- ID:
- ivo://CDS.VizieR/J/ApJ/804/146
- Title:
- Atmospheric parameters for nearby B-F stars
- Short Name:
- J/ApJ/804/146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Age determination is undertaken for nearby early type (BAF) stars, which constitute attractive targets for high-contrast debris disk and planet imaging surveys. Our analysis sequence consists of acquisition of ubvy{beta} photometry from catalogs, correction for the effects of extinction, interpolation of the photometry onto model atmosphere grids from which atmospheric parameters are determined, and finally, comparison to the theoretical isochrones from pre-main sequence through post-main sequence stellar evolution models, accounting for the effects of stellar rotation. We calibrate and validate our methods at the atmospheric parameter stage by comparing our results to fundamentally determined T_eff_ and log g values. We validate and test our methods at the evolutionary model stage by comparing our results on ages to the accepted ages of several benchmark open clusters (IC2602, {alpha} Persei, Pleiades, Hyades). Finally, we apply our methods to estimate stellar ages for 3493 field stars, including several with directly imaged exoplanet candidates.
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Search Results
- ID:
- ivo://CDS.VizieR/J/other/RAA/11.924
- Title:
- Atmospheric parameters for 771 stars
- Short Name:
- J/other/RAA/11.9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A number of spectroscopic surveys have been carried out or are planned to study the origin of the Milky Way. Their exploitation requires reliable automated methods and softwares to measure the fundamental parameters of the stars. Adopting the ULySS package, we have tested the effect of different resolutions and signal-to-noise ratios (SNR) on the measurement of the stellar atmospheric parameters (effective temperature Teff, surface gravity logg, and metallicity [Fe/H]). We show that ULySS is reliable to determine these parameters with medium-resolution spectra (R~2000). Then, we applied the method to measure the parameters of 771 stars selected in the commissioning database of the Guoshoujing Telescope (GSJT). The results were compared with the SDSS/SEGUE Stellar Parameter Pipeline (SSPP), and we derived precisions of 167K, 0.34dex, and 0.16dex for Teff, logg and [Fe/H] respectively. Furthermore, 120 of these stars are selected to construct the primary stellar spectra template library (Version 1.0) of GSJT, and will be deployed as basic ingredients for the GSJT automated parametrization pipeline.
- ID:
- ivo://CDS.VizieR/J/A+A/525/A71
- Title:
- Atmospheric parameters for 1273 stars
- Short Name:
- J/A+A/525/A71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Empirical libraries of stellar spectra play an important role in different fields. For example, they are used as reference for the automatic determination of atmospheric parameters, or for building synthetic stellar populations to study galaxies. The CFLIB (Coude-feed library, Indo-US) database is at present one of the most complete libraries, in terms of its coverage of the atmospheric parameters space (Teff, logg and [Fe/H]) and wavelength coverage 3460-9464{AA} at a resolution of ~1{AA} FWHM. Although the atmospheric parameters of most of the stars were determined from detailed analyses of high-resolution spectra, for nearly 300 of the 1273 stars of the library at least one of the three parameters is missing. For the others, the measurements, compiled from the literature, are inhomogeneous. In this paper, we re-determine the atmospheric parameters, directly using the CFLIB spectra, and compare them to the previous studies. Methods. We use the ULySS program to derive the atmospheric parameters, using the ELODIE library as a reference. Based on comparisons with several previous studies we conclude that our determinations are unbiased. For the 958 F,G, and K type stars the precision on Teff, logg, and [Fe/H] is respectively 43K, 0.13dex and 0.05dex. For the 53 M stars they are 82K, 0.22dex and 0.28dex. And for the 260 OBA type stars the relative precision on Teff is 5.1%, and on logg, and [Fe/H] the precision is respectively 0.19 dex and 0.16 dex. These parameters will be used to re-calibrate the CFLIB fluxes and to produce synthetic spectra of stellar populations.
- ID:
- ivo://CDS.VizieR/J/MNRAS/429/126
- Title:
- Atmospheric parameters from Fe lines
- Short Name:
- J/MNRAS/429/126
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive analysis of different techniques available for the spectroscopic analysis of FGK stars and provide a recommended methodology which efficiently estimates accurate stellar atmospheric parameters for large samples of stars. Our analysis includes a simultaneous equivalent width analysis of FeI and FeII spectral lines, and for the first time, utilizes on-the-fly non-local thermodynamic equilibrium (NLTE) corrections of individual FeI lines. We further investigate several temperature scales, finding that estimates from Balmer line measurements provide the most accurate effective temperatures at all metallicities. We apply our analysis to a large sample of both dwarf and giant stars selected from the Radial Velocity Experiment (RAVE) survey. We then show that the difference between parameters determined by our method and that by the standard 1D LTE excitation-ionization balance of Fe reveals substantial systematic biases: up to 400K in effective temperature, 1.0dex in surface gravity and 0.4dex in metallicity for stars with [Fe/H]~-2.5. This has large implications for the study of the stellar populations in the Milky Way.
- ID:
- ivo://CDS.VizieR/J/AJ/147/137
- Title:
- Atmospheric parameters in luminous stars
- Short Name:
- J/AJ/147/137
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Parameters and abundances for 451 stars of spectral types F, G, and K of luminosity classes I and II have been derived. Absolute magnitudes and E(B-V) have been derived for the warmer stars in order to investigate the galactic abundance gradient. The value found here: d[Fe/H]/dR~-0.06dex/kpc, agrees well with previous determinations. Stellar evolution indicators have also been investigated with the derived C/O ratios indicating that standard CN processing has been operating. Perhaps the most surprising result found in these supposedly relatively young intermediate-mass stars is that both [O/Fe] and [C/Fe] show a correlation with [Fe/H] much the same as found in older populations. While the stars were selected based on luminosity class, there does exist a significant [Fe/H] range in the sample. The likely explanation of this is that there is a significant range in age in the sample; that is, some of the sample are low-mass red-giant stars with types that place them within the selection criteria.
- ID:
- ivo://CDS.VizieR/J/A+A/314/191
- Title:
- Atmospheric parameters in metal-poor stars. I
- Short Name:
- J/A+A/314/191
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present atmospheric parameters for about 300 stars of different chemical composition, whose spectra will be used to study the galactic enrichment of Fe and light elements. These parameters were derived using an homogeneous iterative procedure, which considers new calibrations of colour-T_eff_ relations for F, G and K-type stars based on Infrared Flux Method (IRFM) and interferometric diameters for population I stars, and the Kurucz (1992) model atmospheres. We found that these calibrations yield a self-consistent set of atmospheric parameters for T_eff_>4400K, representing a clear improvement over results obtained with older model atmospheres. Using this T_eff_ -scale and Fe equilibrium of ionization, we obtained very low gravities (implying luminosities incompatible with that expected for RGB stars) for metal-poor stars cooler than 4400K; this might be due either to a moderate Fe overionization (expected from statistical equilibrium calculations) or to inadequacy of Kurucz models to describe the atmospheres of very cool giants. Our T_eff_ scale is compared with other scales recently used for metal-poor stars; it agrees well with those obtained using Kurucz (1992) models, but it gives much larger T_eff_'s than those obtained using OSMARCS models (Edvardsson et al. 1993). This difference is attributed to the different treatment of convection in the two sets of models. For the Sun, the Kurucz (1992) model appears to be preferable to the OSMARCS ones because it better predicts the solar limb darkening; furthermore, we find that our photometric T_eff_ 's for metal-poor stars agree well with both direct estimates based on the IRFM, and with T_eff_'s derived from H{alpha} wings when using Kurucz models.
- ID:
- ivo://CDS.VizieR/J/A+A/350/955
- Title:
- Atmospheric parameters in metal-poor stars. II
- Short Name:
- J/A+A/350/955
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present non-LTE corrections to abundances of Fe, O, Na, and Mg derived from LTE analyses of F-K stars over a broad range of gravities and metal abundances; they were obtained using statistical equilibrium calculations and new model atoms. Line opacity was considered by means of an empirical procedure where it was attributed to a veil of weak Fe I lines; in the case of solar-type dwarfs, results were compared with those obtained using (LTE) mean intensities computed from OSMARCS models. We think that the empirical procedure produces better results for metal-poor stars, while mean intensities should perhaps be preferred for the Sun (where departures from LTE are anyway not very large). Collisions with both electrons and H I atoms were considered. Since cross sections for this second mechanism are very poorly known, we calibrated them empirically by matching observations of RR Lyrae variables at minimum light (discussed in Clementini et al., 1995, Cat. <J/AJ/110/2319>). These stars were selected because non-LTE effects are expected to be larger in these stars than in those usually considered in the study of the chemical evolution of the Galaxy (cool main sequence and red giant branch stars). We found that different non-LTE mechanisms are important for the different species and transitions considered; on the whole, our calculations yielded moderate corrections to LTE abundances for high excitation O lines in warm dwarfs and giants, Na and Mg lines in giants and supergiants, and Fe I lines in F-supergiants (where corrections becomes very large for IR O lines). Non-LTE corrections were found to be negligible in the other cases studied.
- ID:
- ivo://CDS.VizieR/J/A+A/356/238
- Title:
- Atmospheric parameters in metal-poor stars. III.
- Short Name:
- J/A+A/356/238
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the analysis of an extensive set of new and literature high quality data concerning Fe, C, N, O, Na, and Mg. This analysis exploited the T_eff_ scale determined in Gratton et al. (1996, Cat. <J/A+A/314/191>), and the non-LTE abundance corrections computed in Gratton et al. (1999, Cat. <J/A+A/350/955>). Results obtained with various abundance indices are discussed and compared.
- ID:
- ivo://CDS.VizieR/J/A+A/271/515
- Title:
- Atmospheric parameters of A and F stars I.
- Short Name:
- J/A+A/271/515
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/ApJ/631/1100
- Title:
- Atmospheric parameters of DA white dwarfs
- Short Name:
- J/ApJ/631/1100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present atmospheric parameters for a large sample of DA white dwarfs that are known to be photometrically constant. For each star, we determine the effective temperature and surface gravity by comparing high signal-to-noise ratio optical spectra to the predictions of detailed model atmosphere calculations. We also report the successful prediction and detection of photometric variability in G232-38 based on similar Teff and logg determinations. The atmospheric parameters derived for this sample of constant stars, as well as those for the known sample of bright ZZ Ceti stars (now boosted to a total of 39), have been obtained in a highly homogeneous way.
