- ID:
- ivo://CDS.VizieR/J/AJ/150/88
- Title:
- Abundances in the local region. I. G and K giants
- Short Name:
- J/AJ/150/88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Parameters and abundances for 1133 stars of spectral types F, G, and K of luminosity class III have been derived. In terms of stellar parameters, the primary point of interest is the disagreement between gravities derived with masses determined from isochrones, and gravities determined from an ionization balance. This is not a new result per se, but the size of this sample emphasizes the severity of the problem. A variety of arguments led to the selection of the ionization-balance gravity as the working value. The derived abundances indicate that the giants in the solar region have Sun-like total abundances and abundance ratios. Stellar evolution indicators have also been investigated with the Li abundances and the [C/Fe] and C/O ratios, indicating that standard processing has been operating in these stars. The more salient result for stellar evolution is that the [C/Fe] data across the red-giant clump indicates the presence of mass-dependent mixing in accord with standard stellar evolution predictions.
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- ID:
- ivo://CDS.VizieR/J/AJ/153/21
- Title:
- Abundances in the local region. II. F, G, and K dwarfs
- Short Name:
- J/AJ/153/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Parameters and abundances have been derived for 1002 stars of spectral types F, G, and K, and luminosity classes IV and V. After culling the sample for rotational velocity and effective temperature, 867 stars remain for discussion. Twenty-eight elements are considered in the analysis. The {alpha}, iron-peak, and Period 5 transition metal abundances for these stars show a modest enhancement over solar averaging about 0.05dex. The lanthanides are more abundant, averaging about +0.2dex over solar. The question is: Are these stars enhanced, or is the Sun somewhat metal-poor relative to these stars? The consistency of the abundances derived here supports an argument for the latter view. Lithium, carbon, and oxygen abundances have been derived. The stars show the usual lithium astration as a function of mass/temperature. There are more than 100 planet-hosts in the sample, and there is no discernible difference in their lithium content, relative to the remaining stars. The carbon and oxygen abundances show the well-known trend of decreasing [x/Fe] ratio with increasing [Fe/H].
- ID:
- ivo://CDS.VizieR/J/AJ/155/111
- Title:
- Abundances in the local region. III. Southern dwarfs
- Short Name:
- J/AJ/155/111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stellar parameters and abundances have been derived from a sample of 907 F, G, and K dwarfs. The high-resolution, high signal-to-noise spectra utilized were acquired with the HARPS spectrograph of the European Southern Observatory. The stars in the sample with -0.2<[Fe/H]<+0.2 have abundances that strongly resemble that of the Sun, except for the lithium content and the lanthanides. Near the solar temperature, stars show two orders of magnitude range in lithium content. The average content of stars in the local region appears to be enhanced at about the +0.1 level relative to the Sun for the lanthanides. There are over 100 planet hosts in this sample, and there is no discernible difference between them and the non-hosts regarding their lithium content.
- ID:
- ivo://CDS.VizieR/J/A+A/377/911
- Title:
- Age-metallicity relation in solar neighbourhood
- Short Name:
- J/A+A/377/911
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive stellar ages, from evolutionary tracks, and metallicities, from Stroemgren photometry, for a sample of 5828 dwarf and sub-dwarf stars from the Hipparcos (Cat. <I/239>) Catalogue. This stellar disk sample is used to investigate the age-metallicity diagram in the solar neighbourhood. Such diagrams are often used to derive a so called age-metallicity relation. Because of the size of our sample, we are able to quantify the impact on such diagrams, and derived relations, due to different selection effects. Some of these effects are of a more subtle sort, giving rise to erroneous conclusions. In particular we show that [1] the age-metallicity diagram is well populated at all ages and especially that old, metal-rich stars do exist, [2] the scatter in metallicity at any given age is larger than the observational errors, [3] the exclusion of cooler dwarf stars from an age-metallicity sample preferentially excludes old, metal-rich stars, depleting the upper right-hand corner of the age-metallicity diagram, [4] the distance dependence found in the Edvardsson et al. (1993, Cat. <J/A+A/275/101>) sample by Garnett & Kobulnicky (2000ApJ...532.1192G) is an expected artifact due to the construction of the original sample. We conclude that, although some of it can be attributed to stellar migration in the galactic disk, a large part of the observed scatter is intrinsic to the formation processes of stars.
- ID:
- ivo://CDS.VizieR/J/AJ/161/100
- Title:
- Ages and alpha-abundances of population in K2
- Short Name:
- J/AJ/161/100
- Date:
- 19 Jan 2022 13:30:38
- Publisher:
- CDS
- Description:
- We explore the relationships between the chemistry, ages, and locations of stars in the Galaxy using asteroseismic data from the K2 mission and spectroscopic data from the Apache Point Galactic Evolution Experiment survey. Previous studies have used giant stars in the Kepler field to map the relationship between the chemical composition and the ages of stars at the solar circle. Consistent with prior work, we find that stars with high [{alpha}/Fe] have distinct, older ages in comparison to stars with low [{alpha}/Fe]. We provide age estimates for red giant branch (RGB) stars in the Kepler field, which support and build upon previous age estimates by taking into account the effect of {alpha}-enrichment on opacity. Including this effect for [{alpha}/Fe]-rich stars results in up to 10% older ages for low- mass stars relative to corrected solar mixture calculations. This is a significant effect that Galactic archeology studies should take into account. Looking beyond the Kepler field, we estimate ages for 735 RGB stars from the K2 mission, mapping age trends as a function of the line of sight. We find that the age distributions for low- and high-[{alpha}/Fe] stars converge with increasing distance from the Galactic plane, in agreement with suggestions from earlier work. We find that K2 stars with high [{alpha}/Fe] appear to be younger than their counterparts in the Kepler field, overlapping more significantly with a similarly aged low-[{alpha}/Fe] population. This observation may suggest that star formation or radial migration proceeds unevenly in the Galaxy.
- ID:
- ivo://CDS.VizieR/J/ApJ/836/77
- Title:
- A library of high-S/N optical spectra of FGKM stars
- Short Name:
- J/ApJ/836/77
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Classification of stars, by comparing their optical spectra to a few dozen spectral standards, has been a workhorse of observational astronomy for more than a century. Here, we extend this technique by compiling a library of optical spectra of 404 touchstone stars observed with Keck/HIRES by the California Planet Search. The spectra have high resolution (R~60000), high signal-to-noise ratio (S/N~150/pixel), and are registered onto a common wavelength scale. The library stars have properties derived from interferometry, asteroseismology, LTE spectral synthesis, and spectrophotometry. To address a lack of well-characterized late-K dwarfs in the literature, we measure stellar radii and temperatures for 23 nearby K dwarfs, using modeling of the spectral energy distribution and Gaia parallaxes. This library represents a uniform data set spanning the spectral types ~M5-F1 (T_eff_~3000-7000K, R_*_~0.1-16R_{Sun}_). We also present "Empirical SpecMatch" (SpecMatch-Emp), a tool for parameterizing unknown spectra by comparing them against our spectral library. For FGKM stars, SpecMatch-Emp achieves accuracies of 100K in effective temperature (T_eff_), 15% in stellar radius (R_*_), and 0.09dex in metallicity ([Fe/H]). Because the code relies on empirical spectra it performs particularly well for stars ~K4 and later, which are challenging to model with existing spectral synthesizers, reaching accuracies of 70K in T_eff_, 10% in R_*_, and 0.12dex in [Fe/H]. We also validate the performance of SpecMatch-Emp, finding it to be robust at lower spectral resolution and S/N, enabling the characterization of faint late-type stars. Both the library and stellar characterization code are publicly available.
- ID:
- ivo://CDS.VizieR/J/AJ/143/39
- Title:
- Analysis of hot Jupiters in Kepler Q2
- Short Name:
- J/AJ/143/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we present the results of searching the Kepler Q2 public data set for the secondary eclipses of 76 hot Jupiter planet candidates from the list of 1235 candidates published by Borucki et al., 2011, Cat. J/ApJ/736/19. This search has been performed by modeling both the Kepler pre-search data conditioned light curves and new light curves produced via our own photometric pipeline. We derive new stellar and planetary parameters for each system, while calculating robust errors for both. We find 16 systems with 1{sigma}-2{sigma}, 14 systems with 2{sigma}-3{sigma}, and 6 systems with >3{sigma} confidence level secondary eclipse detections in at least one light curve produced via the Kepler pre-search data conditioned light curve or our own pipeline; however, results can vary depending on the light curve modeled and whether eccentricity is allowed to vary or not. We estimate false alarm probabilities of 31%, 10%, and 6% for the 1{sigma}-2{sigma}, 2{sigma}-3{sigma}, and >3{sigma} confidence intervals, respectively.
- ID:
- ivo://CDS.VizieR/J/AJ/156/18
- Title:
- APOGEE DR14:Binary companions of evolved stars
- Short Name:
- J/AJ/156/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Multi-epoch radial velocity measurements of stars can be used to identify stellar, substellar, and planetary-mass companions. Even a small number of observation epochs can be informative about companions, though there can be multiple qualitatively different orbital solutions that fit the data. We have custom-built a Monte Carlo sampler (The Joker) that delivers reliable (and often highly multimodal) posterior samplings for companion orbital parameters given sparse radial velocity data. Here we use The Joker to perform a search for companions to 96231 red giant stars observed in the APOGEE survey (DR14) with >=3 spectroscopic epochs. We select stars with probable companions by making a cut on our posterior belief about the amplitude of the variation in stellar radial velocity induced by the orbit. We provide (1) a catalog of 320 companions for which the stellar companion's properties can be confidently determined, (2) a catalog of 4898 stars that likely have companions, but would require more observations to uniquely determine the orbital properties, and (3) posterior samplings for the full orbital parameters for all stars in the parent sample. We show the characteristics of systems with confidently determined companion properties and highlight interesting systems with candidate compact object companions.
- ID:
- ivo://CDS.VizieR/J/ApJS/239/32
- Title:
- APOKASC-2 catalog of Kepler evolved stars
- Short Name:
- J/ApJS/239/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of stellar properties for a large sample of 6676 evolved stars with Apache Point Observatory Galactic Evolution Experiment spectroscopic parameters and Kepler asteroseismic data analyzed using five independent techniques. Our data include evolutionary state, surface gravity, mean density, mass, radius, age, and the spectroscopic and asteroseismic measurements used to derive them. We employ a new empirical approach for combining asteroseismic measurements from different methods, calibrating the inferred stellar parameters, and estimating uncertainties. With high statistical significance, we find that asteroseismic parameters inferred from the different pipelines have systematic offsets that are not removed by accounting for differences in their solar reference values. We include theoretically motivated corrections to the large frequency spacing ({Delta}{nu}) scaling relation, and we calibrate the zero-point of the frequency of the maximum power ({nu}max) relation to be consistent with masses and radii for members of star clusters. For most targets, the parameters returned by different pipelines are in much better agreement than would be expected from the pipeline-predicted random errors, but 22% of them had at least one method not return a result and a much larger measurement dispersion. This supports the usage of multiple analysis techniques for asteroseismic stellar population studies. The measured dispersion in mass estimates for fundamental calibrators is consistent with our error model, which yields median random and systematic mass uncertainties for RGB stars of order 4%. Median random and systematic mass uncertainties are at the 9% and 8% level, respectively, for red clump stars.
- ID:
- ivo://CDS.VizieR/J/ApJS/215/19
- Title:
- APOKASC catalog of Kepler red giants
- Short Name:
- J/ApJS/215/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first APOKASC catalog of spectroscopic and asteroseismic properties of 1916 red giants observed in the Kepler fields. The spectroscopic parameters provided from the Apache Point Observatory Galactic Evolution Experiment project are complemented with asteroseismic surface gravities, masses, radii, and mean densities determined by members of the Kepler Asteroseismology Science Consortium. We assess both random and systematic sources of error and include a discussion of sample selection for giants in the Kepler fields. Total uncertainties in the main catalog properties are of the order of 80K in T_eff_, 0.06dex in [M/H], 0.014dex in logg, and 12% and 5% in mass and radius, respectively; these reflect a combination of systematic and random errors. Asteroseismic surface gravities are substantially more precise and accurate than spectroscopic ones, and we find good agreement between their mean values and the calibrated spectroscopic surface gravities. There are, however, systematic underlying trends with T_eff_ and logg. Our effective temperature scale is between 0 and 200K cooler than that expected from the infrared flux method, depending on the adopted extinction map, which provides evidence for a lower value on average than that inferred for the Kepler Input Catalog (KIC). We find a reasonable correspondence between the photometric KIC and spectroscopic APOKASC metallicity scales, with increased dispersion in KIC metallicities as the absolute metal abundance decreases, and offsets in T_eff_ and logg consistent with those derived in the literature. We present mean fitting relations between APOKASC and KIC observables and discuss future prospects, strengths, and limitations of the catalog data.