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- ID:
- ivo://CDS.VizieR/J/ApJS/85/315
- Title:
- F, G and K dwarf stars of the Pleiades
- Short Name:
- J/ApJS/85/315
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/AJ/160/217
- Title:
- 342 FGK-dwarfs ages using GALEX FUV magnitudes
- Short Name:
- J/AJ/160/217
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stellar age cannot be directly measured, yet age determinations are fundamental to understanding the evolution of stars, planets, and galaxies. The work presented here builds upon the idea of a stellar-activity age. We utilized far-ultraviolet (FUV) photometry acquired by the Galaxy Evolution Explorer (GALEX) space telescope as an indicator of chromospheric activity to infer ages of late-F, G, and K type dwarf stars. We derived a purely empirical correlation between FUV magnitudes and stellar age in conjunction with (B-V) color. Our attention is restricted to Sun-like stars with color range 0.55<=(B-V)<=0.71 and absolute magnitude range 4.3<=MV<=5.3. The correlation is defined in terms of a FUV-excess parameter Q(FUV-B,B-V). We related stellar age, {tau}, to Q through the relation log_e_({tau})=log_e_(a)+bQ, where a and b are fit parameters and functions of (B-V). This correlation is functional up to 6Gyr for FGK dwarfs. With such a correlation, one only needs Johnson (B-V) and FUV measurements to estimate the stellar age for Population i dwarf stars of solar-like temperature and metallicity. Such a calibration has utility in population studies of FGK dwarfs for further understanding of the chemical evolution of the Milky Way. As an illustration of one such application, we have constructed activity and FUV-age distributions for a sample of thin and thick disk stars, as distinguished by their chemical abundances. Considerable overlap is found between the activity distribution and age range of the two populations. We discuss the possibility that some high-[{alpha}/Fe] thick disk stars were formed as a result of the accretion of dwarf galaxies as recently as 4Gyr ago.
- ID:
- ivo://CDS.VizieR/J/A+A/658/A57
- Title:
- F-G-K stars activity indicators
- Short Name:
- J/A+A/658/A57
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Different relationships between the H{alpha} and CaII chromospheric emissions have been reported in solar-type stars. In particular, the time-series of emissions in these two lines are clearly anti-correlated for a few percent of the stars, contrary to what is observed on the Sun. Our objective is to characterise these relationships in more detail using complementary criteria, and to constrain the properties of filaments and plages that are necessary to explain the observations. We analysed the average level and variability of the H{alpha} and CaII emission for 441 F-G-K stars, paying particular attention to their (anti-)correlations on both short and long timescales. We also computed synthetic H{alpha} and CaII time-series for different assumptions of plage and filament properties and compared them with the observations. We were not able to find plage properties that, alone, are sufficient to reproduce the observations at all timescales simultaneously, even when allowing different H{alpha} and CaII emission relationships for different stars. We also specified the complex and surprising relationship between the average activity levels of both indexes, in particular for low-activity stars. We conclude that plages alone are unlikely to explain the observed variety of relationships between CaII and H{alpha} emission, and that the presence of other phenomena like filaments may help to reconcile the models with observations.
- ID:
- ivo://CDS.VizieR/J/ApJS/247/9
- Title:
- FGK stars magnetic activity in LAMOST-Kepler field
- Short Name:
- J/ApJS/247/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Monitoring chromospheric and photospheric indexes of magnetic activity can provide valuable information, especially the interaction between different parts of the atmosphere and their response to magnetic fields. We extract chromospheric indexes, S and R_HK_^+^, for 59816 stars from LAMOST spectra in the LAMOST-Kepler program, and photospheric index, Reff, for 5575 stars from Kepler light curves. The log Reff shows positive correlation with logR_HK_^+^. We estimate the power-law indexes between Reff and R_HK_^+^ for F-, G-, and K-type stars, respectively. We also confirm the dependence of both chromospheric and photospheric activity on stellar rotation. Ca ii H and K emissions and photospheric variations generally decrease with increasing rotation periods for stars with rotation periods exceeding a few days. The power-law indexes in exponential decay regimes show different characteristics in the two activity-rotation relations. The updated largest sample including the activity proxies and reported rotation periods provides more information to understand the magnetic activity for cool stars.
- ID:
- ivo://CDS.VizieR/J/A+A/636/A85
- Title:
- 3748 FGK stars spectroscopic parameters
- Short Name:
- J/A+A/636/A85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has observed the H-band spectra of over 200000 stars with R~22 000. The main motivation for this work is to test an alternative method to the standard APOGEE pipeline (APOGEE Stellar Parameter and Chemical Abundances Pipeline, ASPCAP) to derive parameters in the near-infrared (NIR) for FGK dwarfs. iSpec and Turbospectrum are used to generate synthetic spectra matching APOGEE observations and to determine the parameters through chi^2^ minimization. We present spectroscopic parameters (Teff, [M/H], logg, v_mic_) for a sample of 3748 main-sequence and subgiant FGK stars, obtained from their APOGEE H-band spectra. We compare our output parameters with the ones obtained with ASPCAP for the same stellar spectrum, and find that the values agree within the expected uncertainties. A comparison with the optical samples, California Planet Survey, HARPS-GTO, and PASTEL is also available, and median differences below 10K for Teff and 0.2dex for [M/H] are found. Reasons for these differences are explored. The full H-band line list, the line selection for the synthesis, and the synthesized spectra are available for download, as are the calculated parameters and their estimated uncertainties.
- ID:
- ivo://CDS.VizieR/J/AJ/144/19
- Title:
- Follow-up photometry for HAT-P-34 through HAT-P-37
- Short Name:
- J/AJ/144/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of four transiting extrasolar planets (HAT-P-34b-HAT-P-37b) with masses ranging from 1.05 to 3.33M_J_ and periods from 1.33 to 5.45days. These planets orbit relatively bright F and G dwarf stars (from V=10.16 to V=13.2). Of particular interest is HAT-P-34b which is moderately massive (3.33M_J_), has a high eccentricity of e=0.441+/-0.032 at a period of P=5.452654+/-0.000016days, and shows hints of an outer component. The other three planets have properties that are typical of hot Jupiters.
- ID:
- ivo://CDS.VizieR/J/AJ/147/87
- Title:
- From binaries to multiples. II. Statistical data
- Short Name:
- J/AJ/147/87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Statistics of hierarchical multiplicity among solar-type dwarfs are studied using the distance-limited sample of 4847 targets presented in the accompanying Paper I. Known facts about binaries (multiplicity fraction 0.46, lognormal period distribution with median period 100yr and logarithmic dispersion 2.4, and nearly uniform mass-ratio distribution independent of the period) are confirmed with a high statistical significance. The fraction of hierarchies with three or more components is 0.13+/-0.01, and the fractions of targets with n=1,2,3,... components are 54:33:8:4:1. Subsystems in the secondary components are almost as frequent as in the primary components, but in half of such cases both inner pairs are present. The high frequency of those 2+2 hierarchies (4%) suggests that both inner pairs were formed by a common process. The statistics of hierarchies can be reproduced by simulations, assuming that the field is a mixture coming from binary-rich and binary-poor environments. Periods of the outer and inner binaries are selected recursively from the same lognormal distribution, subject to the stability constraint and accounting for the correlation between inner subsystems. The simulator can be used to evaluate the frequency of multiple systems with specified parameters. However, it does not reproduce the observed excess of inner periods shorter than 10days, caused by tidal evolution.
- ID:
- ivo://CDS.VizieR/J/AJ/147/86
- Title:
- From binaries to multiples. I. The FG-67 sample
- Short Name:
- J/AJ/147/86
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Data on the multiplicity of F- and G-type dwarf stars within 67pc of the Sun are presented. This distance-limited sample based on the Hipparcos catalog contains 4847 primary stars (targets) with 0.5<V-I_C_<0.8 and is >90% complete. There are 2196 known stellar pairs; some of them belong to 361 hierarchical systems from triples to quintuples. Models of companion detection by radial velocity, astrometric acceleration, direct resolution, and common proper motion are developed. They serve to compute completeness for each target, using the information on its coverage collected here. About 80% of companions to the primary stars are detected, but the census of subsystems in the secondary components is only about 30%. Masses of binary components are estimated from their absolute magnitudes or by other methods; the periods of wide pairs are evaluated from their projected separations. A third of binaries with periods shorter than ~100yr are spectroscopic and/or astrometric pairs with yet unknown periods and mass ratios. These data are used in the accompanying Paper II to derive unbiased statistics of hierarchical multiple systems.
- ID:
- ivo://CDS.VizieR/J/A+A/592/A70
- Title:
- Gaia FGK stars: low-metallicities candidates
- Short Name:
- J/A+A/592/A70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have entered an era of large spectroscopic surveys in which we can measure, through automated pipelines, the atmospheric parameters and chemical abundances for large numbers of stars. Calibrating these survey pipelines using a set of "benchmark stars" in order to evaluate the accuracy and precision of the provided parameters and abundances is of utmost importance. The recent proposed set of Gaia FGK benchmark stars has up to five metal-poor stars but no recommended stars within -2.0<[Fe/H]<-1.0dex. However, this metallicity regime is critical to calibrate properly. In this paper, we aim to add candidate Gaia benchmark stars inside of this metal-poor gap. We began with a sample of 21 metal-poor stars which was reduced to 10 stars by requiring accurate photometry and parallaxes, and high-resolution archival spectra. The procedure used to determine the stellar parameters was similar to the previous works in this series for consistency. The difference was to homogeneously determine the angular diameter and effective temperature (Teff) of all of our stars using the Infrared Flux Method utilizing multi-band photometry. The surface gravity (logg) was determined through fitting stellar evolutionary tracks. The [Fe/H] was determined using four different spectroscopic methods fixing the Teff and logg from the values determined independent of spectroscopy.
