- 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/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.
- ID:
- ivo://CDS.VizieR/J/AJ/147/25
- Title:
- Atmospheric parameters of M4 stars
- Short Name:
- J/AJ/147/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report new metallicities for stars of Galactic globular cluster M4 using the largest number of stars ever observed at high spectral resolution in any cluster. We analyzed 7250 spectra for 2771 cluster stars gathered with the Very Large Telescope (VLT) FLAMES+GIRAFFE spectrograph at VLT. These medium-resolution spectra cover a small wavelength range, and often have very low signal-to-noise ratios. We approached this data set by reconsidering the whole method of abundance analysis of large stellar samples from beginning to end. We developed a new algorithm that automatically determines the atmospheric parameters of a star. Nearly all of the data preparation steps for spectroscopic analyses are processed on the syntheses, not the observed spectra. For 322 red giant branch (RGB) stars with V<=14.7, we obtain a nearly constant metallicity, <[Fe/H]>=-1.07 ({sigma}=0.02). No difference in the metallicity at the level of 0.01 dex is observed between the two RGB sequences identified by Monelli et al. (2013MNRAS.431.2126M). For 1869 subgiant and main-sequence stars with V>14.7, we obtain <[Fe/H]>=-1.16 ({sigma}=0.09) after fixing the microturbulent velocity. These values are consistent with previous studies that have performed detailed analyses of brighter RGB stars at higher spectroscopic resolution and wavelength coverage. It is not clear if the small mean metallicity difference between brighter and fainter M4 members is real or is the result of the low signal-to-noise characteristics of the fainter stars. The strength of our approach is shown by recovering a metallicity close to a single value for more than 2000 stars, using a data set that is non-optimal for atmospheric analyses. This technique is particularly suitable for noisy data taken in difficult observing conditions.
- ID:
- ivo://CDS.VizieR/J/PASJ/57/27
- Title:
- Atmospheric parameters of nearby F-K stars
- Short Name:
- J/PASJ/57/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on a collection of high-dispersion spectra obtained at Okayama Astrophysical Observatory, the atmospheric parameters (Teff, logg, vt, and [Fe/H]) of 160 mid-F through early-K stars were extensively determined by the spectroscopic method using the equivalent widths of Fe I and Fe II lines along with the numerical technique of Takeda et al. (2002PASJ...54..451T). The results are comprehensively discussed and compared with the parameter values derived by different approaches (e.g., photometric colors, theoretical evolutionary tracks, Hipparcos parallaxes, etc.) as well as with the published values found in various literature. It has been confirmed that our purely spectroscopic approach yields fairly reliable and consistent results.
- ID:
- ivo://CDS.VizieR/J/A+A/538/A143
- Title:
- Atmospheric parameters of stars for UV models
- Short Name:
- J/A+A/538/A143
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The spectral predictions of stellar population models are not as accurate in the ultra-violet (UV) as in the optical wavelength domain. One of the reasons is the lack of high-quality stellar libraries. The New Generation Stellar Library (NGSL), recently released, represents a significant step towards the improvement of this situation. To prepare NGSL for population synthesis, we determined the atmospheric parameters of its stars, we assessed the precision of the wavelength calibration and characterised its intrinsic resolution. We also measured the Galactic extinction for each of the NGSL stars. For our analyses we used ULySS, a full spectrum fitting package, fitting the NGSL spectra against the MILES interpolator. We find that the wavelength calibration is precise up to 0.1pix, after correcting a systematic effect in the optical range. The spectral resolution varies from 3{AA} in the UV to 10{AA} in the near-infrared (NIR), corresponding to a roughly constant reciprocal resolution R~1000 and an instrumental velocity dispersion 130km/s. We derived the atmospheric parameters homogeneously. The precision for the FGK stars is 42K, 0.24 and 0.09dex for Teff, logg and [Fe/H], respectively. The corresponding mean errors are 29K, 0.50 and 0.48dex for the M stars, and for the OBA stars they are 4.5 percent, 0.44 and 0.18dex. The comparison with the literature shows that our results are not biased.
- ID:
- ivo://CDS.VizieR/J/MNRAS/434/1422
- Title:
- Atmospheric param. of 169 FGKM stars
- Short Name:
- J/MNRAS/434/1422
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The asteroseismic and planetary studies, like all research related to stars, need precise and accurate stellar atmospheric parameters as input. We aim at deriving the effective temperature (Teff), the surface gravity (logg), the metallicity ([Fe/H]), the projected rotational velocity (vsini) and the MK type for 169 F-, G-, K- and M-type Kepler targets which were observed spectroscopically from the ground with five different instruments. We use two different spectroscopic methods to analyse 189 high-resolution, high-signal-to-noise spectra acquired for the 169 stars. For 67 stars, the spectroscopic atmospheric parameters are derived for the first time. KIC 9693187 and 11179629 are discovered to be double-lined spectroscopic binary systems. The results obtained for those stars for which independent determinations of the atmospheric parameters are available in the literature are used for a comparative analysis. As a result, we show that for solar-type stars the accuracy of present determinations of atmospheric parameters is +/-150K in Teff, +/-0.15dex in [Fe/H] and +/-0.3dex in logg. Finally, we confirm that the curve-of-growth analysis and the method of spectral synthesis yield systematically different atmospheric parameters when they are applied to stars hotter than 6000K.