- ID:
- ivo://CDS.VizieR/J/ApJ/860/109
- Title:
- Keck HIRES obs. of 245 subgiants (retired A stars)
- Short Name:
- J/ApJ/860/109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Exoplanet surveys of evolved stars have provided increasing evidence that the formation of giant planets depends not only on stellar metallicity ([Fe/H]) but also on the mass (M*). However, measuring accurate masses for subgiants and giants is far more challenging than it is for their main-sequence counterparts, which has led to recent concerns regarding the veracity of the correlation between stellar mass and planet occurrence. In order to address these concerns, we use HIRES spectra to perform a spectroscopic analysis on a sample of 245 subgiants and derive new atmospheric and physical parameters. We also calculate the space velocities of this sample in a homogeneous manner for the first time. When reddening corrections are considered in the calculations of stellar masses and a -0.12M_{sun}_ offset is applied to the results, the masses of the subgiants are consistent with their space velocity distributions, contrary to claims in the literature. Similarly, our measurements of their rotational velocities provide additional confirmation that the masses of subgiants with M*>=1.6M_{sun}_ (the "retired A stars") have not been overestimated in previous analyses. Using these new results for our sample of evolved stars, together with an updated sample of FGKM dwarfs, we confirm that giant planet occurrence increases with both stellar mass and metallicity up to 2.0M_{sun}_. We show that the probability of formation of a giant planet is approximately a one-to-one function of the total amount of metals in the protoplanetary disk M* 10^[Fe/H]. This correlation provides additional support for the core accretion mechanism of planet formation.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/827/50
- Title:
- Kepler faint red giants
- Short Name:
- J/ApJ/827/50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Asteroseismology has proven to be an excellent tool to determine not only global stellar properties with good precision, but also to infer the stellar structure, dynamics, and evolution for a large sample of Kepler stars. Prior to the launch of the mission, the properties of Kepler targets were inferred from broadband photometry, leading to the Kepler Input Catalog (KIC). The KIC was later revised in the Kepler Star Properties Catalog, based on literature values and an asteroseismic analysis of stars that were unclassified in the KIC. Here, we present an asteroseismic analysis of 45400 stars that were classified as dwarfs in the Kepler Star Properties Catalog. We found that around 2% of the sample shows acoustic modes in the typical frequency range that put them in the red-giant category rather than the cool dwarf category. We analyze the asteroseismic properties of these stars, derive their surface gravities, masses, and radii, and present updated effective temperatures and distances. We show that the sample is significantly fainter than the previously known oscillating giants in the Kepler field, with the faintest stars reaching down to a Kepler magnitude of Kp~16. We demonstrate that 404 stars are at distances beyond 5kpc and that the stars are significantly less massive than for the original Kepler red-giant sample, consistent with a population of distant halo giants. A comparison with a galactic population model shows that up to 40 stars might be genuine halo giants, which would increase the number of known asteroseismic halo stars by a factor of 4. The detections presented here will provide a valuable sample for galactic archeology studies.
- ID:
- ivo://CDS.VizieR/J/A+A/648/A113
- Title:
- Kepler red giants in eclipsing binaries RVs
- Short Name:
- J/A+A/648/A113
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Eclipsing binaries (EBs) are unique targets for measuring accurate stellar properties and constraining stellar evolution models. In particular, it is possible to measure masses and radii at the few percent level for both components of a double-lined spectroscopic EB (SB2-EB). On the one hand, detached EBs hosting at least one star with detectable solar-like oscillations constitute ideal test objects to verify the ability of ensemble asteroseismology to derive stellar properties. On the other hand, the oscillations and surface activity of stars that belong to EBs offer unique information about the evolution of binary systems. This paper builds upon previous works dedicated to red giant stars (RG) in EBs; so far 20 known systems have been discovered by the NASA Kepler mission. We report the discovery of 16 RGs in EBs, which are also from the Kepler data, leading to a total of 36 confirmed RG stars in EBs from the original Kepler mission. This new sample includes three SB2-EBs with oscillations, resulting in a total of 14 known SB2-EBs with an oscillating RG component. This sample also includes six close systems in which the RG display a clear surface activity and complete oscillation suppression. Based on dedicated high-resolution spectroscopic observations (Apache Point Observatory, Observatoire de Haute Provence), we focus on three main aspects. Firstly, from the extended sample of 14 SB2-EBs, we confirm that the simple application of the asteroseismic scaling relations to RGs overestimates masses and radii of RGs by about 15% and 5 %. This bias can be reduced by employing either new asteroseismic reference values for RGs or model-based corrections of the asteroseismic parameters. Secondly, we confirm that close binarity leads to a high level of photometric modulation (up to 10%) and a suppression of solar-like oscillations. In particular, we show that it reduces the lifetime of radial modes by a factor of up to 10. Thirdly, we use our 16 new systems to complement previous observational studies that aimed to constrain tidal dissipation in interacting binaries. We confirm the important role of the equilibrium tide in binary evolution, but we also identify systems with circular orbits despite relatively young ages, which suggests the need to explore complementary tidal dissipation mechanisms in the future. Finally, as a by-product, we report the measurements of mass, radius, and age of three M-dwarf companion stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/835/83
- Title:
- K2 GAP data release. I. Campaign 1
- Short Name:
- J/ApJ/835/83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NASA's K2 mission is observing tens of thousands of stars along the ecliptic, providing data suitable for large-scale asteroseismic analyses to inform galactic archaeology studies. Its first campaign covered a field near the north Galactic cap, a region never covered before by large asteroseismic-ensemble investigations, and was therefore of particular interest for exploring this part of our Galaxy. Here we report the asteroseismic analysis of all stars selected by the K2 Galactic Archaeology Program during the mission's "north Galactic cap" campaign 1. Our consolidated analysis uses six independent methods to measure the global seismic properties, in particular the large frequency separation and the frequency of maximum power. From the full target sample of 8630 stars we find about 1200 oscillating red giants, a number comparable with estimates from galactic synthesis modeling. Thus, as a valuable by-product we find roughly 7500 stars to be dwarfs, which provide a sample well suited for galactic exoplanet occurrence studies because they originate from our simple and easily reproducible selection function.
- ID:
- ivo://CDS.VizieR/J/ApJS/251/23
- Title:
- K2 GAP DR2: campaigns 4, 6 & 7
- Short Name:
- J/ApJS/251/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Studies of Galactic structure and evolution have benefited enormously from Gaia kinematic information, though additional, intrinsic stellar parameters like age are required to best constrain Galactic models. Asteroseismology is the most precise method of providing such information for field star populations en masse, but existing samples for the most part have been limited to a few narrow fields of view by the CoRoT and Kepler missions. In an effort to provide well-characterized stellar parameters across a wide range in Galactic position, we present the second data release of red giant asteroseismic parameters for the K2 Galactic Archaeology Program (GAP). We provide {nu}_max_ and {Delta}{nu} based on six independent pipeline analyses; first-ascent red giant branch (RGB) and red clump (RC) evolutionary state classifications from machine learning; and ready-to-use radius and mass coefficients, {kappa}_R_ and {kappa}_M_, which, when appropriately multiplied by a solar-scaled effective temperature factor, yield physical stellar radii and masses. In total, we report 4395 radius and mass coefficients, with typical uncertainties of 3.3% (stat.) +/-1% (syst.) for {kappa}_R_ and 7.7% (stat.) +/-2% (syst.) for {kappa}_M_ among RGB stars, and 5.0% (stat.) +/-1% (syst.) for {kappa}_R_ and 10.5% (stat.) +/-2% (syst.) for {kappa}_M_ among RC stars. We verify that the sample is nearly complete- except for a dearth of stars with {nu}_max_<~10-20{mu}Hz-by comparing to Galactic models and visual inspection. Our asteroseismic radii agree with radii derived from Gaia Data Release 2 parallaxes to within 2.2%+/-0.3% for RGB stars and 2.0%+/-0.6% for RC stars.
- ID:
- ivo://CDS.VizieR/J/AJ/110/1774
- Title:
- K giants in Baade's window
- Short Name:
- J/AJ/110/1774
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the first in a series of papers in which we analyze medium-resolution spectra of over 400 K and M giants in Baade's Window. Our sample was selected from the proper motion study of Spaenhauer et al. (1992AJ....103..297S). We have measured radial velocities for most of the sample, as well as line-strength indices on the system of Faber et al. (1985ApJS...57..711F). We analyze the random and systematic errors in velocities and line strengths, and show that the bright (V<16.0) stars in our sample are predominantly foreground disk stars along the line of sight toward Baade's Window. We find that most of the bulge K giants have stronger Mg absorption at a given color than do stars in the solar neighborhood. If the K giants in our sample are moderately old, we suggest that on average they may have [Mg/Fe] approximately +0.3, consistent with the results of recent high-resolution spectroscopy in Baade's Window.
- ID:
- ivo://CDS.VizieR/J/AJ/112/171
- Title:
- K Giants in Baade's Window. II
- Short Name:
- J/AJ/112/171
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the second in a series of papers in which we analyze spectra of over 400 K and M giants in Baade's Window, including most of the stars with proper motions measured by Spaenhauer et al. (1992AJ....103..297S). In our first paper, we measured line-strength indices of Fe, Mg, CN, and HBeta and calibrated them on the system of Faber et al. (1985ApJS...57..711F). Here, we use the <Fe> index to derive an abundance distribution of [Fe/H] for 322 stars with effective temperatures between 3900K and 5160K. Our derived values of [Fe/H] agree well with those measured from high-resolution echelle spectra (e.g., McWilliam & Rich, 1994ApJS...91..749M) for the small number of stars in common. We find a mean abundance <[Fe/H]>=-0.11+/-0.04 for our sample of Baade's Window K giants. More than half the sample lie in the range -0.4<[Fe/H]<+0.3. We estimate line-of-sight distances for individual stars in our sample and confirm that, in Baade's Window, most K giants with V<15.5 are foreground disk stars, but the great majority (more than 80%) with V>16 belong to the bulge. We also compare the metallicities derived from the CN and Mg2 indices to those from iron. Most of the metal-rich stars in our sample appear to be CN-weak, in contrast to the situation in metal-rich globular clusters and elliptical galaxies. The metal-poor half of our sample ([Fe/H]<0) shows evidence for a mild Mg overenhancement ([Mg/Fe]~+0.2); but this is not seen in the more metal-rich stars ([Fe/H]>=0). The K giants in Baade's Window therefore share some, but not all, of the characteristics of stars in elliptical galaxies as inferred from their integrated light.
- ID:
- ivo://CDS.VizieR/J/other/RAA/17.76
- Title:
- K giant stars along Sagittarius streams
- Short Name:
- J/other/RAA/17.7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Large Sky-Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Data Release 3 provided 341 691 K giant stars with stellar parameters. Based on the models of Law & Majewski (2010ApJ...714..229L), we identified 252 K giant stars in the leading stream associated with the Sagittarius (Sgr) dwarf galaxy. We obtained 132 K giant stars belonging to the trailing arm of Sgr using the model of Belokurov et al. We studied the metallicity distribution of member stars along the streams and found a flat gradient in the first wrap of the leading stream, -(0.88+/-0.3)x10^-3^dex/deg in the second wrap of the leading stream and -(1.2+/-0.3)x10^-3^dex/deg in the first wrap of the trailing stream. Moreover, we obtained a combined metallicity gradient with our sample and data from the literature. We also analyzed the properties of an overdensity, which is located in the leading stream of the Sgr.
- ID:
- ivo://CDS.VizieR/J/A+A/644/A1
- Title:
- 4 K giants velocity curves
- Short Name:
- J/A+A/644/A1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present radial-velocity (RV) measurements for the K giant stars HD 25723, 17 Sco, 3 Cnc and 44 UMa, taken at the Lick Observatory between 2000 and 2011. The best Keplerian fits to the data yield minimum masses of 2.5MJup and 4.3M_Jup_ for the planets orbiting HD 25723 and 17 Sco, respectively. The minimum masses of an additional candidate around HD 25723, and of planet candidates around 3 Cnc and 44 UMa, would be 1.3M_Jup_, 20.7M_Jup_ and 12.1M_Jup_, respectively.
- ID:
- ivo://CDS.VizieR/J/MNRAS/445/2758
- Title:
- KIC giants Bayesian distances and extinctions
- Short Name:
- J/MNRAS/445/2758
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a first determination of distances and extinctions for individual stars in the first release of the APOKASC catalogue, built from the joint efforts of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and the Kepler Asteroseismic Science Consortium (KASC). Our method takes into account the spectroscopic constraints derived from the APOGEE Stellar Parameters and Chemical Abundances Pipeline, together with the asteroseismic parameters from KASC. These parameters are then employed to estimate intrinsic stellar properties, including absolute magnitudes, using the Bayesian tool param. We then find the distance and extinction that best fit the observed photometry in Sloan Digital Sky Survey (SDSS), 2MASS, and WISE passbands. The first 1989 giants targetted by APOKASC are found at typical distances between 0.5 and 5kpc, with individual uncertainties of just ~1.8%. Our extinction estimates are systematically smaller than provided in the Kepler Input Catalogue and by the Schlegel et al. maps. Distances to individual stars in the NGC 6791 and NGC 6819 star clusters agree to within their credible intervals. Comparison with the APOGEE red clump and SAGA catalogues provide another useful check, exhibiting agreement with our measurements to within a few per cent. Overall, present methods seem to provide excellent distance and extinction determinations for the bulk of the APOKASC sample. Approximately one third of the stars present broad or multiple-peaked probability density functions and hence increased uncertainties. Uncertainties are expected to be reduced in future releases of the catalogue, when a larger fraction of the stars will have seismically determined evolutionary status classifications.
