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- ID:
- ivo://CDS.VizieR/J/A+A/512/A54
- Title:
- Teff and Fbol from Infrared Flux Method
- Short Name:
- J/A+A/512/A54
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Various effective temperature scales have been proposed over the years. Despite much work and the high internal precision usually achieved, systematic differences of order 100K (or more) among various scales are still present. We present an investigation based on the Infrared Flux Method aimed at assessing the source of such discrepancies and pin down their origin. We break the impasse among different scales by using a large set of solar twins, stars which are spectroscopically and photometrically identical to the Sun, to set the absolute zero point of the effective temperature scale to within few degrees. Our newly calibrated, accurate and precise temperature scale applies to dwarfs and subgiants, from super-solar metallicities to the most metal-poor stars currently known. At solar metallicities our results validate spectroscopic effective temperature scales, whereas for [Fe/H]<-2.5 our temperatures are roughly 100 K hotter than those determined from model fits to the Balmer lines and 200 K hotter than those obtained from the excitation equilibrium of Fe lines. Empirical bolometric corrections and useful relations linking photometric indices to effective temperatures and angular diameters have been derived. Our results take full advantage of the high accuracy reached in absolute calibration in recent years and are further validated by interferometric angular diameters and space based spectrophotometry over a wide range of effective temperatures and metallicities.
- ID:
- ivo://CDS.VizieR/J/A+A/566/A132
- Title:
- Teff and L for stars in 7 open clusters
- Short Name:
- J/A+A/566/A132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To study the time evolution of magnetic fields, chemical abundance peculiarities, and other characteristics of magnetic Ap and Bp stars during their main sequence lives, a sample of these stars in open clusters has been obtained, as such stars can be assumed to have the same ages as the clusters to which they belong. However, in exploring age determinations in the literature, we find a large dispersion among different age determinations, even for bright, nearby clusters. Our aim is to obtain ages that are as accurate as possible for the seven nearby open clusters {alpha} Per, Coma Ber, IC 2602, NGC 2232, NGC 2451A, NGC 2516, and NGC 6475, each of which contains at least one magnetic Ap or Bp star. Simultaneously, we test the current calibrations of T_e_ and luminosity for the Ap/Bp star members, and identify clearly blue stragglers in the clusters studied. We explore the possibility that isochrone fitting in the theoretical Hertzsprung-Russell diagram (i.e. log(L/L_{sun}_) vs. logT_e_), rather than in the conventional colour-magnitude diagram, can provide more precise and accurate cluster ages, with well-defined uncertainties.
- ID:
- ivo://CDS.VizieR/J/ApJ/562/528
- Title:
- Teff and log(g) of low-metallicity stars
- Short Name:
- J/ApJ/562/528
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We explore the application of artificial neural networks (ANNs) for the estimation of atmospheric parameters (T_eff_, log(g), and [Fe/H]) for Galactic F- and G-type stars. The ANNs are fed with medium-resolution ({Delta}{lambda}~1-2{AA}) nonflux-calibrated spectroscopic observations. From a sample of 279 stars with previous high-resolution determinations of metallicity and a set of (external) estimates of temperature and surface gravity, our ANNs are able to predict T_eff_ with an accuracy of {sigma}(T_eff_)=135-150K over the range 4250K<=T_eff_<=6500K, logg with an accuracy of {sigma}(logg)=0.25-0.30dex over the range 1.0<=logg<=5.0, and [Fe/H] with an accuracy {sigma}([Fe/H])=0.15-0.20dex over the range -4.0<=[Fe/H]<=0.3. Such accuracies are competitive with the results obtained by fine analysis of high-resolution spectra. It is noteworthy that the ANNs are able to obtain these results without consideration of photometric information for these stars. We have also explored the impact of the signal-to-noise ratio (S/N) on the behavior of ANNs and conclude that, when analyzed with ANNs trained on spectra of commensurate S/N, it is possible to extract physical parameter estimates of similar accuracy with stellar spectra having S/N as low as 13. Taken together, these results indicate that the ANN approach should be of primary importance for use in present and future large-scale spectroscopic surveys. The stars that comprise our study are a subset of the calibration stars used in the Beers et al. (1999, Cat. <J/AJ/117/981>) medium-resolution surveys.
- ID:
- ivo://CDS.VizieR/V/136
- Title:
- Teff and metallicities for Tycho-2 stars
- Short Name:
- V/136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have created specialized target lists for radial velocity surveys that are biased toward stars that (1) possess planets and (2) are easiest to observe with current detection techniques. We use a procedure that uniformly estimates fundamental stellar properties of Tycho 2 stars, with errors, using spline functions of broadband photometry and proper motion found in Hipparcos/Tycho 2 and 2MASS. We provide estimates of effective temperature and distance for 2.4 million Tycho 2 stars that lack trigonometric distances. For stars that appear to be FGK dwarfs, we also derive [Fe/H] and identify unresolved binary systems with mass ratios 1.25<M1/M2<3.0. For FGK dwarfs with photometric error {sigma}_V_<0.05, or V<9, our temperature model gives a 1{sigma} error of {sigma}_T_=+58.7/-65.9K and our metallicity model gives a 1{sigma} error of {sigma}_[Fe/H]_=+0.13/-0.14dex. The binarity model can be used to remove 70% of doubles with 1.25<M1/M2<3.0 from a magnitude-limited sample of dwarfs at a cost of cutting 20% of the sample. Our estimates of distance and spectral type enable us to isolate 354,822 Tycho 2 dwarfs, 321,996 absent from Hipparcos, with giant contamination of 2.6% and 7.2%, respectively. Roughly 100,000 of these stars, not in Hipparcos, have sufficiently low photometric errors to retain 0.13-0.3dex [Fe/H] accuracy and 80-100K temperature accuracy (1{sigma}). Our metallicity estimates have been used to identify targets for N2K, a large-scale radial velocity search for hot jupiters, which has verified the errors presented here. The catalogs that we publish can be used to further large-scale studies of Galactic structure and chemical evolution and to provide potential reference stars for narrow-angle astrometry programs such as the Space Interferometry Mission and large-aperture optical interferometry.
- ID:
- ivo://CDS.VizieR/J/ApJ/892/31
- Title:
- Teff and metallicities of M dwarfs in APOGEE DR14
- Short Name:
- J/ApJ/892/31
- Date:
- 07 Mar 2022 13:23:27
- Publisher:
- CDS
- Description:
- M dwarfs have enormous potential for our understanding of structure and formation on both Galactic and exoplanetary scales through their properties and compositions. However, current atmosphere models have limited ability to reproduce spectral features in stars at the coolest temperatures (Teff<4200K) and to fully exploit the information content of current and upcoming large-scale spectroscopic surveys. Here we present a catalog of spectroscopic temperatures, metallicities, and spectral types for 5875 M dwarfs in the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and Gaia-DR2 surveys using The Cannon (Ness+ 2015, J/ApJ/808/16 ; Casey+ 2016, arXiv:1603.03040; Ho+ 2017, J/ApJ/836/5; Behmard+ 2019ApJ...876...68B): a flexible, data-driven spectral-modeling and parameter-inference framework demonstrated to estimate stellar-parameter labels (Teff, logg, [Fe/H], and detailed abundances) to high precision. Using a training sample of 87 M dwarfs with optically derived labels spanning 2860K<Teff<4130K calibrated with bolometric temperatures, and -0.5<[Fe/H]<0.5dex calibrated with FGK binary metallicities, we train a two-parameter model with predictive accuracy (in cross-validation) to 77K and 0.09dex respectively. We also train a one-dimensional spectral classification model using 51 M dwarfs with Sloan Digital Sky Survey optical spectral types ranging from M0 to M6, to predictive accuracy of 0.7 types. We find Cannon temperatures to be in agreement to within 60 K compared to a subsample of 1702 sources with color-derived temperatures, and Cannon metallicities to be in agreement to within 0.08 dex metallicity compared to a subsample of 15 FGK+M or M+M binaries. Finally, our comparison between Cannon and APOGEE pipeline (ASPCAP DR14) labels finds that ASPCAP is systematically biased toward reporting higher temperatures and lower metallicities for M dwarfs.
21377. Teff, B-V and BC relation
- ID:
- ivo://CDS.VizieR/J/ApJ/469/355
- Title:
- Teff, B-V and BC relation
- Short Name:
- J/ApJ/469/355
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The table provides improved numerical relations between effective temperatures of stars, their B-V colors, and their bolometric corrections (BC) for the purpose of comparing theoretical stellar evolutionary calculations to color-magnitude diagrams of star clusters. Temperature and bolometric correction measurements for 335 stars from the literature form the observational basis for the transformations. Measured temperatures range from 2900 to 52500K.
- ID:
- ivo://CDS.VizieR/J/A+AS/110/553
- Title:
- Teff for B, A and F main sequence stars
- Short Name:
- J/A+AS/110/553
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A method of determination of the effective temperature of B, A and F main sequence stars is proposed, using the slope of the continuum between 3200A and 3600A. We have determined the Balmer jump and the effective temperatures for 235 main sequence stars.
- ID:
- ivo://CDS.VizieR/J/AN/328/938
- Title:
- Teff/line-depth ratio for ELODIE spectra
- Short Name:
- J/AN/328/938
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The dependence on the temperature of photospheric line-depth ratios (LDRs) in the spectral range 619.0-628.0nm is investigated by using a sample of 174 ELODIE Archive stellar spectra of luminosity class from V to III. The rotational broadening effect on LDRs is also studied. We provide useful calibrations of effective temperature versus LDRs for giant and main sequence stars with 3800<~T_eff_<~6000K and vsini in the range 0-30km/s. We found that, with the exception of very few line pairs, LDRs, measured at a spectral resolution as high as 42000, depend on vsini and that, by neglecting the rotational broadening effect, the T_eff_ determination can be wrong by ~100K in the worst cases.
- ID:
- ivo://CDS.VizieR/J/ApJ/851/26
- Title:
- Teff, metallicity and Ti abundance of M dwarfs
- Short Name:
- J/ApJ/851/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The ability to perform detailed chemical analysis of Sun-like F-, G-, and K-type stars is a powerful tool with many applications, including studying the chemical evolution of the Galaxy and constraining planet formation theories. Unfortunately, complications in modeling cooler stellar atmospheres hinders similar analyses of M dwarf stars. Empirically calibrated methods to measure M dwarf metallicity from moderate-resolution spectra are currently limited to measuring overall metallicity and rely on astrophysical abundance correlations in stellar populations. We present a new, empirical calibration of synthetic M dwarf spectra that can be used to infer effective temperature, Fe abundance, and Ti abundance. We obtained high-resolution (R~25000), Y-band (~1{mu}m) spectra of 29 M dwarfs with NIRSPEC on Keck II. Using the PHOENIX stellar atmosphere modeling code (version 15.5), we generated a grid of synthetic spectra covering a range of temperatures, metallicities, and alpha-enhancements. From our observed and synthetic spectra, we measured the equivalent widths of multiple Fe I and Ti I lines and a temperature-sensitive index based on the FeH band head. We used abundances measured from widely separated solar-type companions to empirically calibrate transformations to the observed indices and equivalent widths that force agreement with the models. Our calibration achieves precisions in Teff, [Fe/H], and [Ti/Fe] of 60K, 0.1dex, and 0.05dex, respectively, and is calibrated for 3200K<Teff<4100K, -0.7<[Fe/H]<+0.3, and -0.05<[Ti/Fe]<+0.3. This work is a step toward detailed chemical analysis of M dwarfs at a precision similar to what has been achieved for FGK stars.