends on the internal structure (porosity) of aggregates. Aims: To quantify the importance of the internal structure on the collisional evolution of particles, and to create a new coagulation model to investigate the difference between porous and compact coagulation in the context of a turbulent protoplanetary disk. Methods: We have developed simple prescriptions for the collisional evolution of porosity of grain-aggregates in grain-grain collisions. Three regimes can then be distinguished: `hit-and-stick' at low velocities, with an increase in porosity; compaction at intermediate velocities, with a decrease of porosity; and fragmentation at high velocities. (..) Results: (..) We can discern three different stages in the particle growth process (..) We find that when compared to standard, compact models of coagulation, porous growth delays the onset of settling, because the surface area-to-mass ratio is higher, a consequence of the build-up of porosity during the initial stages. As a result, particles grow orders of magnitudes larger in mass before they rain-out to the mid-plane. Depending on the turbulent viscosity and on the position in the nebula, aggregates can grow to (porous) sizes of ~ 10 cm in a few thousand years. We also find that collisional energies are higher than in the limited PCA/CCA fractal models, thereby allowing aggregates to restructure. It is concluded that the microphysics of collisions plays a key role in the growth process.
Recent observational and theoretical breakthroughs make this an exciting time to be working towards understanding the physics of galaxy formation. The goal of this review is to make the principles behind the hierarchical paradigm accessible to a wide audience by providing a pedagogical introduction to modern theories of galaxy formation. I outline the ingredients of the powerful approach called semi-analytical modelling and contrast this method with numerical simulations of the gas dynamics of baryons. Semi-analytical models have enjoyed many successes, but it is the observations which the models struggle to match which mark out areas where future progress is most likely to be made; these are also reviewed.
It is believed that the observed diffuse gamma ray emission from the galactic plane is the result of interactions between cosmic rays and the interstellar gas. Such emission can be amplified if cosmic rays penetrate into dense molecular clouds. The propagation of cosmic rays inside a molecular cloud has been studied assuming an arbitrary energy and space dependent diffusion coefficient. If the diffusion coefficient inside the cloud is significantly smaller compared to the average one derived for the galactic disk, the observed gamma ray spectrum appears harder than the cosmic ray spectrum, mainly due to the slower penetration of the low energy particles towards the core of the cloud. This may produce a great variety of gamma ray spectra.
The stellar abundance ratio of Mg/Fe is an important tool in diagnostics of galaxy evolution. In order to make reliable measurements of the Mg abundance of stars, it is necessary to have accurate values for the oscillator strength (f-value) of each of the observable transitions. In metal-poor stars the Mg I 3p-4s triplet around 5175 AA (Fraunhofer's so-called b lines) are the most prominent magnesium lines. The lines also appear as strong features in the solar spectrum. We present new and improved experimental oscillator strengths for the optical Mg I 3p-4s triplet, along with experimental radiative lifetimes for six terms in Mg I. With these data we discuss the implications on previous and future abundance analyses of metal-poor stars. The oscillator strengths have been determined by combining radiative lifetimes with branching fractions, where the radiative lifetimes are measured using the laser induced fluorescence technique and the branching fractions are determined using intensity calibrated Fourier Transform (FT) spectra. The FT spectra are also used for determining new accurate laboratory wavelengths for the 3p-4s transitions. The f-values of the Mg I 3p-4s lines have been determined with an absolute uncertainty of 9 %, giving an uncertainty of +-0.04 dex in the log gf values. Compared to values previously used in abundance analyses of metal-poor stars, rescaling to the new values implies an increase of typically 0.04 dex in the magnesium abundance.
Gravitational lensing observations of galaxy clusters have identified dark matter ``blobs'' with remarkably low baryonic content. We use such a system to probe the particle nature of dark matter with X-ray observations. We also study high resolution X-ray grating spectra of a cluster of galaxies. From these grating spectra we improve the conservative constraints on a particular dark matter candidate, the sterile neutrino, by more than one order of magnitude. Based on these conservative constraints obtained from Cosmic X-ray observations alone, the low mass (m_s < 10keV) and low mixing angle (sin^2(2\theta) 10^{-6}) sterile neutrino is still a viable dark matter candidate.
Power density spectra (PDS) that are characteristic of low mass X-ray binaries (LMXBs) have been previously reported for M31 X-ray sources observed by XMM-Newton. However, we have recently discovered that these PDS are false positives resulting from the improper manipulation of non-simultaneous lightcurves. The lightcurves produced by the XMM-Newton Science Analysis Software (SAS) are non-synchronised by default. This affects not only the combination of lightcurves from the three EPIC detectors (MOS1, MOS2 and pn), but also background subtraction in the same CCD. It is therefore imperative that all SAS-generated lightcurves are synchronised by time filtering, even if the whole observation is to be used. We combined simulated lightcurves at various intensities with various offsets and found that the artefact is more dependent on the offset than the intensity. While previous timing results from M31 have been proven wrong, and also the broken power law PDS in NGC 4559 ULX-7, XMM-Newton was able to detect aperiodic variability in just 3 ks of observations of NGC 5408 ULX1. Hence XMM-Newton remains a viable tool for analysing variability in extra-galactic X-ray sources.
We show that electromagnetic excitations of rotating black holes can lead to the appearance of narrow singular beams which break up the black hole horizon forming a tube-like region which connects the interior and exterior. It is argued that this effect may be at the origin of jet formation.
In this paper we present the first SiO multiline analysis (from J=2-1 to J=11-10) of the molecular bullets along the outflows of the Class 0 sources L1448-mm and L1157-mm, obtained through observations with IRAM and JCMT. We have computed the main physical parameters in each bullet and compared them with other tracers of warm and dense gas and with models for the SiO excitation in shocks. We find that the bullets close to L1448--mm, associated with high velocity gas, have higher excitation conditions (n(H2) ~ 10^{6} cm^{-3}, T > 500 K) with respect to the L1157 bullets (n(H2) ~1-5 10^{5} cm^{-3}, T ~ 100-300 K). In both the sources, there is a clear evidence of the presence of velocity components having different excitation conditions, with the denser and/or warmer gas associated with the gas at the higher speed. In L1448 the bulk of the emission is due to the high-excitation and high velocity gas, while in L1157 most of the emission comes from the low excitation gas at ambient velocity. The observed velocity-averaged line ratios are well reproduced by shocks with speeds v_s larger than ~ 30 km/s and densities ~ 10^{5} - 10^{6} cm^{-3}. Plane-parallel shock models, however, fail to predict all the observed line profiles and in particular the very similar profiles shown by both low and high excitation lines. The overall observations support the idea that the L1157 clumps are shock interaction events older than the L1448 bullets close to the driving source. In the latter objects, the velocity structure and the variations of physical parameters with the velocity resemble very closely those found in optical/IR jets near the protostar, suggesting that similar launching and excitation mechanisms are also at the origin of collimated jets seen at millimetre wavelengths.
We use the Chandra X-ray Observatory to study the dark matter halos of 34 massive, dynamically relaxed galaxy clusters, spanning the redshift range 0.06<z<0.7. The observed dark matter and total mass (dark-plus-luminous matter) profiles can be approximated by the Navarro Frenk & White (hereafter NFW) model for cold dark matter (CDM) halos; for ~80 per cent of the clusters, the NFW model provides a statistically acceptable fit. In contrast, the singular isothermal sphere model can, in almost every case, be completely ruled out. We observe a well-defined mass-concentration relation for the clusters with a normalization and intrinsic scatter in good agreement with the predictions from simulations. The slope of the mass-concentration relation, c\propto M_vir^a/(1+z)^b with a=-0.41\pm0.11 at 95 per cent confidence, is steeper than the value a~-0.1 predicted by CDM simulations for lower mass halos. With the slope a included as a free fit parameter, the redshift evolution of the concentration parameter, b=0.54\pm0.47 at 95 per cent confidence, is also slower than, but marginally consistent with, the same simulations (b~1). Fixing a~-0.1 leads to an apparent evolution that is significantly slower, b=0.20\pm0.45, although the goodness of fit in this case is significantly worse. Using a generalized NFW model, we find the inner dark matter density slope, alpha, to be consistent with unity at 95 per cent confidence for the majority of clusters. Combining the results for all clusters for which the generalized NFW model provides a good description of the data, we measure alpha=0.88\pm0.29 at 95 per cent confidence, in agreement with CDM model predictions.
Our first aim is to calculate the minimum mass for Primary Fragmentation in a variety of potential star-formation scenarios, i.e. (i) hierarchical fragmentation of a 3-D medium; (ii) one-shot, 2-D fragmentation of a shock-compressed layer; (iii) fragmentation of a circumstellar disc. Our second aim is to evaluate the role of H2 dissociation in facilitating Secondary Fragmentation and thereby producing close, low-mass binaries. Results: (i)For contemporary, local star formation, the minimum mass for Primary Fragmentation is in the range 0.001-0.004Msun, irrespective of the scenario considered. (ii)Circumstellar discs are only able to radiate fast enough to undergo Primary Fragmentation in their cool outer parts (R>100AU). Therefore brown dwarfs (BDs) should have difficulty forming by Primary Fragmentation at R<30AU, explaining the Brown Dwarf Desert.Conversely, Primary Fragmentation at R>100AU could be the source of brown dwarfs in wide orbits, and could explain why massive discs with Rd>100AU are rarely seen.(iii)H2 dissociation can lead to collapse and Secondary Fragmentation, thereby converting primary fragments into close, low-mass binaries, with semi-major axes a~5AU(Msystem/0.1Msun), in good agreement with observation; in this case, the minimum mass for Primary Fragmentation becomes a minimum system mass, rather than a minimum stellar mass.(iv)Any primary fragment can undergo Secondary Fragmentation, producing a close low-mass binary, provided only that the fragment is spinning. Secondary Fragmentation is therefore most likely in fragments formed in the outer parts of discs, and this could explain why a BD in a wide orbit about a Sun-like star has a greater likelihood of having a BD companion than a BD in the field -as seems to be observed.
We have performed the first three-dimensional non-linear simulation of the turbulent convective envelope of a rotating 0.8 Msun RGB star using the ASH code. Adopting a global typical rotation rate of a tenth of the solar rate, we have analyzed the dynamical properties of the convection and the transport of angular momentum within the inner 50% in radius of the convective envelope. The convective patterns consist of a small number of large cell, associated with fast flows (about 3000 m/s) and large temperature fluctuations (about 300 K) in order to carry outward the large luminosity (L* = 400 Lsun) of the star. The interactions between convection and rotation give rise to a large radial differential rotation and a meridional circulation possessing one cell per hemisphere, the flow being poleward in both hemisphere. By analysing the redistribution of angular momentum, we find that the meridional circulation transports the angular momentum outward in the radial direction, and poleward in the latitudinal direction, and that the transport by Reynolds stresses acts in the opposite direction. From this 3-D simulation, we have derived an average radial rotation profile, that we will ultimately introduce back into 1-D stellar evolution code.
We present abundances for a sample of F,G,K dwarfs of the HR1614 moving group based on high resolution, high S/N ratio spectra from AAT/UCLES. Our sample includes stars from Feltzing & Holmberg (2000, A&A, 357, 153), as well as from Eggen (1998, AJ, 115, 2453). Abundances were derived for Na, Mg, Al, Si, Ca, Mn, Fe, Ni, Zr, Ba, Ce, Nd, and Eu. The alpha, Fe, and Fe-peak element abundances show a bimodal distribution, with four stars having solar metallicities while the remaining 14 stars are metal rich [Fe/H] >= 0.25 dex. However the abundances of these two groups converge for the heavier n-capture elements. Based on their photometry and kinematics, three of the four deviating stars are likely non-members or binaries. Although one star cannot be excluded on these grounds, we do expect low-level contamination from field stars within the HR1614 moving group's range of magnitude, color and space velocities. Disregarding these four stars, the abundance scatter across the group members for all elements is low. We find that there is an 80% probability that the intrinsic scatter does not exceed the following values: Fe 0.01; Na 0.08; Mg 0.02; Al 0.06; Si 0.02; Ca 0.02; Mn 0.01; Ni 0.01; Zr 0.03; Ba 0.03; Ce 0.04; Nd 0.01 and Eu 0.02 dex. The homogeneity of the HR 1614 group in age and abundance suggests that it is the remnant of a dispersed star-forming event. Its kinematical coherence shows that such a dispersing system need not be significantly perturbed by external dynamical influences like galactic spiral structure or giant molecular clouds, at least over a period of 2 Gyr.
The existence of FR II objects that are kinetically dominated, the jet kinetic luminosity, $Q$, is larger than the total thermal luminosity (IR to X-ray) of the accretion flow, $L_{bol}$, is of profound theoretical interest. Such objects are not expected in most theoretical models of the central engine of radio loud AGN. Thus, establishing such a class of objects is an important diagnostic for filtering through the myriad of theoretical possibilities. This paper attempts to establish a class of quasars that have existed in a state of kinetic dominance, $R(t)\equiv Q(t)/L_{bol}(t)>1$, at some epoch, $t$. It is argued that the 10 quasars in this article with a long term time average $Q(t)$, $\bar{Q}$, that exceed $L_{Edd}$ are likely to have satisfied the condition $R(t)>1$ either presently or in the past based on the rarity of $L_{bol}>L_{Edd}$ quasars. Finally, the existence of these sources is discussed in the context of the theory of the central engine.
A simple physical model for long-duration gamma ray bursts (GRBs) is used to fit the redshift (z) and the jet opening-angle distributions measured with earlier GRB missions and with Swift. The effect of different sensitivities for GRB triggering is sufficient to explain the difference in the z distributions of the pre-Swift and Swift samples, with mean redshifts of <z> ~1.4 and <z>~2.8, respectively. Assuming that the emission properties of GRBs do not change with time, we find that the data can only be fitted if the comoving rate-density of GRB sources exhibits positive evolution to z >~ 3-5. The mean intrinsic beaming factor of GRBs is found to range from ~34-42, with the Swift average opening half-angle <\theta_j> ~10 degree, compared to the pre-Swift average of <\theta_j> ~7 degree. Within the uniform jet model, the GRB luminosity function is proportional to L^{-3.25}_*, as inferred from our best fit to the opening angle distribution. Because of the unlikely detection of several GRBs with z <~ 0.25, our analysis indicates that low redshift GRBs represent a different population of GRBs than those detected at higher redshifts. Neglecting possible metallicity effects on GRB host galaxies, we find that ~1 GRB occurs every 600,000 yrs in a local L_* spiral galaxy like the Milky Way. The fraction of high-redshift GRBs is estimated at 8-12% and 2.5-6% at z >= 5 and z >= 7, respectively, assuming continued positive evolution of the GRB rate density to high redshifts.
We have obtained spectra of HII regions in the heavily obscured spiral galaxy Maffei 2. The observations have allowed for a determination of the Galactic extinction of this galaxy using a correlation between extinction and hydrogen column density observed among spirals. The technique reveals that the optical depth of Galactic dust at 1 micron obscuring Maffei 2 is tau1 = 2.017 +/- 0.211, which implies that A_V = 5.58 +/- 0.58 mag, significantly higher than observed for the giant elliptical Maffei 1 despite its similar latitude. For comparison, we apply the same technique to IC 342, a neighbouring spiral to Maffei 2 but with more moderate obscuration by Galactic dust, owing to its higher Galactic latitude. For this galaxy, we obtain tau1 = 0.692 +/- 0.066, which agrees within errors with the value of 0.639 +/- 0.102 derived from the reddening estimate of Schlegel et al. (1998, ApJ, 500, 525). We therefore adopt the weighted mean of tau1 = 0.677 +/- 0.056 for the extinction of IC 342, which implies that A_V = 1.92 +/- 0.16 mag. A new distance estimate for Maffei 2 of 3.34 +/- 0.56 Mpc is obtained from a self-consistent Tully-Fisher relation in I adjusted to the NGC 4258 maser zero-point. With our new measurement of M_I, Maffei 2 joins Maffei 1 and IC 342 as one of three giant members of the nearby IC 342/Maffei group of galaxies. We present the revised properties of all three galaxies based on the most accurate extinction and distance estimates to date, accounting for shifts in the effective wavelengths of broadband filters as this effect can be significant for highly reddened galaxies. The revised distances are consistent with what would be suspected for the Hubble Flow, making it highly unlikely that the galaxies interacted with the Local Group since the Big Bang.
The high end of the stellar mass function of galaxies is observed to have little evolution since z~1. This represents a stringent constraint for merger--based models, aimed at explaining the evolution of the most massive galaxies in the concordance LambdaCDM cosmology. In this Letter we show that it is possible to remove the tension between the above observations and model predictions by allowing a fraction of stars to be scattered to the Diffuse Stellar Component (DSC) of galaxy clusters at each galaxy merger, as recently suggested by the analysis of N-body hydrodynamical simulations. To this purpose, we use the MORGANA model of galaxy formation in a minimal version, in which gas cooling and star formation are switched off after z=1. In this way, any predicted evolution of the galaxy stellar mass function is purely driven by mergers. We show that, even in this extreme case, the predicted degree of evolution of the high end of the stellar mass function is larger than that suggested by data. Assuming instead that a significant fraction, ~30 per cent, of stars are scattered in the DSC at each merger event, leads to a significant suppression of the predicted evolution, in better agreement with observational constraints, while providing a total amount of DSC in clusters which is consistent with recent observational determinations.
We present radio observations of 8 ultracool dwarfs with a narrow spectral type range (M8-M9.5) using the Very Large Array at 8.5 GHz. Only the tight M8 binary LP 349-25 was detected. LP 349-25 is the tenth ultracool dwarf system detected in radio and its trigonometric parallax pi = 67.6 mas, recently measured by Gatewood et al., makes it the furthest ultracool system detected by the Very Large Array to date, and the most radio-luminous outside of obvious flaring activity or variability.
Star formation may take place in a variety of locations in interacting systems: in the dense core of mergers, in the shock regions at the interface of the colliding galaxies and even within the tidal debris expelled into the intergalactic medium. Along tidal tails, objects may be formed with masses ranging from those of super-star clusters to dwarf galaxies: the so-called Tidal Dwarf Galaxies (TDGs). Based on a set of multi-wavelength observations and extensive numerical simulations, we show how TDGs may simultaneously be used as laboratories to study the process of star-formation (SFE, IMF) in a specific environment and as probes of various cosmological properties, such as the distribution of dark matter and satellites around galaxies.
We report the detection, for the first time, of HCO+ (J=1-0) emission as well as marginal CO (J=1-0) emission toward the planetary nebula (PN) K3-35 as a result of a molecular survey carried out toward this source. We also report new observations of the previously detected CO (J=2-1) and water maser emission, as well as upper limits for the emission of the SiO, H13CO+, HNC, HCN, HC3OH, HC5N, CS, HC3N, 13CO, CN, and NH3 molecules. From the ratio of CO (J=2-1) to CO (J=1-0) emission we have estimated the kinetic temperature of the molecular gas, obtaining a value of ~20 K. Using this result, we have estimated a molecular mass for the envelope of ~ 0.017 M_Sun, and an HCO+ abundance relative to H_2 of 6 X 10^-7, similar to the abundances found in other PNe. K~3-35 is remarkable because it is one of the two PNe reported to exhibit water maser emission, which is present in the central region as well as at a distance of $\simeq$ 5000 AU away from the center. The presence of molecular emission provides some clues that could help to understand the persistence of water molecules in the envelope of K 3-35. The HCO$^{+}$ emission could be arising in dense molecular clumps, that may provide the shielding mechanism which protects water molecules in this source.
One of the key aspects of a detector material for space-borne hard X-ray and gamma-ray telescopes is the rate of prompt and delayed background events generated inside the material by charged and neutral particles striking the detector. These particles are Cosmic Rays, particles trapped in Earth's magnetic field, and secondaries from Cosmic Ray interacting with the atmosphere and the spacecraft. Here, we present a preliminary study of Cadmium Zinc Telluride (CZT) and its behaviour in space environments. We have used the simulation package MGGPOD to estimate the background of the CZT detectors in the proposed Energetic X-ray Imaging Survey Telescope (EXIST) for possible orbital parameters. The EXIST mission will make use of 6 square meters of 0.5 cm thick CZT detectors to record cosmic X-rays in the energy range from 10 keV to 600 keV. The detectors will be shielded by a fully or partly active shield. For the specific detector and shielding geometry considered here and an orbit with a low (7 deg) inclination, the background rate is dominated by the diffuse extragalactic below 200 keV. Prompt and delayed hadronic backgrounds grow increasingly important above this energy, becoming the main contributors to the total background above 1 MeV. A fully active shield performs slightly better than a half active/half passive shield.
We present near-infrared polarimetric images of the dusty circumstellar envelope (CSE) of IRAS 19306+1407, acquired at the United Kingdom Infrared Telescope (UKIRT) using the UKIRT 1-5 um Imager Spectrometer (UIST) in conjunction with the half-waveplate module IRPOL2. We present additional 450 and 850 um photometry obtained with the Sub-mm Common User Bolometer Array (SCUBA) at the James Clerk Maxwell Telescope (JCMT), as well as archived Hubble Space Telescope (HST) F606W- and F814W-filter images. The CSE structure in polarized flux at J- and K-bands shows an elongation NNE-SSW with two bright scattering shoulders NW-SE. These features are not perpendicular to each other and could signify a recent `twist' in the outflow axis. We model the CSE using an axisymmetric light scattering (ALS) code to investigate the polarization produced by the CSE, and an axisymmetric radiation transport (DART) code to fit the SED. A good fit was achieved with the ALS and DART models using silicate grains, 0.1-0.4 um with a power-law size distribution of a^-3.5, and an axisymmetric shell geometry with an equator-to-pole contrast of 7:1. The spectral type of the central star is determined to be B1I supporting previous suggestions that the object is an early PN. We have constrained the CSE and interstellar extinction as 2.0 and 4.2 mag respectively, and have estimated a distance of 2.7 kpc. At this distance the stellar luminosity is ~4500 L_sun and the ~5300 yrs with a mass-loss rate of ~3.4x10^-5 M_sun yr^-1.
We have carried out a hydrodynamical code comparison study of interacting multiphase fluids. The two commonly used techniques of grid and smoothed particle hydrodynamics (SPH) show striking differences in their ability to model processes that are fundamentally important across many areas of astrophysics. Whilst Eulerian grid based methods are able to resolve and treat important dynamical instabilities, such as Kelvin-Helmholtz or Rayleigh-Taylor, these processes are poorly or not at all resolved by existing SPH techniques. We show that the reason for this is that SPH, at least in its standard implementation, introduces spurious pressure forces on particles in regions where there are steep density gradients. This results in a boundary gap of the size of the SPH smoothing kernel over which information is not transferred.
We have used 4752 days of data collected by the Birmingham Solar-Oscillations Network (BiSON) to determine very precise oscillation frequencies of acoustic low-degree modes that probe the solar core. We compare the fine (small frequency) spacings and frequency separation ratios formed from these data with those of different solar models. We find that models constructed with low metallicity are incompatible with the observations. The results provide strong support for lowering the theoretical uncertainties on the neutrino fluxes. These uncertainties had recently been raised due to the controversy over the solar abundances.
It is shown that, if gas accretion via a disk onto the central supermassive black hole is efficient only for surface density Sigma >= 10 g/cm^2, the black hole mass - galactic bulge velocity dispersion relation (Tremaine et al 2002) is naturally borne out, so is the modest dispersion in that relation, in the context of hierarchical structure formation theory. This relation is not expected to evolve with redshift in this model.
We consider the contribution of 3rd and 4th order terms to the power spectrum of 21 cm brightness temperature fluctuations during the epoch of reionization, which arise because the 21 cm brightness temperature involves a product of the hydrogenic neutral fraction and the gas density. The 3rd order terms vanish for Gaussian random fields, and have been previously neglected or ignored. We measure these higher order terms from radiative transfer simulations and estimate them using cosmological perturbation theory. In our simulated models, the higher order terms are significant: neglecting them leads to a >~100% error in 21 cm power spectrum predictions on scales of k >~ 1 Mpc^{-1} when the neutral fraction is <x_H>~0.5. The higher order terms have a simple physical interpretation. On small scales they are produced by gravitational mode coupling. Small scale structure grows more readily in large-scale overdense regions, but the same regions tend to be ionized and hence do not contribute to the 21 cm signal. This acts to suppress the influence of non-linear density fluctuations and the small-scale amplitude of the 21 cm power spectrum. These results modify earlier intuition that the 21 cm power spectrum simply traces the density power spectrum on scales smaller than that of a typical bubble, and imply that small scale measurements contain more information about the nature of the ionizing sources than previously believed. On large scales, higher order moments are not directly related to gravity. They are non-zero because over-dense regions tend to ionize first and are important in magnitude at late times owing to the large fluctuations in the neutral fraction. (Abridged)
We present sub-arcsecond imaging in [Ne V] of N49, the brightest optical SNR in the LMC. Between the "cool" optical and "hot" X-ray regimes, [Ne V] emission indicates intermediate temperatures for collisionally excited plasmas (2--6 x 10E5 K), for which imaging has been extremely limited. We compare the flux in these images to the O VI measured spectroscopically by FUSE in individual apertures and find dereddened line ratios that are reasonably consistent with our predictions for intermediate velocity shocks. The overall luminosity in [Ne V] for the entire remnant is 1.2E36 erg/s, which, given the measured line ratios, implies an overall O VI luminosity of 1.5E38 erg/s. These large radiative losses indicate that this material must have been shocked recently relative to the total lifetime of the remnant. We also explore the complex spatial structure. We find [Ne V] tracing the [O III] emission more closely than it does H-alpha, measure significant shifts (~0.1 pc) between the peaks of different emission lines, and find two orders of magnitude variations in the flux ratios for different filaments across the remnant. These properties as well as the general filamentary character of the optical emission suggest thermally unstable intermediate velocity shocks.
The phenomena customly described with the standard $\Lambda$CDM model are broadly reproduced by an extremely simple model in TeVeS, Bekenstein's (2004) modification of General Relativity motivated by galaxy phenomenology. Our model can account for the acceleration of the universe seen in SNeIa distances without a cosmological constant, and the accelerations seen rotation curves of nearby spiral galaxies and gravitational lensing of high-redshift elliptical galaxies without cold dark matter. The model is consistent with BBN and the neutrino mass. The TeVeS scalar field is shown to play the effective dural roles of Dark Matter and Dark Energy with the amplitudes of the effects controled by a $\mu$-function of the scalar field, called the $\mu-$essence here. We also discuss outliers to the theory's predictions on multi-imaged galaxy lenses and outliers on sub-galaxy scale.
We study the luminosity functions of high-redshift galaxies in detailed hydrodynamic simulations of cosmic reionization, which are designed to reproduce the evolution of the Lyman-alpha forest between z=5 and z=6. We find that the luminosity functions and total stellar mass densities are in agreement with observations when plausible assumptions about reddenning at z=6 are made. Our simulations support the conclusion that stars alone reionized the universe.
We have re-analyzed archival HST and Subaru data of the recently discovered planetary mass companion (PMC) GQ Lup B. With these we produce the first R and I band photometry of the companion and fit a radius and effective temperature using detailed model atmospheres. We find an effective temperature of 2335 +/- 100K, and a radius of 0.38 +/- 0.05 Rsol and luminosity of log(L/Lsol) = -2.42 +/- 0.07 (at 140pc). Since we fit wavelengths that span most of the emitted radiation from GQ Lup this luminosity estimate is robust, with uncertainty dominated by the distance uncertainty (+/- 50 pc). The radius obtained for 140pc (0.38Rsol) is significantly larger than the one originally derived and larger than model predictions. The mass of the object is much more model-dependent than the radiative properties, but for the GAIA dusty models we find a mass between 9-20 MJup, in the range of the brown dwarf and PMC deuterium burning boundary. Assuming a distance of 140pc, observations fit to 1sigma the Baraffe evolution model for a ~15 MJup brown dwarf. Additionally, the F606W photometric band is significantly overluminous compared to model predictions and other brown dwarfs. Such overluminosity could be explained by a bright Halpha emission from chromospheric activity, interaction with another undetected companion, or accretion. Assuming that GQ Lup B has a bright Halpha emission line, its Halpha emission strength is 10^(-1.71 +/- 0.10) Lbol, significantly larger than field late-type dwarfs. GQ Lup B might be strongly accreting and still be in its formation phase.
We derive a general ansatz for optimizing pseudo-C_l estimators used to measure CMB anisotropy power spectra, and apply it to the recently-proposed pure pseudo-C_l formalism, to obtain an estimator which achieves near-optimal B-mode power spectrum errors for any specified noise distribution while minimizing leakage from ambiguous modes. Our technique should be relevant for upcoming CMB polarization experiments searching for B-mode polarization. We compare our technique both to the theoretical limits based on a full Fisher matrix calculation and to the standard pseudo-C_l technique. We demonstrate it by applying it to a fiducial survey with realistic inhomogeneous noise, complex boundaries, point source masking, and noise level comparable to what is expected for next generation experiments (~5.75 uK-arcmin). For such an experiment our technique could improve the constraints on the amplitude of a gravity wave background by over a factor of ten compared to what could be obtained using ordinary pseudo-C_l, coming quite close to saturating the theoretical limit. Constraints on the amplitude of the lensing B-modes are improved by about a factor of 3.
We report the discovery of water maser emission in five active galactic nuclei (AGN) with the 100-m Green Bank Telescope (GBT). The positions of the newly discovered masers, measured with the VLA, are consistent with the optical positions of the host nuclei to within 1 sigma (0.3 arcsec radio and 1.3 arcsec optical) and most likely mark the locations of the embedded central engines. The spectra of three sources, 2MASX J08362280+3327383, NGC 6264, and UGC 09618 NED02, display the characteristic spectral signature of emission from an edge-on accretion disk with maximum orbital velocity of ~700, ~800, and ~1300 km s^-1, respectively. We also present a GBT spectrum of a previously known source MRK 0034 and interpret the narrow Doppler components reported here as indirect evidence that the emission originates in an edge-on accretion disk with orbital velocity of ~500 km s^-1. We obtained a detection rate of 12 percent (5 out of 41) among Seyfert 2 and LINER systems with 10000 km s^-1 < v_sys < 15000 km s^-1. For the 30 nuclear water masers with available hard X-ray data, we report a possible relationship between unabsorbed X-ray luminosity (2-10 keV) and total isotropic water maser luminosity, L_{2-10} proportional to L_{H2O}^{0.5+-0.1}, consistent with the model proposed by Neufeld and Maloney in which X-ray irradiation and heating of molecular accretion disk gas by the central engine excites the maser emission.
We report on the first results of an imaging survey for strong gravitational lensing which targets the richest optically selected clusters selected from photometric data of the Sloan Digital Sky Survey (SDSS) for follow-up deep imaging observations from the Wisconsin Indiana Yale NOAO 3.5m telescope and the University of Hawaii 88-inch telescope. The clusters are selected from an area of 8000 deg^2 using the Red Cluster Sequence technique and span the redshift range 0.1 < z < 0.6, corresponding to a cosmological volume of > Gpc^3. Our imaging survey thus targets a volume more than an order of magnitude larger than any previous search. A total of 240 clusters were imaged of which 141 had sub-arcsecond image quality. Our survey has uncovered 16 new lensing clusters with definite giant arcs, an additional 12 tentative systems for which the lensing interpretation is very likely, and 9 systems which contain shorter arclets or candidate arcs which are less certain and will require further observations to confirm their lensing origin. The number of new cluster lenses presented here is likely > 30. Among these new systems are some of the most dramatic examples of gravitational lensing ever discovered with multiple bright arcs at large angular separation. They will likely become `poster-child' gravitational lenses similar to Abell 1689 and CL0024+1654.
Understanding the nature of Dark Matter and Dark Energy is one of the most pressing issues in cosmology and fundamental physics. The purpose of the DUNE (Dark UNiverse Explorer) mission is to study these two cosmological components with high precision, using a space-based weak lensing survey as its primary science driver. Weak lensing provides a measure of the distribution of dark matter in the universe and of the impact of dark energy on the growth of structures. DUNE will also include a complementary supernovae survey to measure the expansion history of the universe, thus giving independent additional constraints on dark energy. The baseline concept consists of a 1.2m telescope with a 0.5 square degree optical CCD camera. It is designed to be fast with reduced risks and costs, and to take advantage of the synergy between ground-based and space observations. Stringent requirements for weak lensing systematics were shown to be achievable with the baseline concept. This will allow DUNE to place strong constraints on cosmological parameters, including the equation of state parameter of the dark energy and its evolution from redshift 0 to 1. DUNE is the subject of an ongoing study led by the French Space Agency (CNES), and is being proposed for ESA's Cosmic Vision programme.
The nature of a dark matter in the Universe can be connected with realization of the (plus/minus) Planck mass in final state of the beta-plus-decay of the nuclei Na-22, Ga-68, etc. and in a gravitational field of sufficient force. This hypothesis (the topological quantum transition - a generalized "displacement current") follows out of the phenomenological model that has explained the anomalies of the orthopositronium, forming in substance by the beta-decay positrons. Vacuumlike state of substance of the positive mass (Gliner, 1965) is structured in this model (the "microstructure" of vacuum) as the long-range "atom" with the Planck mass in the limited macroscopic "volume" of space-time. Accordingly, the negative mass C-field (Hoyle & Narlikar, 1964) plays the role of a compensating field.
We present a covariant formalism to study nonlinear perturbations of scalar fields. In particular, we consider the case of two scalar fields and introduce the notion of adiabatic and isocurvature covectors. We obtain differential equations governing the evolution of these two covectors, as well as the evolution equation for the covector associated to the curvature perturbation. The form of these equations is very close to the analogous equations obtained in the linear theory but our equations are fully nonlinear and exact. As an application of our formalism, we expand these equations at second order in the perturbations. On large scales, we obtain a closed system of coupled scalar equations giving the evolution of the second-order adiabatic and entropy perturbations in terms of the first-order perturbations. These equations in general contain a nonlocal term which, however, rapidly decays in an expanding universe.
We present new echelle spectrophotometry of the Galactic H II regions M8 and M17. The data have been taken with the VLT UVES echelle spectrograph in the 3100 to 10400 angstroms range. We have measured the intensities of 375 and 260 emission lines in M8 and M17 respectively, increasing significatively the number of emission lines measured in previous spectrophotometric studies of these nebulae. Most of the detected lines are permitted lines. Electron temperatures and densities have been determined using different diagnostics. We have derived He+, C++, O+ and O++ ionic abundances from pure recombination lines. We have also derived abundances from collisionally excited lines for a large number of ions of different elements. Highly consistent estimations of t2 have been obtained by using different independent indicators, the values are moderate and very similar to those obtained in other Galactic H II regions. We report the detection of deuterium Balmer emission lines, up to D$\epsilon$, in M8 and show that their intensities are consistent with continuum fluorescence as their main excitation mechanism.
We present new medium-resolution spectropolarimetric observations of HD 45677
in the B and R-bands. A change in polarisation is detected across Halpha, Hbeta
and Hgamma confirming that the ionised region around the star is aspherical.
(Q,U) points associated with these emission lines occur away from the
continuum, defining a polarisation vector which points in the same direction
for each of the lines at an average intrinsic polarisation angle of 164 +/- 3
degrees.
These data were combined with past photometric and polarimetric data from the
literature to investigate any variability. We find that HD 45677 is both
photometrically and polarimetrically variable and that these changes are
linked. We suggest that these variations may be caused by an aspherical blowout
and by deriving a least-squares fit to the B-band polarimetric data in Q-U
space, we show that the blowout occurs at an intrinsic polarisation angle of
175 +/- 1 degrees, along the same angle as the proposed geometry of the ionised
region.
Our multi-wavelength analysis of GRB 060124 shows the unusual behaviour of the decaying lightcurve as well as supporting the recently proposed phenomenon of long-lasting central engine activity. The prompt X-ray emission displays uncommonly well resolved flaring behaviour, with spectral evolution - indicative of central engine activity - which allows us to estimate the energy injection time for each flare. The otherwise smooth X-ray & optical afterglows demonstrate achromatic breaks at about 1 day which differ significantly from the usual jet break in the blastwave model of afterglows.
We determine the gas-phase oxygen abundance for a sample of 695 galaxies and H II regions with reliable detections of [O III]4363, using the temperature-sensitive Te method. Our aims are to estimate the validity of empirical methods such as R23, R23-P, log([N II]/Halpha) (N2), log[([O III]/Hbeta)/([N II]/Halpha)] (O3N2), and log([S II]/Halpha) (S2), and especially to re-derive (or add) the calibrations of R23, N2, O3N2 and S2 indices for oxygen abundances on the basis of this large sample of galaxies with Te-based abundances. We select 531 star-forming galaxies from the SDSS-DR4, and 164 galaxies and H II regions from literature for such study. Their (O/H) abundances obtained from Te are within 7.1<12+log(O/H)<8.5 mostly. For roughly half of the SDSS samples, the Bayesian abundances obtained by the MPA/JHU group are overestimated by ~0.34 dex compared with the Te-based (O/H) measurements, possibly due to the treatment of nitrogen enrichment in the models they used. R23 and R23-P methods systematically overestimate the O/H abundance by a factor of ~0.20 dex and ~0.06 dex, respectively. The N2 index, rather than the O3N2 index, provides relatively consistent O/H abundances with the Te-method, but with some scatter. The relations of N2, O3N2, S2 with log(O/H) are consistent with the photoionization model calculations of Kewley & Doptita (2002), but R23 does not match well. Then we derive analytical calibrations for O/H from R23, N2, O3N2 and S2 indices on the basis of this large sample of galaxies, especially including the excitation parameter P as an additional parameter in the N2 calibration. These can be used as calibration references in the future studies about metallicities of galaxies.
We study the physics of the solar tachocline and related MHD instabilities. We have performed 3-D MHD simulations of the solar radiative interior to check whether a fossil magnetic field is able to prevent the spread of the tachocline. Starting with a purely poloidal magnetic field and a latitudinal shear meant to be imposed by the convection zone at the top of the radiation zone, we have investigated the interactions between magnetic fields, rotation and shear, using the spectral code ASH on massive parallel supercomputers. In all cases we have explored, the fossil field diffuses outward and ends up connecting with the convection zone, whose differential rotation is then imprinted at latitudes above 40 deg throughout the radiative interior, according to Ferraro's law of isorotation. Rotation remains uniform in the lower latitude region which is contained within closed field lines. We find that the meridional flow cannot stop the inward progression of the differential rotation. Further, we observe the development of non-axisymmetric magnetohydrodynamic instabilities, first due to the initial poloidal configuration of the fossil field, and later to the toroidal field produced by shearing the poloidal field through the differential rotation. We do not find dynamo action as such in the radiative interior, since the mean poloidal field is not regenerated. But the instability persists during the whole evolution, while slowly decaying with the mean poloidal field. According to our numerical simulations, a fossil magnetic field cannot prevent the radiative spread of the tachocline, and thus it is unable to enforce uniform rotation in the radiation zone. Neither can the observed thinness of that layer be invoked as a proof for such an internal fossil magnetic field.
We have attempted to analyse all the available data taken by XMM-Newton as it slews between targets. This slew survey, the resultant source catalogue and the analysis procedures used are described in an accompanying paper. In this letter we present the initial science results from the survey. To date, detailed source-searching has been performed in three X-ray bands (soft, hard and total) in the EPIC-pn 0.2-12 keV band over ~6300 sq.degrees (~15% of the sky), and of order 4000 X-ray sources have been detected (~55% of which have IDs). A great variety of sources are seen, including AGN, galaxies, clusters and groups, active stars, SNRs, low- and high-mass XRBs and white dwarfs. In particular, as this survey constitutes the deepest ever hard-band 2-12 keV all-sky survey, a large number of hard sources are detected. Furthermore, the great sensitivity and low-background of the EPIC-pn camera are especially suited to emission from extended sources, and interesting spatial structure is observed in many supernova remnants and clusters of galaxies. The instrument is very adept at mapping large areas of the X-ray sky. Also, as the slew survey is well matched to the ROSAT all-sky survey, long-term variability studies are possible, and a number of extremely variable X-ray sources, some possibly due to the tidal disruption of stars by central supermassive black holes, have been discovered.
Recent progress on the nature of short duration Gamma Ray Bursts (GRBs) has shown that a fraction of them originate in the local universe. These systems may well be the result of giant flares from Soft Gamma Repeaters (SGRs) believed to be magnetars (neutron stars with extremely large magnetic fields >= 10^14 G). If these magnetars are formed via the core collapse of massive stars, then it would be expected that the bursts should originate from predominantly young stellar populations. However, correlating the positions of BATSE short bursts with structure in the local universe reveals a correlation with all galaxy types, including those with little or no ongoing star formation. This is a natural outcome if, in addition to magnetars forming via the core collapse of massive stars, they also form via Accretion Induced Collapse following the merger of two white dwarfs, one of which is magnetic. We investigate this possibility and find that the rate of magnetar production via WD-WD mergers in the Milky Way is comparable to the rate of production via core collapse. However, while the rate of magnetar production by core collapse is proportional to the star formation rate, the rate of production via WD-WD mergers (which have long lifetimes) is proportional to the stellar mass density, which is concentrated in early-type systems. Therefore magnetars produced via WD-WD mergers may produce SGR giant flares which can be identified with early type galaxies. We also comment on the possibility that this mechanism could produce a fraction of the observed short duration GRB population at low redshift.
Core convection and dynamo activity deep within rotating A-type stars of 2 solar masses are studied with 3--D nonlinear simulations. Our modeling considers the inner 30% by radius of such stars, thus capturing within a spherical domain the convective core and a modest portion of the surrounding radiative envelope. The MHD equations are solved using the ASH code to examine turbulent flows and magnetic fields, both of which exhibit intricate time dependence. By introducing small seed magnetic fields into our progenitor hydrodynamic models rotating at one and four times the solar rate, we assess here how the vigorous convection can amplify those fields and sustain them against ohmic decay. Dynamo action is indeed realized, ultimately yielding magnetic fields that are in energy equipartion with the flow. Such magnetism reduces the differential rotation obtained in the progenitors, partly by Maxwell stresses that transport angular momentum poleward and oppose the Reynolds stresses in the latitudinal balance. In contrast, in the radial direction we find that the Maxwell and Reynolds stresses may act together to transport angular momentum. The central columns of slow rotation established in the progenitors are weakened, with the differential rotation waxing and waning in strength as the simulations evolve. We assess the morphology of the flows and magnetic fields, their complex temporal variations, and the manner in which dynamo action is sustained. Differential rotation and helical convection are both found to play roles in giving rise to the magnetic fields. The magnetism is dominated by strong fluctuating fields throughout the core, with the axisymmetric (mean) fields there relatively weak.
The operation of the solar global dynamo appears to involve many dynamical elements. Self-consistent MHD simulations which realistically incorporate all of these processes are not yet computationally feasible, though some elements can now be studied with reasonable fidelity. Here we consider the manner in which turbulent compressible convection within the bulk of the solar convection zone can generate large-scale magnetic fields through dynamo action. We accomplish this through a series of three-dimensional numerical simulations of MHD convection within rotating spherical shells using our ASH code on massively parallel supercomputers. Since differential rotation is a key ingredient in all dynamo models, we also examine here the nature of the rotation profiles that can be sustained within the deep convection zone as strong magnetic fields are built and maintained. We find that the convection is able to maintain a solar-like angular velocity profile despite the influence of Maxwell stresses which tend to oppose Reynolds stresses and thus reduce the latitudinal angular velocity contrast throughout the convection zone. The dynamo-generated magnetic fields exhibit a complex structure and evolution, with radial fields concentrated in downflow lanes and toroidal fields organized into twisted ribbons which are extended in longitude and which achieve field strengths of up to 5000 G. The flows and fields exhibit substantial kinetic and magnetic helicity although systematic hemispherical patterns are only apparent in the former. Fluctuating fields dominate the magnetic energy and account for most of the back-reaction on the flow via Lorentz forces. Mean fields are relatively weak and do not exhibit systematic latitudinal propagation or periodic polarity reversals as in the sun. This may be attributed to the absence of a tachocline.
We reconsider the original model of quadratic hybrid inflation in light of the WMAP three-year results and study the possibility of obtaining a spectral index of primordial density perturbations, $n_s$, smaller than one from this model. The original hybrid inflation model naturally predicts $n_s\geq1$ in the false vacuum dominated regime but it is also possible to have $n_s<1$ when the quadratic term dominates. We therefore investigate whether there is also an intermediate regime compatible with the latest constraints, where the scalar field value during the last 50 e-folds of inflation is less than the Planck scale.
We study the vertical settling of solid bodies in a turbulent protoplanetary
disc. We consider the situation when the coupling to the gas is weak or
equivalently when the particle stopping time tau_{st} due to friction with the
gas is long compared to the orbital timescale Omega^{-1}. An analytical model,
which takes into account the stochastic nature of the sedimentation process
using a Fokker-Planck equation for the particle distribution function in phase
space, is used to obtain the vertical scale height of the solid layer as a
function of the vertical component of the turbulent gas velocity correlation
function and the particle stopping time. This is found to be of the same form
as the relation obtained for strongly coupled particles in previous work.
We compare the predictions of this model with results obtained from local
shearing box MHD simulations of solid particles embedded in a vertically
stratified disc in which there is turbulence driven by the MRI. We find that
the ratio of the dust disc thickness to the gas disc thickness satifies
H_d/H=0.08 (Omega tau_{st})^{-1/2}, which is in very good agreement with the
analytical model. By discussing the conditions for gravitational instability in
the outer regions of protoplanetary discs in which there is a similar level of
turbulence, we find that bodies in the size range 50 to 600 metres can
aggregate to form Kuiper belt-like objects with characteristic radii ranging
from tens to hundreds of kilometres.
The observed samples of supernovae (SN) and double compact objects (DCOs)
provide several critical constraints on population-synthesis models: the
parameters of these models must be carefully chosen to reproduce, among other
factors, (i) the formation rates of double neutron star (NS-NS) binaries and of
white dwarf-neutron star (WD-NS) binaries and (ii) the type II and Ib/c
supernova rates. Even allowing for extremely conservative accounting of the
uncertainties in observational and theoretical predictions, we find only a few
plausible population synthesis models
(roughly 9%) are consistent with DCO and SN rates empirically determined from
observations. As a proof of concept, we describe the information that can be
extracted about population synthesis models given such stringent observational
tests, including surprisingly good agreement with the observed pulsar proper
motion distribution. In the present study, we find that the current
observational constraints favor: kicks described by a single Maxwellian with a
typical velocity of about 300km/s; mass-loss fractions during non-conservative,
but stable, mass transfer episodes of about 90%; and common envelope parameters
of about 0.2-0.5. Finally, we use the subset of astrophysically consistent
models to predict the rates at which double black hole (BH-BH), black
hole-neutron star (BH-NS), and NS-NS binaries merge in the Milky Way through
the emission of gravitational waves.
A homogeneous spectroscopic analysis of unevolved and evolved stars in the metal-poor globular cluster NGC 6397 with FLAMES-UVES reveals systematic trends of stellar surface abundances that are likely caused by atomic diffusion. This finding helps to understand, among other issues, why the lithium abundances of old halo stars are significantly lower than the abundance found to be produced shortly after the Big Bang.
Narrow Line Seyfert 1 galaxies are generally accreting at high fractions of the Eddington limit. They can show complex X-ray spectra, with a strong `soft excess' below 2 keV and a sharp drop at ~7 keV. There is strong evidence linking the soft excess to either reflection or absorption from relativistic, partially ionized material close to the black hole. The reflection models can also simultaneously produce the 7 keV feature from fluorescent iron Ka line emission from the disc. Here we show that absorption can also produce a sharp feature at 7 keV from the P Cygni profile which results from absorption/scattering/emission of He- and H-like iron Ka resonance lines in the wind. We demonstrate this explicitly by fitting the iron feature seen in XMM-Newton data from 1H 0707-495 to a P Cygni profile. The resulting column and ionization required to produce this feature are probably larger than those needed to produce the soft excess. Nonetheless, the absorbing material could still be a single structure with stratified ionization such as that produced by the ionization instability.
We present the properties of the central stars from a sample of 54 Planetary Nebulae (PNe) observed in the Large Magellanic Cloud (LMC) with the Hubble Space Telescope Imaging Spectrograph (STIS). The Hubble Space Telescope's spatial resolution allows us to resolve the central star from its nebula (and line-of-sight stars) at the distance of the LMC, eliminating the dependency on photoionization modeling in the determination of the stellar flux. For the PNe in which the central star is detected we obtain the stellar luminosities by directly measuring the stellar fluxes through broad-band imaging and the stellar temperatures through Zanstra analysis. From the position of the central stars in the HR diagram with respect to theoretical evolutionary tracks, we are able to determine reliable core masses for 21 central stars. By including the central star masses determined in this paper to the 16 obtained previously using the same technique (Villaver et al. 2003), we have increased the sample of central star masses in the LMC to 37, for which we find a non-Gaussian mass distribution. The average central star mass for this sample is <m_CS, LMC>= 0.65\pm 0.07 Msun, slightly higher than the one reported in the literature for both white dwarfs and the central stars of PNe in the Galaxy. If significant, this higher average central star mass in the LMC can be understood in terms of a metallicity dependency on mass-loss rates during the Asymptotic Giant Branch, since the LMC has on average half the metallicity compared to the Galaxy. Finally, for the 37 objects analyzed in the LMC, we do not find any significant correlation between the mass of the central star and the morphology of the nebula.
We present $^{12}$CO(1-0) observations of the interacting galaxy system Arp 94, which contains the Seyfert galaxies NGC 3227 and NGC 3226 as well as the star-forming candidate dwarf galaxy J1023+1952. We mapped the CO distribution in J1023+1952 with the IRAM 30m telescope and found molecular gas across the entire extent of the neutral hydrogen cloud -- an area of about 9 by 6 kpc. The region where star formation (SF) takes place is restricted to a much smaller ($\sim$ 1.5 by 3 kpc) region in the south where the narrow line width of the CO shows that the molecular gas is dynamically cold. Neither the molecular nor the total gas surface density in the SF region are significantly higher than in the rest of the object suggesting that an external trigger is causing the SF. The fact that CO is abundant and apparently a good tracer for the molecular gas in J1023+1952 indicates that its metallicity is relatively high and argues for a tidal origin of this object.
We use high-resolution spectra obtained with the ESO Very Large Telescope to measure surface abundance patterns of 43 Blue Stragglers stars (BSS) in 47 Tuc. We discovered that a sub-population of BSS shows a significant depletion of Carbon and Oxygen with respect to the dominant population. This evidence would suggest the presence of CNO burning products on the BSS surface coming from a deeply peeled parent star, as expected in the case of mass-transfer process. This is the first detection of a chemical signature clearly pointing to a specific BSS formation process in a globular cluster.
Mean-motion resonances between a Keplerian disc and an orbiting companion are analysed within a Hamiltonian formulation using complex canonical Poincare variables, which are ideally suited to the description of eccentricity and inclination dynamics. Irreversibility is introduced by allowing for dissipation within the disc. A method is given for determining the rates of change of eccentricity and inclination variables of the disc and companion associated with resonances of various orders, including both reversible and irreversible effects, which extend and generalize previous results. Preliminary applications to protoplanetary systems and close binary stars are discussed.
We present the 12CO(1-0) and 13CO(2-1) line maps obtained observing with the SEST a $\sim 1\degr \times 1\degr$ region of the Vela Molecular Ridge, Cloud D. This cloud is part of an intermediate-mass star forming region that is relatively close to the Sun. Our observations reveal, over a wide range of spatial scales (from $\sim 0.1$ to a few parsecs), a variety of dense structures such as arcs, filaments and clumps, that are in many cases associated with far-IR point-like sources, recognized as young stellar objects and embedded star clusters. The velocity field analysis highlights the presence of possible expanding shells, extending over several parsecs, probably related to the star forming activity of the cloud. Furthermore, the analysis of the line shapes in the vicinity of the far-IR sources allowed the detection of 13 molecular outflows. Considering a hierarchical scenario for the gas structure, a cloud decomposition was obtained for both spectral lines by means of the CLUMPFIND algorithm. The CLUMPFIND output has been discussed critically and a method is proposed to reasonably correct the list of the identified clumps. We find that the corresponding mass spectrum shows a spectral index $\alpha\sim1.3 \div 2.0$ and the derived clump masses are below the corresponding virial masses. The mass-radius and velocity dispersion-radius relationships are also briefly discussed for the recovered clump population.
We present late-epoch optical photometry (BVRI) of seven normal/super-luminous Type Ia supernovae: SN 2000E, SN 2000ce, SN 2000cx, SN 2001C, SN 2001V, SN 2001bg, SN 2001dp. The photometry of these objects was obtained using a template subtraction method to eliminate galaxy light contamination during aperture photometry. We show the optical light curves of these supernovae out to epochs of up to ~640 days after the explosion of the supernova. We show a linear decline in these data during the epoch of 200-500 days after explosion with the decline rate in the B,V,& R bands equal to about 1.4 mag/100 days, but the decline rate of the I-band is much shallower at 0.94 mag/100 days.
We present the first multi-epoch radial velocity study of embedded young massive stars using near-infrared spectra obtained with ISAAC mounted at the ESO Very Large Telescope, with the aim to detect massive binaries. Our 16 targets are located in high-mass star-forming regions and many of them are associated to known ultracompact HI I regions, whose young age ensures that dynamic evolution of the clusters did not influence the intrinsic binarity rate. We identify two stars with about 90 km/s velocity differences between two epochs proving the presence of close massive binaries. The fact that 2 out of the 16 observed stars are binary systems suggests that at least 20% of the young massive stars are formed in close multiple systems, but may also be consistent with most if not all young massive stars being binaries. In addition, we show that the radial velocity dispersion of the full sample is about 35 km/s, significantly larger than our estimated uncertainty (25 km/s). This finding is consistent with similar measurements of the young massive cluster 30 Dor which might have a high intrinsic binary rate. Furthermore, we argue that virial cluster masses derived from the radial velocity dispersion of young massive stars may intrinsically overestimate the cluster mass due to the presence of binaries.
Phase-resolved VLT spectroscopy of the bursting Low Mass X-ray Binaries 4U 1636-536/V801 Ara and 4U 1735-444/V926 Sco is presented. Doppler images of the NIII 4640 Bowen transition reveal compact spots which we attribute to fluorescent emission from the donor star and enable us to define a new set of spectroscopic ephemerides. We measure Kem=277+-22 km/s and Kem=226+-22 km/s from the NIII spots in V801 Ara and V926 Sco respectively which represent strict lower limits to the radial velocity semi-amplitude of the donor stars. Our new ephemerides provide confirmation that lightcurve maxima in V801 Ara and likely V926 Sco occur at superior conjunction of the donor star and hence photometric modulation is caused by the visibility of the X-ray heated donor. The velocities of HeII 4686 and the broad Bowen blend are strongly modulated with the orbital period, with phasing supporting emission dominated by the disc bulge. In addition, a reanalysis of burst oscillations in V801 Ara, using our spectroscopic T0, leads to K1=90-113 km/s. We also estimate the K-corrections for all possible disc flaring angles and present the first dynamical constraints on the masses of these X-ray bursters. These are K2=360+-74 km/s, f(M)=0.76+-0.47 Msun and q=0.21-0.34 for V801 Ara and K2=298+-83 km/s, f(M)=0.53+-0.44 Msun and q=0.05-0.41 for V926 Sco. Disc flaring angles alpha>12 deg and q~0.26-0.34 are favoured for V801 Ara whereas the lack of K1 constraint for V926 Sco prevents tight constraints on this system. Although both binaries seem to have intermediate inclinations, the larger equivalent width of the narrrow NIII line in V801 Ara at phase 0.5 relative to phase 0 suggests that it has the higher inclination of the two.
We discuss axisymmetric force-free pulsar magnetospheres with magnetically
collimated jets and a disk-wind obtained by numerical solution of the pulsar
equation.
This solution represents an alternative to the quasi-spherical wind solutions
where a major part of the current flow is in a current sheet which is unstable
to magnetic field annihilation.
Ram pressure stripping is an important process in the evolution of both dwarf galaxies and large spirals. Large spirals are severely stripped in rich clusters and may be mildly stripped in groups. Dwarf galaxies can be severely stripped in both clusters and groups. A model is developed that describes the stripping of a satellite galaxy's outer H \textsc{i} disk and hot galactic halo. The model can be applied to a wide range of environments and satellite galaxy masses. Whether ram pressure stripping of the outer disk or hot galactic halo occurs is found to depend primarily on the ratio of the satellite galaxy mass to the mass of the host group or cluster. How the effectiveness of ram pressure stripping depends on the density of the inter-group gas, the dark matter halo concentrations, and the scale lengths and masses of the satellite components is explored. The predictions of the model are shown to be well matched to H \textsc{i} observations of spirals in a sample of nearby clusters. The model is used to predict the range of H \textsc{i} gas fractions a satellite of mass $M_{v,sat}$ can lose orbiting in a cluster of mass $M_{v,gr}$.
Ram pressure stripping may be one of the dominant mechanisms driving the evolution of galaxies in groups and clusters. In this paper, models of ram pressure stripping are confronted with observations of galaxy colors and star formation rates using a group catalog drawn from the Sloan Digital Sky Survey and model predictions based on an analytical model of stripping presented in Hester (2006). An observed increase in the fraction of galaxies residing on the red sequence, the red fraction, with both increasing group mass, $M_{gr}$, and decreasing satellite luminosity, $L_{sat}$, can be understood using the model. The size of the change in the red fraction with changing $M_{gr}$ or $L_{sat}$ can be understood in terms of the effect of the scatter in satellite and cluster morphologies and satellite orbits on the relationship between $M_{gr}$ and $L_{sat}$ and the stripped gas fraction. Observations of the group galaxies' H$\delta$ and 4000\AA break spectral measures and a comparison of the distribution of $SFR/M_{\ast}$ for star forming galaxies in the groups and in isolation both indicate that the color differences observed in the groups are the result of slowly declining SFRs, as expected if the color change is driven by stripping of the outer H \textsc{i} disk.
We investigate the effect of an assembly history on the evolution of dark matter (DM) halos of 10^{12} Msun/h using Constrained Realizations of random Gaussian fields. Five different realizations of a DM halo with distinct merging histories were constructed and evolved. Our main results are: A halo evolves via a sequence of quiescent phases of a slow mass accretion intermitted by violent episodes of major mergers. In the quiescent phases, the density is well fitted by an NFW profile, the inner scale radius Rs and the mass enclosed within it remain constant, and the virial radius (Rvir) grows linearly with the expansion parameter "a". Within each quiescent phase the concentration parameter ("c") scales as "a", and the mass accretion history (Mvir) is well described by the Tasitsiomi etal. fitting formula. In the violent phases the halos are not in a virial equilibrium and both Rs and Rvir grow discontinuously. The violent episodes drive the halos from one NFW dynamical equilibrium to another. The final structure of a halo, including "c", depends on the degree of violence of the major mergers and on their number. Next, we find a distinct difference between the behavior of various NFW parameters taken as averages over an ensemble of halos and those of individual halos. Moreover, the simple scaling relations c--Mvir do not apply to the entire evolution of individual halos, and so is the common notion that late forming halos are less concentrated than early forming ones. The entire evolution of the halo cannot be fitted by single analytical expressions.
Putative organisms on the Martian surface would be exposed to potentially high doses of ionizing radiation during strong solar X-ray flares. We extrapolate the observed flare frequency-energy release scaling relation to releases much larger than seen so far for the sun, an assumption supported by observations of flares on other solar- and subsolar-mass main sequence stars. We calculate the surficial reprocessed X-ray spectra using a Monte Carlo code we have developed. Biological doses from indirect genome damage are calculated for each parameterized flare spectrum by integration over the X-ray opacity of water. We estimate the mean waiting time for solar flares producing a given biological dose of ionizing radiation on Mars and compare with lethal dose data for a wide range of terrestrial organisms. These timescales range from decades for significant human health risk to 0.5 Myr for D. radiodurans lethality. Such doses require total flare energies of 10^33--10^38 erg, the lower range of which has been observed for other stars. Flares are intermittent bursts, so acute lethality will only occur on the sunward hemisphere during a sufficiently energetic flare, unlike low-dose-rate, extended damage by cosmic rays. We estimate the soil and CO_2 ice columns required to provide 1/e shielding as 4--9 g cm^-2, depending on flare mean energy and atmospheric column density. Topographic altitude variations give a factor of two variation in dose for a given flare. Life in ice layers that may exist ~ 100 g cm^-2 below the surface would be well protected.
If the dark energy equation of state parameter w(z) crosses the phantom divide line w=-1 (or equivalently if the expression d(H^2(z))/dz - 3\Omega_m H_0^2 (1+z)^2 changes sign) at recent redshifts, then there are two possible cosmological implications: Either the dark energy consists of multiple components with at least one non-canonical phantom component or general relativity needs to be extended to a more general theory on cosmological scales. The former possibility requires the existence of a phantom component which has been shown to suffer from serious theoretical problems and instabilities. Therefore, the later possibility is the simplest realistic theoretical framework in which such a crossing can be realized. After providing a pedagogical description of various dark energy observational probes, we use a set of such probes (including the Gold SnIa sample, the first year SNLS dataset, the 3-year WMAP CMB shift parameter, the SDSS baryon acoustic oscillations peak (BAO), the X-ray gas mass fraction in clusters and the linear growth rate of perturbations at z=0.15 as obtained from the 2dF galaxy redshift survey) to investigate the priors required for cosmological observations to favor crossing of the phantom divide. We find that a low \Omega_m prior (0.2<\Omega_m <0.25) leads, for most observational probes (except of the SNLS data), to an increased probability (mild trend) for phantom divide crossing. An interesting degeneracy of the ISW effect in the CMB perturbation spectrum is also pointed out.
Planetesimal accretion during planet formation is usually treated as collisionless. Such accretion from a uniform and dynamically cold disk predicts protoplanets with slow retrograde rotation. However, if the building blocks of protoplanets, planetesimals, are small, of order of a meter in size, then they are likely to collide within the protoplanet's sphere of gravitational influence, creating a prograde accretion disk around the protoplanet. The accretion of such a disk results in the formation of protoplanets spinning in the prograde sense with the maximal spin rate allowed before centrifugal forces break them apart. As a result of semi-collisional accretion, the final spin of a planet after giant impacts is not completely random but is biased toward prograde rotation. The eventual accretion of the remaining planetesimals in the post giant-impact phase might again be in the semi-collisional regime and delivers a significant amount of additional prograde angular momentum to the terrestrial planets. We suggest that in our Solar System, semi-collisional accretion gave rise to the preference for prograde rotation observed in the terrestrial planets and perhaps the largest asteroids.
It is possible that the properties of HII regions during reionization depend sensitively on many poorly constrained quantities (the nature of the ionizing sources, the clumpiness of the gas in the IGM, the degree to which photo-ionizing feedback suppresses the abundance of low mass galaxies, etc.), making it extremely difficult to interpret upcoming observations of this epoch. We demonstrate that the actual situation is more encouraging, using a suite of radiative transfer simulations, post-processed on outputs from a 1024^3, 94 Mpc N-body simulation. Analytic prescriptions are used to incorporate small scale structures that affect reionization, yet remain unresolved in the N-body simulation. We show that the morphology of the HII regions is most dependent on the global ionization fraction x_i. This is not to say that the bubble morphology is completely independent of all parameters besides x_i. The next most important dependence is that of the nature of the ionizing sources. The rarer the sources, the larger and more spherical the HII regions become. The typical bubble size can vary by as much as a factor of 4 at fixed x_i between different possible source prescriptions. The final relevant factor is the abundance of minihalos or of Lyman-limit systems. These systems suppress the largest bubbles from growing, and the magnitude of this suppression depends on the thermal history of the gas as well as the rate at which minihalos are photo-evaporated. We find that neither source suppression owing to photo-heating nor gas clumping significantly affect the large scale structure of the HII regions. We discuss how observations of the 21cm line with MWA and LOFAR can constrain properties of reionization, and we study the effect patchy reionization has on the statistics of Lyman-alpha emitting galaxies. [abridged]
The interaction between supernova ejecta and circumstellar matter, arising from previous episodes of mass loss, provides us with a means with which to constrain the progenitors of supernovae. Radio observations of a number of supernovae show quasi-periodic deviations from a strict power-law decline at late times. Although several possibilities have been put forward to explain these modulations, no single explanation has proven to be entirely satisfactory. Here we suggest that Luminous Blue Variables undergoing S-Doradus type variations give rise to enhanced phases of mass loss which are imprinted on the immediate environment of the exploding star as a series of density enhancements. The variations in mass loss arise from changes in the ionization balance of Fe, the dominant ion that drives the wind. With this idea, we find that both the recurrence timescale of the variability, as well as the amplitude of the modulations are in line with the observations. Our scenario thus provides a natural, single-star explanation for the observed behaviour that is, in fact, expected on theoretical grounds.
We present Gemini GMOS and Magellan LDSS-3 optical spectroscopy for seven ultracool subdwarf candidates color-selected from the Two Micron All Sky Survey. Five are identified as late-type subdwarfs, including the previously reported sdM9.5 SSSPM 1013-1356 and L subdwarf 2MASS 1626+3925, and a new sdM8.5 2MASS 0142+0523. 2MASS 1640+1231 exhibits spectral features intermediate between a late-type M dwarf and subdwarf, similar to the previously identified high proper motion star SSSPM 1444-2019, and we classify both sources as mild subdwarfs, d/sdM9. 2MASS 1227-0447 is a new ultracool extreme subdwarf, spectral type esdM7.5. Spectral model fits yield metallicities that are consistent with these metallicity classifications. Effective temperatures track with numerical subtype within a metallicity class, although they are not equivalent across metallicity classes. As a first attempt to delineate subtypes in the L subdwarf regime we classify 2MASS 1626+3925 and the previously identified 2MASS 0532+8246 as sdL4 and sdL7, respectively, to reflect their similarity to equivalently classified, solar metallicity L-type field dwarfs over the 7300-9000 A region. We also detail preliminary criteria for distinguishing L subdwarf optical spectra as a roadmap for defining this new spectral class. The strong TiO bands and Ca I and Ti I lines in the spectrum of 2MASS 1626+3925 provide further evidence that condensate formation may be inhibited in metal-deficient L subdwarfs. We conclude with a compendium of currently known, optically classified ultracool subdwarfs.
Using five independent analytic and Monte Carlo simulation codes, we have studied the performance of wide field ground layer adaptive optics (GLAO), which can use a single, relatively low order deformable mirror to correct the wavefront errors from the lowest altitude turbulence. GLAO concentrates more light from a point source in a smaller area on the science detector, but unlike traditional adaptive optics, images do not become diffraction-limited. Rather the GLAO point spread function (PSF) has the same functional form as a seeing-limited PSF, and can be characterized by familiar performance metrics such as Full-Width Half-Max (FWHM). The FWHM of a GLAO PSF is reduced by 0.1" or more for optical and near-infrared wavelengths over different atmospheric conditions. For the Cerro Pachon atmospheric model this correction is even greater when the image quality is worst, which effectively eliminates "bad-seeing" nights; the best seeing-limited image quality, available only 20% of the time, can be achieved 60 to 80% of the time with GLAO. This concentration of energy in the PSF will reduce required exposure times and improve the efficiency of an observatory up to 30 to 40%. These performance gains are relatively insensitive to a number of trades including the exact field of view of a wide field GLAO system, the conjugate altitude and actuator density of the deformable mirror, and the number and configuration of the guide stars.
More than 200 extrasolar planets have been discovered around relatively nearby stars, primarily through the Doppler line shifts owing to the reflex motions of their host stars, and more recently through transits of some planets across the face of the host stars. The detection of planets with the shortest known periods, 1.2 to 2.5 days, has mainly resulted from transit surveys which have generally targeted stars more massive than 0.75 M_sun. Here we report the results from a planetary transit search performed in a rich stellar field towards the Galactic bulge. We discovered 16 candidates with orbital periods between 0.4 and 4.2 days, five of which orbit stars of 0.44 to 0.75 M_sun. In two cases, radial-velocity measurements support the planetary nature of the companions. Five candidates have orbital periods below 1.0 day, constituting a new class of ultra-short-period planets (USPPs), which occur only around stars of less than 0.88 M_sun. This indicates that those orbiting very close to more luminous stars might be evaporatively destroyed, or that jovian planets around lower-mass stars might migrate to smaller radii.
We examine the age-dependence of dark matter halo clustering in an unprecedented accuracy using a set of 7 high-resolution cosmological simulations each with $N=1024^3$ particles. We measure the bias parameters for halos over a large mass range using the cross-power-spectrum method that can effectively suppress the random noise even in the sparse sampling of the most massive halos. This enables us to find, for the first time, that younger halos are more strongly clustered than older ones for halo masses $M>10M_{\ast}$, where $M_\ast$ is the characteristic nonlinear mass scale. For $M<M_{\ast}$, our results confirm the previous finding of Gao et al. that older halos are clustered more strongly than the younger ones. We also study the halo bias as a function of halo concentration, and find that the concentration dependence is weaker than the age dependence for $M<M_{\ast}$, but stronger for $M\ga 50 M_{\ast}$. The accurate and robust measurement of the age dependences of halo bias points to a limitation of the simple excursion set theory which predicts that the formation and structure of a halo of given mass is independent of its environment.
The persistent symbiosis of the craters and volcanoes without exception, in both terrestrial and celestial bodies, raises suspicion that they are deeply correlated with each other, and their relation may run even deeper to include gravity.
A {\em Spitzer} IRAC survey of 17 nearby metal-rich white dwarfs, nominally DAZ stars, reveals excess emission from only 3 targets: G29-38, GD 362 and G167-8. Observations of GD 362 with all three {\em Spitzer} instruments reveals a warm ($\approx1000$ K) dust continuum, very strong silicate emission, and the likely presence of cooler ($\approx500$ K) dust. While there is a general similarity between the mid-infrared spectral energy distributions of G29-38 and GD 362, the IRAC fluxes of G167-8 are so far unique among white dwarfs. However, further observations of G167-8 are required before the measured excess can be definitely associated with the white dwarf.
There is currently debate over whether the dust content of planetary systems is stochastically regenerated or originates in planetesimal belts evolving in steady state. In this paper a simple model for the steady state evolution of debris disks due to collisions is developed and confronted with the properties of the emerging population of 8 sun-like stars that have hot dust <10AU. The model shows there is a maximum possible disk mass at a given age, since more massive primordial disks process their mass faster. The corresponding maximum dust luminosity is f_max=0.00016r^(7/3)/t_age. The majority (5/8) of the hot disks exceed this limit by >1000 and so cannot be the products of massive asteroid belts, rather the following systems must be undergoing transient events characterized by an unusually high dust content near the star: eta Corvi, HD69830, HD72905, BD+20307 and HD128400. It is also shown that the hot dust cannot originate in a recent collision in an asteroid belt, since there is also a maximum rate at which collisions of sufficient magnitude to reproduce a given dust luminosity can occur. Further it is shown that the planetesimal belt feeding the dust in these systems must be located further from the star than the dust, typically at >2AU. Other notable properties of the 5 hot dust systems are: two also have a planetesimal belt at >10AU (eta Corvi and HD72905); one has 3 Neptune mass planets at <1AU (HD69830); all but one exhibit strong silicate features in the mid-IR. We consider the most likely origin for the dust in these systems to be a dynamical instability which scattered planetesimals inwards from a more distant planetesimal belt in an event akin to the Late Heavy Bombardment in our own system, the dust being released from such planetesimals in collisions and possibly also sublimation.
Context: We report new polarization measurements of the variable near-infrared emission of the SgrA* counterpart associated with the massive 3--4 10^6 solar masses Black Hole at the Galactic Center. Aims: We investigate the physical processes responsible for the variable emission from SgrA*. Methods: The observations have been carried out using the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope Results: We find that the variable NIR emission of SgrA* is highly polarized and consists of a contribution of a non- or weakly polarized main flare with highly polarized sub-flares. The flare activity shows a possible quasi-periodicity of 20+-3 minutes consistent with previous observations. Conclusions: The highly variable and polarized emission supports that the NIR emission is non-thermal. The observations can be interpreted in a jet or temporary disk model. In the disk model the quasi-periodic flux density variations can be explained due to spots on relativistic orbits around the central MBH. Alternative explanations for the high central mass concentration involving boson or fermion balls are increasingly unlikely.
Context: Recent near-infrared polarization measurements of SgrA* show that its emission is significantly polarized during flares and consists of a non- or weakly polarized main flare with highly polarized sub-flares. The flare activity suggests a quasi-periodicity of ~20 minutes in agreement with previous observations. Aims: By simultaneous fitting of the lightcurve fluctuations and the time-variable polarization angle, we address the question of whether these changes are consistent with a simple hot spot/ring model, in which the interplay of relativistic effects plays the major role, or whether some more complex dependency of the intrinsic emissivity is required. Methods: We discuss the significance of the 20min peak in the periodogram of a flare from 2003. We consider all general relativistic effects that imprint on the polarization degree and angle and fit the recent polarimetric data, assuming that the synchrotron mechanism is responsible for the intrinsic polarization and considering two different magnetic field configurations. Results: Within the quality of the available data, we think that the model of a single spot in addition to an underlying ring is favoured. In this model the broad near-infrared flares of Sgr A* are due to a sound wave that travels around the MBH once while the sub-flares, superimposed on the broad flare, are due to transiently heated and accelerated electrons which can be modeled as a plasma blob. Within this model it turns out that a strong statement about the spin parameter is difficult to achieve, while the inclination can be constrained to values > 35 deg on a 3sigma level.
Wide field near-infrared observations and Spitzer Space Telescope IRAC observations of the DR21/W75 star formation regions are presented. The photometric data are used to analyse the extinction, stellar content and clustering in the entire region by using standard methods. A young stellar population is identified all over the observed field, which is found to be distributed in embedded clusters that are surrounded by a distributed halo population extending over a larger projected area. The Spitzer/IRAC data are used to compute a spectral index value, "alpha", for each YSO in the field. We use these data to separate pure photospheres from disk excess sources. We find a small fraction of sources with "alpha" in excess of 2 to 3 (plus a handful with "alpha"~4), which is much higher than the values found in the low mass star forming region IC348 ("alpha" < 2). The sources with high values of "alpha" spatially coincide with the densest regions of the filaments and also with the sites of massive star formation. Star formation is found to be occuring in long filaments stretching to few parsecs that are fragmented over a scale of ~ 1 pc. The spatial distribution of young stars are found to be correlated with the filamentary nebulae that are prominently revealed by 8micron and 850micron observations. Five filaments are identified that appear to converge on a center that includes the DR21/DR21(OH) regions. The morphological pattern of filaments and clustering compare well with numerical simulations of star cluster formation by Bate et al. 2003.
Observations of stellar prominences on young rapidly rotating stars provide unique probes of their magnetic fields out to many stellar radii. We compare two independently obtained datasets of the K3 dwarf Speedy Mic using the Anglo-Australian Telescope (AAT) and the ESO Very Large Telescope (VLT). Taken more than a fortnight apart they provide the first insight into the evolution of the prominence system on such a young rapidly rotating star. The largest prominences observed transiting the stellar disc are found at very similar rotational phases between the epochs. This suggests that the magnetic structures supporting the prominences retain their identity on a two to three week timescale. We identify prominences as transient absorption features in all lines of the Hydrogen Balmer series down to H_10. We use the ratios of the prominence EWs in these lines to determine their column densities in the first excited state of hydrogen. We determine the optical depths, finding prominences to be rather optically thick (\tau \approx 20) in the H_alpha line. The total hydrogen column density and thus the prominence masses are determined via observations of the CaII H&K lines. We find typical masses for four of the largest prominences to be in the range 0.5 - 2.3 x10^{14} kg, slightly larger than giant solar prominence masses. Rotationally modulated emission is seen outside of the H_alpha line. These loops of emission are shown to be caused by prominences seen off the stellar disc. We find that all of the large emission loops can be associated with prominences we see transiting the stellar disc. This combined with the fact that many prominences appear to eclipse the off-disc emission of others, strongly suggests that the prominence system is highly flattened and likely confined to low stellar latitudes.
A new scenario for the interaction of a jet with a background medium with cold clouds is investigated by means of hydrodynamic turbulence simulations with cooling. The idea is that the cold clouds are overtaken by a radio cocoon and stirred up by turbulence in this cocoon. The 2D multiphase turbulence simulations contain all the three gas phases and have a number of interesting properties. The produced power spectrum is proportional to the inverse square of the wavevector. The Mach number - density relation may explain the observed velocities in emission line gas associated with radio galaxies. The model also explains the increased optical visibility within the radio structures, the correlation between emission line and radio luminosity, and the evolution of the alignment effect with source size. I also propose this to be a useful model for the recently discovered neutral outflows in nearby radio sources.
The outbursts of low mass X-ray binaries are prolonged relative to those of dwarf nova cataclysmic variables as a consequence of X-ray irradiation of the disc. We show that the time-scale of the decay light curve and its luminosity at a characteristic time are linked to the radius of the accretion disc. Hence a good X-ray light curve permits two independent estimates of the disc radius. In the case of the milli-second pulsars SAX J1808.4-3658 and XTE J0929-314 the agreement between these estimates is very strong. Our analysis allows new determinations of distances and accretion disc radii. Our analysis will allow determination of accretion disc radii for sources in external galaxies, and hence constrain system parameters where other observational techniques are not possible. We also use the X-ray light curves to estimate the mass transfer rate. The broken exponential decay observed in the 2002 outburst of SAX J1808.4-3658 may be caused by the changing self-shadowing of the disc.
We present the Galactic model parameters for thin disc estimated by Sloan Digital Sky Survey (SDSS) data of 14 940 stars with apparent magnitudes $16<g_{o}\leq21$ in six intermediate latitude fields in the first Galactic quadrant. Star/galaxy separation was performed by using the $SDSS$ photometric pipeline and the isodensity contours in the $(g-r)_{0}-(r-i)_{0}$ two colour diagram. The separation of thin disc stars is carried out by the bimodal distribution of stars in the $(g-r)_{o}$ histogram, and the absolute magnitudes were evaluated by a procedure presented in the literature Bilir et al. (2005). Exponential density law fits better to the derived density functions for the absolute magnitude intervals $8<M(g)\leq9$ and $11<M(g)\leq12$, whereas sech/sech$^{2}$ laws are more appropriate for absolute magnitude intervals $9<M(g)\leq10$ and $10<M(g)\leq11$. We showed that the scaleheight and scalelength are Galactic longitude dependent. The average values and ranges of the scaleheight and the scalelength are $<H>=220$ pc ($196\leq H \leq 234$ pc) and $<h>=1900$ pc ($1561\leq h \leq 2280$ pc) respectively. This result would be useful to explain different numerical values claimed for those parameters obtained by different authors for the fields in different directions of the Galaxy.
We provide an analytical approach to the second-order Cosmic Microwave Background (CMB) anisotropies generated by the non-linear dynamics taking place at last scattering. We study the acoustic oscillations of the photon-baryon fluid in the tight coupling limit and we extend at second-order the Meszaros effect.We allow for a generic set of initial conditions due to primordial non-Gaussianity and we compute all the additional contributions arising at recombination. Our results are useful to provide the full second-order radiation transfer function at all scales necessary for establishing the level of non-Gaussianity in the CMB.
Broadening and asymmetry of spectral lines in slowly rotating late A-type stars provide evidence for high-amplitude convective motions. The properties of turbulence observed in the A-star atmospheres are not understood theoretically and contradict results of previous numerical simulations of convection. Here we describe an ongoing effort to understand the puzzling convection signatures of A stars with the help of 3-D hydrodynamic simulations. Our approach combines realistic spectrum synthesis and non-grey hydrodynamic models computed with the CO5BOLD code. We discuss these theoretical predictions and confront them with high-resolution spectra of A stars. Our models have, for the first time, succeeded in reproducing the observed profiles of weak spectral lines without introducing fudge broadening parameters.
An XMM-Newton observation of the bright QSO PG1211+143 in 2001 revealed a blue-shifted absorption line spectrum indicative of a high velocity radial outflow of highly ionised gas. Unless highly collimated, the outflow mass rate was shown to be comparable to the accretion rate, with mechanical energy a significant fraction of the bolometric luminosity. Analysis of the full XMM-Newton data set now allows the wider effects of that energetic outflow to be explored. We find that absorption and re-emission of the primary continuum flux in the ionised outflow, together with a second, less strongly absorbed, continuum component can explain the strong `soft excess' in PG1211+143 without the extreme velocity `smearing' in conflict with observed absorption line widths. Previously unpublished data from a second XMM-Newton observation of PG1211+143 is shown to be consistent with the new spectral model, finding that the additional continuum component dominates the spectral variability. We speculate that this variable continuum component is powered by the high velocity outflow.
I discuss several aspects of secular evolution linked to bars and to boxy/peanut bulges, based on a very large number of high resolution, fully self-consistent $N$-body simulations. When the bar forms, it is as thin as the disc. Its three-dimensional shape, however, evolves, so that, at later times, it has a thick inner part and a thin, more extended outer part. The former, when viewed edge-on, is called a boxy/peanut bulge, because of its shape. The strength of the box/peanut correlates with the bar strength, the strongest cases having formed after two buckling episodes. The extent of the box/peanut is considerably shorter than the bar length, in good agreement with orbital structure studies and with observations. Viewed at an angle near to, but not quite edge-on, barred galaxies show specific isodensity/isophotal shapes, which are different in the thick and in the thin part of the bar. The isophotes of M31 also have such shapes. This, taken together with radial photometric profiles and kinematics, argue that M31 is a barred galaxy. Thus, the pseudo-ring seen at roughly 50' could be an outer ring formed at the outer Lindblad resonance of the bar.
We have obtained moderately deep radio continuum imaging at 18 and 22cm with the Westerbork array of 34 nearby galaxies drawn from the Spitzer SINGS and Starburst samples to enable complimentary analysis. The sub-sample have an optical major axis diameter in excess of 5 arcmin and are North of Declination 12.5 deg. Sub-sample galaxies span a very wide range of morphological types and star formation rates. Resolved detection was possible for every galaxy. This constitutes a first time detection at GHz radio frequencies for about half of the sample. Analysis of both total intensity and polarization properties of the sample will be published in companion papers. Both the HI and OH main-lines of the target galaxies were within the observed band-pass, albeit with only coarse velocity resolution. Only two low mass elliptical galaxies were undetected in HI. Four of the sub-sample galaxies were detected in OH main-line absorption, including two new detections. The results are presented in the form of an image atlas for which a standard transfer function and image size are used throughout and whereby the radio continuum, DSS optical and integrated HI are displayed side-by-side. Continuum and HI line photometry are tabulated for all targets.
We report measurements of the Sunyaev-Zel'dovich (SZ) effect in three high-redshift (0.89 < z < 1.03), X-ray selected galaxy clusters. The observations were obtained at 30 GHz during the commissioning period of a new, eight-element interferometer -- the Sunyaev-Zel'dovich Array (SZA) -- built for dedicated SZ effect observations. The SZA observations are sensitive to angular scales larger than those subtended by the virial radii of the clusters. Assuming isothermality and hydrostatic equilibrium for the intracluster medium, and gas-mass fractions consistent with those for clusters at moderate redshift, we calculate electron temperatures, gas masses, and total cluster masses from the SZ data. The SZ-derived masses, integrated approximately to the virial radii, are 1.9 ^{+0.5}_{-0.4}x10^{14} solar masses for CLl1415.1+3612, 3.4^{+0.6}_{-0.5}x10^{14} solar masses for CL1429.0+4241, and 7.2^{+1.3}_{-0.9}x10^{14} solar masses for CL1226.9+3332. The SZ-derived quantities are in good agreement with the cluster properties derived from X-ray measurements.
We present a comprehensive study of the local environments of four E+S galaxy pairs with the main goal to investigate their formation/evolution histories. New XMM-Newton data were obtained for two pairs (RR 143 and RR 242) that complements existing ROSAT data for the other two (RR 210 and RR 216). The new observations reveal diffuse X-ray emission in both pairs. The emission is asymmetric in both cases and extends out to 120 kpc and 160 kpc in RR 143 and RR 242 respectively. The nucleus of RR 242 hosts a low luminosity mildly absorbed AGN. We find that the early-type components of pairs with diffuse hot gas appear to be relaxed objects while those in RR 210 and RR 216, where no diffuse emission has been found, display unambiguous signatures of ongoing interaction. Wide-field V and R-band data are used to study the photometric properties of the early-type components and to search for a candidate faint galaxy populations around each of the pairs. While no diffuse optical light is found for any of the pairs, all of the early-type members show very extended and concentric luminous envelopes. We identify a faint galaxy sample in each field and we consider whether they could be physically associated with the luminous pairs based upon (V-R) colors and photometric properties. We find that the distribution of r_e and M_R for the candidates are similar in three of the fields (RR 143, 216 and 242). The same selection criteria applied to the field of RR 210 suggest a fainter and more compact population possibly suggesting a larger background fraction than in the other fields.
Current, accumulating evidence for (mildly) relativistic blue- and red-shifted absorption lines in AGNs is reviewed. XMM-Newton and Chandra sensitive X-ray observations are starting to probe not only the kinematics (velocity) but also the dynamics (accelerations) of highly ionized gas flowing in-and-out from, likely, a few gravitational radii from the black hole. It is thus emphasized that X-ray absorption-line spectroscopy provides new potential to map the accretion flows near black holes, to probe the launching regions of relativistic jets/outflows, and to quantify the cosmological feedback of AGNs. Prospects to tackle these issues with future high energy missions are briefly addressed.
We have developed a framework for the Monte-Carlo simulation of the X-Ray Telescopes (XRT) and the X-ray Imaging Spectrometers (XIS) onboard Suzaku, mainly for the scientific analysis of spatially and spectroscopically complex celestial sources. A photon-by-photon instrumental simulator is built on the ANL platform, which has been successfully used in ASCA data analysis. The simulator has a modular structure, in which the XRT simulation is based on a ray-tracing library, while the XIS simulation utilizes a spectral "Redistribution Matrix File" (RMF), generated separately by other tools. Instrumental characteristics and calibration results, e.g., XRT geometry, reflectivity, mutual alignments, thermal shield transmission, build-up of the contamination on the XIS optical blocking filters (OBF), are incorporated as completely as possible. Most of this information is available in the form of the FITS (Flexible Image Transport System) files in the standard calibration database (CALDB). This simulator can also be utilized to generate an "Ancillary Response File" (ARF), which describes the XRT response and the amount of OBF contamination. The ARF is dependent on the spatial distribution of the celestial target and the photon accumulation region on the detector, as well as observing conditions such as the observation date and satellite attitude. We describe principles of the simulator and the ARF generator, and demonstrate their performance in comparison with in-flight data.
We discuss the structure, galaxy content and kinematics of a sparse, probably collapsing group around IC 65 and an evolved rich group around NGC 6962
The stochastic acceleration of subrelativistic electrons from a background plasma is studied in order to find a possible explanation of the hard X-ray (HXR) emission detected from the Coma cluster. We calculate the necessary energy supply as a function of the plasma temperature and of the electron energy. We show that, for the same value of the HXR flux, the energy supply changes gradually from its high value (when emitting particle are non-thermal) to lower values (when the electrons are thermal). The kinetic equations we use include terms describing particle thermalization as well as momentum diffusion due to the Fermi II acceleration. We show that the temporal evolution of the particle distribution function has, at its final stationary stage, a rather specific form: it cannot be described by simple exponential or power-law expressions. A broad transfer region is formed by Coulomb collisions at energies between the Maxwellian and power-law parts of the distribution function. In this region the radiative lifetime of a single electron differs greatly from the lifetime of the distribution function as a whole. For a plasma temperature of 8 keV, the particles emitting bremsstrahlung at 20-80 keV lie in this quasi-thermal regime. We show that the energy supply required by quasi-thermal electrons to produce the observed HXR flux from Coma is one or two orders of magnitude smaller than the value derived from the assumption of a nonthermal origin of the emitting particles. This result may solve the problem of rapid cluster overheating by nonthermal electrons. We finally predict the change in Coma's SZ effect caused by the distortions of the Maxwellian electron spectrum, and we show that evidence for acceleration of subrelativistic electrons can be derived from detailed spectral measurements.
We present Chandra HETGS observations of the classical T Tauri star (CTTS) V4046 Sgr. The He-like triplets of O VII, Ne IX, and Si XIII are clearly detected. Similar to the CTTS TW Hya and BP Tau, the forbidden lines of O VII and Ne IX are weak compared to the intercombination line, indicating high plasma densities in the X-ray emitting regions. The Si XIII triplet, however, is within the low-density limit, in agreement with the predictions of the accretion funnel infall model with an additional stellar corona. V4046 Sgr is the first close binary exhibiting these features. Together with previous high-resolution X-ray data on TW Hya and BP Tau, and in contrast to T Tau, now three out of four CTTS show evidence of accretion funnels.
With improving methods and surveys, the young field of extrasolar planets has recently expanded into a qualitatively new domain - terrestrial (mostly rocky) planets. The first such planets were discovered during the past year, judging by their measured masses of less than 10 Earth-masses ($M_{\oplus}$) or Super-Earths. They are introducing a novel physical regime that has not been explored before as such planets do not exist in our Solar System. Their composition can be either completely terrestrial or harbour an extensive ocean (water and ices) above a rocky core. We model the structure and properties of the first Super-Earth (mass $\sim$ 7.5 $M_{\oplus}$) discovered in 2005, illustrating the possibilities in composition and providing radius evaluations in view of future detection of similar planets by transits. We find that a threshold in radius exists for which larger values indicate that a Super-Earth most certainly has an extensive water content. In the case of GJ876d this threshold is at about 12000 km. Our results show that unique characterization of the bulk composition of Super-Earths will be possible in future transit studies.
The solar irradiance in the Extreme Ultraviolet (EUV) spectral bands has been observed with a 15 sec cadence by the SOHO Solar EUV Monitor (SEM) since 1995. During remarkably intense solar flares the SEM EUV measurements are saturated in the central (zero) order channel (0.1 -- 50.0 nm) by the flare soft X-ray and EUV flux. The first order EUV channel (26 -- 34 nm) is not saturated by the flare flux because of its limited bandwidth, but it is sensitive to the arrival of Solar Energetic Particles (SEP). While both channels detect nearly equal SEP fluxes, their contributions to the count rate is sensibly negligible in the zero order channel but must be accounted for and removed from the first channel count rate. SEP contribution to the measured SEM signals usually follows the EUV peak for the gradual solar flare events. Correcting the extreme solar flare SEM EUV measurements may reveal currently unclear relations between the flare magnitude, dynamics observed in different EUV spectral bands, and the measured Earth atmosphere response. A simple and effective correction technique based on analysis of SEM count-rate profiles, GOES X-ray, and GOES proton data has been developed and used for correcting EUV measurements for the five extreme solar flare events of July 14, 2000, October 28, November 2, November 4, 2003, and January 20, 2005. Although none of the 2000 and 2003 flare peaks were contaminated by the presence of SEPs, the January 20, 2005 SEPs were unusually prompt and contaminated the peak. The estimated accuracy of the correction is about 7.5% for large X-class events.
Active galaxies are the most powerful engines in the Universe for converting gravitational energy into radiation, and radio galaxies and radio-loud quasars are highly luminous and can be detected across the Universe. The jets that characterise them need a medium to propagate into, and thus radio galaxies at high redshift point to gaseous atmospheres on scales of at least the radio source diameter, which in many cases can reach hundreds of kpc. The variation with redshift of X-ray properties of radio-selected clusters provides an important test of structure formation theories as, unlike X-ray selection, this selection is not biased towards the most luminous clusters in the Universe. We present new results from a sample of 19 luminous radio galaxies at redshifts between 0.5 and 1. The properties of the gaseous atmosphere around these sources as mapped by Chandra and XMM-Newton observations are discussed. By combining these with observations at radio frequency, we will be able to draw conclusions on cluster size, density, and pressure balance between the radio source and the environment in which it lies.
A self consistent effective field theory of modified gravity has recently been proposed with spontaneous breaking of local Lorentz invariance. The symmetry is broken by a vector field with the wrong-sign mass term and it has been shown to have additional graviton modes and modified dispersion relations. In this paper we study the evolution of a homogeneous and isotropic universe in the presence of such a vector field with a minimum lying along the time-like direction. A plethora of different regimes is identified, such as accelerated expansion, loitering, collapse and tracking.
We compute the Bayesian evidences for one- and two-parameter models of evolving dark energy, and compare them to the evidence for a cosmological constant, using current data from Type Ia supernova, baryon acoustic oscillations, and the cosmic microwave background. We use only distance information, ignoring dark energy perturbations. We find that, under various priors on the dark energy parameters, LambdaCDM is currently favoured as compared to the dark energy models. We consider the parameter constraints that arise under Bayesian model averaging, and discuss the implication of our results for future dark energy projects seeking to detect dark energy evolution. The model selection approach complements and extends the figure-of-merit approach of the Dark Energy Task Force in assessing future experiments, and suggests a significantly-modified interpretation of that statistic.
Weak lensing surveys provide a powerful probe of dark energy through the measurement of the mass distribution of the local Universe. A number of ground-based and space-based surveys are being planned for this purpose. Here, we study the optimal strategy for these future surveys using the joint constraints on the equation of state parameter wn and its evolution wa as a figure of merit by considering power spectrum tomography. For this purpose, we first consider an `ideal' survey which is both wide and deep and exempt from systematics. We find that such a survey has great potential for dark energy studies, reaching one sigma precisions of 0.8% and 6% on the two parameters respectively. We then study the relative impact of various limitations by degrading this ideal survey. In particular, we consider the effect of sky coverage, survey depth, shape measurements systematics, photometric redshifts systematics and uncertainties in the non-linear power spectrum predictions. We find that, for a given observing time, it is always advantageous to choose a wide rather than a deep survey geometry. We also find that the dark energy constraints from power spectrum tomography are robust to photometric redshift errors and catastrophic failures, if a spectroscopic calibration sample of 10^4-10^5 galaxies is available. The impact of these systematics is small compared to the limitations that come from potential uncertainties in the power spectrum, due to shear measurement and theoretical errors. To help the planning of future surveys, we summarize our results with comprehensive scaling relations which avoid the need for the full Fisher matrix calculations.
The polarization observed in the spectral lines of the He I 10830 multiplet carries valuable information on the dynamical and magnetic properties of plasma structures in the solar chromosphere and corona, such as spicules, prominences, filaments, emerging magnetic flux regions, etc. Here we investigate the influence of atomic level polarization on the emergent Stokes profiles for a broad range of magnetic field strengths, in both 90 degree and forward scattering geometry. We show that, contrary to a widespread belief, the selective emission and absorption processes caused by the presence of atomic level polarization may have an important influence on the emergent linear polarization, even for magnetic field strengths as large as 1000 G. Consequently, the modeling of the Stokes Q and U profiles should not be done by taking only into account the contribution of the transverse Zeeman effect within the framework of the Paschen-Back effect theory, unless the magnetic field intensity of the observed plasma structure is sensibly larger than 1000 G. We point out also that in low-lying optically thick plasma structures, such as those of active region filaments, the (horizontal) radiation field generated by the structure itself may substantially reduce the positive contribution to the anisotropy factor caused by the (vertical) radiation field coming from the underlying solar photosphere, so that the amount of atomic level polarization may turn out to be negligible. Only under such circumstances may the emergent linear polarization of the He I 10830 multiplet in such regions of the solar atmosphere be dominated by the contribution caused by the transverse Zeeman effect.
(abridged) Ongoing supernova (SN) surveys find hundreds of candidates, that require confirmation for their use. Traditional classification based on followup spectroscopy of all candidates is virtually impossible for these large samples. We present an automatic Bayesian classifying algorithm for supernovae, the SN-ABC. We rely solely on single-epoch multiband photometry and host-galaxy (photometric) redshift information to sort SN candidates into the two major types, Ia and core-collapse supernovae. We test the SN-ABC performance on published samples of SNe from the SNLS and GOODS projects that have both broad-band photometry and spectroscopic classification (so the true type is known). The SN-ABC correctly classifies up to 97% (85%) of the type Ia (II-P) SNe in SNLS, and similar fractions of the GOODS SNe, depending on photometric redshift quality. We further test our method on large artificial samples to explore possible biases, and find that, in deep surveys, SNe Ia are best classified at redshifts z >~ 0.6, or when near maximum, with success rates of the order of 95%. Core-collapse SNe are best recognized several weeks after maximum, or at z <~ 0.6, and reach success rates near 80%. The SN-ABC also allows the rejection of SN "impostors" such as active galactic nuclei (AGNs), with half of of the AGNs we simulate rejected by the algorithm. In a separate paper, we use our method to classify a new sample of high-z SNe that we have found in the Subaru Deep Field.
An extended data set of extreme ultraviolet images of the solar corona provided by the SOHO spacecraft are analyzed using statistical methods common to studies of self-organized criticality (SOC) and to intermittent turbulence. The data exhibits simultaneous hallmarks of both regimes, namely power-law avalanche statistics as well as multiscaling of structure functions of spatial activity. This indicates that both SOC and intermittent turbulence may be manifestations of a single dynamical process in magnetized plasmas entangling avalanches of magnetic energy dissipation with turbulent particle flows.
Variability amplitudes larger than 1 magnitude over time-scales of a few tens of minutes have recently been reported in the optical light-curves of several blazars. In order to independently verify the real occurrence of such extremely violent events, we undertook an observational study of a selected sample of three blazars: PKS 0048-097, PKS 0754+100, and PKS 1510-089. Possible systematic error sources during data acquisition and reduction were carefully evaluated. We indeed found flux variability at intra-night time-scales in all three sources, although no extremely violent behaviour, as reported by other authors, was detected. We show that an incorrect choice of the stars used for differential photometry will, under fairly normal conditions, lead to spurious variability with large amplitudes on short time-scales. Wrong results of this kind can be avoided with the use of simple error-control techniques.
We present a mean field model based on the approach taken by Rempel (astro-ph/0604451) in order to investigate the influence of stochastic fluctuations in the Reynolds stresses on meridional flow and differential rotation. The stochastic fluctuations found in the meridional flow pattern directly resemble the stochastic fluctuations of the Reynolds stresses, while the stochastic fluctuations in the differential rotation are smaller by almost two orders of magnitude. It is further found that the correlation length and time scale of the stochastic fluctuations have only a weak influence on meridional flow, but a significant influence on the magnitude of variations in the differential rotation. We analyze the energy fluxes within the model to estimate time scales for the replenishment of differential rotation and meridional flow. We find that the time scale for the replenishment of differential rotation (~10 years) is nearly four orders of magnitude longer than the time scale for the replenishment of meridional flow, which explains the differences in the response to stochastic fluctuations of the Reynolds stress found for both flow fields.
In this paper we discuss the transport of toroidal magnetic field by a weak meridional flow at the base of the convection zone. We utilize the differential rotation and meridional flow model developed by Rempel and incorporate feedback of a purely toroidal magnetic field in two ways: directly through the Lorentz force (magnetic tension) and indirectly through quenching of the turbulent viscosity, which affects the parametrized turbulent angular momentum transport in the model. In the case of direct Lorentz force feedback we find that a meridional flow with an amplitude of around 2 m/s can transport a magnetic field with a strength of 20 to 30 kG. Quenching of turbulent viscosity leads to deflection of the meridional flow from the magnetized region and a significant reduction of the transport velocity if the magnetic field is above equipartition strength.
We present radial mass profiles within 0.3 r_vir for 16 relaxed galaxy groups-poor clusters (kT range 1-3 keV) selected for optimal mass constraints from the Chandra and XMM data archives. After accounting for the mass of hot gas, the resulting mass profiles are described well by a two-component model consisting of dark matter (DM), represented by an NFW model, and stars from the central galaxy. The stellar component is required only for 8 systems, for which reasonable stellar mass-to-light ratios (M/L_K) are obtained, assuming a Kroupa IMF. Modifying the NFW dark matter halo by adiabatic contraction does not improve the fit and yields systematically lower M/L_K. In contrast to previous results for massive clusters, we find that the NFW concentration parameter (c_vir) for groups decreases with increasing M_vir and is inconsistent with no variation at the 3 sigma level. The normalization and slope of the c_vir-M_vir relation are consistent with the standard LambdaCDM cosmological model with sigma_8 = 0.9. The small intrinsic scatter measured about the c_vir-M_vir relation implies the groups represent preferentially relaxed, early forming systems. The mean gas fraction (f =0.05 +/- 0.01) of the groups measured within an overdensity Delta=2500 is lower than for hot, massive clusters, but the fractional scatter (sigma_f/f=0.2) for groups is larger, implying a greater impact of feedback processes on groups, as expected. Extrapolating our mass models out to the virial radius defined within Delta=101 suggests the groups are baryonically closed.
We present the concentration (c)-virial mass (M) relation of 39 galaxy systems ranging in mass from individual early-type galaxies up to the most massive galaxy clusters, (0.06-20) x 10^{14} M_sun. We selected for analysis the most relaxed systems possessing the highest quality data currently available in the Chandra and XMM public data archives. A power-law model fitted to the X-ray c-M relation requires at high significance (6.6 sigma) that c decreases with increasing M, which is a general feature of CDM models. The median and scatter of the c-M relation produced by the flat, concordance LCDM model (Omega_m=0.3, sigma_8=0.9) agrees with the X-ray data provided the sample is comprised of the most relaxed, early forming systems, which is consistent with our selection criteria. Within the context of the concordance model the c-M relation requires 0.76< sigma_8 <1.07 (99% conf.). The tilted, low-sigma_8 model suggested by a new WMAP analysis is rejected at >99.99% confidence, but it can be reconciled with the X-ray data by increasing the dark energy equation of state parameter to w ~ -0.8. When imposing the additional constraint of the tight relation between sigma_8 and Omega_m from studies of cluster abundances, the X-ray c-M relation excludes (>99% conf.) both open CDM models and flat CDM models with Omega_m ~1. This result provides novel evidence for a flat, low-Omega_m universe with dark energy using observations only in the local (z << 1) universe. Possible systematic errors in the X-ray mass measurements of a magnitude ~10% suggested by CDM simulations do not change our conclusions.
We have incorporated time-dependent terms into the statistical and radiative equilibrium calculations of the non-LTE line-blanketed radiative transfer code CMFGEN. To illustrate the significant improvements in spectral fitting achieved for photospheric phase Type II SN, and to document the effects associated with time dependence, we model the outer 6.1Msun of ejecta of a BSG/RSG progenitor star. Hopping by 3-day increments, we compute the UV to near-IR spectral evolution for both continuum and lines, from the fully ionized conditions at one week to the partially recombined conditions at 6 weeks after the explosion. We confirm the importance of allowing for time-dependence in the modeling of Type-II SN, as recently discussed by Utrobin & Chugai for SN1987A. However, we allow in our approach for the full interaction between the radiation field and level populations, and study the effects on the full spectrum. At the recombination epoch, HI lines and NaD are stronger and broader than in equivalent steady-state models, while CaII is weakened. Former successes of steady-state CMFGEN models are unaffected, while former discrepancies are cured. Time dependence affects all lines, while the continuum, from the UV to the optical, changes only moderately. We identify two key effects: First, time dependence together with the energy gain through changes in ionization and excitation lead to an over-ionization in the vicinity of the photosphere, dramatically affecting line optical depths and profiles. Second, the ionization is frozen-in at large radii/velocities. This stems solely from the time-scale contrast between recombination and expansion and will occur, modulo non-thermal excitation effects, in all SN types. [abridged]
We present VLBA observations of 1667 MHz OH maser emission from the massive star formation region G5.89-0.39. The observations were phase referenced allowing the absolute positions of the masers to be obtained. The 1667 MHz masers have radial velocities that span ~50 km/s but show little evidence of tracing the bipolar molecular outflow, as has been claimed in previous studies. We identify 23 Zeeman pairs through comparison of masers in left and right circular polarization. Magnetic field strengths range from -2 mG to +2 mG, and an ordered reversal in magnetic field direction is observed toward the southern region of the UC HII region. We suggest that the velocity and magnetic field structure of the 1667 MHz masers can be explained in the context of a model in which the masers arise in a neutral shell just outside a rapidly exanding ionized shell.
Observing the first galaxies formed during the reionisation epoch, i.e. approximately within the first billion years after the Big Bang, remains one of the challenges of contemporary astrophysics. Several efforts are being undertaken to search for such remote objects. Combining the near-IR imaging power of the VLT and the natural effect of strong gravitational lensing our pilot program has allowed us to identify several galaxy candidates at redshift 6 <~ z <~ 10. The properties of these objects and the resulting constraints on the star formation rate density at high redshift are discussed. Finally we present the status of follow-up observations (ISAAC spectroscopy, HST and Spitzer imaging) and discuss future developments.
We discuss the implications of the recent X-ray and TeV gamma-ray observations of the PSR B1259-63 system (a young rotation powered pulsar orbiting a Be star) for the theoretical models of interaction of pulsar and stellar winds. We show that previously considered models in which the pulsar wind is purely electron loaded have problems to account for the observed behaviour of the system in the TeV and X-ray bands. We develop a model in which the broad band (radio, X-ray and high energy gamma-ray) emission from the binary system is produced in result of collisions of GeV-TeV energy protons accelerated by the pulsar wind and interacting with the stellar disk. In this model the high energy gamma-rays are produced in the decays of secondary neutral pions, while radio and X-ray emission are synchrotron and inverse Compton emission produced by low-energy (< 100 MeV) electrons from the decays of secondary charged pi mesons. This model can explain not only the observed energy spectra, but also the correlations between TeV, X-ray and radio emission components.
We present first results from a deep (J = 18.7), wide-field (6.5 square degrees) infrared (ZYJHK) survey in the Upper Sco association conducted within the science verification phase of the UKIRT Infrared Deep Sky Survey Galactic Cluster Survey (GCS). Cluster members define a sequence well separated from field stars in the (Z-J,Z) colour-magnitude diagram. We have selected a total of 164 candidates with J = 10.5-18.7 mag from the (Z-J,Z) and (Y-J,Y) diagrams. We further investigated the location of those candidates in the other colour-magnitude and colour-colour diagrams to weed out contaminants. The cross-correlation of the GCS catalogue with the 2MASS database confirms the membership of 116 photometric candidates down to 20 Jupiter masses as they lie within a 2 sigma circle centred on the association mean motion. The final list of cluster members contains 129 sources with masses between 0.3 and 0.007 Msun. We extracted a dozen new low-mass brown dwarfs below 20 Mjup, the limit of previous surveys in the region. Finally, we have derived the mass function in Upper Sco over the 0.3-0.01 Msun mass range, best fit by a single segment with a slope of index alpha = 0.6+/-0.1, in agreement with previous determination in open clusters.
We consider the acceleration of energetic particles by Fermi processes (i.e., diffusive shock acceleration, second order Fermi acceleration, and gradual shear acceleration) in relativistic astrophysical jets, with particular attention given to recent progress in the field of viscous shear acceleration. We analyze the associated acceleration timescales and the resulting particle distributions, and discuss the relevance of these processes for the acceleration of charged particles in the jets of AGNs, GRBs and microquasars, showing that multi-component powerlaw-type particle distributions are likely to occur.
We present near-infrared H-band imaging of 15 intermediate redshift (0.5<z<1)
radio quiet quasars (RQQ) in order to characterize the properties of their host
galaxies. We are able to clearly detect the surrounding nebulosity in 12
objects, whereas the object remains unresolved in three cases. For all the
resolved objects, we find that the host galaxy is well represented by a de
Vaucouleurs r^{1/4} surface brightness law. This is the first reasonably sized
sample of intermediate redshift RQQs studied in the near-infrared.
The RQQ host galaxies are luminous (average M_H=-26.3+-0.6) and large giant
elliptical galaxies (average bulge scale length R_e = 11.3\pm5.8 kpc). RQQ
hosts are about 1 mag brighter than the typical low redshift galaxy luminosity
L^*, and their sizes are similar to those of galaxies hosting lower redshift
RQQs, indicating that there is no significant evolution at least up to z=1 of
the host galaxy structure. We also find that RQQ hosts are about 0.5-1 mag
fainter than radio-loud quasars (RLQ) hosts at the similar redshift range. The
comparison of the host luminosity of intermediate redshift RQQ hosts with that
for lower z sources shows a trend that is consistent with that expected from
the passive evolution of the stars in the host galaxies. The nuclear luminosity
and the nucleus/host galaxy luminosity ratio of the objects in our sample are
intermediate between those of lower redshift RQQs and those of higher redshift
(z>1) RQQs.
We study intermediate--z SNe Ia using the empirical physical diagrams which enable to learn about those SNe explosions. This information can be very useful to reduce systematic uncertainties of the Hubble diagram of SNe Ia up to high z. The study of the expansion velocities and the measurement of the ratio $\mathcal{R}$(\SiII) allow to subtype those SNe Ia as done for nearby samples. The evolution of this ratio as seen in the diagram $\mathcal{R}$(\SiII)--(t) together with $\mathcal{R}$(\SiII)$_{max}$ versus (B-V)$_{0}$ indicate consistency of the properties at intermediate z compared with local SNe. At intermediate--z, the expansion velocities of Ca II and Si II are similar to the nearby counterparts. This is found in a sample of 6 SNe Ia in the range 0.033$\leq z \leq$0.329 discovered within the {\it International Time Programme} (ITP) of {\it Cosmology and Physics with SNe Ia} during the spring of 2002. Those supernovae were identified using the 4.2m William Herschel Telescope. Two SNe Ia at intermediate z were of the cool FAINT type, one being a SN1986G--like object highly reddened. The $\mathcal{R}$(\SiII) ratio as well as subclassification of the SNe Ia beyond templates help to place SNe Ia in their sequence of brightness and to distinguish between reddened and intrinsically red supernovae. This test can be done with very high z SNe Ia and it will help to reduce systematic uncertainties due to extinction by dust. It should allow to map the high-z sample into the nearby one.
The anisotropy of velocities in MHD turbulence is demonstrated explicitly by calculating the velocity gradients as a function of direction in representative simulations of decaying turbulence. It follows that the optical depths of spectral lines are anisotropic when there is MHD turbulence, and that this anisotropy influences the polarization characteristics of the emergent radiation. We calculate the linear polarization that results for the microwave lines of the CO molecule in star-forming gas and show that it is comparable to the polarization that is observed. This and our earlier result--that the anisotropy of MHD turbulence may be the cause for the absence of the Zeeman $\pi $-components in the spectra of OH mainline masers--are the first demonstrations of the occurrence of anisotropy in the optical depths caused by MHD turbulence. A non-local approximation is developed for the radiative transfer and the results are compared with those from a local (LVG) approximation.
We report the discovery of a dwarf Seyfert 1 active galactic nucleus (AGN) with a candidate intermediate-mass black hole hosted by the dwarf galaxy SDSS J160531.84+174826.1 at z=0.032. A broad component of the H-alpha line with FWHM=781 km/s is detected in its optical spectrum, and a bright, point-like nucleus is evident from a HST imaging observation. Non-thermal X-ray emission is also detected from the nucleus. The black hole mass, as estimated from the luminosity and width of the broad H-alpha component, is about 7x10^4 \msun. The host galaxy appears to be a disk galaxy with a boxy bulge or nuclear bar; with an absolute magnitude of M_R = -17.8, it is among the least luminous host galaxies ever identified for a Seyfert 1.
We used star density maps obtained from 2MASS to obtain a sample of star clusters in the entire Galactic Plane with |b|<20deg. A total of 1788 star cluster candidates are identified in this survey. Among those are 681 previously known open clusters and 86 globular clusters. A statistical analysis indicates that our sample of 1021 new cluster candidates has a contamination of about 50%. Star cluster parameters are obtained by fitting a King profile to the star density. These parameters are used to statistically identify probable new globular cluster candidates in our sample. A detailed investigation of the projected distribution of star clusters in the Galaxy demonstrates that they show a clear tendency to cluster on spatial scales in the order of 12-25pc, a typical size for molecular clouds.
Context: The supermassive black hole at the Galactic center, SgrA*, shows frequent radiation outbursts, often called 'flares'. In the near-infrared some of these flares were reported as showing intrinsic quasi-periodicities. The flux peaks associated with the quasi-periodic behavior were found to be highly polarized. Aims: The aim of this work is to present new evidence to support previous findings of the properties of the polarized radiation from SgrA* and to again provide strong support for the quasi-periodicity of ~18+-3 min reported earlier. Methods: Observations were carried out at the European Southern Observatory's Very Large Telescope on Paranal, Chile. We used the NAOS/CONICA adaptive optics/near-infrared camera instrument. By fitting the polarimetric lightcurves with a hot-spot model, we addressed the question of whether the data are consistent with this model. To fit the observed data we used a general relativistic ray-tracing code in combination with a simple hot-spot/ring model. Results: We report on new polarization measurements of a K-band flare from the supermassive black hole at the Galactic center. The data provide very strong support for a quasi-periodicity of 15.5+-2 min. The mean polarization of the flare is consistent with the direction of the electric field vector that was reported in previous observations. The data can be modeled successfully with a combined blob/ring model. The inclination i of the blob orbit must be i > 20 deg on a 3sigma level, and the dimensionless spin parameter of the black hole is derived to be a > 0.5.
We present optical linear spectropolarimetry of the microquasar LS I +61$^{\circ}$ 303. The continuum emission is mildly polarized (up to 1.3 %) and shows almost no temporal change. We find a distinct change of polarization across the H$\alpha$ emission line, indicating the existence of polarization component intrinsic to the microquasar. We estimate the interstellar polarization (ISP) component from polarization of the H$\alpha$ line and derive the intrinsic polarization component. The wavelength dependence of the intrinsic component is well explained by Thomson scattering in equatorial disk of the Be-type mass donor. The position angle (PA) of the intrinsic polarization $\sim 25^{\circ}$ represents the rotational axis of the Be disk. This PA is nearly perpendicular to the PA of the radio jet found during quiescent phases. Assuming an orthogonal disk-jet geometry around the compact star, the rotational axis of the accretion disk is almost perpendicular to that of the Be disk. Moreover, according to the orbital parameters of the microquasar, the compact star is likely to get across the Be disk around their periastron passage. We discuss the peculiar circumstellar structure of this microquasar inferred from our observation and possible connection with its high-energy activities.
Aims: We present a comparison of the visual and NIR intensity profile of the M0 giant gamma Sagittae to plane-parallel ATLAS 9 as well as to plane-parallel & spherical PHOENIX model atmospheres. Methods: We use previously described visual interferometric data obtained with the NPOI in July 2000. We apply the recently developed technique of coherent integration, and thereby obtain visibility data of more spectral channels and with higher precision than before. In addition, we employ new measurements of the K-band diameter of gamma Sagittae obtained with the instrument VINCI at the VLTI in 2002. Results: The spherical PHOENIX model leads to a precise definition of the Rosseland angular diameter and a consistent high-precision diameter value for our NPOI and VLTI/VINCI data sets of Theta_Ross=6.06 pm 0.02 mas, with the Hipparcos parallax corresponding to R_Ross=55 pm 4 R_sun, and with the bolometric flux corresponding to an effective temperature T_eff=3805 pm 55 K. Our visual visibility data close to the first minimum and in the second lobe constrain the limb-darkening effect and are generally consistent with the model atmosphere predictions. The visual closure phases exhibit a smooth transition between 0 and pi. Conclusions: The agreement between the NPOI and VINCI diameter values increases the confidence in the model atmosphere predictions from optical to NIR wavelengths as well as in the calibration and accuracy of both interferometric facilities. The consistent night-by-night diameter values of VINCI give additional confidence in the given uncertainties. The closure phases suggest a slight deviation from circular symmetry, which may be due to surface features, an asymmetric extended layer, or a faint unknown companion.
We present K-band interferometric and optical spectroscopic observations of Menkar obtained with the instruments VINCI and UVES at Paranal Observatory. Spherically symmetric PHOENIX stellar model atmospheres are constrained by comparison to our interferometric and spectroscopic data, and high-precision fundamental parameters of Menkar are obtained. Our high-precision VLTI/VINCI observations in the first and second lobes of the visibility function directly probe the model-predicted strength of the limb darkening effect in the K-band and the stellar angular diameter. The high spectral resolution of UVES allows us to confront observed and model-predicted profiles of atomic lines and molecular bands. We show that our derived PHOENIX model atmosphere for Menkar is consistent with both the measured strength of the limb-darkening in the near-infrared K-band and the profiles of spectral bands around selected atomic lines and TiO bandheads. At the detailed level of our high spectral resolution, however, noticeable discrepancies between observed and synthetic spectra exist. We obtain a Rosseland angular diameter of Theta_Ross=12.20 mas pm 0.04 mas. Together with the Hipparcos parallax, it corresponds to R_Ross=89 pm 5 R_sun, and together with the bolometric flux to T_eff=3795 K pm 70 K.Our approach illustrates the power of combining interferometry and high-resolution spectroscopy to constrain and calibrate stellar model atmospheres. The simultaneous agreement of the model atmosphere with our interferometric and spectroscopic data increases confidence in the reliability of the modelling of this star, while discrepancies at the detailed level of the high resolution spectra can be used to further improve the underlying model.
We present preliminary results on the properties of relativistically broadened Fe K-alpha lines in a collection of more then 100 Active Galactic Nuclei (AGN) observed by the XMM-Newton EPIC-pn camera. Our main conclusions can be summarized as follows: a) we detect broad lines in about 25% of the sample objects. This fraction increases to 42+/-13% if we consider only objects with more than 10000 counts in the hard (2-10 keV) band, and to 50+/-32% for the small sub-sample (6 objects) of type~1 Piccinotti AGN with optimal XMM-Newton exposure (at least 200000 counts in the hard band); b) we find no significant difference in the detection rate of broad lines between obscured and unobscured AGN; c) the strongest relativistic profiles are measured in low-luminosity (< 10^43 erg/s) AGN; d) Equivalent Widths (EWs) associated with relativistic profiles in stacked spectra are ~150 eV for all luminosity classes; e) models of relativistically broadened iron line profiles ("kyrline", Dovciak et al. 2005), which include full relativistic treatment of the accretion disk emission around a Kerr black hole in the strong gravity regime, yield an average disk inclination angle ~30 degrees, and a radial dependence of the disk emissivity profile ~-3. The distribution of EW is very broad, with <log (EW)>=2.4. We estimate that an investment of about 1 Ms of XMM-Newton time would be required to put these results on a sound statistical basis.
This paper presents accurate homogeneous positions, velocities and other pertinent properties for 460 newly discovered and 169 previously known planetary nebulae (PNe) in the central 25 sq deg bar region of the Large Magellanic Cloud (LMC). Candidate emission sources were discovered using a deep, high resolution H-alpha map of the LMC obtained by median stacking a dozen 2 hour H-alpha exposures taken with the UK Schmidt Telescope (UKST). Our spectroscopic followup of more than 2,000 compact (ie. <20 arcsec) H-alpha emission candidates uncovered has tripled the number of PNe in this area. All of the 169 previously known PNe within this region have also been independently recovered and included in this paper to create a homogeneous data set. Of the newly discovered PNe, we classify 291 as "true", 54 as "likely" and 115 as "possible" based on the strength of photometric and spectroscopic evidence. Radial velocities have been measured using both weighted averaging of emission lines and cross-correlation techniques against high quality templates. Based on the median comparison of the two systems, we define a measurement error of pm4 km/s. A new velocity map of the central 25 sq deg of the LMC, based on results from the combined new and previously known PNe, is presented, indicating an averaged heliocentric velocity differential of 65 km/s perpendicular to the line of nodes for the entire PN population across our survey area. Averaged velocities of our PNe and molecular hydrogen (from the literature) across 37 x 37 arcmin sub areas are compared.
There is no accepted mechanism that explains the equilibrium structures that form in collisionless cosmological N-body simulations. Recent work has identified nonextensive thermodynamics as an innovative approach to the problem. The distribution function that results from adopting this framework has the same form as for polytropes, but the polytropic index is now related to the degree of nonextensiveness. In particular, the nonextensive approach can mimic the equilibrium structure of dark matter density profiles found in simulations. We extend the investigation of this approach to the velocity structures expected from nonextensive thermodynamics. We find that the nonextensive and simulated N-body rms-velocity distributions do not match one another. The nonextensive rms-velocity profile is either monotonically decreasing or displays little radial variation, each of which disagrees with the rms-velocity distributions seen in simulations. We conclude that the currently discussed nonextensive models require further modifications in order to corroborate dark matter halo simulations. (adapted from TeX)
We use the data from a recent, 100 ksec XMM-Newton observation of the Narrow Line Seyfert 1 galaxy Ark 564 to obtain its time average, X-ray spectrum. The 3-11 keV spectrum is well fitted by a power-law of slope 2.43. We detect a weak (equivalent width ~80 eV) emission line at ~6.7 keV, which implies emission from ionized iron. There is no compelling evidence for significant broadening of the line.We also detect a possible Doppler shifted absorption line at 8.1 keV. At energies lower than 2 keV, the spectrum is dominated by a smooth soft excess component which can be well fitted either by a two black body components (kT~0.15 and 0.07 keV) or by a black body plus a relativistically blurred photoionized disc reflection model. We detect a broad, shallow flux deficit in the 0.65-0.85 keV band, reminiscent of the iron unresolved transition array (UTA) features. We do not detect neither a strong absorption edge around 0.7 keV nor an emission line around 1 keV. The soft excess emission is consistent with being reflected emission from a geometrically flat disc, with solar abundances, illuminated by an isotropic source. The weakness of the iron line emission can be explained by relativistic blurring. The UTA feature implies the presence of warm material with a column density of 2-5*10^{20} cm^{-2}. If the absorption line at 8.1 keV corresponds to FeXXVI Kalpha, it suggests the presence of a highly ionized absorbing material with N_H > 10^{23} cm^{-2}, outflowing at a high velocity of ~0.17c.
Blazars, a beamed population of active galactic nuclei, radiate high-energy gamma-rays, and thus are a good target for the Gamma Ray Large Area Space Telescope (GLAST). As the blazars trace the large-scale structure of the universe, one may observe spatial clustering of blazars. We calculate the angular power spectrum of blazars that would be detected by GLAST. We show that we have the best chance of detecting their clustering at large angular scales, \theta >~ 10 deg, where shot noise is less important, and the dominant contribution to the correlation comes from relatively low redshift, z <~ 0.1. The GLAST can detect the correlation signal, if the blazars detected by GLAST trace the distribution of low-z quasars observed by optical galaxy surveys, which have the bias of unity. If the bias of blazars is greater than 1.5, GLAST will detect the correlation signal unambiguously. We also find that GLAST may detect spatial clustering of clusters of galaxies in gamma-rays. The shape of the angular power spectrum is different for blazars and clusters of galaxies; thus, we can separate these two contributions on the basis of the shape of the power spectrum.
The present work is our first attempt to understand the role of reconnection in the pulsar magnetosphere. Our discussion is based on the observationaly infered fact that, as the pulsar spins down, the region of closed corotating dipolar field lines grows with time. This implies that reconnection must take place in the magnetosphere. We argue that non-dissipative reconnection along the equatorial current sheet allows for the continuous channeling of pulsar spindown energy into particle energy, all the way from the light cylinder to the pulsar wind termination shock, and we propose that this effect may account for the low \sigma values inferred by observations. We present a simple model that allows us to relate the magnetic diffusivity in the equatorial current sheet to an observable pulsar parameter, the braking index n. When n~1, the global structure of the magnetosphere approaches that of a relativistic split monopole where the pulsar spindown energy is carried by the electromagnetic field. However, for values of n>1.5, almost all field lines close inside the pulsar wind termination shock, and thus most of the electromagnetic pulsar spindown energy flux is effectively transformed into particle energy in the equatorial current sheet.
In this work, we present a multi-wavelength study of XRF 040912, aimed at measuring its distance scale and the intrinsic burst properties. We performed a detailed spectral and temporal analysis of both the prompt and the afterglow emission and we estimated the distance scale of the likely host galaxy. We then used the currently available sample of XRFs with known distance to discuss the connection between XRFs and classical Gamma-ray Bursts (GRBs). We found that the prompt emission properties unambiguously identify this burst as an XRF, with an observed peak energy of E_p=17+/-13 keV and a burst fluence ratio S(2-30keV)/S(30-400keV)>1. A non-fading optical source with R~24 mag and with an apparently extended morphology is spatially consistent with the X-ray afterglow, likely the host galaxy. XRF 040912 is a very dark burst since no afterglow optical counterpart is detected down to R>25 mag (3 sigma limiting magnitude) at 13.6 hours after the burst. The host galaxy spectrum detected from 3800A to 10000A, shows a single emission line at 9552A. The lack of any other strong emission lines blue-ward of the detected one and the absence of the Ly alpha cut-off down to 3800A are consistent with the hypothesis of the [OII] line at redshift z=1.563+/-0.001. The intrinsic spectral properties rank this XRF among the soft GRBs in the E_peak-E_iso diagram. Similar results were obtained for most XRFs at known redshift. Only XRF 060218 and XRF 020903 represent a good example of instrinsic XRF(i-XRF) and are possibly associated with a different progenitor population. This scenario may calls for a new definition of XRFs.
4U 1954+319 was discovered 25 years ago, but only recently has a clear picture of its nature begun to emerge. We present for the first time a broad-band spectrum of the source and a detailed timing study using more than one year of monitoring data. The timing and spectral analysis was done using publicly available Swift, INTEGRAL, BeppoSAX, and RXTE/ASM data in the 0.7-150 keV energy band. The source spectrum is described well by a highly absorbed (N_H~10^23 cm^-2) power law with a high-energy exponential cutoff around 15 keV. An additional black body component is needed below 3 keV to account for a soft excess. The derived ~5 hr periodicity, with a spin-up timescale of ~25 years, could be identified as the neutron star spin period. The spectral and timing characteristics indicate that we are dealing both with the slowest established wind-accreting X-ray pulsar and with the second confirmed member of the emerging class dubbed "symbiotic low mass X-ray binaries" to host a neutron star.
We present a combined analysis of all publicly available, visible HST observations of transits of the planet HD 209458b. We derive the times of transit, planet radius, inclination, period, and ephemeris. The transit times are then used to constrain the existence of secondary planets in the system. We show that planets near an Earth mass can be ruled out in low-order mean-motion resonance, while planets less than an Earth mass are ruled out in interior, 2:1 resonance. We also present a combined analysis of the transit times and 68 high precision radial velocity measurements of the system. These results are compared to theoretical predictions for the constraints that can be placed on secondary planets.
We present the first results for anisotropy searches around the galactic center at EeV energies using data from the Pierre Auger Observatory. Our analysis, based on a substantially larger data set, do not support previous claim of anisotropy found in this region by the AGASA and Sugar experiment. Furthermore we place un upper limit on a possible point like source located at the galactic center which exclude several scenarios predicting neutron sources in this location.
We present the results of UBVRI broad-band aperture CCD photometry of 51 compact star clusters located in the South-West part of the M31 disk. The mean rms errors of all measured star cluster colors are less than 0.02 mag. In color vs. color diagrams the star clusters show significantly tighter sequences when compared with the photometric data from the compiled catalog of the M31 star clusters published by Galleti et al. (2004).
Most of the cosmological information extracted from the CMB has been obtained through the power spectrum, however there is much more to be learnt from the statistical distribution of the temperature random field. We review some recent developments in the study of the Cosmic Microwave Background (CMB) anisotropies and present a description of the novel tools developed to analyse the properties of the CMB anisotropies beyond the power spectrum.
We compare stellar photometry data in the South-West part of the M31 disk published by Magnier et al. (1992), Mochejska et al. (2001) and Massey et al. (2006) as the local photometric standards for the calibration of star cluster aperture photometry. Large magnitude and color differences between these catalogs are found. This makes one to be cautious in using these data as the local photometric standards for new photometry.
We present the Spitzer/IRS mid-infrared spectrum of the infrared-luminous (L_{IR}=4e11 L_sun) brightest cluster galaxy (BCG) in the X-ray-luminous cluster Z3146 (z=0.29). The spectrum shows strong aromatic emission features, indicating that the dominant source of the infrared luminosity is star formation. The most striking feature of the spectrum, however, is the exceptionally strong molecular hydrogen (H2) emission lines, which seem to be shock-excited. The line luminosities and inferred warm H2 gas mass (~1e10 M_sun) are 6 times larger than those of NGC 6240, the most H2-luminous galaxy at z <~ 0.1. Together with the large amount of cold H2 detected previously (~1e11 M_sun), this indicates that the Z3146 BCG contains disproportionately large amounts of both warm and cold H2 gas for its infrared luminosity, which may be related to the intracluster gas cooling process in the cluster core.
The primordial elements, H, He and Li are included in a low temperature equation of state and monochromatic opacity function. The equation of state and opacity function are incorporated into the stellar evolution code NG-ELMS, which makes use of a non-grey model atmosphere computed at runtime. NG-ELMS is used to compute stellar evolution models for primordial and lithium free element mixtures, for stars in the sub-Solar mass range 0.8--0.15 Msol. We find that lithium has little or no effect upon the structure and observable properties of of stars in this mass range. Furthermore lithium is completely destroyed by fusion before the main sequence in stars of mass less than ~0.7 Mol. We find that on the red giant branch and Hayashi track, the use of a non-grey model atmosphere to provide the upper boundary conditions for the stellar evolution calculation, results in significantly cooler less luminous stars, across the mass range
We report observations with the MIPS instrument aboard the {\it Spitzer Space Telescope} (SST) of four supernova remnants (SNRs) believed to be the result of core-collapse SNe: N132D (0525-69.6), N49B (0525-66.0), N23 (0506-68.0), and 0453-68.5. All four of these SNRs were detected in whole at 24 $\mu$m and in part at 70 $\mu$m. Comparisons with {\it Chandra} broadband X-ray images show an association of infrared (IR) emission with the blast wave. We attribute the observed IR emission to dust that has been collisionally heated by electrons and ions in the hot, X-ray emitting plasma, with grain size distributions appropriate for the LMC and the destruction of small grains via sputtering by ions. As with our earlier analysis of Type Ia SNRs, models can reproduce observed 70/24 $\mu$m ratios only if effects from sputtering are included, destroying small grains. We calculate the mass of dust swept up by the blast wave in these remnants, and we derive a dust-to-gas mass ratio of several times less than the often assumed value of 0.25% for the LMC. We believe that one explanation for this discrepancy could be porous (fluffy) dust grains.
We present the results of the INTEGRAL monitoring campaign on the accreting low mass X-ray binary pulsar GX 1+4 performed during the Galactic plane scan of the INTEGRAL Core Programme. The source has been observed in different luminosity states ranging from L(20-40 keV)= 1.7x10^{-10} erg/cm^2/s, to L(20-40 keV)=10.5x10^{-10} erg/cm^2/s for about 779 ks from 2003 March until 2004 October. Our observations confirm the secular spin down of GX 1+4 with spin period varying from 139.63 s to 141.56 s. In the highest luminosity state a spin-up phase is observed. The phase averaged spectrum of the source has been modelled either with an absorbed cut-off power law or with a Comptonization model with parameters significantly different in the two brightest luminosity states. No evidence for any absorption-like feature is observed in the phase averaged spectrum up to 110 keV. At highest luminosity, the source is found to pulsate up to 130 keV. Phase resolved spectroscopy reveals a phase dependent continuum and marginal evidence for an absorption feature at 34 keV in the descending part of the pulse. If interpreted as due to electron resonant cyclotron scattering, the magnetic field in the emitting region would be 2.9x10^{12}(1+z) G where z is the gravitational red-shift of the emitting region. We also observed a very low luminosity state, typical of this source, which lasted for about two days during which the source spectrum was modelled by a simple power-law and a pulsed signal was still detectable in the 15-100 keV energy range.
The thermonuclear explosion of a massive white dwarf in a Type Ia supernova
explosion is characterized by vastly disparate spatial and temporal scales. The
extreme dynamic range inherent to the problem prevents the use of direct
numerical simulation and forces modelers to resort to subgrid models to
describe physical processes taking place on unresolved scales.
We consider the evolution of a model thermonuclear flame in a constant
gravitational field on a periodic domain. The gravitational acceleration is
aligned with the overall direction of the flame propagation, making the flame
surface subject to the Rayleigh-Taylor instability. The flame evolution is
followed through an extended initial transient phase well into the steady-state
regime. The properties of the evolution of flame surface are examined. We
confirm the form of the governing equation of the evolution suggested by
Khokhlov (1995). The mechanism of vorticity production and the interaction
between vortices and the flame surface are discussed. The results of our
investigation provide the bases for revising and extending previous
subgrid-scale model.
Splaver and coworkers have measured the masses of the white dwarf and the
neutron star components of the PSR J1713+0747 binary system pair by Shapiro
Delay. We attempt to find the original configuration of this system performing
a set of binary evolution calculations to simultaneously account for the masses
of both stars and the orbital period. We considered initial masses of 1.5 and
1.4 \msun for the normal (donor) and the neutron star, respectively. We assumed
two metallicity values (Z = 0.010 and 0.020), and an initial orbital period
near 3 days. We assume that the neutron star is only able to retain \lesssim
0.10 of the matter transferred by the donor star.
Calculations were performed employing our binary hydro code that handles the
mass transfer rate in a fully implicit way together with state-of-the-art
physical ingredients, diffusion and a non-grey atmospheres.
We compare the structure of the resulting white dwarfs with the
characteristic age of PSR J1713+0747 finding a nice agreement with observations
by Lundgren et al. especially for the case of a donor star with Z= 0.010. This
result indicates that the evolution of this kind of binary system is well
understood.
The models predict that, due to diffusion, the atmosphere of the white dwarf
is an almost hydrogen-pure one. We find that such structures are unable to
account for the colours measured by Lundgren et al. within their error bars.
Thus, some discrepances in the white dwarf emergent radiation remain to be
explained.
We consider the problem of estimating the parameter $\fnl$ in the standard local model of primordial CMB non-Gaussianity. We determine the properties of maximum likelihood (ML) estimates and show that the problem is not the typical ML estimation problem as there are subtle issues involved. In particular, The Cramer-Rao inequality is not applicable and the likelihood function is unbounded with several points of maxima. However, the particular characteristics of the likelihood function lead to ML estimates that are simple and easy to compute. We compare their performance to that of moment estimators. We find that ML is better than the latter for values $\fnl$ away from the origin. For small values of $\fnl$, the fifth order moment is better than ML and the other moment estimators. However, we show how for small $\fnl$, one can easily improve the estimators by a simple shrinkage procedure. This is clearly important when the goal is to estimate a very small $\fnl$. In the process of studying the inference problem, we address some basic issues regarding statistical estimation in general that were raised at the Workshop on Non-Gaussianity in Cosmology held in Trieste in July 2006.
We use the Fourth Data Release of the Sloan Digital Sky Survey to investigate the relation between galaxy colour and environmental density for a sample of 79,553 galaxies at z <~ 0.1 and compare it to that between morphology and density for a sample of 13,655 galaxies with Hubble types assigned by an artificial neural network. As found by previous authors, the rest frame u-r is well described by a sum of two Gaussians, forming a bimodal distribution. In contrast, the Hubble type morphology is not well described by such a sum. This indicates that either (1) there are more than two significant populations in morphology, for example elliptical, S0, and spiral; (2) that there are physical processes not seen in colour space, or (3) that the morphological measures, particularly the different subtypes of spirals Sa--Sd, are intrinsically `fuzzy' when related to environmental density. It is not likely an artefact of using a neural network as these have been shown to perform very similarly to human classifiers. On removing the density relation due to morphology, we find a residual relation due to colour, however on removing the colour-density relation there is no evidence for a residual relation due to morphology.