- ID:
- ivo://CDS.VizieR/J/A+A/611/A11
- Title:
- STAGGER-grid of 3D stellar models. V.
- Short Name:
- J/A+A/611/A11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have calculated spectra from 1000 to 200000{AA} with a constant resolving power of {lambda}/{Delta}{lambda}=20000 and from 8470 and 8710{AA} (Gaia Radial Velocity Spectrometer - RVS - spectral range) with a constant resolving power of {lambda}/{Delta}{lambda}=300000. This for the Stagger-grid 3D stellar atmosphere models in the ranges: Teff from 4000 to 7000K, logg from 1.5 to 5.0, and [Fe/H], from -4.0 to +0.5. We used synthetic spectra to compute theoretical colours in the Johnson-Cousins UBV(RI)C, SDSS, 2MASS, Gaia, SkyMap- per, Stroemgren systems, and HST-WFC3.
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- ID:
- ivo://CDS.VizieR/J/A+A/393/225
- Title:
- Starspot cycles of six young solar analogues
- Short Name:
- J/A+A/393/225
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A long-term photometric monitoring of a selected sample of solar analogues has been carried out since early nineties as part of "The Sun in tim" project, which is aimed at a multiwavelength study of stars with solar-like global properties, but with different ages and thus at different stages of their evolution. The extended time sequence of ground-based observations collected over more than a decade as part of this program has revealed the existence of starspot cycles. Also from these data it is possible to investigate surface differential rotation of the stars. In this paper we present the photometry collected to date and report on cycles search for a selected subsample of five young single G0-G5V stars with ages between ~130Myr and 700Myr: EK Dra, {pi}^1^ UMa, HN Peg, {kappa}^1^ Cet, BE Cet. Also we include in this study the Pleiades-age (~130Myr) K0V star DX Leo (HD 82443). All the cited stars show activity cycles whose period is, furthermore, the first determined from photometric data. They are compared to those activity cycles derived from CaII H&K emission fluxes and differences are discussed. All the cycle periods, except for EK Dra, fit well the empirical relations with global stellar parameters derived from larger stellar samples. The following results are also inferred from the present study: i) the fastest rotating stars tend to have longer cycles; ii) the range in the observed cycle lengths seems to converge with stellar age from a maximum dispersion around the Pleiades' age towards the solar cycle value at the Sun's age; iii) the overall short- and long-term photometric variability increases with inverse Rossby number with very high correlation degree, indicating that the level of magnetic activity at least in photosphere is still controlled by the stellar rotation even on the longest time scales; iiii) the increase with inverse Rossby number of the long-term overall photometric variability seems to level off at the highest rotation rate, which may be interpreted as due to a saturation in the level of photospheric magnetic activity around the activity maximum.
- ID:
- ivo://CDS.VizieR/J/ApJ/743/48
- Title:
- Stars with rotation periods and X-ray luminosities
- Short Name:
- J/ApJ/743/48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a sample of 824 solar and late-type stars with X-ray luminosities and rotation periods. This is used to study the relationship between rotation and stellar activity and derive a new estimate of the convective turnover time. From an unbiased subset of this sample the power law slope of the unsaturated regime, L_X_/L_{bol}_{propto}Ro^{beta}^, is fit as {beta}=-2.70+/-0.13. This is inconsistent with the canonical {beta}=-2 slope to a confidence of 5{sigma}, and argues for an additional term in the dynamo number equation. From a simple scaling analysis this implies {Delta}{Omega}/{Omega}{propto}{Omega}^0.7^, i.e. the differential rotation of solar-type stars gradually declines as they spin down. Super-saturation is observed for the fastest rotators in our sample and its parametric dependencies are explored. Significant correlations are found with both the corotation radius and the excess polar updraft, the latter theory providing a stronger dependence and being supported by other observations. We estimate mass-dependent empirical thresholds for saturation and super- saturation and map out three regimes of coronal emission. Late F-type stars are shown never to pass through the saturated regime, passing straight from super-saturated to unsaturated X-ray emission. The theoretical threshold for coronal stripping is shown to be significantly different from the empirical saturation threshold (Ro<0.13), suggesting it is not responsible. Instead we suggest that a different dynamo configuration is at work in stars with saturated coronal emission. This is supported by a correlation between the empirical saturation threshold and the time when stars transition between convective and interface sequences in rotational spin-down models.
- ID:
- ivo://CDS.VizieR/J/A+A/552/A27
- Title:
- Stellar activity and kinematics of FGK stars
- Short Name:
- J/A+A/552/A27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a study of the stellar activity in the solar neighborhood using complete kinematics (galactocentric velocities U,V,W) and the chromospheric activity index log RHK. We analyzed the average activity level near the centers of known moving groups using a sample of 2529 stars and found that the stars near these associations tend to be more active than field stars. This supports the hypothesis that these structures, or at least the dominant fraction of them, are composed of kinematically bound, young stars. We confirmed our results by using Galaxy Evolution Explorer (GALEX) UV data and kinematics taken from the Geneva-Copenhagen Survey for the stars in the sample. Finally, we present a compiled catalog with kinematics and activities for 2529 stars and a list of potential moving group members selected based on their stellar activity level.
- ID:
- ivo://CDS.VizieR/J/A+AS/142/275
- Title:
- Stellar activity of late-type stars
- Short Name:
- J/A+AS/142/275
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results from a spectroscopic CaII H&K survey of 1058 late-type stars selected from a color-limited subsample of the Hipparcos (Cat. <I/239>) catalog. Out of these 1058 stars, 371 stars were found to show significant H&K emission, most of them previously unknown; 23% with strong emission, 36% with moderate emission, and 41% with weak emission. These spectra are used to determine absolute H&K emission-line fluxes, radial velocities, and equivalent widths of the luminosity-sensitive Sr II line at 4077{AA}. Red-wavelength spectroscopic and Stroemgren y photometric follow-up observations of the 371 stars with H&K emission are used to additionally determine the absolute H{alpha}-core flux, the lithium abundance from the Li I 6708{AA} equivalent width, the rotational velocity vsini, the radial velocity, and the light variations and its periodicity.
- ID:
- ivo://CDS.VizieR/J/ApJ/757/112
- Title:
- Stellar diameters. II. K and M-stars
- Short Name:
- J/ApJ/757/112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present interferometric angular diameter measurements of 21 low-mass, K- and M-dwarfs made with the CHARA Array. This sample is enhanced by adding a collection of radius measurements published in the literature to form a total data set of 33 K-M-dwarfs with diameters measured to better than 5%. We use these data in combination with the Hipparcos parallax and new measurements of the star's bolometric flux to compute absolute luminosities, linear radii, and effective temperatures for the stars. We develop empirical relations for ~K0 to M4 main-sequence stars that link the stellar temperature, radius, and luminosity to the observed (B-V), (V-R), (V-I), (V-J), (V-H), and (V-K) broadband color index and stellar metallicity [Fe/H]. These relations are valid for metallicities ranging from [Fe/H]=-0.5 to +0.1dex and are accurate to ~2%, ~5%, and ~4% for temperature, radius, and luminosity, respectively. Our results show that it is necessary to use metallicity-dependent transformations in order to properly convert colors into stellar temperatures, radii, and luminosities.
- ID:
- ivo://CDS.VizieR/J/A+A/446/267
- Title:
- Stellar latitudinal differential rotation
- Short Name:
- J/A+A/446/267
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- More than 600 high resolution spectra of stars with spectral type F and later were obtained in order to search for signatures of differential rotation in line profiles. In 147 stars the rotation law could be measured, with 28 of them found to be differentially rotating.
- ID:
- ivo://CDS.VizieR/J/ApJ/753/90
- Title:
- Stellar parameters of K5 and later type Kepler stars
- Short Name:
- J/ApJ/753/90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We estimate the stellar parameters of late K- and early M-type Kepler target stars. We obtain medium-resolution visible spectra of 382 stars with K_P_-J>2 (=~K5 and later spectral type). We determine luminosity class by comparing the strength of gravity-sensitive indices (CaH, K I, Ca II, and Na I) to their strength in a sample of stars of known luminosity class. We find that giants constitute 96%+/-1% of the bright (K_P_<14) Kepler target stars, and 7%+/-3% of dim (K_P_>14) stars, significantly higher than fractions based on the stellar parameters quoted in the Kepler Input Catalog (KIC). The KIC effective temperatures are systematically (110^+15^_-35_K) higher than temperatures we determine from fitting our spectra to PHOENIX stellar models. Through Monte Carlo simulations of the Kepler exoplanet candidate population, we find a planet occurrence of 0.36+/-0.08 when giant stars are properly removed, somewhat higher than when a KIC log g>4 criterion is used (0.27+/-0.05). Last, we show that there is no significant difference in g-r color (a probe of metallicity) between late-type Kepler stars with transiting Earth-to-Neptune-size exoplanet candidates and dwarf stars with no detected transits. We show that a previous claimed offset between these two populations is most likely an artifact of including a large number of misidentified giants.
- ID:
- ivo://CDS.VizieR/J/AJ/158/56
- Title:
- Stellar parameters of M and K dwarfs
- Short Name:
- J/AJ/158/56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Empirical correlations between stellar parameters such as rotation or radius and magnetic activity diagnostics require estimates of the effective temperatures and the stellar radii. The aim of this study is to propose simple methods that can be applied to large samples of stars in order to derive estimates of the stellar parameters. Good empirical correlations between red/infrared colors (e.g., (R-I)_C_) and effective temperatures have been well established for a long time. The more recent (R-I)_C_ color-T_eff_ correlation using the data of Mann et al. (2015, J/ApJ/804/64, hereafter M15) and Boyajian et al. (2012, J/ApJ/757/112, hereafter B12) shows that this color can be applied as a temperature estimate for large samples of stars. We find that the mean scatter in T_eff_ relative to the (R-I)_C_-T_eff_ relationship of B12 and M15 data is only +/-3{sigma}=44.6 K for K dwarfs and +/-3{sigma}=39.4 K for M dwarfs. These figures are small and show that the (R-I)_C_ color can be used as a first-guess effective temperature estimator for K and M dwarfs. We derive effective temperatures for about 1910 K and M dwarfs using the calibration of (R-I)_C_ color-T_eff_ from B12 and M15 data. We also compiled T_eff_ and metallicity measurements available in the literature using the VizieR database. We determine T_eff_ for 441 stars with previously unknown effective temperatures. We also identified 21 new spectroscopic binaries and one triple system from our high-resolution spectra.
- ID:
- ivo://CDS.VizieR/J/ApJS/168/297
- Title:
- Stellar parameters of nearby cool stars
- Short Name:
- J/ApJS/168/297
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive detailed theoretical models for 1074 nearby stars from the SPOCS (Spectroscopic Properties of Cool Stars) Catalog. We provide a catalog of physical parameters for 1074 stars that are based on a uniform set of high-quality spectral observations, a uniform spectral reduction procedure, and a uniform set of stellar evolutionary models.
