- ID:
- ivo://CDS.VizieR/J/A+A/654/A137
- Title:
- Evolution of Li in FGK dwarf stars
- Short Name:
- J/A+A/654/A137
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We investigate two topics regarding solar mass FGK-type stars, the lithium rotation connection (LRC) and the existence of the "lithium desert". We determine the minimum critical rotation velocity (vsini) related with the LRC separating slow from rapid stellar rotators, as being 5km/s. This value also split different stellar properties. For the first time we explore the behaviour of the LRC for some stellar associations with ages between 45Myr and 120Myr. This allows us to study the LRC age dependence at the beginning of the general spin down stage for low mass stars, which starts at ~30-40Myr. We find that each stellar group presents a characteristic minimum lithium (Li) depletion connected to a specific large rotation velocity and that this minimum changes with age. For instance, this minimum changes from ~50km/s to less than 20km/s in 200Myr. Regarding the lithium desert, it was described as a limited region in the A(Li)-Teff map containing no stars. Using Teff from Gaia DR2 we detect 30 stars inside and/or near the same box defined originally as the Li desert. Due to their intrinsic Teff errors some of these stars may be inside or outside the box, implying a large probability that the box contains several stars. Considering this last fact the "lithium desert" appears to be more a statistical distribution fluctuation than a real problem.
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- ID:
- ivo://CDS.VizieR/J/A+A/557/A70
- Title:
- Evolved planet hosts - stellar parameters
- Short Name:
- J/A+A/557/A70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is still being debated whether the well-known metallicity - giant planet correlation for dwarf stars is also valid for giant stars. For this reason, having precise metallicities is very important. Precise stellar parameters are also crucial to planetary research for several other reasons. Different methods can provide different results that lead to discrepancies in the analysis of planet hosts. To study the impact of different analyses on the metallicity scale for evolved stars, we compare different iron line lists to use in the atmospheric parameter derivation of evolved stars. Therefore, we use a sample of 71 evolved stars with planets. With these new homogeneous parameters, we revisit the metallicity - giant planet connection for evolved stars. A spectroscopic analysis based on Kurucz models in local thermodynamic equilibrium (LTE) was performed through the MOOG code to derive the atmospheric parameters. Two different iron line list sets were used, one built for cool FGK stars in general, and the other for giant FGK stars. Masses were calculated through isochrone fitting, using the Padova models. Kolmogorov-Smirnov tests (K-S tests) were then performed on the metallicity distributions of various different samples of evolved stars and red giants. All parameters compare well using a line list set, designed specifically for cool and solar-like stars to provide more accurate temperatures. All parameters derived with this line list set are preferred and are thus adopted for future analysis. We find that evolved planet hosts are more metal-poor than dwarf stars with giant planets. However, a bias in giant stellar samples that are searched for planets is present. Because of a colour cut-off, metal-rich low-gravity stars are left out of the samples, making it hard to compare dwarf stars with giant stars. Furthermore, no metallicity enhancement is found for red giants with planets (logg<3.0dex) with respect to red giants without planets.
- ID:
- ivo://CDS.VizieR/J/ApJ/895/52
- Title:
- EW and chemical abundances in 211 stars with HARPS
- Short Name:
- J/ApJ/895/52
- Date:
- 15 Mar 2022 07:30:10
- Publisher:
- CDS
- Description:
- Magnetic fields and stellar spots can alter the equivalent widths of absorption lines in stellar spectra, varying during the activity cycle. This also influences the information that we derive through spectroscopic analysis. In this study, we analyze high-resolution spectra of 211 sunlike stars observed at different phases of their activity cycles, in order to investigate how stellar activity affects the spectroscopic determination of stellar parameters and chemical abundances. We observe that the equivalent widths of lines can increase as a function of the activity index log R_HK_' during the stellar cycle, which also produces an artificial growth of the stellar microturbulence and a decrease in effective temperature and metallicity. This effect is visible for stars with activity indexes log R_HK_'>=-5.0 (i.e., younger than 4-5Gyr), and it is more significant at higher activity levels. These results have fundamental implications on several topics in astrophysics that are discussed in the paper, including stellar nucleosynthesis, chemical tagging, the study of Galactic chemical evolution, chemically anomalous stars, the structure of the Milky Way disk, stellar formation rates, photoevaporation of circumstellar disks, and planet hunting.
- ID:
- ivo://CDS.VizieR/J/A+A/635/A114
- Title:
- EW and [Fe/H] for 30000 globular cluster RGB stars
- Short Name:
- J/A+A/635/A114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The CaII triplet in the near-infrared at 8498, 8542, and 8662{AA} is visible in stars with spectral types between F and M and can be used to determine their metallicities. We calibrated the relation using average cluster metallicities from literature and MUSE spectra, and extend it below the horizontal branch - a cutoff that has traditionally been made to avoid a non-linear relation - using a quadratic function. In addition to the classic relation based on V-\vhb$ we used calibrations based on absolute magnitude and luminosity and used it for those cluster, for which no HB brightness was available. The obtained relations are then used to calculate metallicities for all the stars in the sample.
- ID:
- ivo://CDS.VizieR/J/ApJ/786/74
- Title:
- EW measurements of 6 Segue 1 red giants
- Short Name:
- J/ApJ/786/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Magellan/MIKE and Keck/HIRES high-resolution spectra of six red giant stars in the dwarf galaxy Segue 1. Including one additional Segue 1 star observed by Norris et al. (2010ApJ...722L.104N), high-resolution spectra have now been obtained for every red giant in Segue 1. Remarkably, three of these seven stars have metallicities below [Fe/H]=-3.5, suggesting that Segue 1 is the least chemically evolved galaxy known. We confirm previous medium-resolution analyses demonstrating that Segue 1 stars span a metallicity range of more than 2 dex, from [Fe/H]=-1.4 to [Fe/H]=-3.8. All of the Segue 1 stars are {alpha}-enhanced, with [{alpha}/Fe]~0.5. High {alpha}-element abundances are typical for metal-poor stars, but in every previously studied galaxy [{alpha}/Fe] declines for more metal-rich stars, which is typically interpreted as iron enrichment from supernova Ia. The absence of this signature in Segue 1 indicates that it was enriched exclusively by massive stars. Other light element abundance ratios in Segue 1, including carbon enhancement in the three most metal-poor stars, closely resemble those of metal-poor halo stars. Finally, we classify the most metal-rich star as a CH star given its large overabundances of carbon and s-process elements. The other six stars show remarkably low neutron-capture element abundances of [Sr/H]<-4.9 and [Ba/H]<-4.2, which are comparable to the lowest levels ever detected in halo stars. This suggests minimal neutron-capture enrichment, perhaps limited to a single r-process or weak s-process synthesizing event. Altogether, the chemical abundances of Segue 1 indicate no substantial chemical evolution, supporting the idea that it may be a surviving first galaxy that experienced only one burst of star formation.
- ID:
- ivo://CDS.VizieR/J/MNRAS/476/724
- Title:
- EW of 4 primary stars and the Sun
- Short Name:
- J/MNRAS/476/724
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Study of primary stars lying in Sirius-like systems with various masses of white dwarf (WD) companions and orbital separations is one of the key aspects to understand the origin and nature of barium (Ba) stars. In this paper, based on high-resolution and high-S/N spectra, we present systematic analysis of photospheric abundances for 18 FGK primary stars of Sirius-like systems including six giants and 12 dwarfs. Atmospheric parameters, stellar masses, and abundances of 24 elements (C, Na, Mg, Al, Si, S, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Sr, Y, Zr, Ba, La, Ce, and Nd) are determined homogeneously. The abundance patterns in these sample stars show that most of the elements in our sample follow the behaviour of field stars with similar metallicity. As expected, s-process elements in four known Ba giants show overabundance. A weak correlation was found between anomalies of s-process elemental abundance and orbital separation, suggesting that the orbital separation of the binaries could not be the main constraint to differentiate strong Ba stars from mild Ba stars. Our study shows that the large mass (>0.51M_{sun}_) of a WD companion in a binary system is not a sufficient condition to form a Ba star, even if the separation between the two components is small. Although not sufficient, it seems to be a necessary condition since Ba stars with lower mass WDs in the observed sample were not found. Our results support that [s/Fe] and [hs/ls] ratios of Ba stars are anti-correlated with the metallicity. However, the different levels of s-process overabundance among Ba stars may not be dominated mainly by the metallicity.
- ID:
- ivo://CDS.VizieR/J/A+A/633/A38
- Title:
- EW of 10 solar-type stars of Praesepe
- Short Name:
- J/A+A/633/A38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Open clusters exquisitely track the Galactic disc chemical properties and its time evolution; a substantial number of studies and large spectroscopic surveys focus mostly on the chemical content of relatively old clusters (age>1Gyr). Interestingly, the less studied young counterpart populating the solar surrounding has been found to be solar (at most), with a notable surprising lack of young metal-rich objects. While there is wide consensus about the moderately above-solar composition of the Hyades cluster, the metallicity of Praesepe is still controversial. Recent studies suggest that these two clusters share identical chemical composition and age, but this conclusion is disputed. With the aim of reassessing the metallicity of Praesepe, and its difference (if any) with the Hyades cluster, we present in this paper a spectroscopic investigation of ten solar-type dwarf members. We exploited GIARPS at the TNG to acquire high-resolution, high-quality optical and near-IR spectra and derived stellar parameters, metallicity ([Fe/H]), light elements, alpha- and iron-peak elements, by using a strictly differential (line-by-line) approach. We also analysed in the very same way the solar spectrum and the Hyades solar analogue HD 28099. Our findings suggest that Praesepe is more metal-rich than the Hyades, at the level of [Fe/H]=+0.05+/-0.01dex, with a mean value of [Fe/H]=+0.21+/-0.01dex. All the other elements scale with iron, as expected. This result seems to reject the hypothesis of a common origin for these two open clusters. Most importantly, Praesepe is currently the most metal-rich, young open cluster living in the solar neighbourhood
- ID:
- ivo://CDS.VizieR/J/ApJS/225/32
- Title:
- Extended abundance analysis of cool stars
- Short Name:
- J/ApJS/225/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of uniformly determined stellar properties and abundances for 1615 F, G, and K stars using an automated spectral synthesis modeling procedure. All stars were observed using the HIRES spectrograph at Keck Observatory. Our procedure used a single line list to fit model spectra to observations of all stars to determine effective temperature, surface gravity, metallicity, projected rotational velocity, and the abundances of 15 elements (C, N, O, Na, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Ni, and Y). Sixty percent of the sample had Hipparcos parallaxes and V-band photometry, which we combined with the spectroscopic results to obtain mass, radius, and luminosity. Additionally, we used the luminosity, effective temperature, metallicity and {alpha}-element enhancement to interpolate in the Yonsei-Yale isochrones to derive mass, radius, gravity, and age ranges for those stars. Finally, we determined new relations between effective temperature and macroturbulence for dwarfs and subgiants. Our analysis achieved precisions of 25K in T_eff_, 0.01dex in [M/H], 0.028dex for logg, and 0.5km/s in vsini based on multiple observations of the same stars. The abundance results were similarly precise, between ~0.01 and ~0.04dex, though trends with respect to T_eff_ remained for which we derived empirical corrections. The trends, though small, were much larger than our uncertainties and are shared with published abundances. We show that changing our model atmosphere grid accounts for most of the trend in [M/H] between 5000 and 5500K, indicating a possible problem with the atmosphere models or opacities.
- ID:
- ivo://CDS.VizieR/J/ApJS/237/38
- Title:
- Extended abundance analysis of KOIs
- Short Name:
- J/ApJS/237/38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Accurate stellar parameters and precise elemental abundances are vital pieces to correctly characterize discovered planetary systems, better understand planet formation, and trace galactic chemical evolution. We have performed a uniform spectroscopic analysis for 1127 stars, yielding accurate gravity, temperature, and projected rotational velocity in addition to precise abundances for 15 elements (C, N, O, Na, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Ni, and Y). Most of the stars in this sample are Kepler Objects of Interest, observed by the California-Kepler Survey, and include 1003 stars hosting 1562 confirmed planets. This catalog extends the uniform analysis of our previous catalog, bringing the total number of homogeneously analyzed stars to almost 2700 F, G, and K dwarfs. To ensure consistency between the catalogs, we performed an analysis of our ability to recover parameters as a function of signal-to-noise ratio (S/N) and present individual uncertainties as well as functions to calculate uncertainties for parameters derived from lower S/N spectra. With the updated parameters, we used isochrone fitting to derive new radii, masses, and ages for the stars. We use our abundance analysis to support the finding that the radius gap is likely a result of evolution rather than the result of primordial compositional differences between the two populations.
- ID:
- ivo://CDS.VizieR/V/137D
- Title:
- Extended Hipparcos Compilation (XHIP)
- Short Name:
- V/137D
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Extended Hipparcos Compilation (XHIP) cross-references the New Hipparcos Reduction (HIP2, Cat. I/311) with relatable data from a broad survey of presently available sources. The resulting collection uniquely assigns 116,096 spectral classifications, 46,392 radial velocities, and 19,097 iron abundances [Fe/H] to Hipparcos stars. Stellar classifications from SIMBAD and indications of multiplicity from either CCDM (Cat. I/274) or WDS (Cat. B/wds) are provided. Parameters for solar encounters and Galactic orbits are calculated for a subset of stars that can be made kinematically complete. Memberships in open clusters and stellar associations are assigned. We also provide stellar ages from The Geneva-Copenhagen survey of the Solar neighbourhood III (Cat. V/130), identifications of exoplanet host stars, and supplemental photometry from 2MASS (Cat. II/246) and SIMBAD.
