- ID:
- ivo://CDS.VizieR/J/A+A/425/187
- Title:
- Chemical abundances of 23 subgiants & giants
- Short Name:
- J/A+A/425/187
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Chemical abundances, stellar parameters, and atomic and molecular line data are given for a study of 23 subgiant and giant stars in the solar vicinity. With the exception of Li and possibly C we show that subgiant stars show no "chemical" traces of post-main-sequence evolution and that they are therefore and because of their simple age dating very useful targets for studies of galactic chemical evolution.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/695/L134
- Title:
- Chemical anomalies in old LMC clusters
- Short Name:
- J/ApJ/695/L134
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- By using the multifiber spectrograph FLAMES mounted at the ESO-VLT, we have obtained high-resolution spectra for 18 giant stars, belonging to three old globular clusters of the Large Magellanic Cloud (namely NGC 1786, 2210, and 2257). While stars in each cluster showed quite homogeneous iron content, within a few cents of dex (the mean values being [Fe/H]=-1.75+/-0.01dex, -1.65+/-0.02dex and -1.95+/-0.02dex for NGC 1786, 2210, and 2257, respectively), we have detected significant inhomogeneities for the [Na/Fe], [Al/Fe], [O/Fe], and [Mg/Fe] abundance ratios, with evidence of [O/Fe] versus [Na/Fe] and [Mg/Fe] versus [Al/Fe] anticorrelations. The trends detected nicely agree with those observed in Galactic Globular Clusters, suggesting that such abundance anomalies are ubiquitous features of old stellar systems and they do not depend on the parent galaxy environment. In NGC 1786 we also detected two extreme O-poor, Na-rich stars. This is the first time that a firm signature of extreme chemical abundance anomalies has been found in an extragalactic stellar cluster.
- ID:
- ivo://CDS.VizieR/J/AZh/78/807
- Title:
- Chemical composition of eta Ser
- Short Name:
- J/AZh/78/807
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Table2 contains the results of an analysis of elemental abundances in the atmosphere of eta Ser - a red giant of spectral type K2IIIabCN1. The resulting atmosphere parameters correspond to a K0 giant, and the peculiarities of the star chemical composition provide evidence that the assignment of Eta Ser to a class of CN stars was erroneous.
- ID:
- ivo://CDS.VizieR/J/A+A/599/A97
- Title:
- Chemical composition of globular cluster NGC 6426
- Short Name:
- J/A+A/599/A97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present our detailed spectroscopic analysis of the chemical composition of four red giant stars in the halo globular cluster NGC 6426. We obtained high-resolution spectra using the Magellan2/MIKE spectrograph, from which we derived equivalent widths and subsequently computed abundances of 24 species of 22 chemical elements. For the purpose of measuring equivalent widths, we developed a new semi-automated tool, called EWCODE. We report a mean Fe content of [Fe/H]=-2.34+/-0.05dex (stat.) in accordance with previous studies. At a mean {alpha}-abundance of [(Mg,Si,Ca)/3Fe]=0.39+/-0.03dex, NGC 6426 falls on the trend drawn by the Milky Way halo and other globular clusters at comparably low metallicities. The distribution of the lighter {alpha}-elements as well as the enhanced ratio [Zn/Fe]=0.39dex could originate from hypernova enrichment of the pre-cluster medium. We find tentative evidence for a spread in the elements Mg, Si, and Zn, indicating an enrichment scenario, where ejecta of evolved massive stars of a slightly older population polluted a newly born younger one. The heavy element abundances in this cluster fit well into the picture of metal-poor globular clusters, which in that respect appear to be remarkably homogeneous. The pattern of the neutron-capture elements heavier than Zn point towards an enrichment history governed by the r-process with only little - if any - sign of s-process contributions. This finding is supported by the striking similarity of our program stars to the metal-poor field star HD 108317.
- ID:
- ivo://CDS.VizieR/J/AJ/136/375
- Title:
- Chemical composition of LMC red giants
- Short Name:
- J/AJ/136/375
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents the chemical abundance analysis of a sample of 27 red giant stars located in four populous intermediate-age globular clusters in the Large Magellanic Cloud, namely NGC 1651, 1783, 1978, and 2173. This analysis is based on high-resolution (R~47000) spectra obtained with the UVES@VLT spectrograph. For each cluster we derived up to 20 abundance ratios sampling the main chemical elemental groups, namely light odd-Z, {alpha} iron-peak, and neutron-capture elements.
- ID:
- ivo://CDS.VizieR/J/ApJ/717/277
- Title:
- Chemical composition of old LMC clusters
- Short Name:
- J/ApJ/717/277
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents the chemical abundance analysis of a sample of 18 giant stars in three old globular clusters in the Large Magellanic Cloud (LMC), NGC 1786, NGC 2210, and NGC 2257. The derived iron content is [Fe/H]=-1.75+/-0.01dex ({sigma}=0.02dex), -1.65+/-0.02dex ({sigma}=0.04dex), and -1.95+/-0.02dex ({sigma}=0.04dex) for NGC 1786, NGC 2210, and NGC 2257, respectively. All the clusters exhibit similar abundance ratios, with enhanced values (~+0.30dex) of [{alpha}/Fe], consistent with the Galactic halo stars, thus indicating that these clusters have formed from a gas enriched by Type II supernovae. We also found evidence that r-process is the main channel of production of the measured neutron capture elements (Y, Ba, La, Nd, Ce, and Eu). In particular, the quite large enhancement of [Eu/Fe] (~+0.70dex) found in these old clusters clearly indicates a relevant efficiency of the r-process mechanism in the LMC environment.
- ID:
- ivo://CDS.VizieR/J/AJ/161/128
- Title:
- Chemical composition of 15 red giant stars with HPF
- Short Name:
- J/AJ/161/128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used the Habitable Zone Planet Finder (HPF) to gather high-resolution, high signal-to-noise near-infrared spectra of 13 field red horizontal branch (RHB) stars, one open cluster giant, and one very metal-poor halo red giant. The HPF spectra cover the 0.81-1.28{mu}m wavelength range of the zyJ bands, partially filling the gap between the optical (0.4-1.0{mu}m) and infrared (1.5-2.4{mu}m) spectra already available for the program stars. We derive abundances of 17 species from LTE-based computations involving equivalent widths and spectrum syntheses, and estimate abundance corrections for the species that are most affected by departures from LTE in RHB stars. Generally good agreement is found between HPF-based metallicities and abundance ratios and those from the optical and infrared spectral regions. Light element transitions dominate the HPF spectra of these red giants, and HPF data can be used to derive abundances from species with poor or no representation in optical spectra (e.g., C i, P i, S i, K i). Attention is drawn to the HPF abundances in two field solar-metallicity RHB stars of special interest: one with an extreme carbon isotope ratio, and one with a rare, very large lithium content. The latter star is unique in our sample in exhibiting very strong He i 10830{AA} absorption. The abundances of the open cluster giant concur with those derived from other wavelength regions. Detections of CI and SI in HD122563 are reported, yielding the lowest metallicity determination of [S/Fe] from more than one multiplet.
- ID:
- ivo://CDS.VizieR/J/ApJ/706/1095
- Title:
- Chemical compositions of 26 outer halo stars
- Short Name:
- J/ApJ/706/1095
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Chemical abundances of 26 metal-poor dwarfs and giants are determined from high-resolution and high signal-to-noise ratio spectra obtained with the Subaru/High Dispersion Spectrograph. The sample is selected so that most of the objects have outer-halo kinematics. Self-consistent atmospheric parameters were determined by an iterative procedure based on spectroscopic analysis. Abundances of 13 elements, including {alpha}-elements (Mg, Si, Ca, Ti), odd-Z light elements (Na, Sc), iron-peak elements (Cr, Mn, Fe, Ni, Zn), and neutron-capture elements (Y, Ba), are determined by two independent data reduction and local thermodynamic equillibrium analysis procedures, confirming the consistency of the stellar parameters and abundances results.
- ID:
- ivo://CDS.VizieR/J/ApJ/719/931
- Title:
- Chemical evolution of the UMi dSph
- Short Name:
- J/ApJ/719/931
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an abundance analysis based on high-resolution spectra of 10 stars selected to span the full range in metallicity in the Ursa Minor (UMi) dwarf spheroidal (dSph) galaxy. We find that [Fe/H] for the sample stars ranges from -1.35 to -3.10 dex. Combining our sample with previously published work for a total of 16 luminous UMi giants, we establish the trends of abundance ratios [X/Fe] as functions of [Fe/H] for 15 elements. In key cases, particularly for the {alpha}-elements, these trends resemble those for stars in the outer part of the Galactic halo, especially at the lowest metallicities probed. The neutron-capture elements show an r-process distribution over the full range of Fe metallicity reached in this dSph galaxy. This suggests that the duration of star formation in the UMi dSph was shorter than in other dSph galaxies. The derived ages for a larger sample of UMi stars with more uncertain metallicities also suggest a population dominated by uniformly old (~13Gyr) stars, with a hint of an age-metallicity relationship. We note the presence of two UMi giants with [Fe/H]<-3.0 dex in our sample and reaffirm that the inner Galactic halo could have been formed by early accretion of Galactic satellite galaxies and dissolution of young globular clusters, while the outer halo could have formed from those satellite galaxies that accreted somewhat later.
- ID:
- ivo://CDS.VizieR/J/ApJ/761/33
- Title:
- Chemical properties of 89 stars in the LMC disk
- Short Name:
- J/ApJ/761/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used high-resolution spectra obtained with the multifiber facility FLAMES at the Very Large Telescope of the European Southern Observatory to derive kinematic properties and chemical abundances of Fe, O, Mg, and Si for 89 stars in the disk of the Large Magellanic Cloud (LMC). The derived metallicity and [{alpha}/Fe], obtained as the average of O, Mg, and Si abundances, allow us to draw a preliminary scheme of the star formation history of this region of the LMC. The derived metallicity distribution shows two main components: one component (comprising ~84% of the sample) peaks at [Fe/H]=-0.48dex and it shows an [{alpha}/Fe] ratio slightly under solar ([{alpha}/Fe]~-0.1dex). This population probably originated in the main star formation event that occurred 3-4Gyr ago (possibly triggered by tidal capture of the Small Magellanic Cloud). The other component (comprising ~16% of the sample) peaks at [Fe/H]~-0dex and it shows an [{alpha}/Fe]~0.2dex. This population was probably generated during the long quiescent epoch of star formation between the first episode and the most recent bursts. Indeed, in our sample we do not find stars with chemical properties similar to the old LMC globular clusters nor to the iron-rich and {alpha}-poor stars recently found in the LMC globular cluster NGC 1718 and also predicted to be in the LMC field, thus suggesting that both of these components are small (<1%) in the LMC disk population.
