- ID:
- ivo://CDS.VizieR/J/ApJ/725/L186
- Title:
- Orbital eccentricities of 31535 G-dwarfs
- Short Name:
- J/ApJ/725/L186
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We test four competing models that aim to explain the nature of stars in spiral galaxies that are well away (>1kpc) from the midplane, the so-called thick disk: the stars may have gotten there through orbital migration, through satellite mergers and accretion, or through heating of pre-existing thin disk stars. The eccentricity distribution of thick disk stars has recently been proposed as a diagnostic to differentiate between these mechanisms. Drawing on SDSS-DR7, we have assembled a sample of 31535 G-dwarfs with six-dimensional phase-space information and metallicities and have derived the orbital eccentricities for them.
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- ID:
- ivo://CDS.VizieR/J/ApJ/764/78
- Title:
- Oxygen abundances in nearby FGK stars
- Short Name:
- J/ApJ/764/78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Atmospheric parameters and oxygen abundances of 825 nearby FGK stars are derived using high-quality spectra and a non-local thermodynamic equilibrium analysis of the 777nm OI triplet lines. We assign a kinematic probability for the stars to be thin-disk (P_1_), thick-disk (P_2_), and halo (P_3_) members. We confirm previous findings of enhanced [O/Fe] in thick-disk (P_2_>0.5) relative to thin-disk (P_1_>0.5) stars with [Fe/H]<~-0.2, as well as a "knee" that connects the mean [O/Fe]-[Fe/H] trend of thick-disk stars with that of thin-disk members at [Fe/H]>~-0.2. Nevertheless, we find that the kinematic membership criterion fails at separating perfectly the stars in the [O/Fe]-[Fe/H] plane, even when a very restrictive kinematic separation is employed. Stars with "intermediate" kinematics (P_1_<0.7, P_2_<0.7) do not all populate the region of the [O/Fe]-[Fe/H] plane intermediate between the mean thin-disk and thick-disk trends, but their distribution is not necessarily bimodal. Halo stars (P_3_>0.5) show a large star-to-star scatter in [O/Fe]-[Fe/H], but most of it is due to stars with Galactocentric rotational velocity V<-200km/s; halo stars with V>-200km/s follow an [O/Fe]-[Fe/H] relation with almost no star-to-star scatter. Early mergers with satellite galaxies explain most of our observations, but the significant fraction of disk stars with "ambiguous" kinematics and abundances suggests that scattering by molecular clouds and radial migration have both played an important role in determining the kinematic and chemical properties of solar neighborhood stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/640/1051
- Title:
- 25pc sample of Sun-like stars
- Short Name:
- J/ApJ/640/1051
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Sun-like stars have stellar, brown dwarf, and planetary companions. To help constrain their formation and migration scenarios, we analyze the close companions (orbital period<5yr) of nearby Sun-like stars. By using the same sample to extract the relative numbers of stellar, brown dwarf, and planetary companions, we verify the existence of a very dry brown dwarf desert and describe it quantitatively.
- ID:
- ivo://CDS.VizieR/J/ApJ/834/207
- Title:
- Periodicity & magnitude of Kepler LCs variation
- Short Name:
- J/ApJ/834/207
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The variation of a stellar light curve owing to rotational modulation by magnetic features (starspots and faculae) on the star's surface can be used to investigate the magnetic properties of the host star. In this paper, we use the periodicity and magnitude of the light-curve variation as two proxies to study the stellar magnetic properties for a large sample of G-type main sequence Kepler targets, for which the rotation periods were recently determined. By analyzing the correlation between the two magnetic proxies, it is found that: (1) the two proxies are positively correlated for most of the stars in our sample, and the percentages of negative, zero, and positive correlations are 4.27%, 6.81%, and 88.91%, respectively; (2) negative correlation stars cannot have a large magnitude of light-curve variation; and (3) with the increase of rotation period, the relative number of positive correlation stars decreases and the negative correlation one increases. These results indicate that stars with shorter rotation period tend to have positive correlation between the two proxies, and a good portion of the positive correlation stars have a larger magnitude of light-curve variation (and hence more intense magnetic activities) than negative correlation stars.
- ID:
- ivo://CDS.VizieR/J/AJ/161/82
- Title:
- Photometric & spectroscopic obs. of TOI-954 and K2-329
- Short Name:
- J/AJ/161/82
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of two short-period Saturn-mass planets, one transiting the G subgiant TOI-954 (TIC44792534, V=10.343, T=9.78) observed in TESS sectors 4 and 5 and one transiting the G dwarf K2-329 (EPIC246193072, V=12.70, K=10.67) observed in K2 campaigns 12 and 19. We confirm and characterize these two planets with a variety of ground-based archival and follow-up observations, including photometry, reconnaissance spectroscopy, precise radial velocity, and high-resolution imaging. Combining all available data, we find that TOI-954b has a radius of 0.852_-0.062_^+0.053^R_Jup_ and a mass of 0.174_-0.017_^+0.018^M_Jup_ and is in a 3.68day orbit, while K2-329b has a radius of 0.774_-0.024_^+0.026^R_Jup_ and a mass of 0.260_-0.022_^+0.020^M_Jup_ and is in a 12.46day orbit. As TOI-954b is 30 times more irradiated than K2-329b but more or less the same size, these two planets provide an opportunity to test whether irradiation leads to inflation of Saturn-mass planets and contribute to future comparative studies that explore Saturn-mass planets at contrasting points in their lifetimes.
- ID:
- ivo://CDS.VizieR/J/AJ/150/33
- Title:
- Photometry and spectroscopy of HATS-9 and HATS-10
- Short Name:
- J/AJ/150/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of two transiting extrasolar planets by the HATSouth survey. HATS-9b orbits an old (10.8+/-1.5Gyr) V=13.3 G dwarf star with a period p~~1.9153days. The host star has a mass of 1.03M_{sun}_, radius of 1.503R_{sun}_, and effective temperature 5366+/-70K. The planetary companion has a mass of 0.837M_J_ and radius of 1.065R_J_, yielding a mean density of 0.85g/cm^-3^. HATS-10b orbits a V=13.1 G dwarf star with a period p~~3.3128days. The host star has a mass of 1.1M_{sun}_, radius of 1.11R_{sun}_, and effective temperature 5880+/-120K. The planetary companion has a mass of 0.53M_J_ and radius of 0.97R_J_, yielding a mean density of 0.7g/cm3. Both planets are compact in comparison with planets receiving similar irradiation from their host stars and lie in the nominal coordinates of Field 7 of K2, but only HATS-9b falls on working silicon. Future characterization of HATS-9b with the exquisite photometric precision of the Kepler telescope may provide measurements of its reflected light signature.
- ID:
- ivo://CDS.VizieR/J/AJ/156/37
- Title:
- Photometry & Li abund. of cool dwarfs in M35
- Short Name:
- J/AJ/156/37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Hydra spectra of 85 G-K dwarfs in the young cluster M35 near the Li 6708 {AA} line region are analyzed. From velocities and Gaia astrometry, 78 are likely single-star members that, combined with previous work, produce 108 members with T_eff_ ranging from 6150 to 4000 K as defined by multicolor, broadband photometry, E(B-V)=0.20, and [Fe/H]=-0.15, though there are indications the metallicity may be closer to solar. The Lithium abundance A(Li) follows a well-delineated decline from 3.15 for the hottest stars to upper limits =<1.0 among the coolest dwarfs. Contrary to earlier work, M35 includes single stars at systematically higher A(Li) than the mean cluster relation. This subset exhibits higher V_ROT_ than the more Li-depleted sample and, from photometric rotation periods, is dominated by stars classed as convective (C); all others are interface (I) stars. The cool, high-Li rapid rotators (RRs) are consistent with models that simultaneously consider rapid rotation and radius inflation; RRs hotter than the Sun exhibit excess Li depletion, as predicted by the models. The A(Li) distribution with color and rotation period, when compared to the Hyades/Praesepe and the Pleiades, is consistent with gyrochronological analysis placing M35's age between the older M34 and younger Pleiades. However, the Pleiades display a more excessive range in A(Li) and rotation period than M35 on the low-Li, slow-rotation side of the distribution, with supposedly younger stars at a given T_eff_ in the Pleiades spinning slower, with A(Li) reduced by more than a factor of four compared to M35.
- ID:
- ivo://CDS.VizieR/J/MNRAS/465/2734
- Title:
- Planet-hosting solar-type stars magnetic fields
- Short Name:
- J/MNRAS/465/2734
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectropolarimetric snapshot survey of solar-type planet-hosting stars. In addition to 14 planet-hosting stars observed as part of the BCool magnetic snapshot survey, we obtained magnetic observations of a further 19 planet-hosting solar-type stars in order to see if the presence of close-in planets had an effect on the measured surface magnetic field (|B_l_|). Our results indicate that the magnetic activity of this sample is congruent with that of the overall BCool sample. The effects of the planetary systems on the magnetic activity of the parent star, if any, are too subtle to detect compared to the intrinsic dispersion and correlations with rotation, age and stellar activity proxies in our sample. Four of the 19 newly observed stars, two of which are subgiants, have unambiguously detected magnetic fields and are future targets for Zeeman-Doppler mapping.
- ID:
- ivo://CDS.VizieR/J/A+A/572/A34
- Title:
- Pulsating solar-like stars in Kepler
- Short Name:
- J/A+A/572/A34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Kepler ultra-high precision photometry of long and continuous observations provides a unique dataset in which surface rotation and variability can be studied for thousands of stars. Because many of these old field stars also have independently measured asteroseismic ages, measurements of rotation and activity are particularly interesting in the context of age-rotation-activity relations. In particular, age-rotation relations generally lack good calibrators at old ages, a problem that this Kepler sample of old-field stars is uniquely suited to address. We study the surface rotation and photometric magnetic activity of a subset of 540 solar-like stars on the main-sequence and the subgiant branch for which stellar pulsations have been measured.
- ID:
- ivo://CDS.VizieR/J/A+A/634/L9
- Title:
- Rotation periods of 97 solar-like stars
- Short Name:
- J/A+A/634/L9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The accurate determination of stellar rotation periods is important for estimating stellar ages and for understanding stellar activity and evolution. While rotation periods can be determined for about thirty thousand stars in the Kepler field, there are over one hundred thousand stars, especially with low photometric variability and irregular pattern of variations, for which rotational periods are unknown. Here we investigate the effect of metallicity on the detectability of rotation periods. This is done by synthesising light curves of hypothetical stars that are identical to our Sun with the exception of the metallicity. These light curves are then used as an input to the period determination algorithms. We find that the success rate for recovering the rotation signal has a minimum close to the solar metallicity value. This can be explained by the compensation effect of facular and spot contributions. In addition, selecting solar-like stars with near-solar effective temperature and photometric variability, and with metallicity between M/H=-0.35 and M/H=0.35 from the Kepler sample, we analyse the fraction of stars for which rotational periods have been detected as a function of metallicity. In agreement with our theoretical estimate we find a local minimum for the detection fraction close to the solar metallicity. We further report rotation periods of 87 solar-like Kepler stars for the first time.
