- ID:
- ivo://CDS.VizieR/J/ApJ/705/328
- Title:
- Abundance measurements in Sculptor dSph
- Short Name:
- J/ApJ/705/328
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present measurements of Fe, Mg, Si, Ca, and Ti abundances for 388 radial velocity member stars in the Sculptor dwarf spheroidal galaxy (dSph), a satellite of the Milky Way (MW). This is the largest sample of individual {alpha} element (Mg, Si, Ca, and Ti) abundance measurements in any single dSph. The measurements are made from Keck/Deep Imaging Multi-Object Spectrometer medium-resolution spectra (6400-9000{AA}, R~6500). Based on comparisons to published high-resolution (R>~20000) spectroscopic measurements, our measurements have uncertainties of {alpha}[Fe/H]=0.14 and {alpha}[{alpha}/Fe]=0.13. We have discovered one star with [Fe/H]=-3.80+/-0.28, which is the most metal-poor star known anywhere except the MW halo, but high-resolution spectroscopy is needed to measure this star's detailed abundances.
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- ID:
- ivo://CDS.VizieR/J/ApJ/900/4
- Title:
- Abundances and ages of stars in the Milky Way bulge
- Short Name:
- J/ApJ/900/4
- Date:
- 14 Mar 2022 07:37:10
- Publisher:
- CDS
- Description:
- The age and chemical characteristics of the Galactic bulge link to the formation and evolutionary history of the Galaxy. Data-driven methods and large surveys enable stellar ages and precision chemical abundances to be determined for vast regions of the Milky Way, including the bulge. Here, we use the data-driven approach of The Cannon, to infer the ages and abundances for 125367 stars in the Milky Way, using spectra from Apache Point Observatory Galaxy Evolution Experiment (apogee) DR14. We examine the ages and metallicities of 1654 bulge stars within R_GAL_<3.5kpc. We focus on fields with b<12{deg}, and out to longitudes of l<15{deg}. We see that stars in the bulge are about twice as old ({tau}=8Gyr), on average, compared to those in the solar neighborhood ({tau}=4Gyr), with a larger dispersion in [Fe/H] (~0.38 compared to 0.23dex). This age gradient comes primarily from the low-{alpha} stars. Looking along the Galactic plane, the very central field in the bulge shows by far the largest dispersion in [Fe/H] ({sigma}[Fe/H]~0.4dex) and line-of- sight velocity ({sigma}vr~90km/s), and simultaneously the smallest dispersion in age. Moving out in longitude, the stars become kinematically colder and less dispersed in [Fe/H], but show a much broader range of ages. We see a signature of the X-shape within the bulge at a latitude of b=8{deg}, but not at b=12{deg}. Future apogee and other survey data, with larger sampling, affords the opportunity to extend our approach and study in more detail, to place stronger constraints on models of the Milky Way.
- ID:
- ivo://CDS.VizieR/J/AJ/150/187
- Title:
- Abundances and stellar parameters of LAMOST stars
- Short Name:
- J/AJ/150/187
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe an application of the SEGUE Stellar Parameter Pipeline (SSPP) to medium-resolution stellar spectra obtained by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), in order to determine estimates of the stellar atmospheric parameters (T_eff_, logg, and [Fe/H]) and the abundance ratios ([{alpha}/Fe] and [C/Fe]). By performing a coordinate match with the LAMOST stellar database, we selected stars with LAMOST spectra in common with stars having available spectroscopy from the Apache Point Observatory Galactic Evolution Experiment (APOGEE), the RAdial Velocity Experiment (RAVE), and the Sloan Extension for Galactic Understanding and Exploration (SEGUE). We ran the selected LAMOST stellar spectra from each survey through SSPP, and compared the stellar parameters down to signal-to-noise ratio (S/N) of 10 and chemical abundances down to S/N=20 derived by SSPP with those determined by the APOGEE, RAVE, and SEGUE software pipelines. Our results show that the derived stellar parameters generally agree quite well, even though there exist some small systematic offsets with small scatter in T_eff_, logg, and [Fe/H], due to the use of different temperature scales, abundance scales, and calibrations adopted by each survey. Comparison of the [{alpha}/Fe] determinations for LAMOST spectra suggests no sign of significant systematic offsets (< -0.04dex), with a small scatter (<0.08dex) relative to stars in common with APOGEE and SEGUE. The [C/Fe] estimates determined for the LAMOST spectra also exhibit good agreement, with a very small offset (~0.01dex) and scatter (~0.12dex) relative to the SEGUE stars, while there exists about a -0.19dex offset, with a small scatter of ~0.13dex, for the APOGEE sample. Due to the existence of small offsets in the stellar parameters and abundances among difference data sets, optimal results when combining the different data sets will be obtained by removing the offsets. Once accomplished, the stellar parameters and chemical abundances estimated by SSPP from the LAMOST stellar spectra should provide a reliable database for studies of the Galactic disk and halo systems.
- ID:
- ivo://CDS.VizieR/J/A+A/458/997
- Title:
- Abundances for 6 transiting planet host stars
- Short Name:
- J/A+A/458/997
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We used the UVES spectrograph (VLT-UT2 telescope) to obtain high-resolution spectra of 6 stars hosting transiting planets, namely for OGLE-TR-10, 56, 111, 113, 132, and TrES-1. These spectra are now used to derive and discuss the chemical abundances for C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, and Zn.
- 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.
- 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.
- ID:
- ivo://CDS.VizieR/J/A+A/579/A104
- Title:
- Abundances in NGC 5053 and NGC 5634
- Short Name:
- J/A+A/579/A104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The tidal disruption of the Sagittarius dwarf Spheroidal galaxy (Sgr dSph) is producing the most prominent substructure in the Milky Way (MW) halo, the Sagittarius Stream. Aside from field stars, the Sgr dSph is suspected to have lost a number of globular clusters (GC). Many Galactic GC are suspected to have originated in the Sgr dSph. While for some candidates an origin in the Sgr dSph has been confirmed due to chemical similarities, others exist whose chemical composition has never been investigated. NGC 5053 and NGC 5634 are two among these scarcely studied Sgr dSph candidate-member clusters. To characterize their composition we analyzed one giant star in NGC 5053, and two in NGC 5634. We analize high-resolution and signal-to-noise spectra by means of the MyGIsFOS code, determining atmospheric parameters and abundances for up to 21 species between O and Eu. The abundances are compared with those of MW halo field stars, of "unassociated" MW halo globulars, and of the metal poor Sgr dSph main body population. We derive a metallicity of [FeII/H]=-2.26+/-0.10 for NGC 5053, and of [FeI/H]=-1.99+/-0.075 and -1.97+/-0.076 for the two stars in NGC 5634. This makes NGC 5053 one of the most metal poor globular clusters in the MW. Both clusters display an alpha enhancement similar to the one of the halo at comparable metallicity. The two stars in NGC 5634 clearly display the Na-O anticorrelation widespread among MW globulars. Most other abundances are in good agreement with standard MW halo trends. The chemistry of the Sgr dSph main body populations is similar to the one of the halo at low metallicity. It is thus difficult to discriminate between an origin of NGC 5053 and NGC 5634 in the Sgr dSph, and one in the MW. However, the abundances of these clusters do appear closer to that of Sgr dSph than of the halo, favoring an origin in the Sgr dSph system.
- ID:
- ivo://CDS.VizieR/J/ApJ/682/1217
- Title:
- Abundances in red giants in 7 globular clusters
- Short Name:
- J/ApJ/682/1217
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a technique that applies spectral synthesis to medium-resolution spectroscopy (MRS; R~6000) in the red (6300{AA}<{lambda}<9100{AA}) to measure [Fe/H] and [{alpha}/Fe] of individual red giant stars over a wide metallicity range. We apply our technique to 264 red giant stars in seven Galactic globular clusters and demonstrate that it reproduces the metallicities and {alpha}-enhancements derived from high-resolution spectroscopy (HRS). The MRS technique excludes the three CaII triplet lines and instead relies on a plethora of weaker lines. Unlike empirical metallicity estimators, such as the equivalent width of the CaII triplet, the synthetic method presented here is applicable over an arbitrarily wide metallicity range and is independent of assumptions about the {alpha}-enhancement.
- ID:
- ivo://CDS.VizieR/J/ApJS/191/352
- Title:
- Abundances in stars of Milky Way dwarf satellites
- Short Name:
- J/ApJS/191/352
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of Fe, Mg, Si, Ca, and Ti abundances for 2961 stars in eight dwarf satellite galaxies of the Milky Way (MW): Sculptor, Fornax, Leo I, Sextans, Leo II, Canes Venatici I, Ursa Minor, and Draco. For the purposes of validating our measurements, we also observed 445 red giants in MW globular clusters and 21 field red giants in the MW halo. The measurements are based on Keck/DEIMOS medium-resolution spectroscopy (MRS) combined with spectral synthesis. We estimate uncertainties in [Fe/H] by quantifying the dispersion of [Fe/H] measurements in a sample of stars in monometallic globular clusters (GCs). We estimate uncertainties in Mg, Si, Ca, and Ti abundances by comparing to high-resolution spectroscopic abundances of the same stars. For this purpose, a sample of 132 stars with published high-resolution spectroscopy in GCs, the MW halo field, and dwarf galaxies has been observed with MRS. The standard deviations of the differences in [Fe/H] and <[{alpha}/Fe]> (the average of [Mg/Fe], [Si/Fe], [Ca/Fe], and [Ti/Fe]) between the two samples is 0.15 and 0.16, respectively.
- ID:
- ivo://CDS.VizieR/J/A+A/554/A84
- Title:
- Abundances of evolved stars
- Short Name:
- J/A+A/554/A84
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Currently, the core accretion model has its strongest observational evidence on the chemical signature of mostly main sequence stars with planets. We aim to test whether the well-established correlation between the metallicity of the star and the presence of giant planets found for main sequence stars still holds for the evolved and generally more massive giant and subgiant stars. Although several attempts have been made so far, the results are not conclusive since they are based on small or inhomogeneous samples. We determine in a homogeneous way the metallicity and individual abundances of a large sample of evolved stars, with and without known planetary companions, and discuss their metallicity distribution and trends. Our methodology is based on the analysis of high-resolution echelle spectra (R~67000) from 2-3 meter class telescopes. It includes the calculation of the fundamental stellar parameters (effective temperature, surface gravity, microturbulent velocity, and metallicity) by applying iron ionisation and excitation equilibrium conditions to several isolated FeI and FeII lines, as well as, calculating individual abundances of different elements such as Na, Mg, Si, Ca, Ti, Cr, Co, or Ni.
