Showing papers in "Astronomy and Astrophysics in 2005"

The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI - Final data release of the combined LDS and IAR surveys with improved stray-radiation corrections

Abstract: We present the final data release of observations of ?21-cm emission from Galactic neutral hydrogen over the entire sky, merging the Leiden/Dwingeloo Survey (LDS: Hartmann & Burton 1997, Atlas of Galactic Neutral Hydrogen) of the sky north of ? = ?30? with the Instituto Argentino de Radioastronomia Survey (IAR: Arnal et al. 2000, AA and Bajaja et al. 2005, A&A, 440, 767) of the sky south of ? = ?25?. The angular resolution of the combined material is HPBW ? 0. ?6. The LSR velocity coverage spans the interval ?450 km s?1 to +400 km s?1, at a resolution of 1.3 kms?1. The data were corrected for stray radiation at the Institute for Radioastronomy of the University of Bonn, refining the original correction applied to the LDS. The rms brightness-temperature noise of the merged database is 0.07?0.09 K. Residual errors in the profile wings due to defects in the correction for stray radiation are for most of the data below a level of 20?40 mK. It would be necessary to construct a telescope with a main beam efficiency of ?MB >? 99% to achieve the same accuracy. The merged and refined material entering the LAB Survey of Galactic HI is intended to be a general resource useful to a wide range of studies of the physical and structural characteristices of the Galactic interstellar environment. The LAB Survey is the most sensitive Milky Way HI survey to date, with the most extensive coverage both spatially and kinematically.

An atomic and molecular database for analysis of submillimetre line observations

Abstract: Atomic and molecular data for the transitions of a number of astrophysically interesting species are summarized, in- cluding energy levels, statistical weights, Einstein A-coefficients and collisional rate coefficients. Available collisional data from quantum chemical calculations and experiments are extrapolated to higher energies (up to E/k ∼ 1000 K). These data, which are made publically available through the WWW at http://www.strw.leidenuniv.nl/∼moldata, are essential input for non-LTE line radiative transfer programs. An online version of a computer program for performing statistical equilibrium calcu- lations is also made available as part of the database. Comparisons of calculated emission lines using different sets of collisional rate coefficients are presented. This database should form an important tool in analyzing observations from current and future (sub)millimetre and infrared telescopes.

A new calibration of stellar parameters of Galactic O stars

Abstract: We present new calibrations of stellar parameters of O stars at solar metallicity taking non-LTE, wind, and line-blanketing effects into account. Gravities and absolute visual magnitudes are derived from results of recent spectroscopic analyses. Two types of effective temperature scales are derived: one from a compilation based on recent spectroscopic studies of a sample of massive stars – the “observational scale” – and the other from direct interpolations on a grid of non-LTE spherically extended line-blanketed models computed with the code CMFGEN (Hillier & Miller 1998) – the “theoretical scale”. These T eff scales are then further used together with the grid of models to calibrate other parameters (bolometric correction, luminosity, radius, spectroscopic mass and ionising fluxes) as a function of spectral type and luminosity class. Compared to the earlier calibrations of Vacca et al. (1996) the main results are: [–] The effective temperature scales of dwarfs, giants and supergiants are cooler by 2000 to 8000 K, the theoretical scale being slightly cooler than the observational one. The reduction is the largest for the earliest spectral types and for supergiants. [–] Bolometric corrections as a function of T eff are reduced by 0.1 mag due to line blanketing which redistributes part of the UV flux in the optical range. For a given spectral type the reduction of BC is larger for early types and for supergiants. Typically BCs derived using the theoretical T eff scale are 0.40 to 0.60 mag lower than that of Vacca et al. (1996), whereas the differences using the observational T eff scale are somewhat smaller. [–] Luminosities are reduced by 0.20 to 0.35 dex for dwarfs, by ~0.25 for all giants and by 0.25 to 0.35 dex for supergiants. The reduction is essentially the same for both T eff scales. It is independent of spectral type for giants and supergiants and is slightly larger for late type than for early type dwarfs. [–] Lyman continuum fluxes are reduced. Our theoretical values for the hydrogen ionising photon fluxes for dwarfs are 0.20 to 0.80 dex lower than those of Vacca et al. (1996), the difference being larger at late spectral types. For giants the reduction is of 0.25 to 0.55 dex, while for supergiants it is of 0.30 to 0.55 dex. Using the observational T eff scale leads to smaller reductions at late spectral types. The present results should represent a significant improvement over previous calibrations, given the detailed treatment of non-LTE line-blanketing in the expanding atmospheres of massive stars.

Simulations of magneto-convection in the solar photosphere Equations, methods, and results of the MURaM code

Abstract: We have developed a 3D magnetohydrodynamics simulation code for applications in the solar convection zone and photosphere. The code includes a non-local and non-grey radiative transfer module and takes into account the effects of partial ionization. Its parallel design is based on domain decomposition, which makes it suited for use on parallel computers with distributed memory architecture. We give a description of the equations and numerical methods and present the results of the simulation of a solar plage region. Starting with a uniform vertical field of 200 G, the processes of flux expulsion and convective field amplification lead to a dichotomy of strong, mainly vertical fields embedded in the granular downflow network and weak, randomly oriented fields filling the hot granular upflows. The strong fields form a magnetic network with thin, sheet- like structures extending along downflow lanes and micropores with diameters of up to 1000 km which form occasionally at vertices where several downflow lanes merge. At the visible surface around optical depth unity, the strong field concentrations are in pressure balance with their weakly magnetized surroundings and reach field strengths of up to 2 kG, strongly exceeding the values corresponding to equipartition with the kinetic energy density of the convective motions. As a result of the channelling of radiation, small flux concentrations stand out as bright features, while the larger micropores appear dark in brightness maps owing to the suppression of the convective energy transport. The overall shape of the magnetic network changes slowly on a timescale much larger than the convective turnover time, while the magnetic flux is constantly redistributed within the network leading to continuous formation and dissolution of flux concentrations.

Dust coagulation in protoplanetary disks: A rapid depletion of small grains

Abstract: We model the process of dust coagulation in protoplanetary disks and calculate how it affects their observational appearance. Our model involves the detailed solution of the coagulation equation at every location in the disk. At regular time intervals we feed the resulting 3D dust distribution functions into a continuum radiative transfer code to obtain spectral energy distributions. We find that, even if only the very basic - and well understood - coagulation mechanisms are included, the process of grain growth is much too quick to be consistent with infrared observations of T Tauri disks. Small grains are removed so efficiently that, long before the disk reaches an age of 10 6 years typical of T Tauri stars, the SED shows only very weak infrared excess. This is inconsistent with observed SEDs of most classical T Tauri stars. Small grains must be replenished, for instance by aggregate fragmentation through high-speed collisions. A very simplified calculation shows that when aggregate fragmentation is included, a quasi-stationary grain size distribution is obtained in which growth and fragmentation are in equilibrium. This quasi-stationary state may last 10 6 years or even longer, depending on the circumstances in the disk, and may bring the time scales into the right regime. If this is indeed the case, or if other processes are responsible for the replenishment of small grains, then the typical grain sizes inferred from infrared spectral features of T Tauri disks do not necessarily reflect the age of the system (small grains → young, larger grains → older), as is often proposed. Indeed, there is evidence reported in the literature that the typical inferred grain sizes do not correlate with the age of the star. Instead, it is more likely that the typical grain sizes found in T Tauri star (and Herbig Ae/Be star and Brown Dwarf) disks reflect the state of the disk in some more complicated way, e.g. the strength of the turbulence, the amount of dust mass transformed into planetesimals, the amount of gas lost via evaporation etc. A simple evolutionary scenario in which grains slowly grow from pristine 0.1 µm grains to larger grains over a period of a few Myr is most likely incorrect.

The VIMOS VLT deep survey. First epoch VVDS-deep survey: 11 564 spectra with 17.5 ≤ IAB ≤ 24, and the redshift distribution over 0 ≤ z ≤ 5

Abstract: This paper presents the ``First Epoch\'\' sample from the VIMOS VLT Deep Survey (VVDS). The VVDS goals, observations, data reduction with VIPGI, and redshift measurement with KBRED are discussed. Data have been obtained with the VIsible Multi Object Spectrograph (VIMOS) on the ESO-VLT UT3, allowing to observe ~600 slits simultaneously at R~230. A total of 11564 objects have been observed in the VVDS-02h and VVDS-CDFS Deep fields over a total area of 0.61deg^2, selected solely on the basis of apparent magnitude 17.5 <=I_{AB} <=24. The VVDS covers the redshift range 0 < z <= 5. It is successfully going through the ``redshift desert\'\' 1.523.5, probing the bright star forming population of galaxies. This sample provides an unprecedented dataset to study galaxy evolution over 90% of the life of the universe

Astrophysical parameters of Galactic open clusters

Abstract: We present a catalogue of astrophysical data of 520 Galactic open clusters. These are the clusters, for which at least three most probable members (18 on average) could be identified in the ASCC-2.5, a catalogue of stars based on the Tycho-2 observations from the Hipparcos mission. We applied homogeneous methods and algorithms to determine angular sizes of cluster cores and coronae, heliocentric distances, mean proper motions, mean radial velocities and ages. For the first time we derive distances for 200 clusters, radial velocities for 94 clusters and determine ages of 196 clusters. This homogeneous new parameter set is compared with earlier determinations. In particular, we find that the angular sizes were systematically underestimated in the literature.

Models of giant planet formation with migration and disc evolution

Abstract: We present a new model of giant planet formation that extends the core-accretion model of Pollack et al. (1996, Icarus, 124, 62) to include migration, disc evolution and gap formation. We show that taking these effects into account can lead to much more rapid formation of giant planets, making it compatible with the typical disc lifetimes inferred from observations of young circumstellar discs. This speed up is due to the fact that migration prevents the severe depletion of the feeding zone as observed in in situ calculations. Hence, the growing planet is never isolated and it can reach cross-over mass on a much shorter timescale. To illustrate the range of planets that can form in our model, we describe a set of simulations in which we have varied some of the initial parameters and compare the final masses and semi-major axes with those inferred from observed extra-solar planets.

Luminosity-dependent evolution of soft X-ray selected AGN : New Chandra and XMM-Newton surveys

Abstract: We present new results on the cosmological evolution of unabsorbed (type-1) active galactic nuclei (AGN) selected in the soft (0.5-2 keV) X-ray band. From a variety of ROSAT, XMM-Newton and Chandra surveys we selected a total of -1000 AGN with an unprecedented spectroscopic and photometric optical/NIR identification completeness. For the first time we are able to derive reliable space densities for low-luminosity (Seyfert-type) X-ray sources at cosmological redshifts. The evolutionary behaviour of AGN shows a strong dependence on X-ray luminosity: while the space density of high-luminosity AGN reaches a peak around z ∼ 2, similar to that of optically selected QSO, the space density of low-luminosity AGNs peaks at redshifts below z = 1. This confirms previous ROSAT findings of a luminosity-dependent density evolution. Using a rigorous treatment of the optical identification completeness we are able to show that the space density of AGN with X-ray luminosities I x < 10 45 erg s -1 declines significantly towards high redshifts.

Faraday rotation measure synthesis

Abstract: We extend the rotation measure work of Burn ( 1966, MNRAS, 133, 67) to the cases of limited sampling of lambda(2) space and non-constant emission spectra. We introduce the rotation measure transfer function (RMTF), which is an excellent predictor of n pi ambiguity problems with the lambda(2) coverage. Rotation measure synthesis can be implemented very efficiently on modern computers. Because the analysis is easily applied to wide fields, one can conduct very fast RM surveys of weak spatially extended sources. Difficult situations, for example multiple sources along the line of sight, are easily detected and transparently handled. Under certain conditions, it is even possible to recover the emission as a function of Faraday depth within a single cloud of ionized gas. Rotation measure synthesis has already been successful in discovering widespread, weak, polarized emission associated with the Perseus cluster (de Bruyn & Brentjens 2005, A&A, 441, 931). In simple, high signal to noise situations it is as good as traditional linear fits to chi versus lambda(2) plots. However, when the situation is more complex or very weak polarized emission at high rotation measures is expected, it is the only viable option.

Star counts in the Galaxy - Simulating from very deep to very shallow photometric surveys with the TRILEGAL code

Abstract: We describe TRILEGAL, a new populations synthesis code for simulating the stellar photometry of any Galaxy field. The code attempts to improve upon several technical aspects of star count models, by: dealing with very complete input libraries of evolutionary tracks; using a stellar spectral library to simulate the photometry in virtually any broad-band system; being very versatile allowing easy changes in the input libraries and in the description of all of its ingredients - like the star formation rate, age-metallicity relation, initial mass function, and geometry of Galaxy components. In a previous paper (Groenewegen et al. 2002, Paper I), the code was first applied to describe the very deep star counts of the CDFS stellar catalogue. Here, we briefly describe its initial calibration using EIS-deep and DMS star counts, which, as we show, are adequate samples to probe both the halo and the disc components of largest scale heights (oldest ages). We then present the changes in the calibration that were necessary to cope with some improvements in the model input data, and the use of more extensive photometry datasets: now the code is shown to successfully simulate also the relatively shallower 2MASS catalogue, which probes mostly the disc at intermediate ages, and the immediate solar neighbourhood as sampled by Hipparcos - in particular its absolute magnitude versus colour diagram -, which contains a somewhat larger fraction of younger stars than deeper surveys. Remarkably, the same model calibration can reproduce well the star counts in all the above-mentioned data sets, that span from the very deep magnitudes of CDFS (16 < R < 23) to the very shallow ones of Hipparcos (V < 8). Significant deviations (above 50 percent in number counts) are found just for fields close to the Galactic Center (since no bulge component was included) and Plane, and for a single set of South Galactic Pole data. The TRILEGAL code is ready to use for the variety of wide-angle surveys in the optical/infrared that will become available in the coming years.

alpha-, r-, and s-process element trends in the Galactic thin and thick disks

Abstract: From a detailed elemental abundance analysis of 102 F and G dwarf starswe present abundance trends in the Galactic thin and thick disks for 14elements (O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zn, Y, Ba, and Eu).Stellar parameters and elemental abundances (except for Y, Ba and Eu)for 66 of the 102 stars were presented in our previous studies (Bensbyet al. 2003, 2004a). The 36 stars that are new in this study extend andconfirm our previous results and allow us to draw further conclusionsregarding abundance trends. The s-process elements Y and Ba, and ther-element Eu have also been considered here for the whole sample for thefirst time. With this new larger sample we now have the followingresults: 1) Smooth and distinct trends that for the thin and thick disksare clearly separated; 2) The alpha-element trends for the thick diskshow typical signatures from the enrichment of SNIa; 3) The thick diskstellar sample is in the mean older than the thin disk stellar sample;4) The thick disk abundance trends are invariant with galactocentricradii (R_m); 5) The thick disk abundance trends appear to be invariantwith vertical distance (Z_max) from the Galactic plane. Adding furtherevidence from the literaure we argue that a merger/interacting scenariowith a companion galaxy to produce a kinematical heating of the stars(that make up today's thick disk) in a pre-existing old thin disk is themost likely formation scenario for the Galactic thick disk.

Evolution of rapidly rotating metal-poor massive stars towards gamma-ray bursts

Abstract: Recent models of rotating massive stars including magnetic fields prove it difficult for the cores of single stars to retain enough angular momentum to produce a collapsar and gamma-ray burst. At low metallicity, even very massive stars may retain a massive hydrogen envelope due to the weakness of the stellar winds, posing an additional obstacle to the collapsar model. Here, we consider the evolution of massive, magnetic stars where rapid rotation induces almost chemically homogeneous evolution. We find that in this case, the requirements of the collapsar model are rather easily fulfilled if the metallicity is sufficiently small: 1) rapidly rotating helium stars are formed without the need to remove the hydrogen envelope, avoiding mass-loss induced spin-down. 2) Angular momentum transport from the helium core to hydrogen envelope by magnetic torques is insignificant. We demonstrate this by calculating evolutionary models of massive stars with various metallicities, and derive an upper metallicity limit for this scenario based on currently proposed mass loss rates. Our models also suggest the existence of a lower CO-core mass limit of about 10 {M}_⊙ - which relates to an initial mass of only about 20 {M}_⊙ within our scenario - for GRB production. We argue that the relative importance of the considered GRB progenitor channel, compared to any channel related to binary stars, may increase with decreasing metallicity, and that this channel might be the major path to GRBs from first stars.

Stellar evolution with rotation XI. Wolf-Rayet star populations at different metallicities

Abstract: Grids of models of massive stars (M ≥ 20 M� ) with rotation are computed for metallicities Z ranging from that of the Small Magellanic Cloud (SMC) to that of the Galactic Centre. The hydrostatic effects of rotation, the rotational mixing and the enhancements of the mass loss rates by rotation are included. The evolution of the surface rotational velocities of the most massive O-stars mainly depends on the mass loss rates and thus on the initial Z value. The minimum initial mass for a star for entering the Wolf-Rayet (WR) phase is lowered by rotation. For all metallicities, rotating stars enter the WR phase at an earlier stage of evolution and the WR lifetimes are increased, mainly as a result of the increased duration of the eWNL phase. Models of WR stars predict in general rather low rotation velocities (<50 km s −1 ) with a few possible exceptions, particularly at metallicities lower than solar where WR star models have in general faster rotation and more chance to reach the break-up limit. The properties of the WR populations as predicted by the rotating models are in general in much better agreement with the observations in nearby galaxies. Some possible remaining difficulties in these comparisons are mentioned. The evolution of the chemical abundances is largely influenced by rotation in all phases from the MS phase to the WN and WC phases. We also show that the interval of initial masses going through the LBV stage is changing with Z and Ω. The observed variation with metallicity of the fractions of type Ib/Ic supernovae with respect to type II supernovae as found by Prantzos & Boissier (2003) is very well reproduced by the rotating models, while non-rotating models predict much too low ratios. This indicates that the minimum initial masses of single stars going through a WR phase are consistently predicted. At Z = 0.040, stars with initial masses above 50 Mreach a final mass at the time of supernova explosion between 5 and 7.5 M� , while at Z = 0.004, like in the SMC, the final masses of stars are in the range of 17-29 M� . On the whole, rotation appears to be an essential parameter even for the WR properties. Detailed tables describing the evolutionary tracks are available on the web.

The Supernova rate per unit mass

Abstract: We compute the rate of supernovae (SNe) of different types along the Hubble sequence normalized to the near- infrared luminosity and to the stellar mass of the parent galaxies. This is made possible by the new complete catalog of near- infrared galaxy magnitudes obtained by 2MASS. We find that the rates of all SN types, including Ia, Ib/c and II, show a sharp dependence on both the morphology and the (B − K) colors of the parent galaxies and, therefore, on the star formation activity. In particular we find, with a high statistical significance, that the type Ia rate in late type galaxies is a factor ∼20 higher than in E/S0. Similarly, the type Ia rate in the galaxies bluer than B − K = 2.6 is about a factor of 30 larger than in galaxies with B − K > 4.1. These findings can be explained by assuming that a significant fraction of Ia events in late spirals/irregulars originates in a relatively young stellar component.

Structured jets in TeV BL Lac objects and radiogalaxies. Implications for the observed properties

Abstract: TeV BL Lacertae objects require extreme relativistic bulk motions in the gamma-ray emission region, but at the VLBI scale their radio knots hardly move. The same sources show evidence, in radio, of a structure made of a fast spine plus a slow layer. We propose that this structure exists even on the spatial scale of regions responsible for the gamma-ray emission. One component sees the (beamed) radiation produced by the other, and this enhances the inverse Compton emission of both components. In addition, this allows the magnetic field to be nearly in equipartition with the emitting particles. The inverse Compton emission of the spine is anisotropic in its frame, possibly producing a deceleration of the spine by the Compton rocket effect. In this scenario, the slow layer is also a relatively strong high-energy emitter, and thus radiogalaxies become potentially detectable by GLAST.

The Hamburg/ESO R-process enhanced star survey (HERES). II. Spectroscopic analysis of the survey sample

Abstract: We present the results of analysis of "snapshot" spectra of 253 metal-poor halo stars −3.8 ≤ (Fe/H) ≤− 1.5 obtained in the HERES survey. The snapshot spectra have been obtained with VLT/UVES and have typically S /N ∼ 54 per pixel (ranging from 17 to 308), R ∼ 20 000, λ = 3760-4980 A. This sample represents the major part of the complete HERES sample of 373 stars; however, the CH strong content of the sample is not dealt with here. The spectra are analysed using an automated line profile analysis method based on the Spectroscopy Made Easy (SME) codes of Valenti & Piskunov. Elemental abundances of moderate precision (absolute rms errors of order 0.25 dex, relative rms errors of order 0.15 dex) have been obtained for 22 elements, C, Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Sr, Y, Zr, Ba, La, Ce, Nd, Sm, and Eu, where detectable. Of these elements, 14 are usually detectable at the 3σ confidence level for our typical spectra. The remainder can be detected in the least metal-poor stars of the sample, spectra with higher than average S /N ,o r when the abundance is enhanced. Among the sample of 253 stars, disregarding four previously known comparison stars, we find 8 r-II stars and 35 r-I stars. The r-II stars, including the two previously known examples CS 22892-052 and CS 31082-001, are centred on a metallicity of (Fe/H) = −2.81, with a very small scatter, on the order of 0.16 dex. The r-I stars are found across practically the entire metallicity range of our sample. We also find three stars with strong enhancements of Eu which are s-process rich. A significant number of new very metal-poor stars are confirmed: 49 stars with (Fe/H) < −3 and 181 stars with −3 < (Fe/H) < −2. We find one star with (Fe/H) < −3.5. We find the scatter in the abundance ratios of Mg, Ca, Sc, Ti, Cr, Fe, Co, and Ni, with respect to Fe and Mg, to be similar to the estimated relative errors and thus the cosmic scatter to be small, perhaps even non-existent. The elements C, Sr, Y, Ba and Eu, and perhaps Zr, show scatter at (Fe/H) < −2.5 significantly larger than can be explained from the errors in the analysis, implying scatter which is cosmic in origin. Significant scatter is observed in abundance ratios between light and heavy neutron-capture elements at low metallicity and low levels of r-process enrichment.

Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data: Revisiting the concept of superclusters

Abstract: The availability of the Hipparcos Catalogue has triggered many kinematic and dynamical studies of the solar neighbourhood. Nevertheless, those studies generally lacked the third component of the space velocities, i.e., the radial velocities. This work presents the kinematic analysis of 5952 K and 739 M giants in the solar neighbourhood which includes for the first time radial velocity data from a large survey performed with the CORAVEL spectrovelocimeter. It also uses proper motions from the Tycho-2 catalogue, which are expected to be more accurate than the Hipparcos ones. An important by-product of this study is the observed fraction of only 5.7% of spectroscopic binaries among M giants as compared to 13.7% for K giants. After excluding the binaries for which no center-of-mass velocity could be estimated, 5311 K and 719 M giants remain in the final sample. The UV -plane constructed from these data for the stars with precise parallaxes (%) reveals a rich small-scale structure, with several clumps corresponding to the Hercules stream, the Sirius moving group, and the Hyades and Pleiades superclusters. A maximum-likelihood method, based on a Bayesian approach, has been applied to the data, in order to make full use of all the available stars (not only those with precise parallaxes) and to derive the kinematic properties of these subgroups. Isochrones in the Hertzsprung-Russell diagram reveal a very wide range of ages for stars belonging to these groups. These groups are most probably related to the dynamical perturbation by transient spiral waves (as recently modelled by De Simone et al. [CITE]) rather than to cluster remnants. A possible explanation for the presence of young group/clusters in the same area of the UV -plane is that they have been put there by the spiral wave associated with their formation, while the kinematics of the older stars of our sample has also been disturbed by the same wave. The emerging picture is thus one of dynamical streams pervading the solar neighbourhood and travelling in the Galaxy with similar space velocities. The term dynamical stream is more appropriate than the traditional term supercluster since it involves stars of different ages, not born at the same place nor at the same time. The position of those streams in the UV -plane is responsible for the vertex deviation of for the whole sample. Our study suggests that the vertex deviation for younger populations could have the same dynamical origin. The underlying velocity ellipsoid, extracted by the maximum-likelihood method after removal of the streams, is not centered on the value commonly accepted for the radial antisolar motion: it is centered on km s-1 . However, the full data set (including the various streams) does yield the usual value for the radial solar motion, when properly accounting for the biases inherent to this kind of analysis (namely, km s-1 ). This discrepancy clearly raises the essential question of how to derive the solar motion in the presence of dynamical perturbations altering the kinematics of the solar neighbourhood: does there exist in the solar neighbourhood a subset of stars having no net radial motion which can be used as a reference against which to measure the solar motion?

The XMM-Newton view of PG quasars - I. X-ray continuum and absorption

Abstract: We present results of a systematic analysis of the XMM-Newton spectra of 40 quasars (QSOs) (z ≤ 1.72) from the Palomar-Green (PG) Bright Quasar Survey sample (MB < −23). The sample includes 35 radio-quiet quasars (RQQs) and 5 radio-loud quasars (RLQs). The analysis of the spectra above 2 keV reveals that the hard X-ray continuum emission can be modeled with a power law component with � Γ2−12 keV� = 1.89 ± 0.11 and � Γ2−12 keV� = 1.63 +0.02 −0.01 for the RQQs and RLQs, respectively. Below 2 keV, a strong, broad excess is present in most QSO spectra. This feature has been fitted with four different models assuming several physical scenarios. All tested models (blackbody, multicolor blackbody, bremsstrahlung and power law) satisfactorily fitted the majority of the spectra. However, none of them is able to provide an adequate parameterization for the soft excess emission in all QSOs, indicating the absence of a universal shape for this spectral feature. An additional cold absorption component was required only in three sources. On the other hand, as recently pointed out by Porquet et al. (2004) for a smaller sample of PG QSOs, warm absorber features are present in 50% of the QSO spectra in contrast with their rare occurrence (∼5−10%) in previous studies. The XMM-Newton view of optically selected bright QSOs therefore suggests that there are no significant differences in the X-ray spectral properties compared with those of the low-luminosity Seyfert 1 galaxies. Properties of the Fe Kα emission lines are presented in a companion paper.

ELODIE metallicity-biased search for transiting Hot Jupiters. II. A very hot Jupiter transiting the bright K star HD 189733

Abstract: Among the 160 known exoplanets, mainly detected in large radial-velocity surveys, only 8 have a characterization of their actual mass and radius thanks to the two complementary methods of detection: radial velocities and photometric transit. We started in March 2004 an exoplanet-search programme biased toward high-metallicity stars which are more frequently host extra-solar planets. This survey aims to detect close-in giant planets, which are most likely to transit their host star. For this programme, high-precision radial velocities are measured with the ELODIE fiber-fed spectrograph on the 1.93-m telescope, and high-precision photometry is obtained with the CCD Camera on the 1.20-m telescope, both at the Haute-Provence Observatory. We report here the discovery of a new transiting hot Jupiter orbiting the star HD189733. The planetary nature of this object is confirmed by the observation of both the spectroscopic and photometric transits. The exoplanet HD189733b, with an orbital period of 2.219 days, has one of the shortest orbital periods detected by radial velocities, and presents the largest photometric depth in the light curve (~ 3%) observed to date. We estimate for the planet a mass of 1.15 +- 0.04 Mjup and a radius of 1.26 +- 0.03 RJup. Considering that HD189733 has the same visual magnitude as the well known exoplanet host star HD209458, further ground-based and space-based follow-up observations are very promising and will permit a characterization of the atmosphere and exosphere of this giant exoplanet.

On the metallicity dependence of Wolf-Rayet winds

Abstract: We have performed a pilot study of mass loss predictions for late-type Wolf-Rayet (WR) stars as a function of metal abundance, over a range between 10 -5 ≤ (Z/Z ○. ) ≤ 10. We find that the winds of nitrogen-rich Wolf-Rayet stars are dominated by iron lines, with a dependence of mass loss on Z similar to that of massive OB stars. For more evolved, carbon-rich, WR stars the wind strength is also found to be dependent on the Fe abundance, so that they depend on the chemical environment of the host galaxy, but with a mass loss metallicity dependence that is less steep than for OB stars. Our finding that WR mass loss is Z-dependent is a new one, with important consequences for black hole formation and X-ray population studies in external galaxies. A further finding of our study is that the Z dependence of C-rich WR stars becomes weaker at melallicities below Z/Z ○. ≤ 1/10, and mass loss no longer declines once the metal abundance drops below (Z/Z ○. ) ≃ 10 -3 . This is the result of an increased importance of radiative driving by intermediate mass elements, such as carbon. In combination with rapid rotation and/or proximity to the Eddington limit - likely to be relevant for massive Population III stars - this effect may indicate a role for mass loss in the appearance and evolution of these objects, as well as a potential role for stellar winds in enriching the intergalactic medium of the early Universe.

Diagnostics of irradiated gas in galaxy nuclei. I. A far-ultraviolet and X-ray dominated region code

Abstract: We present a far-ultraviolet (PDR) and an X-ray dominated region (XDR) code. We include and discuss thermal and chemical processes that pertain to irradiated gas. An elaborate chemical network is used and a careful treatment of PAHs and H(2) formation, destruction and excitation is included. For both codes we calculate four depth-dependent models for different densities and radiation fields, relevant to conditions in starburst galaxies and active galactic nuclei. A detailed comparison between PDR and XDR physics is made for total gas column densities between similar to 10(20) and similar to 10(25) cm(-2). We show cumulative line intensities for a number of fine-structure lines (e.g., [CII], [OI], [CI], [SiII], [FeII]), as well as cumulative column densities and column density ratios for a number of species ( e. g., CO/H(2), CO/C, HCO(+)/HCN, HNC/HCN). The comparison between the results for the PDRs and XDRs shows that column density ratios are almost constant up to N(H) = 1022 cm(-2) for XDRs, unlike those in PDRs. For example, CO/C in PDRs changes over four orders of magnitude from the edge to NH = 10(22) cm(-2). The CO/C and CO/H(2) ratios are lower in XDRs at low column densities and rise at NH > 1023 cm-2. At most column densities NH > 10(21.5) cm-2, HNC/HCN ratios are lower in XDRs too, but they show a more moderate increase at higher N(H).

Atmospheric NLTE-models for the spectroscopic analysis of blue stars with winds. II. Line-blanketed models

Abstract: We present new or improved methods for calculating NLTE, line-blanketed model atmospheres for hot stars with winds (spectral types A to O), with particular emphasis on fast performance These methods have been implemented into a previous, more simple version of the model atmosphere code F (Santolaya-Rey et al 1997) and allow us to spec- troscopically analyze large samples of massive stars in a reasonable time-scale, using state-of-the-art physics Although this updated version of the code has already been used in a number of recent investigations, the corresponding methods have not been explained in detail so far, and no rigorous comparison with results from alternative codes has been performed This paper intends to address both topics In particular, we describe our (partly approximate) approach to solve the equations of statistical equilibrium for those elements that are primarily responsible for line-blocking and blanketing, as well as an approximate treatment of the line-blocking itself, which is based on a simple statistical approach using suitable means of line opacities and emissivities Both methods are validated by specific tests Furthermore, we comment on our implementation of a consistent temperature structure In the second part, we concentrate on a detailed comparison with results from two codes used in alternative spectroscopical investigations, namely  (Hillier & Miller 1998) and -Basic (Pauldrach et al 2001) All three codes predict almost identical temperature structures and fluxes for λ> 400 A, whereas at lower wavelengths a number of discrepancies are found Particularly in the He continua, where fluxes and corresponding numbers of ionizing photons react extremely sensitively to subtle differences in the models, we consider any uncritical use of these quantities (eg, in the context of nebula diagnostics) as unreliable Optical H/He lines as synthesized by  are compared with results from , obtaining a remarkable coincidence, except for the He singlets in the temperature range between 36 000 to 41 000 K for dwarfs and between 31 000 to 35 000 K for supergiants, where  predicts much weaker lines Consequences of these discrepancies are discussed Finally, suggestions are presented as to adequately parameterize model-grids for hot stars with winds, with only one additional parameter compared to standard grids from plane-parallel, hydrostatic models

A library of high resolution synthetic stellar spectra from 300 nm to 1.8 μm with solar and α-enhanced composition

Abstract: Libraries of stellar spectra are fundamental tools for the study of stellar populations, and both empirical and synthetic libraries have been used for this purpose. In this paper, a new library of high resolution synthetic spectra is presented, ranging from the near-ultraviolet (300 nm) to the near-infrared (1.8 m). The library spans all the stellar types that are relevant to the integrated light of old and intermediate-age stellar populations in the involved spectral region (spectral types F through M and all luminosity classes). The grid was computed for metallicities ranging from [Fe/H] = –2.5 to +0.5, including both solar and α -enhanced ([ α /Fe] = 0.4) chemical compositions. The synthetic spectra are a good match to observations of stars throughout the stellar parameter space encompassed by the library and over the whole spectral region covered by the computations.

The evolution of the timing properties of the black-hole transient GX 339-4 during its 2002/2003 outburst

Abstract: We present the results of the timing and color analysis of more than two hundred RXTE/PCA observations of the bright black-hole transient GX 339-4 obtained during its 2002/2003 outburst. The color-intensity evolution of the system, coupled to the properties of its fast time variability, allow the identification of four separate states. Depending on the state, strong noise is detected, together with a variety of quasi-periodic oscillations at frequencies from 0.2 to 8 Hz. We present a characterization of the timing parameters of these states and compare them to what has been observed in other systems. These results, together with those obtained from energy spectra, point towards a common evolution of black-hole transients through their outbursts.

First stars VI - Abundances of C, N, O, Li, and mixing in extremely metal-poor giants. Galactic evolution of the light elements

Abstract: We have investigated the poorly-understood origin of nitrogen in the early Galaxy by determining N abundances from the NH band at 336 nm in 35 extremely metal-poor halo giants, with carbon and oxygen abundances from Cayrel et al. (\cite{CDS04}, AA these stars are generally more evolved and located on the upper Red Giant Branch (RGB) or Horizontal Branch (HB). The second group has [N/Fe] < 0.5, shows no evidence for C to N conversion, and Li is only moderately diluted; these stars belong to the lower RGB and we conclude that their C and N abundances are very close to those of the gas from which they formed in the early Galaxy, they are called ``unmixed stars''. The [O/Fe] and [(C+N)/Fe] ratios are the same in the two groups, confirming that the differences between them are caused by dredge-up of CN-processed material in the first group, with negligible contributions from the O-N cycle. The ``unmixed'' stars reflect the abundances in the early Galaxy: the [C/Fe] ratio is constant (about +0.2 dex) and the [C/Mg] ratio is close to solar at low metallicity, favouring a high C production by massive zero-metal supernovae. The [N/Fe] and [N/Mg] ratios scatter widely. Their mean values in each metallicity bin decrease with increasing metallicity, but this trend could be a statistical effect. The larger values of these ratios define a flat upper plateau ([N/Mg] = 0.0, [N/Fe] = +0.1), which could reflect higher values within a wide range of yields of zero-metal SNe II. Alternatively, by analogy with the DLAs, the lower abundances ([N/Mg] = -1.1, [N/Fe] = -0.7) could reflect generally low yields from the first SNe II, the other stars being N enhanced by winds of massive Asymptotic Giant Branch (AGB) stars. Since all the stars show clear [?/Fe] enhancements, they were formed before any significant enrichment of the Galactic gas by SNe Ia, and their composition should reflect the yields of the first SNe II. However, if massive AGB stars or AGB supernovae evolved more rapidly than SNe Ia and contaminated the ISM, our stars would also reflect the yields of these AGB stars. At present it cannot be decided whether primary N is produced primarily in SNe II or in massive AGB stars, or in both. The stellar N abundances and [N/O] ratios are compatible with those found in Damped Lyman-? (DLA) systems. They extend the well-known DLA ``plateau'' at [N/O] ? -0.8 to lower metallicities, albeit with more scatter; no star is found below the putative ``low [N/?] plateau'' at [N/O] ? -1.55 in DLAs. Based on observations obtained with the ESO VLT under ESO programme ID 165.N-0276(A). This work has made use of the SIMBAD database.

The structural and scaling properties of nearby galaxy clusters. II. The M-T relation

Abstract: Using a sample often nearby (z ≤ 0.15), relaxed galaxy clusters in the temperature range [2-9] keV, we have investigated the scaling relation between the mass at various density contrasts (6 = 2500, 1000, 500, 200) and the cluster temperature. The masses are derived from NFW-type model fits to mass profiles, obtained under the hydrostatic assumption using precise measurements, with XMM-Newton, at least down to 6 = 1000. The logarithmic slope of the M-T relation is well constrained and is the same at all 6, reflecting the self-similarity of the mass profiles. At 6 = 500, the slope of the relation for the sub-sample of hot clusters (kT > 3.5 keV) is consistent with the standard self-similar expectation: a = 1.49 ± 0.15. The relation steepens when the whole sample is considered: a = 1.71 ± 0.09. The normalisation of the relation is discrepant (by ∼30 per cent), at all density contrasts, with the prediction from purely gravitation based models. Models that take into account radiative cooling and galaxy feedback are generally in better agreement with our data. We argue that remaining discrepancies, in particular at low 6, are more likely due to problems with models of the ICM thermal structure rather than to an incorrect estimate of the mass from X-ray data.

Line formation in solar granulation VI. [Cl], Cl, CH and C2 lines and the photospheric C abundance

Abstract: The solar photospheric carbon abundance has been determined from (C ), C , CH vibration-rotation, CH A-X electronic and C2 Swan electronic lines by means of a time-dependent, 3D, hydrodynamical model of the solar atmosphere. Departures from LTE have been considered for the C  lines. These turned out to be of increasing importance for stronger lines and are crucial to remove a trend in LTE abundances with the strengths of the lines. Very gratifying agreement is found among all the atomic and molecular abundance diagnostics in spite of their widely different line formation sensitivities. The mean value of the solar carbon abundance based on the four primary abundance indicators ((C ), C , CH vibration-rotation, C2 Swan) is logC = 8.39 ± 0.05, including our best estimate of possible systematic errors. Consistent results also come from the CH electronic lines, which we have relegated to a supporting role due to their sensitivity to the line broadening. The new 3D based solar C abundance is significantly lower than previously estimated in studies using 1D model atmospheres.

The Great disk of Milky Way satellites and cosmological sub-structures

Abstract: We show that the shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 99.5 per cent. Most of the MW satellites therefore cannot be related to dark-matter dominated satellites.

An Empirical formula for the mass-loss rates of dust-enshrouded red supergiants and oxygen-rich asymptotic giant branch stars

Abstract: We present an empirical determination of the mass-loss rate as a function of stellar luminosity and effective tem- perature, for oxygen-rich dust-enshrouded Asymptotic Giant Branch stars and red supergiants To this aim we obtained optical spectra of a sample of dust-enshrouded red giants in the Large Magellanic Cloud, which we complemented with spectroscopic and infrared photometric data from the literature Two of these turned out to be hot emission-line stars, of which one is a definite B(e) star The mass-loss rates were measured through modelling of the spectral energy distributions We thus obtain the mass- loss rate formula log u M = −565 + 105 log(L/10 000 L� ) − 6 3l og(Teff/3500 K), valid for dust-enshrouded red supergiants and oxygen-rich AGB stars Despite the low metallicity of the LMC, both AGB stars and red supergiants are found at late spectral types A comparison with galactic AGB stars and red supergiants shows excellent agreement between the mass-loss rate as predicted by our formula and that derived from the 60 µm flux density for dust-enshrouded objects, but not for optically bright objects We discuss the possible implications of this for the mass-loss mechanism