- ID:
- ivo://CDS.VizieR/J/A+A/639/A7
- Title:
- Li-rich and non-Li-rich K giants RVs
- Short Name:
- J/A+A/639/A7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The origin of the Li-rich K giants is still highly debated. Here, we investigate the incidence of binarity among this family from a nine-year radial-velocity monitoring of a sample of 11 Li-rich K giants using the HERMES spectrograph attached to the 1.2m Mercator Telescope. A sample of 13 non-Li-rich giants (8 of them being surrounded by dust according to IRAS, WISE, and ISO data) was monitored alongside. When compared to the binary frequency in a reference sample of 190K giants (containing 17.4% of definite spectroscopic binaries - SB - and 6.3% of possible spectroscopic binaries - SB?), the binary frequency appears normal among the Li-rich giants (2/11 definite binaries plus 2 possible binaries, or 18.2% SB + 18.2% SB?), after taking account of the small sample size through the hypergeometric probability distribution. Therefore, there appears to be no causal relationship between Li enrichment and binarity. Moreover, there is no correlation between Li enrichment and the presence of circumstellar dust, and the only correlation that could be found between Li enrichment and rapid rotation is that the most Li-enriched K giants appear to be fast-rotating stars. However, among the dusty K giants, the binary frequency is much higher (4/8 definite binaries plus 1 possible binary). The remaining 3 dusty K giants suffer from a radial-velocity jitter, as is expected for the most luminous K giants, which these are.
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- ID:
- ivo://CDS.VizieR/J/A+A/613/A63
- Title:
- Lithium content for 148 Pleiades stars
- Short Name:
- J/A+A/613/A63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The evolution of lithium abundance over a star's lifetime is indicative of transport processes operating in the stellar interior. Aims. We revisit the relationship between lithium content and rotation rate previously reported for cool dwarfs in the Pleiades cluster. Methods. We derive new LiI 670.8nm equivalent width measurements from high-resolution spectra obtained for low-mass Pleiades members. We combine these new measurements with previously published ones, and use the Kepler/K2 rotational periods recently derived for Pleiades cool dwarfs to investigate the lithium-rotation connection in this 125Myr-old cluster. Results. The new data confirm the correlation between lithium equivalent width and stellar spin rate for a sample of 51 early K-type members of the cluster, where fast rotating stars are systematically lithium-rich compared to slowly rotating ones. The correlation is valid for all stars over the (J-Ks) color range 0.50-0.70mag, corresponding to a mass range from about 0.75 to 0.90M_{sun}_, and may extend down to lower masses. Conclusions. We argue that the dispersion in lithium equivalent widths observed for cool dwarfs in the Pleiades cluster reflects an intrinsic scatter in lithium abundances, and suggest that the physical origin of the lithium dispersion pattern is to be found in the pre-main sequence rotational history of solar-type stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/886/19
- Title:
- Ly{alpha} obs. of low-mass stars Ross 825 & 1044
- Short Name:
- J/ApJ/886/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The discovery of habitable zone (HZ) planets around low-mass stars has highlighted the need for a comprehensive understanding of the radiation environments in which such planets reside. Of particular importance is knowledge of the far-ultraviolet (FUV) radiation, as low-mass stars are typically much more active than solar-type stars and the proximity of their HZs can be one-tenth the distance. The vast majority of the flux emitted by low-mass stars at FUV wavelengths occurs in the Ly{alpha} line at 1216 {AA}. However, measuring a low-mass star's Ly{alpha} emission directly is almost always impossible because of the contaminating effects of interstellar hydrogen and geocoronal airglow. We observed Ross825 (K3) and Ross1044 (M0), two stars with exceptional radial velocities, with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. Their radial velocities resulted in significant line shifts, allowing for a more complete view of their Ly{alpha} line profiles. We provide an updated relation between effective temperature and Ly{alpha} flux using Gaia DR2 astrometry as well as updated, model-independent relationships between Ly{alpha} flux and UV flux measurements from the Galaxy Evolution Explorer (GALEX) for low-mass stars. These new relations, in combination with GALEX's considerable spatial coverage, provide substantial predictive power for the Ly{alpha} environments for thousands of nearby, low-mass stars.
- ID:
- ivo://CDS.VizieR/J/A+A/598/A43
- Title:
- 2MASS J16042165-2130284 high-contrast images
- Short Name:
- J/A+A/598/A43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The large cavities observed in the dust and gas distributions of transition disks may be explained by planet-disk interactions. At 145pc, 2MASS J16042165-2130284 (J1604) is a 5-12Myr old transitional disk with different gap sizes in the mm- and micron-sized dust distributions (outer edges at 79 and at 63AU, respectively). Its ^12^CO emission shows a 30 au cavity. This radial structure suggests that giant planets are sculpting this disk. We aim to constrain the masses and locations of plausible giant planets around J1604. We observed J1604 with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) at the Very Large Telescope (VLT), in IRDIFS_EXT, pupil-stabilized mode, obtaining YJH- band images with the integral field spectrograph (IFS) and K1K2-band images with the Infra-Red Dual-beam Imager and Spectrograph (IRDIS). The dataset was processed exploiting the angular differential imaging (ADI) technique with high-contrast algorithms. Our observations reach a contrast of {Delta}K, {Delta}YH~12mag from 0.15" to 0.80" (~22 to 115AU), but no planet candidate is detected. The disk is directly imaged in scattered light at all bands from Y to K, and it shows a red color. This indicates that the dust particles in the disk surface are mainly >~0.3um-sized grains. We confirm the sharp dip/decrement in scattered light in agreement with polarized light observations. Comparing our images with a radiative transfer model we argue that the southern side of the disk is most likely the nearest. This work represents the deepest search yet for companions around J1604. We reach a mass sensitivity of >~2-3M_Jup_ from ~22 to ~115AU according to a hot start scenario. We propose that a brown dwarf orbiting inside of ~15AU and additional Jovian planets at larger radii could account for the observed properties of J1604 while explaining our lack of detection.
- ID:
- ivo://CDS.VizieR/J/A+A/564/A90
- Title:
- M subdwarfs VLT/UVES high resolution spectra
- Short Name:
- J/A+A/564/A90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- M subdwarfs are metal poor and cool stars. They are important probes of the old galactic populations. However, they remain elusive due to their low luminosity. Observational and modeling efforts are required to fully understand their physics and to investigate the effects of metallicity in their cool atmospheres. We perform a detailed study of a sample of subdwarfs to determine their stellar parameters and constrain the stat-of-the art atmospheric models. We present UVES/VLT high resolution spectra of three late-K subdwarfs and 18 M subdwarfs. Our atlas covers the optical region from 6400{AA} up to the near infrared at 8900{AA}. We show spectral details of cool atmospheres at very high resolution (R~40000) and compare with synthetic spectra computed from the recent BT-Settl atmosphere models. Our comparison shows that molecular features (TiO, VO, CaH), and atomic features (FeI, TiI, NaI, KI) are well fitted by current models. We produce an effective temperature versus spectral type relation all over the subdwarf spectral sequence. Thanks to the high resolution of our spectra, we perform a detailed comparison of line profiles of individual elements such as FeI, CaII, TiI, and are able to determine accurate metallicities of these stars. These determinations contribute to calibrate the relation between metallicity and molecular band strength indices from low-resolution spectra. This work shows that the new generation of models are able to reproduce various spectral features of M subdwarfs. Working with these high resolution spectra allowed us to disentangle the atmospheric parameters (effective temperature, gravity, metallicity), which is not possible when using low resolution spectroscopy or photometry.
- ID:
- ivo://CDS.VizieR/J/A+A/619/A81
- Title:
- Multiplicity among solar-type stars. IV.
- Short Name:
- J/A+A/619/A81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A sample of 261 K-type stars was observed with the spectrovelocimeter CORAVEL. The stars with a variable radial velocity were detected and the orbital elements of the spectroscopic binaries were derived.
- ID:
- ivo://CDS.VizieR/III/25A
- Title:
- Na, Mg, Ca abundances in K-type giants
- Short Name:
- III/25A
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Narrow-band photometric measures of the strengths of the Mg b, Ca triplet, and Na D lines on 312 G and K type giant stars have been analysed with a model atmosphere technique to determine abundances of Mg, Ca and Na.
- ID:
- ivo://CDS.VizieR/J/AJ/159/173
- Title:
- Photometry & RVs of 4 dwarfs hosting giant planets
- Short Name:
- J/AJ/159/173
- Date:
- 09 Dec 2021
- Publisher:
- CDS
- Description:
- We report the discovery of four transiting giant planets around K-dwarfs. The planets HATS-47b, HATS-48Ab, HATS-49b, and HATS-72b have masses of 0.369_-0.021_^+0.031^M_J_, 0.243_-0.030_^+0.022^M_J_, 0.353_-0.027_^+0.038^M_J_, and 0.1254{+/-}0.0039M_J_, respectively, and radii of 1.117{+/-}0.014R_J_, 0.800{+/-}0.015R_J_, 0.765{+/-}0.013R_J_, and 0.7224{+/-}0.0032R_J_, respectively. The planets orbit close to their host stars with orbital periods of 3.9228days, 3.1317days, 4.1480days, and 7.3279days, respectively. The hosts are main-sequence K-dwarfs with masses of 0.674_-0.012_^+0.016^M_{odot}_, 0.7279{+/-}0.0066M_{odot}_, 0.7133{+/-}0.0075M_{odot}_, and 0.7311{+/-}0.0028, and with V-band magnitudes of V=14.829{+/-}0.010, 14.35{+/-}0.11, 14.998{+/-}0.040 and 12.469{+/-}0.010. The super-Neptune HATS-72b (a.k.a. WASP-191b and TOI294.01) was independently identified as a transiting planet candidate by the HATSouth, WASP, and TESS surveys, and we present a combined analysis of all of the data gathered by each of these projects (and their follow-up programs). An exceptionally precise mass is measured for HATS-72b thanks to high-precision radial velocity (RV) measurements obtained with VLT/ESPRESSO, FEROS, HARPS, and Magellan/PFS. We also incorporate TESS observations of the warm Saturn-hosting systems HATS-47 (a.k.a. TOI1073.01), HATS-48A, and HATS-49. HATS-47 was independently identified as a candidate by the TESS team, while the other two systems were not previously identified from the TESS data. The RV orbital variations are measured for these systems using Magellan/PFS. HATS-48A has a resolved 5.4" neighbor in Gaia DR2, which is a common-proper-motion binary star companion to HATS-48A with a mass of 0.22M_{odot}_ and a current projected physical separation of ~1400au.
- ID:
- ivo://CDS.VizieR/J/A+A/430/165
- Title:
- Radial velocities for 6691 K and M giants
- Short Name:
- J/A+A/430/165
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The table provides Hipparcos positions, Hipparcos & Tycho-2 proper motions, and CORAVEL radial velocities for 6691 K and M giants in the solar neighbourhood, mostly from the Hipparcos survey. A bayesian maximum-likelihood approach has been used to derive the distances and space velocities. New V-I indices, computed from a color transformation based on Hp-V_T2_, are also provided. Spectroscopic binaries have been identified as well. These data may be used to study the kinematics of giant stars in the solar neighbourhood, and to correlate it with their location in the Hertzsprung-Russell diagram.
- ID:
- ivo://CDS.VizieR/J/A+A/596/A116
- Title:
- Radial velocities of K-M dwarfs
- Short Name:
- J/A+A/596/A116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of this paper is to present complete radial-velocity data for the spectroscopically selected McCormick (MCC) sample of nearby K-M dwarfs and, based on these data, to determine the space-velocity distributions of late-type stars in the solar neighborhood.
