- ID:
- ivo://CDS.VizieR/J/A+A/626/A31
- Title:
- Radial velocities of nearby stars
- Short Name:
- J/A+A/626/A31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We observed stars with variable radial velocities to determine their spectroscopic orbits. Velocities of 132 targets taken over a time span reaching 30 years are presented. They were measured with the correlation radial velocity spectrometers (1913 velocities) and the new VUES echelle spectrograph (632 velocities), with typical accuracy of 0.5 and 0.2km/s, respectively. We derived spectroscopic orbits of 57 stars (including 53 first-time orbits), mostly nearby dwarfs of spectral types K and M. Their periods range from 2.2 days to 14 years, some of those are Hipparcos astrometric binaries. Comments on individual objects are provided. Many stars belong to hierarchical systems containing three or more components, including 20 new hierarchies resulting from this project. The preliminary orbit of the young star HIP 47110B has a large eccentricity e=0.47 despite short period of 4.4d; it could be still circularizing. Our results enrich the data on nearby stars and contribute toa better definition of the multiplicity statistics.
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- ID:
- ivo://CDS.VizieR/J/ApJ/732/39
- Title:
- Rotational velocities of K giant stars
- Short Name:
- J/ApJ/732/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a search for unusually rapidly rotating giant stars in a large sample of K giants (~1300 stars) that had been spectroscopically monitored as potential targets for the Space Interferometry Mission's Astrometric Grid. The stars in this catalog are much fainter and typically more metal-poor than those of other catalogs of red giant star rotational velocities, but the spectra generally only have signal-to-noise ratio (S/N) of ~20-60, making the measurement of the widths of individual lines difficult. To compensate for this, we have developed a cross-correlation method to derive rotational velocities in moderate S/N echelle spectra to efficiently probe this sample for rapid rotator candidates. We have discovered 28 new red giant rapid rotators as well as one extreme rapid rotator with a vsin i of 86.4km/s. Rapid rotators comprise 2.2% of our sample, which is consistent with other surveys of brighter, more metal-rich K giant stars. Although we find that the temperature distribution of rapid rotators is similar to that of the slow rotators, this may not be the case with the distributions of surface gravity and metallicity. The rapid rotators show a slight overabundance of low-gravity stars and as a group are significantly more metal-poor than the slow rotators, which may indicate that the rotators are tidally locked binaries.
- ID:
- ivo://CDS.VizieR/J/AJ/156/64
- Title:
- RV measurements for 6 K giants in the SENS program
- Short Name:
- J/AJ/156/64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of long-period radial velocity (RV) variations in six intermediate-mass K-giant stars using precise RV measurements. These discoveries are part of the Search for Exoplanets around Northern Circumpolar Stars (SENS) survey being conducted at the Bohyunsan Optical Astronomy Observatory. The nature of the RV variations was investigated by looking for photometric and line shape variations. We can find no variability with the RV period in these quantities and conclude that RV variations are most likely due to unseen sub-stellar companions. Orbital solutions for the six stars yield orbital periods in the range 418-1065 days and minimum masses in the range 1.9-8.5 M_J_. These properties are typical on planets around intermediate-mass stars. Our SENS survey so far has about an 8% confirmed planet occurrence rate, and it will provide better statistics on planets around giant stars when the survey is completed.
- ID:
- ivo://CDS.VizieR/J/ApJ/886/154
- Title:
- Sgr stream K- & M-giants and BHB stars
- Short Name:
- J/ApJ/886/154
- Date:
- 07 Dec 2021 13:01:04
- Publisher:
- CDS
- Description:
- We characterize the kinematic and chemical properties of ~3000 Sagittarius (Sgr) stream stars, including K-giants, M-giants, and blue horizontal branch stars (BHBs), selected from SEGUE-2, Large Sky Area Multi-Object Fibre Spectroscopic Telescope, and Sloan Digital Sky Survey separately in Integrals-of-Motion space. The orbit of the Sgr stream is quite clear from the velocity vector in the X-Z plane. Stars traced by K-giants and M-giants show that the apogalacticon of the trailing steam is ~100kpc. The metallicity distributions of Sgr K-giants, M-giants, and BHBs indicate that the M-giants are on average the most metal-rich population, followed by K-giants and BHBs. All of the K-giants, M-giants, and BHBs indicate that the trailing arm is on average more metal-rich than the leading arm, and the K-giants show that the Sgr debris is the most metal-poor part. The {alpha}-abundance of Sgr stars exhibits a similar trend with the Galactic halo stars at lower metallicity ([Fe/H]<~-1.0dex), and then evolve down to lower [{alpha}/Fe] than disk stars at higher metallicity, which is close to the evolution pattern of the {alpha}-element of Milky Way dwarf galaxies. We find that VY and metallicity of K-giants have gradients along the direction of the line of sight from the Galactic center in the X-Z plane, and the K-giants show that VY increases with metallicity at [Fe/H]>~-1.5dex. After dividing the Sgr stream into bright and faint streams according to their locations in equatorial coordinates, the K-giants and BHBs show that the bright and faint streams present different VY and metallicities, the bright stream is on average higher in VY and metallicity than the faint stream.
- ID:
- ivo://CDS.VizieR/J/AJ/162/41
- Title:
- Speckle interferometry at SOAR in 2020
- Short Name:
- J/AJ/162/41
- Date:
- 14 Mar 2022 06:54:42
- Publisher:
- CDS
- Description:
- The results of speckle interferometric observations at the 4.1m Southern Astrophysical Research Telescope in 2020, as well as earlier unpublished data, are given, totaling 1735 measurements of 1288 resolved pairs and nonresolutions of 1177 targets. We resolved for the first time 59 new pairs or subsystems in known binaries, mostly among nearby dwarf stars. This work continues our long-term speckle program. Its main goal is to monitor orbital motion of close binaries, including members of high-order hierarchies and Hipparcos pairs in the solar neighborhood. We also report observations of 892 members of young moving groups and associations, where we resolved 103 new pairs.
- ID:
- ivo://CDS.VizieR/J/ApJ/735/L46
- Title:
- Spectroscopy of 64 K red giants
- Short Name:
- J/ApJ/735/L46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on high-resolution spectra obtained with the MIKE spectrograph on the Magellan telescopes, we present detailed elemental abundances for 20 red giant stars in the outer Galactic disk, located at Galactocentric distances between 9 and 13kpc. The outer disk sample is complemented with samples of red giants from the inner Galactic disk and the solar neighborhood, analyzed using identical methods. For Galactocentric distances beyond 10kpc, we only find chemical patterns associated with the local thin disk, even for stars far above the Galactic plane. Our results show that the relative densities of the thick and thin disks are dramatically different from the solar neighborhood, and we therefore suggest that the radial scale length of the thick disk is much shorter than that of the thin disk. We make a first estimate of the thick disk scale length of L_thick_=2.0kpc, assuming L_thin_=3.8kpc for the thin disk. We suggest that radial migration may explain the lack of radial age, metallicity, and abundance gradients in the thick disk, possibly also explaining the link between the thick disk and the metal-poor bulge.
- ID:
- ivo://CDS.VizieR/J/AJ/147/146
- Title:
- Spectroscopy of Tuc-Hor candidate members
- Short Name:
- J/AJ/147/146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the selection and spectroscopic confirmation of 129 new late-type (SpT=K3-M6) members of the Tucana-Horologium moving group, a nearby (d~40pc), young ({tau}~40Myr) population of comoving stars. We also report observations for 13 of the 17 known Tuc-Hor members in this spectral type range, and that 62 additional candidates are likely to be unassociated field stars; the confirmation frequency for new candidates is therefore 129/191=67%. We have used radial velocities, H{alpha} emission, and Li_6708_ absorption to distinguish between contaminants and bona fide members. Our expanded census of Tuc-Hor increases the known population by a factor of ~3 in total and by a factor of ~8 for members with SpT>=K3, but even so, the K-M dwarf population of Tuc-Hor is still markedly incomplete. Our expanded census allows for a much more detailed study of Tuc-Hor than was previously feasible. The spatial distribution of members appears to trace a two-dimensional sheet, with a broad distribution in X and Y, but a very narrow distribution (+/-5pc) in Z. The corresponding velocity distribution is very small, with a scatter of +/-1.1km/s about the mean UVW velocity for stars spanning the entire 50pc extent of Tuc-Hor. We also show that the isochronal age ({tau}~20-30Myr) and the lithium depletion boundary age ({tau}~40Myr) disagree, following the trend in other pre-main-sequence populations for isochrones to yield systematically younger ages. The H{alpha} emission line strength follows a trend of increasing equivalent width with later spectral type, as is seen for young clusters. We find that moving group members have been depleted of measurable lithium for spectral types of K7.0-M4.5. None of our targets have significant infrared excesses in the WISE W3 band, yielding an upper limit on warm debris disks of F<0.7%. Finally, our purely kinematic and color-magnitude selection procedure allows us to test the efficiency and completeness for activity-based selection of young stars. We find that 60% of K-M dwarfs in Tuc-Hor do not have ROSAT counterparts and would have been omitted in X-ray-selected samples. In contrast, GALEX UV-selected samples using a previously suggested criterion for youth achieve completeness of 77% and purity of 78%, and we suggest new SpT-dependent selection criteria that will yield >95% completeness for {tau}~40Myr populations with GALEX data available.
- ID:
- ivo://CDS.VizieR/J/A+A/616/A33
- Title:
- Stellar parameters of 372 giant stars
- Short Name:
- J/A+A/616/A33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The determination of accurate stellar parameters of giant stars is essential for our understanding of such stars in general and as exoplanet host stars in particular. Precise stellar masses are vital for determining the lower mass limit of potential substellar companions with the radial velocity method. Our goal is to determine stellar parameters, including mass, radius, age, surface gravity, effective temperature and luminosity, for the sample of giants observed by the Lick planet search. Furthermore, we want to derive the probability of these stars being on the horizontal branch (HB) or red giant branch (RGB), respectively. We compare spectroscopic, photometric and astrometric observables to grids of stellar evolutionary models using Bayesian inference. We provide tables of stellar parameters, probabilities for the current post-main sequence evolutionary stage, and probability density functions for 372 giants from the Lick planet search. We find that 81% of the stars in our sample are more probably on the HB. In particular, this is the case for 15 of the 16 planet host stars in the sample. We tested the reliability of our methodology by comparing our stellar parameters to literature values and find very good agreement. Furthermore, we created a small test sample of 26 giants with available asteroseismic masses and evolutionary stages and compared these to our estimates. The mean difference of the stellar masses for the 24 stars with the same evolutionary stages by both methods is only {Delta}M=0.01+/-0.20M_{sun}_. We do not find any evidence for large systematic differences between our results and estimates of stellar parameters based on other methods. In particular we find no significant systematic offset between stellar masses provided by asteroseismology to our Bayesian estimates based on evolutionary models.
- 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/244/21
- Title:
- Surface rotation & activity of Kepler stars. I.
- Short Name:
- J/ApJS/244/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Brightness variations due to dark spots on the stellar surface encode information about stellar surface rotation and magnetic activity. In this work, we analyze the Kepler long-cadence data of 26521 main-sequence stars of spectral types M and K in order to measure their surface rotation and photometric activity level. Rotation-period estimates are obtained by the combination of a wavelet analysis and autocorrelation function of the light curves. Reliable rotation estimates are determined by comparing the results from the different rotation diagnostics and four data sets. We also measure the photometric activity proxy S_ph_ using the amplitude of the flux variations on an appropriate timescale. We report rotation periods and photometric activity proxies for about 60% of the sample, including 4431 targets for which McQuillan+ (2014, J/ApJS/211/24) did not report a rotation period. For the common targets with rotation estimates in this study and in McQuillan+, our rotation periods agree within 99%. In this work, we also identify potential polluters, such as misclassified red giants and classical pulsator candidates. Within the parameter range we study, there is a mild tendency for hotter stars to have shorter rotation periods. The photometric activity proxy spans a wider range of values with increasing effective temperature. The rotation period and photometric activity proxy are also related, with S_ph_ being larger for fast rotators. Similar to McQuillan+, we find a bimodal distribution of rotation periods.
