Showing papers in "Astronomy and Astrophysics in 2002"

Cosmological hydrodynamics with adaptive mesh refinement - A new high resolution code called RAMSES

Abstract: A new N-body and hydrodynamical code, called RAMSES, is presented. It has been designed to study structure formation in the universe with high spatial resolution. The code is based on Adaptive Mesh Renement (AMR) technique, with a tree-based data structure allowing recursive grid renements on a cell-by-cell basis. The N-body solver is very similar to the one developed for the ART code (Kravtsov et al. 1997), with minor dierences in the exact implementation. The hydrodynamical solver is based on a second-order Godunov method, a modern shock-capturing scheme known to compute accurately the thermal history of the fluid component. The accuracy of the code is carefully estimated using various test cases, from pure gas dynamical tests to cosmological ones. The specic renement strategy used in cosmological simulations is described, and potential spurious eects associated with shock waves propagation in the resulting AMR grid are discussed and found to be negligible. Results obtained in a large N-body and hydrodynamical simulation of structure formation in a low density CDM universe are reported, with 256 3 particles and 4:1 10 7 cells in the AMR grid, reaching a formal resolution of 8192 3 .A convergence analysis of dierent quantities, such as dark matter density power spectrum, gas pressure power spectrum and individual haloe temperature proles, shows that numerical results are converging down to the actual resolution limit of the code, and are well reproduced by recent analytical predictions in the framework of the halo model.

Theoretical isochrones in several photometric systems I. Johnson-Cousins-Glass, HST/WFPC2, HST/NICMOS, Washington, and ESO Imaging Survey filter sets

Abstract: We provide tables of theoretical isochrones in several photometric systems. To this aim, the following steps are followed: (1) first, we re-write the formalism for converting synthetic stellar spectra into tables of bolometric corrections. The resulting formulas can be applied to any photometric system, provided that the zero-points are specified by means of either ABmag, STmag, VEGAmag, or a standard star system that includes well-known spectrophotometric standards. Interstellar ab- sorption can be considered in a self-consistent way. (2) We assemble an extended and updated library of stellar intrinsic spectra. It is mostly based on "non-overshooting" ATLAS9 models, suitably extended to both low and high eective temperatures. This oers an excellent coverage of the parameter space of Te ,l ogg ,a nd (M/H). We briefly discuss the main uncertainties and points still deserving more improvement. (3) From the spectral library, we derive tables of bolometric corrections for Johnson- Cousins-Glass, HST/WFPC2, HST/NICMOS, Washington, and ESO Imaging Survey systems (this latter consisting on the WFI, EMMI, and SOFI filter sets). (4) These tables are used to convert several sets of Padova isochrones into the corresponding absolute magnitudes and colours, thus providing a useful database for several astrophysical applications. All data files are made available in electronic form.

Intrinsic spectra and energetics of BeppoSAX Gamma-Ray Bursts with known redshifts

Abstract: We present the main results of a study of spectral and energetics properties of twelve gamma-ray bursts (GRBs) with redshift estimates. All GRBs in our sample were detected by BeppoSAX in a broad energy range (2-700 keV). From the redshift estimates and the good-quality BeppoSAX time-integrated spectra we deduce the main properties of GRBs in their cosmological rest frames. All spectra in our sample are satisfactorily represented by the Band model, with no significant soft X-ray excesses or spectral absorptions. We find a positive correlation between the estimated total (isotropic) energies in the 1-10 000 keV energy range (Erad) and redshifts z. Interestingly, more luminous GRBs are characterized also by larger peak energies Ep so f theirEF(E) spectra. Furthermore, more distant GRBs appear to be systematically harder in the X-ray band compared to GRBs with lower redshifts. We discuss how selection and data truncation eects could bias our results and give possible explanations for the correlations that we found.

A box-fitting algorithm in the search for periodic transits

Abstract: We study the statistical characteristics of a box-fitting algorithm to analyze stellar photometric time series in the search for periodic transits by extrasolar planets. The algorithm searches for signals characterized by a periodic alternation between two discrete levels, with much less time spent at the lower level. We present numerical as well as analytical results to predict the possible detection significance at various signal parameters. It is shown that the crucial parameter is the eective signal-to-noise ratio - the expected depth of the transit divided by the standard deviation of the measured photometric average within the transit. When this parameter exceeds the value of 6 we can expect a significant detection of the transit. We show that the box-fitting algorithm performs better than other methods available in the astronomical literature, especially for low signal-to-noise ratios.

New catalogue of optically visible open clusters and candidates

Abstract: We have compiled a new catalogue of open clusters in the Galaxy which updates the previous cat- alogues of Lyng a (1987) and of Mermilliod (1995) (included in the WEBDA database). New objects and new data, in particular, data on kinematics (proper motions) that were not present in the old catalogues, have been included. Virtually all the clusters (1537) presently known were included, which represents an increment of about 347 objects relative to the Lyng a (1987) catalogue. The catalogue is presented in a single table con- taining all the important data, which makes it easy to use. The catalogue can be accessed on line either at http://www.astro.iag.usp.br/~wilton/ or as an electronic table which will be made available at the CDS.

Dynamo action by differential rotation in a stably stratified stellar interior

Abstract: Magnetic fields can be created in stably stratified (non-convective) layers in a differentially rotating star. A magnetic instability in the toroidal field (wound up by differential rotation) replaces the role of convection in closing the field amplification loop. Tayler instability is likely to be the most relevant magnetic instability. A dynamo model is developed from these ingredients, and applied to the problem of angular momentum transport in stellar interiors. It produces a predominantly horizontal field. This dynamo process is found to be more effective in transporting angular momentum than the known hydrodynamic mechanisms. It might account for the observed pattern of rotation in the solar core.

On the properties of massive Population III stars and metal-free stellar populations

Abstract: We present realistic models for massive Population III stars and stellar populations based on non-LTE model atmospheres, recent stellar evolution tracks and up-to-date evolutionary synthesis models, with the aim to study their spectral properties, including their dependence on age, star formation history, and IMF. A comparison of plane parallel non-LTE model atmospheres and comoving frame calculations shows that even in the presence of some putative weak mass loss, the ionising spectra of metal-free populations differ little or negligibly from those obtained using plane parallel non-LTE models. As already discussed by Tumlinson & Shull ([CITE]), the main salient property of Pop III stars is their increased ionising flux, especially in the He+ continuum (>54 eV). The main result obtained for individual Pop III stars is the following: due to their redward evolution off the zero age main sequence (ZAMS) the spectral hardness measured by the He/H ionising flux is decreased by a factor ~2 when averaged over their lifetime. If such stars would suffer strong mass loss, their spectral appearance could, however, remain similar to that of their ZAMS position. The main results regarding integrated stellar populations are: – for young bursts and the case of a constant SFR, nebular continuous emission – neglected in previous studies – dominates the spectrum redward of Lyman-α if the escape fraction of ionising photons out of the considered region is small or negligible. In consequence predicted emission line equivalent widths are considerably smaller than found in earlier studies, whereas the detection of the continuum is eased. Nebular line and continuous emission strongly affect the broad band photometric properties of Pop III objects; – due to the redward stellar evolution and short lifetimes of the most massive stars, the hardness of the ionising spectrum decreases rapidly, leading to the disappearance of the characteristic He ii recombination lines after ~3 Myr in instantaneous bursts; – He ii λ 1640, Hα (and other) line luminosities usable as indicators of the star formation rate are given for the case of a constant SFR. For obvious reasons such indicators depend strongly on the IMF; – due to an increased photon production and reduced metal yields, the relative efficiency of ionising photon energy to heavy element rest mass production, η , of metal-poor and metal-free populations is increased by factors of ~4 to 18 with respect to solar metallicity and for “standard” IMFs; – the lowest values of 1.6–2.2% are obtained for IMFs exclusively populated with high mass stars (). If correct, the yields dominated by pair creation SNae then predict large overabundances of O/C and Si/C compared to solar abundance ratios. Detailed results are given in tabular form and as fit formulae for easy implementation in other calculations. The predicted spectra will be used to study the detectability of Pop III galaxies and to derive optimal search strategies for such objects.

Evolutionary models for low-mass stars and brown dwarfs: uncertainties and limits at very young ages

Abstract: We analyse pre-Main Sequence evolutionary tracks for low mass stars with masses $m \\le 1.4 \\msol$ based on the Baraffe et al. (1998) input physics. We also extend the recent Chabrier et al. (2000) evolutionary models based on dusty atmosphere to young brown dwarfs down to one mass of Jupiter. We analyse current theoretical uncertainties due to molecular line lists, convection and initial conditions. Simple tests on initial conditions show the high uncertainties of models at ages $\\simle$ 1 Myr. We find a significant sensitivity of atmosphere profiles to the treatment of convection at low gravity and $\\te < 4000$ K, whereas it vanishes as gravity increases. This effect adds another source of uncertainty on evolutionary tracks at very early phases. We show that at low surface gravity ($\\log g \\simle 3.5$,) the common picture of vertical Hayashi lines with constant $\\te$ is oversimplified. The effect of a variation of initial deuterium abundance is studied. We compare our models with evolutionary tracks available in the literature and discuss the main differences. We finally analyse to which extent current observations of young systems provide a good test for pre-Main Sequence tracks.

Atmospheric circulation and tides of ``51 Pegasus b-like'' planets

Abstract: We examine the properties of the atmospheres of extrasolar giant planets at orbital distances smaller than 0.1 AU from their stars. We show that these \51 Peg b-like" planets are rapidly synchronized by tidal in- teractions, but that small departures from synchronous rotation can occur because of fluid-dynamical torques within these planets. Previous radiative-transfer and evolution models of such planets assume a homogeneous atmosphere. Nevertheless, we show using simple arguments that, at the photosphere, the day-night temperature dierence and characteristic wind speeds may reach500 K, and 2k m s 1 , respectively. Substantial departures from chemical equilibrium are expected. The cloud coverage depends sensitively on the dynamics; clouds could exist predominantly either on the dayside or nightside, depending on the circulation regime. Radiative-transfer models that assume homogeneous conditions are therefore inadequate in describing the atmospheric properties of 51 Peg b-like planets. We present preliminary three-dimensional, nonlinear simulations of the atmospheric cir- culation of HD 209458b that indicate plausible patterns for the circulation and generally agree with our simpler estimates. Furthermore, we show that kinetic energy production in the atmosphere can lead to the deposition of substantial energy in the interior, with crucial consequences for the evolution of these planets. Future measure- ments of reflected and thermally-emitted radiation from these planets will help test our ideas.

The rich 6 to 9 vec mu m spectrum of interstellar PAHs

Abstract: IR spectroscopy provides a valuable tool for the characterisation and identification of interstellar molecular species. Here, we present 6-9 mum spectra of a sample of reflection nebulae, HII regions, YSOs, evolved stars and galaxies that show strong unidentified infrared bands, obtained with the SWS spectrograph on board ISO. The IR emission features in this wavelength region show pronounced variations. 1) The 6.2 mum feature shifts from 6.22 to 6.3 mum and clearly shows profile variations. 2) The 7.7 mum complex is comprised of at least two subpeaks peaking at 7.6 and one longwards of 7.7 mum. In some cases the main peak can apparently shift up to 8 mum. Two sources do not exhibit a 7.7 mum complex but instead show a broad emission feature at 8.22 mum. 3) The 8.6 mum feature has a symmetric profile in all sources and some sources exhibit this band at slightly longer wavelengths. For the 6.2, 7.7 and 8.6 mum features, the sources have been classified independently based on their profile and peak position. The classes derived for these features are directly linked with each other. Sources with a 6.2 mum feature peaking at similar to6.22 mum exhibit a 7.7 mum complex dominated by the 7.6 mum component. In contrast, sources with a 6.2 mum profile peaking longwards of 6.24 mum show a 7.7 mum complex with a dominant peak longwards of 7.7 mum and a 8.6 mum feature shifted toward the red. Furthermore, the observed 6-9 mum spectrum depends on the type of object. All ISM-like sources and a few PNe and Post-AGB stars belong to the first group while isolated Herbig AeBe stars, a few Post-AGB stars and most PNe belong to the second group. We summarise existing laboratory data and theoretical quantum chemical calculations of the modes emitting in this wavelength region of PAH molecules. We discuss the variations in peak position and profile in view of the exact nature of the carrier. We attribute the observed 6.2 mum profile and peak position to the combined effect of a PAH family and anharmonicity with pure PAHs representing the 6.3 mum component and substituted/complexed PAHs representing the 6.2 mum component. The 7.6 mum component is well reproduced by both pure and substituted/complexed PAHs but the 7.8 mum component remains an enigma. In addition, the exact identification of the 8.22 mum feature remains unknown. The observed variations in the characteristics of the IR emission bands are linked to the local physical conditions. Possible formation and evolution processes that may influence the interstellar PAH class are highlighted.

High-resolution rotation curves of low surface brightness galaxies

Abstract: We present high-resolution rotation curves of a sample of 26 low surface brightness galaxies. From these curves we derive mass distributions using a variety of assumptions for the stellar mass-to-light ratio. We show that the predictions of current Cold Dark Matter models for the density proles of dark matter halos are inconsistent with the observed curves. The latter indicate a core-dominated structure, rather than the theoretically preferred cuspy structure.

Massive Molecular Outflows

Abstract: With the aim of understanding the role of massive outflows in high-mass star formation, we mapped in the 12 CO transition 26 high-mass star-forming regions at very early stages of their evolution. At a spatial resolution of bipolar molecular outflows were found in 21 of them. The other five sources show confusing morphology but strong line wings. This high detection rate of bipolar structure proves that outflows common in low-mass sources are also ubiquitous phenomena in the formation process of massive stars. The flows are large, very massive and energetic, and the data indicate stronger collimation than previously thought. The dynamical timescales of the flows correspond well to the free-fall timescales of the associated cores. Comparing with correlations known for low-mass flows, we find continuity up to the high-mass regime suggesting similar flow-formation scenarios for all masses and luminosities. Accretion rate estimates in the range are around yr-1 , higher than required for low-mass star formation, but consistent with high-mass star formation scenarios. Additionally, we find a tight correlation between the outflow mass and the core mass over many orders of magnitude. The strong correlation between those two quantities implies that the product of the accretion efficiency and (the ratio between jet mass loss rate and accretion rate), which equals the ratio between jet and core mass (), is roughly constant for all core masses. This again indicates that the flow-formation processes are similar over a large range of masses. Additionally, we estimate median and values of approximately 0.2 and 0.01, respectively, which is consistent with current jet-entrainment models. To summarize, the analysis of the bipolar outflow data strongly supports theories which explain massive star formation by scaled up, but otherwise similar physical processes – mainly accretion – to their low-mass counterparts.

The CORALIE survey for southern extra-solar planets VII - Two short-period Saturnian companions to HD 108147 and HD 168746

Abstract: Received 7 February 2002 / Accepted 19 March 2002 We present the discovery of two Saturn-mass companions to HD 108147 and HD 168746. Both belong to the lightest ever discovered planets. The minimum mass of the companion to HD 168746 is of only 0.77 the mass of Saturn and its orbital period is 6.4 days. The companion to HD 108147 orbits its parent star in 10.9 days and its minimum mass is 1.34 that of Saturn. Its orbit is characterized by a high eccentricity, e = 0.50, indicating possibly the presence of a second companion. The detection of Saturn-mass planets by means of the Doppler technique demands high radial-velocity measurement precision. The two new candidates were discovered by means of the CORALIE echelle spectrograph. The instrumental accuracy of CORALIE combined with the simultaneous ThAr-reference technique has reached a level better than 3 m s - 1 . On many observed objects the precision is now limited by photon noise. We present in this paper the weighted cross-correlation technique, which leads to an improvement in the photon noise of the computed radial velocity. We discuss as well a modification of the numerical cross-correlation mask which reduces significantly the residual perturbation effects produced by telluric absorption lines.

First stars. I. The extreme r-element rich, iron-poor halo giant CS 31082-001 - Implications for the r-process site(s) and radioactive cosmochronology

Abstract: We present a high-resolution (R = 75 000, S/N 500) spectroscopic analysis of the bright (V = 11.7), extreme halo giant CS 31082-001 ((Fe/H) = 2.9), obtained in an ESO-VLT Large Programme dedicated to very metal-poor stars. We nd CS 31082-001 to be extremely rich in r-process elements, comparable in this respect only to the similarly metal-poor, but carbon-enriched, giant CS 22892-052. As a result of the extreme overabundance of the heaviest r-process elements, and negligible blending from CH and CN molecular lines, a reliable measurement is obtained of the U II line at 386 nm, for the rst time in a halo star, along with numerous lines of Th II, as well as lines of 25 other r-process elements. Abundance estimates for a total of 43 elements (44 counting Hydrogen) are reported in CS 31082-001, almost half of the entire periodic table. The main atmospheric parameters of CS 31082- 001 are as follows: Te = 4825 50 K, logg =1 :5 0: 3( cgs), (Fe/H) = 2.9 0:1 (in LTE), and microturbulence 1.8 0.2 km s 1 . Carbon and nitrogen are not signicantly enhanced relative to iron. As usual in giant stars, Li is depleted by dilution (log(Li/H) = 0.85). The -elements show the usual enhancements with respect to iron, with (O/Fe) = 0:6 0:2 (from (O I) 6300 A), (Mg/Fe) = 0:45 0:16, (Si/Fe) = 0:24 0:1, and (Ca/Fe) = 0:41 0:08, while (Al/Fe) is near 0.5. The r-process elements show unusual patterns: among the lightest elements (Z 40), Sr and Zr follow the Solar r-element distribution, but Ag is down by 0.8 dex. All elements with 56 Z 72 follow the Solar r-element pattern, reduced by about 1.25 dex. Accordingly, the (r/Fe) enhancement is about +1.7 dex (a factor of 50), very similar to that of CS 22892-052. Pb, in contrast, seems to be below the shifted Solar r-process distribution, possibly indicating an error in the latter, while thorium is more enhanced than the lighter nuclides. In CS 31082-001, log(Th/Eu) is 0:22 0:07, higher than in the Solar System ( 0.46) or in CS 22892-052 ( 0.66). If CS 31082-001 and CS 22892-052 have similar ages, as expected for two extreme halo stars, this implies that the production ratios were dierent by about 0.4 dex for the two objects. Conversely, if the Th/Eu production ratio were universal, an age of 15 Gyr for CS 22892-052 would imply a negative age for CS 31082-001. Thus, while a universal production ratio for the r-process elements seems to hold in the interval 56 Z 72, it breaks down in the actinide region. When available, the U/Th is thus preferable to Th/Eu for radioactive dating, for two reasons: (i) because of its faster decay rate and smaller sensitivity to observational errors, and (ii) because the inital production ratio of the neighboring nuclides 238 Ua nd 232 Th is more robustly predicted than the 151 Eu/ 232 Th ratio. Our current best estimate for the age of CS 31082-001 is 14:0 2: 4G yr. However, the computed actinide production ratios should be veried by observations of daughter elements such as Pb and Bi in the same star, which are independent of the subsequent history of star formation and nucelosynthesis in the Galaxy.

Efficient acceleration and radiation in Poynting flux powered GRB outflows

Abstract: We investigate the eects of magnetic energy release by local magnetic dissipation processes in Poynting flux- powered GRBs. For typical GRB parameters (energy and baryon loading) the dissipation takes place mainly outside the pho- tosphere, producing non-thermal radiation. This process converts the total burst energy into prompt radiation at an eciency of 10-50%. At the same time the dissipation has the eect of accelerating the flow to a large Lorentz factor. For higher baryon loading, the dissipation takes place mostly inside the photosphere, the eciency of conversion of magnetic energy into radia- tion is lower, and an X-ray flash results instead of a GRB. We demonstrate these eects with numerical one-dimensional steady relativistic MHD calculations.

The Nuclear Bulge of the Galaxy. III. Large-Scale Physical Characteristics of Stars and Interstellar Matter

Abstract: We analyse IRAS and COBE DIRBE data at wavelengths between 2.2 and 240 of the central 500 pc of the Galaxy and derive the large-scale distribution of stars and interstellar matter in the Nuclear Bulge. Models of the Galactic Disk and Bulge are developed in order to correctly decompose the total surface brightness maps of the inner Galaxy and to apply proper extinction corrections. The Nuclear Bulge appears as a distinct, massive disk-like complex of stars and molecular clouds which is, on a large scale, symmetric with respect to the Galactic Centre. It is distinguished from the Galactic Bulge by its flat disk-like morphology, very high density of stars and molecular gas, and ongoing star formation. The Nuclear Bulge consists of an R^(-2) Nuclear Stellar Cluster at the centre, a large Nuclear Stellar Disk with radius 230 ± 20 pc and scale height 45 ± 5 pc, and the Nuclear Molecular Disk of same size. The total stellar mass and luminosity of the Nuclear Bulge are 1.4 ± 0.6 x 10^9 and 2.5 ± 1 x 10^9, respectively. About 70% of the luminosity is due to optical and UV radiation from young massive Main-Sequence stars which are most abundant in the Nuclear Stellar Cluster. For the first time, we derive a photometric mass distribution for the central 500 pc of the Galaxy which is fully consistent with the kinematic mass distribution. We find that the often cited R^(-2) distribution holds only for the central ~30 pc and that at larger radii the mass distribution is dominated by the Nuclear Stellar Disk which has a flatter density profile. The total interstellar hydrogen mass in the Nuclear Bulge is M_H = 2 ± 0.3 x 10^7, distributed in a warm inner disk with R = 110 ± 20 pc and a massive, cold outer torus which contains more than 80% of this mass. Interstellar matter in the Nuclear Bulge is very clumpy with ~90% of the mass contained in dense and massive molecular clouds with a volume filling factor of only a few per cent. This extreme clumpiness, probably caused by the tidal stability limit in the gravitational potential of the Nuclear Bulge, enables the strong interstellar radiation field to penetrate the entire Nuclear Bulge and explains the relatively low average extinction towards the Galactic Centre. In addition, we find 3 x 10^7 of cold and dense material outside the Nuclear Bulge at positive longitudes and 1 x 10^7 at negative longitudes. This material is not heated by the stars in the Nuclear Bulge and gives rise to the observed asymmetry in the distribution of interstellar matter in the Central Molecular Zone.

X-ray background measurements with XMM-Newton EPIC

Abstract: We discuss the methods used to compile a high signal-to-noise dataset representative of both the instrumental and cosmic background signal measured at high galactic latitude by the XMM-Newton EPIC cameras. The characteristics of the EPIC background are described and the potential applications of the de- rived dataset in general science analysis are outlined. In the case of the cosmic X-ray background, the tran- sition between a hard power-law spectrum (due to the integrated emission of unresolved, largely extragalac- tic, point sources) and a softer thermal spectrum (produced by hot plasma associated with the Galactic plane and halo) is unambiguously detected around 1 keV. We derive a value for the intensity of the power-law component of 2:15 0:26 10 11 erg cm 2 s 1 deg 2 in the 2{10 keV band (normalisation at 1 keV of 11.1 photons cm 2 s 1 sr 1 keV 1 ). The implication is that recent, very deep Chandra observations have re- solved70{90% of the 2{10 keV background into discrete sources. Our measurement is towards the higher end of the range of quoted background normalisations.

Stellar evolution with rotation - VIII. Models at $Z$ = 10$^\mathsf{-5}$ and CNO yields for early galactic evolution

Abstract: We calculate a grid of star models with and without the eects of axial rotation for stars in the mass range between 2 and 60 M for the metallicity Z= 10 5 . Star models with initial masses superior or equal to 9 M were computed up to the end of the carbon-burning phase. Star models with masses between 2 and 7 M were evolved beyond the end of the He-burning phase through a few thermal pulses during the AGB phase. Compared to models at Z = 0:02, the low Z models show faster rotating cores and stronger internal-gradients, which favour an important mixing of the chemical elements. The enhancement of N/C at the surface may reach 2 to 3 orders of magnitude for fast rotating stars. Surface enrichments may make the evolved stars less metal poor than they were initially. In very low Z models, primary nitrogen is produced during the He-burning phase by rotational diusion of 12 C into the H-burning shell. A large fraction of the primary 14 N escapes further destruction and enters the envelope of AGB stars, being ejected during the TP-AGB phase and the formation of a planetary nebula. The intermediate mass stars of very lowZ are the main producers of primary 14 N, but massive stars also contribute to this production; no significant primary nitrogen is made in models at metallicity Z= 0:004 or above. We calculate the chemical yields in He, C, N, O and heavy elements and discuss the chemical evolution of the CNO elements at very low Z. Remarkably, the C/ Ov s. O/H diagram is mainly sensitive to the interval of stellar masses, while the N/ Ov s. O/H diagram is mainly sensitive to the average rotation of the stars contributing to the element synthesis. The presently available observations in these diagrams seem to favour contributions either from stars down to about 2 M with normal rotation velocities or from stars above 8 M but with very fast rotation.

Representations of celestial coordinates in FITS

Abstract: In Paper I, Greisen & Calabretta (2002) describe a generalized method for assigning physical coordinates to FITS image pixels. This paper implements this method for all spherical map projections likely to be of interest in astronomy. The new methods encompass existing informal FITS spherical coordinate conventions and translations from them are described. Detailed examples of header interpretation and construction are given.

The Milky Way in X-rays for an outside observer - Log(N)-Log(S) and luminosity function of X-ray binaries from RXTE/ASM data

Abstract: We study the Log(N)-Log(S ) and X-ray luminosity function in the 2-10 keV energy band, and the spatial (3-D) distribution of bright, LX 10 34 10 35 erg s 1 , X-ray binaries in the Milky Way. In agreement with theoretical expectations and earlier results we found significant dierences between the spatial distributions of low (LMXB) and high (HMXB) mass X-ray binaries. The volume density of LMXB sources peaks strongly at the Galactic Bulge whereas HMXBs tend to avoid the inner 3 4 kpc of the Galaxy. In addition HMXBs are more concentrated towards the Galactic Plane (scale heights of150 and 410 pc for HMXB and LMXB correspondingly) and show clear signatures of the spiral structure in their spatial distribution. The Log(N)-Log(S ) distributions and the X-ray luminosity functions are also noticeably dierent. LMXB sources have a flatter Log(N)-Log(S ) distribution and luminosity function. The integrated 2-10 keV luminosities of all X-ray binaries in the Galaxy, averaged over 1996-2000, are2 3 10 39 (LMXB) and2 3 10 38 (HMXB) erg s 1 . Normalised to the stellar mass and the star formation rate, respectively, these correspond to5 10 28 erg s 1 M 1 for LMXBs and5 10 37 erg s 1 /(M yr 1 ) for HMXBs. Due to the shallow slopes of the luminosity functions the integrated emission of X-ray binaries is dominated by the5-10 most luminous sources which determine the appearance of the Milky Way in the standard X-ray band for an outside observer. In particular variability of individual sources or an outburst of a bright transient source can increase the integrated luminosity of the Milky Way by as much as a factor of2. Although the average LMXB luminosity function shows a break near the Eddington luminosity for a 1.4 M neutron star, at least 12 sources showed episodes of super-Eddington luminosity during ASM observations. We provide the maps of distribution of X-ray binaries in the Milky Way in various projections, which can be compared to images of nearby galaxies taken by CHANDRA and XMM-Newton.

Radiation hydrodynamics with neutrinos - Variable Eddington factor method for core-collapse supernova simulations

Abstract: Neutrino transport and neutrino interactions in dense matter play a crucial role in stellar core collapse, supernova explosions and neutron star formation. Here we present a detailed description of a new numerical code for treating the time and energy dependent neutrino transport in hydrodynamical simulations of such events. The code is based on a variable Eddington factor method to deal with the integro-differential character of the Boltzmann equation. The moments of the neutrino distribution function and the energy and lepton number exchange with the stellar medium are determined by iteratively solving the zeroth and first order moment equations in combination with a model Boltzmann equation. The latter is discretized on a grid of tangent rays. The integration of the transport equations and the neutrino source terms is performed in a time-implicit way. In the present version of the program, the transport part is coupled to an explicit hydrodynamics code which follows the evolution of the stellar plasma by a finite-volume method with piecewise parabolic interpolation, using a Riemann solver to calculate the hydrodynamic states. The neutrino source terms are implemented in an operator-split step. Neutrino transport and hydrodynamics can be calculated with different spatial grids and different time steps. The structure of the described code is modular and offers a high degree of flexibility for an application to relativistic and multi-dimensional problems at different levels of refinement and accuracy. We critically evaluate results for a number of test cases, including neutrino transport in rapidly moving stellar media and approximate relativistic core collapse, and suggest a path for generalizing the code to be used in multi-dimensional simulations of convection in neutron stars and supernovae.

Coronal loop oscillations - An interpretation in terms of resonant absorption of quasi-mode kink oscillations

Abstract: Damped quasi-mode kink oscillations in cylindrical flux tubes are capable of explaining the observed rapid damping of the coronal loop oscillations when the ratio of the inhomogeneity length scale to the radius of the loop is allowed to vary from loop to loop, without the need to invoke anomalously low Reynolds numbers. The theoretical expressions for the decay time by Hollweg & Yang ([CITE]) and Ruderman & Roberts ([CITE]) are used to estimate the ratio of the length scale of inhomogeneity compared to the loop radius for a collection of loop oscillations.

The Bulk of the Cosmic Infrared Background Resolved by ISOCAM

Abstract: Deep extragalactic surveys with ISOCAM revealed the presence of a large density of faint mid-infrared (MIR) sources. We have computed the 15m integrated galaxy light produced by these galaxies above a sensitivity limit of 50 Jy. It sets a lower limit to the 15m extragalactic background light of (2:4 0:5) nW m 2 sr 1 .T he redshift distribution of the ISOCAM galaxies is inferred from the spectroscopically complete sample of galaxies in the Hubble Deep Field North (HDFN). It peaks around z 0.8 in agreement with studies in other elds. The rest-frame 15m and bolometric infrared (8{1000m) luminosities of ISOCAM galaxies are computed using the correlations that we establish between the 6.75, 12, 15m and infrared (IR) luminosities of local galaxies. The resulting IR luminosities were double-checked using radio (1.4 GHz) flux densities from the ultra-deep VLA and WSRT surveys of the HDFN on a sample of 24 galaxies as well as on a sample of 109 local galaxies in common between ISOCAM and the NRAO VLA Sky Survey (NVSS). This comparison shows for the rst time that MIR and radio luminosities correlate up to z 1. This result validates the bolometric IR luminosities derived from MIR luminosities unless both the radio-far infrared (FIR) and the MIR-FIR correlations become invalid around z 1. The fraction of IR light produced by active nuclei was computed from the cross-correlation with the deepest X-ray surveys from the Chandra and XMM-Newton observatories in the HDFN and Lockman Hole respectively. We nd that at most 20% of the 15m integrated galaxy light is due to active galactic nuclei (AGNs) unless a large population of AGNs was missed by Chandra and XMM-Newton. About 75% of the ISOCAM galaxies are found to belong to the class of luminous infrared galaxies (LIR 10 11 L). They exhibit star formation rates of the order of100 M yr 1 . The comoving density of infrared light due to these luminous IR galaxies was more than 40 times larger at z 1 than today. The contribution of ISOCAM galaxies to the peak of the cosmic infrared background (CIRB) at 140m was computed from the MIR-FIR correlations for star forming galaxies and from the spectral energy distribution of the Seyfert 2, NGC 1068, for AGNs. We nd that the galaxies unveiled by ISOCAM surveys are responsible for the bulk of the CIRB, i.e. (16 5) nW m 2 sr 1 as compared to the (25 7) nW m 2 sr 1 measured with the COBE satellite, with less than 10% due to AGNs. Since the CIRB contains most of the light radiated over the history of star formation in the universe, this means that a large fraction of present-day stars must have formed during a dusty starburst event similar to those revealed by ISOCAM.

Evolution of "51 Pegasus b-like" planets

Abstract: About one-quarter of the extrasolar giant planets discovered so far have orbital distances smaller than 0.1 AU. These "51 Peg b-like" planets can now be directly characterized, as shown by the planet transiting in front the star HD 209458. We review the processes that affect their evolution. We apply our work to the case of HD 209458b, whose radius has been recently measured. We argue that its radius can be reproduced only when the deep atmosphere is assumed to be unrealistically hot. When using more realistic atmospheric temperatures, an energy source appears to be missing in order to explain HD 209458b's large size. The most likely source of energy available is not in the planet's spin or orbit, but in the intense radiation received from the parent star. We show that the radius of HD 209458b can be reproduced if a small fraction (∼1%) of the stellar flux is transformed into kinetic energy in the planetary atmosphere and subsequently converted to thermal energy by dynamical processes at pressures of tens of bars.

Gas accretion on spiral galaxies: Bar formation and renewal

Abstract: The eects of gas accretion on spiral disk dynamics and stability are studied through N-body simulations, including star formation and gas/stars mass exchange. The detailed processes of bar formation, bar destruction and bar re-formation are followed, while in the same time the disk to bulge ratio is varying. The accreted gas might be first prevented to flow inwards to the center by the bar gravity torques, which maintains it to the outer Lindblad resonance. While the first bar is weakening, the accreted gas replenishes the disk, increasing the disk-to-bulge ratio, and the disk self-gravity. A second bar is then unstable, with a higher pattern speed, due both to the increased mass, and shorter bar length. Three or four bar episodes have been followed over a Hubble time. Their strength is decreasing with time, while their pattern speed is increasing. Detailed balance of the angular momentum transfer and evolution can account for these processes. The gas recycled through star formation, and rejected through stellar mass loss plays also a role in the disk dynamics. Implications on the spiral galaxy dynamics and evolution along the Hubble sequence, and as a function of redshift are discussed.

Helium variation due to self–pollution among Globular Cluster stars - Consequences on the horizontal branch morphology

Abstract: It is becoming clear that "self-pollution" by the ejecta of massive asymptotic giant branch stars has an important role in the early chemical evolution of globular cluster stars, producing CNO abundance spreads which are observed also at the surface of unevolved stars. Observing that the ejecta which are CNO processed must also be helium enriched, we have modelled stellar evolution of globular cluster stars by taking into account this possible helium enhancement with respect to the primordial value. We show that the differences between the main evolutionary phases (main sequence, turn-off and red giants) are small enough that it would be very difficult to detect them observationally. However, the difference in the evolving mass may play a role in the morphology of the horizontal branch, and in particular in the formation of blue tails, in those globular clusters which show strong CNO abundance variations, such as M13 and NGC 6752.

Physical structure and CO abundance of low-mass protostellar envelopes

Abstract: We present 1D radiative transfer modelling of the envelopes of a sample of 18 low-mass protostars and pre-stellar cores with the aim of setting up realistic physical models, for use in a chemical description of the sources. The density and temperature proles of the envelopes are constrained from their radial proles obtained from SCUBA maps at 450 and 850 m and from measurements of the source fluxes ranging from 60 mt o 1.3 mm. The densities of the envelopes within 10 000 AU can be described by single power-laws / r for the class 0 and I sources with ranging from 1.3 to 1.9, with typical uncertainties of0.2. Four sources have flatter proles, either due to asymmetries or to the presence of an outer constant density region. No signicant dierence is found between class 0 and I sources. The power-law ts fail for the pre-stellar cores, supporting recent results that such cores do not have a central source of heating. The derived physical models are used as input for Monte Carlo modelling of submillimeter C 18 Oa nd C 17 O emission. It is found that class I objects typically show CO abundances close to those found in local molecular clouds, but that class 0 sources and pre-stellar cores show lower abundances by almost an order of magnitude implying that signicant depletion occurs for the early phases of star formation. While the 2{1 and 3{2 isotopic lines can be tted using a constant fractional CO abundance throughout the envelope, the 1{0 lines are signicantly underestimated, possibly due to contribution of ambient molecular cloud material to the observed emission. The dierence between the class 0 and I objects may be related to the properties of the CO ices.

HST color-magnitude diagrams of 74 galactic globular clusters in the HST F439W and F555W bands ⋆

Abstract: We present the complete photometric database and the color-magnitude diagrams for 74 Galactic globular clusters observed with the HST/WFPC2 camera in the F439W and F555W bands. A detailed discussion of the various reduction steps is also presented, and of the procedures to transform instrumental magnitudes into both the HST F439W and F555W flight system and the standard Johnson B and V systems. We also describe the artificial star experiments which have been performed to derive the star count completeness in all the relevant branches of the color magnitude diagram. The entire photometric database and the completeness function will be made available on the Web immediately after the publication of the present paper.

New algorithms for reducing cross-dispersed echelle spectra

Abstract: We describe advanced image processing algorithms, implemented in a data analysis package for conven- tional and cross-dispersed echelle spectra. Comparisons with results from other packages illustrate the outstanding quality of the new REDUCE package, particularly in terms of resulting noise level and treatment of CCD defects and cosmic ray spikes. REDUCE can be adapted relatively easily to handle a variety of instrument types, including spec- trographs with prism or grating cross-dispersers, possibly fed by a ber or image slicer, etc. In addition to reduced spectra, an accurate spatial prole is recovered, providing valuable information about the spectrograph PSF and simplifying scattered light corrections.

The Westerbork HI survey of spiral and irregular galaxies - I. HI imaging of late-type dwarf galaxies

Abstract: Neutral hydrogen observations with the Westerbork Synthesis Radio Telescope are presented for a sample of 73 late-type dwarf galaxies. These observations are part of the WHISP project (Westerbork Hi Survey of Spiral and Irregular Galaxies). Here we present Hi maps, velocity fields, global profiles and radial surface density profiles of Hi, as well as Hi masses, Hi radii and line widths. For the late-type galaxies in our sample, we find that the ratio of Hi extent to optical diameter, defined as 6.4 disk scale lengths, is on average 1.8 +/- 0.8, similar to that seen in spiral galaxies. Most of the dwarf galaxies in this sample are rich in Hi with a typical M-HI/L-B of 1.5. The relative H I content M-HI/L-R increases towards fainter absolute magnitudes and towards fainter surface brightnesses. Dwarf galaxies with lower average H I column densities also have lower average optical surface brightnesses. We find that lopsidedness is as common among dwarf galaxies as it is in spiral galaxies. About half of the dwarf galaxies in our sample have asymmetric global profiles, a third has a lopsided H I distribution, and about half shows signs of kinematic lopsidedness.