- ID:
- ivo://CDS.VizieR/J/A+AS/103/97
- Title:
- Grids of stellar models V.
- Short Name:
- J/A+AS/103/97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Most outputs of massive star evolution critically depend on the mass loss rates. In order to broaden the comparison basis and to illustrate the effects of different mass loss rates, we have computed new sets of models, with initial masses between 12 and 120 M{sun}, and metallicities, Z, between 0.001 and 0.040, with a mass loss rate increased by a factor of two during the phases when the stellar winds are believed to be essentially driven by the radiation pressure. A moderate core-overshooting and the new radiative opacities from Iglesias et al. (1992ApJ...397..717I) and Kurucz (1991) were taken into account. These models complete the homogeneous and extended theoretical database formed by the previous grids of this series, computed by Schaller et al. (1992, Cat. J/A+AS/96/269) for Z=0.020 and Z=0.001, by Schaerer et al. (1992, Cat. J/A+AS/98/523; 1993, Cat. J/A+AS/102/339) for Z=0.008 and Z=0.040 and by Charbonnel et al. (1993, Cat. J/A+AS/101/415) for Z=0.004. This paper closes this series. Of particular interest is the predicted behaviour of metal rich stars such as may be found in the inner regions of our Galaxy. New evolutionary connexions are found, in particular we show that the most massive and metal rich stars may spend a relatively long time as He and N enriched stars and may even end their evolution as white dwarfs.
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- ID:
- ivo://CDS.VizieR/J/A+AS/128/471
- Title:
- Grids of stellar models. VII.
- Short Name:
- J/A+AS/128/471
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new grid of stellar models from 0.8 to 60M_{sun}_ at Z=0.10, with mass loss and moderate overshooting, from the zero age main sequence to either the helium flash (low mass stars), the early AGB phase (intermediate-mass stars or the end of carbon burning (massive stars). The calculations are done with opacities provided by Iglesias & Rogers (1993ApJ...412..752I), completed by those of Alexander & Ferguson (1994ApJ...437..879A) at low temperatures. This grid is a homogeneous extension to very high metallicity of the previous grids published by the Geneva group. It is useful for the study of galactic bulges, elliptical galaxies and eventually quasars. Calculations of stars more massive than 60M_{sun}_ are not presented as these objects lose almost their entire mass during their main sequence phase, and are likely to end their life as white dwarfs.
- ID:
- ivo://CDS.VizieR/J/A+AS/135/405
- Title:
- Grids of stellar models. VIII.
- Short Name:
- J/A+AS/135/405
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present stellar evolutionary models covering the mass range from 0.4 to 1M_{sun}_ calculated for metallicities Z=0.020 and 0.001 with the MHD equation of state (Hummer & Mihalas, 1988ApJ...331..794H, Mihalas et al., 1988ApJ...331..815M, Daeppen et al., 1988ApJ...332..261D). A parallel calculation using the OPAL (Rogers et al., 1996ApJ...456..902R) equation of state has been made to demonstrate the adequacy of the MHD equation of state in the range of 1.0 to 0.8M_{sun}_ (the lower end of the OPAL tables). Below, down to 0.4M_{sun}_, we have justified the use of the MHD equation of state by theoretical arguments and the findings of Chabrier & Baraffe (1997A&A...327.1039C). We use the radiative opacities by Iglesias & Rogers (1996ApJ...464..943I), completed with the atomic and molecular opacities by Alexander & Fergusson (1994ApJ...437..879A). We follow the evolution from the Hayashi fully convective configuration up to the redgiant tip for the most massive stars, and up to an age of 20Gyr for the less massive ones. We compare our solar-metallicity models with recent models computed by other groups and with observations.
- ID:
- ivo://CDS.VizieR/J/ApJS/187/228
- Title:
- H{alpha} profiles of Be stars
- Short Name:
- J/ApJS/187/228
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a set of theoretical H{alpha} emission-line profiles of Be stars, created by systematically varying model input parameters over a wide range of accepted values. Models were generated with a non-LTE radiative transfer code that incorporates a non-isothermal disk structure and a solar-type chemical composition. The theoretical H{alpha} emission-line profiles were compared to a large set of Be star spectra with the aim of reproducing their global characteristics. We find that the observed profile shapes cannot be used to uniquely determine the inclination angle of Be star+disk systems. Drastically different profile shapes arise at a given inclination angle as a direct result of the state of the gas, and self-consistent disk physical conditions are therefore crucial for interpreting the observations.
- ID:
- ivo://CDS.VizieR/J/A+A/592/A83
- Title:
- HD 100546 and TW Hya model abundances
- Short Name:
- J/A+A/592/A83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The composition of planetary solids and gases is largely rooted in the processing of volatile elements in protoplanetary disks. To shed light on the key processes, we carry out a comparative analysis of the gas-phase carbon abundance in two systems with a similar age and disk mass, but different central stars: HD 100546 and TW Hya. We combine our recent detections of C0 in these disks with observations of other carbon reservoirs (CO, C^+^, C_2_H) and gas-mass and warm-gas tracers (HD, O^0^), as well as spatially resolved ALMA observations and the spectral energy distribution. The disks are modelled with the DALI 2D physical-chemical code. Stellar abundances for HD 100546 are derived from archival spectra. Upper limits on HD emission from HD 100546 place an upper limit on the total disk mass of <=0.1M_{sun}_. The gas-phase carbon abundance in the atmosphere of this warm Herbig disk is, at most, moderately depleted compared to the interstellar medium, with Bootis star, with solar abundances of C and O but a strong depletion of rockforming elements. In the gas of the T Tauri disk TW Hya, both C and O are strongly underabundant, with [C]/[H]_gas_=(0.2-5.0)x10^-6^ and C/O>1. We discuss evidence that the gas-phase C and O abundances are high in the warm inner regions of both disks. Our analytical model, including vertical mixing and a grain size distribution, reproduces the observed [C]/[H]_gas_ in the outer disk of TW Hya and allows to make predictions for other systems.
- ID:
- ivo://CDS.VizieR/J/A+A/635/A6
- Title:
- HD 219134 light and RV curves and code
- Short Name:
- J/A+A/635/A6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- By analysing the transit light-curve of a planet-hosting star or the induced radial velocity oscillations, many useful information on the planet may be retrieved. However, inferring the physical parameters of the planet (mass, size, semi-major axis, etc.) requires the preliminary knowledge of some parameters of the host star, especially its mass and/or radius, that are generally inferred through theoretical evolutionary models. The paper aims at presenting and testing a whole algorithm devoted to the complete characterization of an exoplanetary system thanks to the global analysis of photometric and/or radial velocity time-series combined to observational stellar parameters derived either from spectroscopy or photometry. We developed an integrated tool called MCMCI that combines the Markov Chain Monte Carlo (MCMC) approach for analysing photometric and/or radial velocity time-series with a proper interpolation within stellar evolutionary isochrones and tracks (known as Isochrone placement) to be performed at each chain step, to retrieve stellar theoretical parameters, such as age, mass and radius. We tested the MCMCI both on the HD 219134 multiplanetary system hosting two transiting rocky super-Earths and on WASP-4, that hosts a bloated hot Jupiter. Even considering different input approaches, a final convergence was reached within the code, we found good agreement with the results already stated in the literature and we obtained more precise output parameters, especially concerning planetary masses. The MCMCI tool offers the opportunity of performing an integrated analysis of an exoplanetary system, without splitting it into the preliminary stellar characterization through theoretical models, but rather favouring a close interaction between the light-curve analysis and the isochrones, so that the parameters recovered at each step of the MCMC enter as input of the Isochrone placement.
- ID:
- ivo://CDS.VizieR/J/A+A/569/A43
- Title:
- HE 2252-4225 abundance analysis
- Short Name:
- J/A+A/569/A43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Studies of the r-process enhanced stars are important for better understanding the nature and origin of the r-process. We present a detailed abundance analysis of a very metal-poor giant star discovered in the HERES project, HE 2252-4225, which exhibits overabundances of the r-process elements, with [r/Fe]=+0.80. We determined the stellar atmosphere parameters, Teff=4710K, logg=1.65, and [Fe/H]=-2.63, and chemical abundances by analysing the high-quality VLT/UVES spectra. The surface gravity was calculated from the non-local thermodynamic equilibrium (NLTE) ionisation balance between FeI and FeII. Accurate abundances for a total of 38 elements, including 22 neutron-capture elements beyond Sr and up to Th, were determined in HE 2252-4225. For every chemical species, the dispersion in the single line measurements around the mean does not exceed 0.12dex. This object is deficient in carbon, as expected for a giant star with Teff<4800K. The stellar Na-Zn abundances are well fitted by the yields of a single supernova of 14.4M_{sun}_. For the neutron-capture elements in the Sr-Ru, Ba-Yb, and Os-Ir regions, the abundance pattern of HE 2252-4225 is in excellent agreement with the average abundance pattern of the strongly r-process enhanced stars CS 22892-052, CS 31082-001, HE 1219-0312, and HE 1523-091. This suggests a common origin of the first, second, and third r-process peak elements in HE 2252-4225 in the classical r-process. We tested the solar r-process pattern based on the most recent s-process calculations of Bisterzo, Travaglio, Gallino, Wiescher, and Kappeler and found that elements in the range from Ba to Ir match it very well. No firm conclusion can be drawn about the relationship between the first neutron-capture peak elements, Sr to Ru, in HE 2252-4225 and the solar r-process, due to the uncertainty in the solar r-process. The investigated star has an anomalously high Th/Eu abundance ratio, so that radioactive dating results in a stellar age of {tau}=1.5+/-1.5Gyr that is not expected for a very metal-poor halo star.
- ID:
- ivo://CDS.VizieR/J/A+A/626/A23
- Title:
- Herschel Dwarf Galaxy Survey PACS spectroscopy
- Short Name:
- J/A+A/626/A23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We employ a multiphase approach to model the ISM phases of the galaxies from the Herschel Dwarf Galaxy Survey with the spectral synthesis code Cloudy. We characterize the physical conditions (gas densities, radiation fields, porosity) in those galaxies and investigate correlations with metallicity or star-formation activity. We find that the lower-metallicity galaxies tend to have higher ionization parameters and galaxies with higher specific star-formation rates have higher gas densities. The [CII] emission arises mainly from PDRs and the contribution from the ionized gas phases is small, typically less than 30% of the observed emission. We also find a correlation, with scatter, between metallicity and both the PDR covering factor and the fraction of [CII] from the ionized gas. Overall, the low metal abundances appear to be driving most of the changes in the ISM structure and conditions of these galaxies, and not the high specific star-formation rates. These results demonstrate in a quantitative way the increase of ISM porosity at low metallicity.
- ID:
- ivo://CDS.VizieR/VI/120
- Title:
- High-resolution synthetic stellar library
- Short Name:
- VI/120
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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 (300nm) to the near-infrared (1.8{mu}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 {alpha}-enhanced ([{alpha}/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.
- ID:
- ivo://CDS.VizieR/J/A+A/616/A150
- Title:
- HNCO in planetary atmospheres.
- Short Name:
- J/A+A/616/A150
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Time-resolved Fourier transform infrared emission spectroscopy, Fourier transform absorption infrared spectroscopy, and high-resolution UV-ViS emission spectroscopy have been exploited in order to characterize the chemistry of isocyanic acid (HNCO) under glow discharge conditions in planetary atmospheres. HNCO mixtures (i.e., composed of di-hydrogen or ammonia) have been investigated in order to unveil the possible reaction pathways leading to the synthesis of the key prebiotic molecule formamide (HCONH_2_), upon planetary atmospheres containing isocyanic acid in presence of di-hydrogen and, separately, of ammonia. In addition, ab initio Molecular Dynamics simulations coupled with a state-of-the-art metadynamics technique have been performed in order to identify the most likely chemical pathways connecting HNCO to formamide. It turned out that the direct hydrogenation of HNCO is thermodynamically favored. Incidentally, also the experimental results - supplied by a simplified kinetic model - proved the favorability of the reaction HNCO + H_2_ -> HCONH_2_ which, moreover, spontaneously takes place in unbiased ab initio Molecular Dynamics simulations carried out under the effect of intense electric fields.
