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111. Abundances from Gaia-ESO Survey
ID:
ivo://CDS.VizieR/J/A+A/572/A33
Title:
Abundances from Gaia-ESO Survey
Short Name:
J/A+A/572/A33
Date:
21 Oct 2021
Publisher:
CDS
Description:
Most high-resolution spectroscopic studies of the Galactic discs were mostly confined to objects in the solar vicinity. Here we aim at enlarging the volume in which individual chemical abundances are used to characterise both discs, using the first internal data release of the Gaia-ESO survey. We derive and discuss the abundances of eight elements (Mg, Al, Si, Ca, Ti, Fe, Cr, Ni, and Y). The trends of these elemental abundances with iron are very similar to those in the solar neighbourhood. We find a natural division between {alpha}-rich and {alpha}-poor stars, best seen in the bimodality of the [Mg/M] distributions in bins of metallicity, which we attribute to thick- and thin-disc sequences, respectively. With the possible exception of Al, the observed dispersion around the trends is well described by the expected errors, leaving little room for astrophysical dispersion. Using previously derived distances from Recio-Blanco et al. (2014A&A...567A...5R), we further find that the thick-disc is more extended vertically and is more centrally concentrated towards the inner Galaxy than the thin-disc, which indicates a shorter scale-length. We derive the radial and vertical gradients in metallicity, iron, four {alpha}-element abundances, and Al for the two populations, taking into account the identified correlation between R_GC_ and |Z|. Radial metallicity gradient is found in the thin disc. The positive radial individual [{alpha}/M] gradients found are at variance from the gradients observed in the RAVE survey. The thin disc also hosts a negative vertical metallicity gradient, accompanied by positive individual [{alpha}/M] and [Al/M] gradients. The thick-disc, presents no radial metallicity gradient, a shallower vertical metallicity gradient than the thin-disc, an {alpha}-elements-to-iron radial gradient in the opposite sense than that of the thin disc, and positive vertical individual [{alpha}/M] and [Al/M] gradients.
112. Abundances from SEGUE Stellar Parameters Pipeline
ID:
ivo://CDS.VizieR/J/ApJ/798/122
Title:
Abundances from SEGUE Stellar Parameters Pipeline
Short Name:
J/ApJ/798/122
Date:
21 Oct 2021
Publisher:
CDS
Description:
A fundamental challenge for wide-field imaging surveys is obtaining follow-up spectroscopic observations: there are >10^9^ photometrically cataloged sources, yet modern spectroscopic surveys are limited to ~fewx10^6^ targets. As we approach the Large Synoptic Survey Telescope era, new algorithmic solutions are required to cope with the data deluge. Here we report the development of a machine-learning framework capable of inferring fundamental stellar parameters (T_eff_, logg, and [Fe/H]) using photometric-brightness variations and color alone. A training set is constructed from a systematic spectroscopic survey of variables with Hectospec/Multi-Mirror Telescope. In sum, the training set includes ~9000 spectra, for which stellar parameters are measured using the SEGUE Stellar Parameters Pipeline (SSPP). We employed the random forest algorithm to perform a non-parametric regression that predicts T_eff_, logg, and [Fe/H] from photometric time-domain observations. Our final optimized model produces a cross-validated rms error (RMSE) of 165K, 0.39dex, and 0.33dex for T_eff_, logg, and [Fe/H], respectively. Examining the subset of sources for which the SSPP measurements are most reliable, the RMSE reduces to 125K, 0.37dex, and 0.27dex, respectively, comparable to what is achievable via low-resolution spectroscopy. For variable stars this represents a {approx}12%-20% improvement in RMSE relative to models trained with single-epoch photometric colors. As an application of our method, we estimate stellar parameters for ~54000 known variables. We argue that this method may convert photometric time-domain surveys into pseudo-spectrographic engines, enabling the construction of extremely detailed maps of the Milky Way, its structure, and history.
113. Abundance signature of M dwarf stars
ID:
ivo://CDS.VizieR/J/A+A/644/A68
Title:
Abundance signature of M dwarf stars
Short Name:
J/A+A/644/A68
Date:
21 Oct 2021
Publisher:
CDS
Description:
Most of our current knowledge on planet formation is still based on the analysis of main-sequence, solar-type stars. Conversely, detailed chemical studies of large samples of M-dwarf planet hosts are still missing. We aim to test whether the correlations between the metallicity, individual chemical abundances, and mass of the star and the presence of different type of planets found for FGK stars still holds for the less massive M dwarf stars. Methods to determine in a consistent way stellar abundances of M dwarfs from high-resolution optical spectra are still missing. The present work is a first attempt to fill this gap. We analyse in a coherent and homogeneous way a large sample of M dwarfs with and without known planetary companions. We develop for the first time a methodology to determine stellar abundances of elements others than iron for M dwarf stars from high-resolution, optical spectra. Our methodology is based on the use of principal component analysis and sparse Bayesian's methods. We made use of a set of M dwarfs orbiting around an FGK primary with known abundances to train our methods. We applied our methods to derive stellar metallicities and abundances of a large sample of M dwarfs observed within the framework of current radial velocity surveys. We then used a sample of nearby FGK stars to cross-validate our technique by comparing the derived abundance trends in the M dwarf sample with those found on the FGK stars. The metallicity distribution of the different subsamples shows that M dwarfs hosting giant planets show a planet-metallicity correlation as well as a correlation with the stellar mass. M dwarfs hosting low-mass planets do not seem to follow the planet-metallicity correlation. We also found that the frequency of low-mass planets does not depend on the mass of the stellar host. These results seem in agreement with previous works. However, we note that for giant planet hosts our metallicities predict a weaker planet metallicity correlation but a stronger mass-dependency than photometric values. We show, for the first time, that there seems to be no differences in the abundance distribution of elements different from iron between M dwarfs with and without known planets. Our data shows that low-mass stars with planets follow the same metallicity, mass, and abundance trends than their FGK counterparts, which are usually explained within the framework of core-accretion models.
114. Abundances in atmospheres of cool giants
ID:
ivo://CDS.VizieR/J/AZh/84/429
Title:
Abundances in atmospheres of cool giants
Short Name:
J/AZh/84/429
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have determined the atmospheric abundances of Y, Ba, La, Ce, Pr, Nd, and Eu for a sample of 171 giants selected as clump giants with metallicities [Fe/H] between 0.7 and 0.3dex, based on photometric criteria. In our analysis, we assumed local thermodynamic equilibrium and fit the parameters of model atmospheres to high-resolution (R=42000) echelle spectra with high signal-to-noise ratios. The Ba and Eu abundances were derived using synthetic spectra, including hyperfine structure. We find no significant difference in the abundances of s-or r-process neutron-capture elements between clump giants and ascending-branch giants selected by us earlier. We also analyze the relation between the abundances of neutron-capture elements and [Fe/H].
115. Abundances in atmospheres of stars with planets
ID:
ivo://CDS.VizieR/J/A+A/449/723
Title:
Abundances in atmospheres of stars with planets
Short Name:
J/A+A/449/723
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a uniform and homogeneous study of the abundances of Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Na, Mg and Al in 100 stars with and 94 without known planetary companions. The main purpose of this work is to make a deep investigation of the abundance of refractory elements, using an enlarged set of data which includes new observations, especially for the sample of stars without known planets. The new comparison sample spans metallicity range -0.70<[Fe/H]<0.50 and fills the gap that previously existed, mainly at high metallicities, in the number of field "single" comparison stars. Furthermore, we improved the line list previously studied by other authors: on average we analysed 90 spectral lines in every spectrum and carefully measured more than 16 600 equivalent widths (EW) to calculate the abundances. We investigate possible differences between the chemical abundances of the two groups of stars, with and without planets. The results are globally comparable to those obtained by other authors, and in most cases the abundance trends of planet-host stars are very similar to those of the comparison sample. This work represents a step towards the comprehension of recently discovered planetary systems. These results could also be useful for verifying galactic models at high metallicities and consequently improve our knowledge of stellar nucleosynthesis and galactic chemical evolution.
116. Abundances in Ba stars
ID:
ivo://CDS.VizieR/J/A+A/525/A63
Title:
Abundances in Ba stars
Short Name:
J/A+A/525/A63
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present abundances of Mn, Cu, Zn, and various light and heavy elements for a sample of barium and normal giant stars, and present correlations between abundances contributed to different degrees by the weak-s, main-s, and r-processes of neutron capture, between Fe-peak elements and heavy elements. All spectra for the sample stars were obtained with the 1.52m telescope at ESO, La Silla, using the Fiber Fed Extended Range Optical Spectrograph (FEROS). FEROS spectra have a constant resolving power of R=48000 from 3600{AA} to 9200{AA}. The stellar sample targeted in our study includes eight mild and classical barium stars and six normal giants, with a spectral S/N ratio ranging from 200 to 450 in the visible range.
117. Abundances in dwarfs, subgiants, and giants
ID:
ivo://CDS.VizieR/J/A+A/580/A24
Title:
Abundances in dwarfs, subgiants, and giants
Short Name:
J/A+A/580/A24
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have analyzed high-resolution and high signal-to-noise ratio optical spectra of nearby FGK stars with and without detected giant planets in order to homogeneously measure their photospheric parameters, mass, age, and the abundances of volatile (C, N, and O) and refractory (Na, Mg, Si, Ca, Ti, V, Mn, Fe, Ni, Cu, and Ba) elements. Our sample contains 309 stars from the solar neighborhood (up to the distance of 100pc), out of which 140 are dwarfs, 29 are subgiants, and 140 are giants. The photospheric parameters are derived from the equivalent widths (EWs) of FeI and FeII lines. Masses and ages come from the interpolation in evolutionary tracks and isochrones on the HR diagram. The abundance determination is based on the equivalent widths of selected atomic lines of the refractory elements and on the spectral synthesis of C_2_, CN, CI, OI, and NaI features. We apply a set of statistical methods to analyze the abundances derived for the three subsamples. Our results show that: i) giant stars systematically exhibit underabundance in [C/Fe] and overabundance in [N/Fe] and [Na/Fe] in comparison with dwarfs, a result that is normally attributed to evolution-induced mixing processes in the envelope of evolved stars; ii) for solar analogs only, the abundance trends with the condensation temperature of the elements are correlated with age and anticorrelated with the surface gravity, which is in agreement with recent studies; iii) as in the case of [Fe/H], dwarf stars with giant planets are systematically enriched in [X/H] for all the analyzed elements, except for O and Ba (the former due to limitations of statistics), confirming previous findings in the literature that not only iron has an important relation with the planetary formation; and iv) giant planet hosts are also significantly overabundant for the same metallicity when the elements from Mg to Cu are combined together.
118. Abundances in extragalactic HII regions
ID:
ivo://CDS.VizieR/J/ApJ/662/15
Title:
Abundances in extragalactic HII regions
Short Name:
J/ApJ/662/15
Date:
21 Oct 2021
Publisher:
CDS
Description:
We determine the primordial helium mass fraction Yp using 93 spectra of 86 low-metallicity extragalactic HII regions. This sample constitutes the largest and most homogeneous high-quality data set in existence for the determination of Yp. For comparison, and to improve the statistics in our investigation of systematic effects affecting the Yp determination, we have also considered a sample of 271 low-metallicity HII regions selected from Data Release 5 of the Sloan Digital Sky Survey. Although this larger sample shows more scatter, it gives results that are consistent at the 2{sigma} level with our original sample. We have considered known systematic effects that may affect the ^4^He abundance determination.
119. Abundances in Galactic open clusters
ID:
ivo://CDS.VizieR/J/AZh/93/49
Title:
Abundances in Galactic open clusters
Short Name:
J/AZh/93/49
Date:
21 Oct 2021
Publisher:
CDS
Description:
A catalog compiling the parameters of 346 open clusters, including their metallicities, positions, ages, and velocities has been composed. The elements of the Galactic orbits for 272 of the clusters have been calculated. Spectroscopic determinations of the relative abundances, [el/Fe], for 14 elements synthesized in various nuclear processes averaged over data from 109 publications are presented for 90 clusters. The compiled data indicate that the relative abundances of primary {alpha} elements (oxygen and magnesium) exhibit different dependences on metallicity, age, Galactocentric distance, and the elements of the Galactic orbits in clusters with high, elongated orbits satisfying the criterion (Z_max_^2^+4e^2^)^1/2^>0.40 and in field stars of the Galactic thin disk (Zmax is the maximum distance of the orbit from the Galactic plane in kiloparsec and e is the eccentricity of the Galactic orbit). Since no systematic effects distorting the relative abundances of the studied elements in these clusters have been found, these difference suggest real differences between clusters with high, elongated orbits and field stars. In particular, this supports the earlier conclusion, based on an analysis of the elements of the Galactic orbits, that some clusters formed as a result of interactions between high-velocity,metal-poor clouds and the interstellar medium of the Galactic thin disk. On average, clusters with high, elongated orbits and metallicities [Fe/H]<-0.1 display lower relative abundances of the primary {alpha} elements than do field stars. The low [O, Mg/Fe] ratios of these clusters can be understood if the high-velocity clouds that gave rise to them were formed of interstellar material from regions where the star-formation rate and/or the masses of Type II supernovae were lower than near the Galactic plane. It is also shown that, on average, the relative abundances of the primary {alpha} elements are higher in relatively metal-rich clusters with high, elongated orbits than in field stars. This can be understood if clusters with [Fe/H]>-0.1 formed as a result of interactions between metal-rich clouds with intermediate velocities and the interstellar medium of the Galactic disk; such clouds could form from returning gas in a so-called "Galactic fountain".
120. Abundances in globular cluster Pal 3
ID:
ivo://CDS.VizieR/J/A+A/506/729
Title:
Abundances in globular cluster Pal 3
Short Name:
J/A+A/506/729
Date:
21 Oct 2021
Publisher:
CDS
Description:
Chemical abundances of 25 alpha-, iron peak-, and neutron-capture elements in the remote (R=90kpc) outer halo globular cluster have been determined for 4 red giants observed with the Magellan/MIKE spectrograph and from integrated spectra of 19 stars obtained with the Keck/HIRES instrument. The resulting abundance ratios show that Pal 3 is very similar to globular clusters of the inner halo and very dissimilar from dwarf spheroidal galaxy stars. Its neutron capture element ratios are compatible with a pure r-process enrichment.

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