- ID:
- ivo://CDS.VizieR/J/A+A/549/A110
- Title:
- Metal abundances of sdB stars
- Short Name:
- J/A+A/549/A110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Hot subdwarf B stars (sdBs) are considered to be core helium-burning stars with very thin hydrogen envelopes situated on or near the extreme horizontal branch (EHB). The formation of sdBs is still unclear as well as the chemical composition of their atmospheres. The observed helium depletion is attributed to atmospheric diffusion. Metal abundances have been determined for about a dozen sdBs only resulting in puzzling patterns with enrichment of heavy metals and depletion of lighter ones. In this paper we present a detailed metal abundance analysis of 106 sdBs. From high resolution spectra we measured elemental abundances of up to 24 different ions per star. A semi-automatic analysis pipeline was developed to calculate and fit LTE models to a standard set of spectral lines. A general trend of enrichment was found with increasing temperature for most of the heavier elements. The lighter elements like carbon, oxygen and nitrogen are depleted and less affected by temperature. Although there is considerable scatter from star to star, the general abundance patterns in most sdBs are similar. State-of-the-art diffusion models predict such patterns and are in qualitative agreement with our results. However, the highest enrichments measured cannot not be explained with these models. Peculiar line shapes of the strongest metal lines in some stars indicate vertical stratification to be present in the atmospheres. Such effects are not accounted for in current diffusion models and may be responsible for some of the yet unexplained abundance anomalies.
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- ID:
- ivo://CDS.VizieR/J/A+A/581/A83
- Title:
- Metal enriched X-ray bursting neutron star atmos.
- Short Name:
- J/A+A/581/A83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Low-mass X-ray binaries hosting neutron stars (NS) exhibit thermonuclear (type-I) X-ray bursts, which are powered by unstable nuclear burning of helium and/or hydrogen into heavier elements deep in the NS "ocean". In some cases the burning ashes may rise from the burning depths up to the NS photosphere by convection, leading to the appearance of the metal absorption edges in the spectra, which then force the emergent X-ray burst spectra to shift toward lower energies. These effects may have a substantial impact on the color correction factor fc and the dilution factor w, the parameters of the diluted blackbody model F_E_=wB_E_(f_c_T_eff_) that is commonly used to describe the emergent spectra from NSs. The aim of this paper is to quantify how much the metal enrichment can change these factors. We have developed a new NS atmosphere modeling code, which has a few important improvements compared to our previous code required by inclusion of the metals. The opacities and the internal partition functions (used in the ionization fraction calculations) are now taken into account for all atomic species. In addition, the code is now parallelized to counter the increased computational load.
- ID:
- ivo://CDS.VizieR/J/A+A/640/A25
- Title:
- Metal-poor stars limb-darkening coefficients
- Short Name:
- J/A+A/640/A25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Benchmark stars are crucial as validating standards for current as well as future large stellar surveys of the Milky Way. However, the number of suitable metal-poor benchmark stars is currently limited, owing to the difficulty in determining reliable effective temperatures (Teff) in this regime. We aim to construct a new set of metal-poor benchmark stars, based on reliable interferometric effective temperature determinations and a homogeneous analysis. The aim is to reach a precision of 1% in Teff, as is crucial for sufficiently accurate determinations of the full set of fundamental parameters and abundances for the survey sources. We observed ten late type metal-poor dwarf and giants: HD 2665, HD 6755, HD 6833, HD 103095, HD 122563, HD 127243, HD 140283, HD 175305, HD 221170 and HD 224930. Only three of the ten stars (HD 103095, HD 122563 and HD 140283) have previously been used as benchmark stars. For the observations, we used the high angular resolution optical interferometric instrument PAVO at the CHARA array. We modelled angular diameters using 3D limb darkening models and determined effective temperatures directly from the Stefan-Boltzmann relation, with an iterative procedure to interpolate over tables of bolometric corrections. Surface gravities (log(g)) were estimated from comparisons to Dartmouth stellar evolution model tracks. We collected spectroscopic observations from the ELODIE and FIES spectrographs and estimated metallicities ([Fe/H]) from a 1D non-LTE abundance analysis of unblended lines of neutral and singly ionized iron. We inferred Teff to better than 1% for five of the stars (HD 103095, HD 122563, HD 127243, HD 140283 and HD 224930). The effective temperatures of the other five stars are reliable to between 2-3%; the higher uncertainty on the Teff for those stars is mainly due to their having a larger uncertainty in the bolometric fluxes. We also determined log(g) and [Fe/H] with median uncertainties of 0.03dex and 0.09dex, respectively. This study presents reliable and homogeneous fundamental stellar parameters for ten metal-poor stars that can be adopted as a new set of benchmarks. The parameters are based on our consistent approach of combining interferometric observations, 3D limb darkening modelling and spectroscopic observations. The next paper in this series will extend this approach to dwarfs and giants in the metal-rich regime.
- ID:
- ivo://CDS.VizieR/J/A+AS/105/311
- Title:
- M giants spectra and photometry
- Short Name:
- J/A+AS/105/311
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From a sample of 97 very bright M-giant stars in the Solar neighbourhood, high-quality `intrinsic' spectra in the spectral range [380-900]nm for all M-spectral subclasses of the Case and MK classification systems are obtained. The results are fitted to photospheric synthetic spectra in the range [99-12500]nm in order to infer the corresponding continua. The synthetic spectra are also compared to the intrinsic spectra. The effective temperatures are derived and mathematical spectral classification criteria are found. The (UB)j(VRI)c(JHKLM)eso photometric data of the sample are also given.
- ID:
- ivo://CDS.VizieR/J/A+A/531/A165
- Title:
- MILES atmospheric parameters
- Short Name:
- J/A+A/531/A165
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Empirical libraries of stellar spectra are used to classify stars and synthetize stellar populations. MILES is a medium spectral-resolution library in the optical domain covering a wide range of temperatures, surface gravities and metallicities. We redetermine the atmospheric parameters of these stars in order to improve the homogeneity and accuracy. We build an interpolating function that returns a spectrum as a function of the three atmospheric parameters, and finally we characterize the precision of the wavelength calibration and stability of the spectral resolution. We used the ULySS program with the ELODIE library as a reference and compared the results with those in the literature. Results. We obtain precisions of 60K, 0.13, and 0.05dex, respectively, for Teff, logg, and [Fe/H] for the FGK stars. For the M stars, the mean errors are 38K, 0.26, and 0.12dex and 3.5%, 0.17, and 0.13dex for the OBA. We construct an interpolator that we test against the MILES stars themselves. We test it also by measuring the atmospheric parameters of the CFLIB stars with MILES as reference and find it to be more reliable than the ELODIE interpolator for the evolved hot stars, like those of the blue horizontal branch in particular.
- ID:
- ivo://CDS.VizieR/J/A+A/317/761
- Title:
- Miras temperatures, distances & magnitudes
- Short Name:
- J/A+A/317/761
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Effective temperatures are determined for a sample of 165 oxygen-rich Miras using indices related to molecular band strength of titanium oxide and vanadium oxide. Using a theoretical evolutionary track on AGB, absolute bolometric magnitudes are computed. Apparent bolometric magnitudes are determined from narrow-band photometry observations. They are used to calibrate distances.
107. Model Atmospheres
- ID:
- ivo://CDS.VizieR/VI/39
- Title:
- Model Atmospheres
- Short Name:
- VI/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/A+A/281/817
- Title:
- Model atmospheres for Vega
- Short Name:
- J/A+A/281/817
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/ApJ/813/47
- Title:
- Model atmospheres of irradiated exoplanets
- Short Name:
- J/ApJ/813/47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Many parameters constraining the spectral appearance of exoplanets are still poorly understood. We therefore study the properties of irradiated exoplanet atmospheres over a wide parameter range including metallicity, C/O ratio and host spectral type. We calculate a grid of 1-d radiative-convective atmospheres and emission spectra. We perform the calculations with our new Pressure-Temperature Iterator and Spectral Emission Calculator for Planetary Atmospheres (PETIT) code, assuming chemical equilibrium. The atmospheric structures and spectra are made available online. We find that atmospheres of planets with C/O ratios ~1 and Teff>~1500K can exhibit inversions due to heating by the alkalis because the main coolants CH_4_, H_2_O and HCN are depleted. Therefore, temperature inversions possibly occur without the presence of additional absorbers like TiO and VO. At low temperatures we find that the pressure level of the photosphere strongly influences whether the atmospheric opacity is dominated by either water (for low C/O) or methane (for high C/O), or both (regardless of the C/O). For hot, carbon-rich objects this pressure level governs whether the atmosphere is dominated by methane or HCN. Further we find that host stars of late spectral type lead to planetary atmospheres which have shallower, more isothermal temperature profiles. In agreement with prior work we find that for planets with Teff<1750K the transition between water or methane dominated spectra occurs at C/O~0.7, instead of ~1, because condensation preferentially removes oxygen.
- ID:
- ivo://CDS.VizieR/J/AcA/41/73
- Title:
- Model atmospheres of X-ray bursting neutron stars
- Short Name:
- J/AcA/41/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- X-ray burst sources represent a class of accreting neutron stars in close binary systems which do not exhibit any traces of the magnetic field. We present the first detailed tables which show the structure of plane--parallel hydrogen-helium atmospheres of bursting neutron stars. Hydrogen-helium models were computed with precise angle-dependent radiative transfer under constrains of radiative and hydrostatic equilibrium. Compton scattering opacity included both the Klein-Nishina corrections and the effects of relativistic Maxwellian thermal motion of scattering electrons. Compton redistribution function allows for large energy exchange between X-ray photons and scattering electrons.
