- ID:
- ivo://CDS.VizieR/J/ApJ/865/129
- Title:
- Abundance analysis of HD 222925
- Short Name:
- J/ApJ/865/129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed abundance analysis of the bright (V=9.02), metal-poor ([Fe/H]=-1.47+/-0.08) field red horizontal-branch star HD222925, which was observed as part of an ongoing survey by the R-Process Alliance. We calculate stellar parameters and derive abundances for 46 elements based on 901 lines examined in a high-resolution optical spectrum obtained using the Magellan Inamori Kyocera Echelle spectrograph. We detect 28 elements with 38<=Z<=90; their abundance pattern is a close match to the solar r-process component. The distinguishing characteristic of HD222925 is an extreme enhancement of r-process elements ([Eu/Fe]=+1.33+/-0.08, [Ba/Eu]=-0.78+/-0.10) in a moderately metal-poor star, so the abundance of r-process elements is the highest ([Eu/H]=-0.14+/-0.09) in any known r-process-enhanced star. The abundance ratios among lighter (Z<=30) elements are typical for metal-poor stars, indicating that production of these elements was dominated by normal Type II supernovae, with no discernible contributions from Type Ia supernovae or asymptotic giant branch stars. The chemical and kinematic properties of HD 222925 suggest it formed in a low-mass dwarf galaxy, which was enriched by a high-yield r-process event before being disrupted by interaction with the Milky Way.
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- ID:
- ivo://CDS.VizieR/J/MNRAS/369/1677
- Title:
- Abundance analysis of LSS 3378
- Short Name:
- J/MNRAS/369/1677
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Abundance analysis of the cool extreme helium (EHe) star LSS 3378 is presented. The abundance analysis is done using local thermodynamic equilibrium (LTE) line formation and LTE model atmospheres constructed for EHe stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/838/90
- Title:
- Abundance analysis of 9 very metal-poor stars
- Short Name:
- J/ApJ/838/90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed a differential line-by-line chemical abundance analysis, ultimately relative to the Sun, of nine very metal-poor main-sequence (MS) halo stars, near [Fe/H]=-2dex. Our abundances range from -2.66<=[Fe/H]<=-1.40dex with conservative uncertainties of 0.07dex. We find an average [{alpha}/Fe]=0.34+/-0.09dex, typical of the Milky Way. While our spectroscopic atmosphere parameters provide good agreement with Hubble Space Telescope parallaxes, there is significant disagreement with temperature and gravity parameters indicated by observed colors and theoretical isochrones. Although a systematic underestimate of the stellar temperature by a few hundred degrees could explain this difference, it is not supported by current effective temperature studies and would create large uncertainties in the abundance determinations. Both 1D and <3D> hydrodynamical models combined with separate 1D non-LTE effects do not yet account for the atmospheres of real metal-poor MS stars, but a fully 3D non-LTE treatment may be able to explain the ionization imbalance found in this work.
- ID:
- ivo://CDS.VizieR/J/MNRAS/370/163
- Title:
- Abundance distribution of stars with planets
- Short Name:
- J/MNRAS/370/163
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a uniform, high-precision spectroscopic metallicity study of 136 G-type stars from the Anglo-Australian Planet Search, 20 of which are known to harbour extrasolar planets (as at 2005 July). Abundances in Fe, C, Na, Al, Si, Ca, Ti and Ni are presented, along with Stroemgen photometric metallicities. This study is one of several recent studies examining the metallicities of a sample of planet-host and non-planet-host stars that were obtained from a single sample, and analysed in an identical manner, providing an unbiased estimate of the metallicity trends for planet-bearing stars. We find that non-parametric tests of the distribution of metallicities for planet-host and non-planet-host stars are significantly different at a level of 99.4 per cent confidence. We confirm the previously observed trend for planet-host stars to have higher mean metallicities than non-planet-host stars, with a mean metallicity for planet-host stars of [Fe/H]=0.06+/-0.03dex compared with [Fe/H]=0.09+/-0.01dex for non-host-stars in our sample. This enrichment is also seen in the other elements studied. Based on our findings, we suggest that this observed enhancement is more likely a relic of the original gas cloud from which the star and its planets formed, rather than being due to 'pollution' of the stellar photosphere.
- ID:
- ivo://CDS.VizieR/J/A+A/345/629
- Title:
- Abundance gradients in planetary nebulae
- Short Name:
- J/A+A/345/629
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Radial abundance gradients of the element ratios O/H, Ne/H, S/H, and Ar/H are determined on the basis of a sample of disk planetary nebulae. The behaviour of the gradients at large distances from the galactic centre, R>R_0_=7.6kpc, is emphasized. It is concluded that the derived gradients are consistent with an approximately constant slope in the inner parts of the Galaxy, and some flattening for distances larger than R_0_. A comparison is made with previous determinations using both photoionized nebulae and young stars, and some consequences on theoretical models for the chemical evolution of the galactic disk are discussed.
- ID:
- ivo://CDS.VizieR/J/AJ/127/1545
- Title:
- Abundance ratios of 4 stars in Pal 12
- Short Name:
- J/AJ/127/1545
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed abundance analysis for 21 elements based on high-dispersion, high spectral resolution Keck spectra for four members of the outer halo "young" Galactic globular cluster Palomar 12. All four stars show identical abundance distributions with no credible indication of any star-to-star scatter. However, the abundance ratios of the Pal 12 stars are very peculiar.
- ID:
- ivo://CDS.VizieR/J/ApJ/743/140
- Title:
- Abundances (Be,{alpha}) in metal-poor stars
- Short Name:
- J/ApJ/743/140
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The light elements, Li, Be, and B, provide tracers for many aspects of astronomy including stellar structure, Galactic evolution, and cosmology. We have made observations of Be in 117 metal-poor stars ranging in metallicity from [Fe/H]=-0.5 to -3.5 with Keck I/HIRES. Our spectra are high resolution (~42000) and high signal to noise (the median is 106 per pixel). We have determined the stellar parameters spectroscopically from lines of FeI, FeII, TiI, and TiII. The abundances of Be and O were derived by spectrum synthesis techniques, while abundances of Fe, Ti, and Mg were found from many spectral line measurements. We have kinematic information on 114 stars in our sample and they divide equally into dissipative and accretive stars.
- ID:
- ivo://CDS.VizieR/J/A+A/627/A173
- Title:
- Abundances for 4 metal-poor stars
- Short Name:
- J/A+A/627/A173
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Very metal-poor halo stars are the best candidates for being among the oldest objects in our Galaxy. Samples of halo stars with age determination and detailed chemical composition measurements provide key information for constraining the nature of the first stellar generations and the nucleosynthesis in the metal-poor regime. Age estimates are very uncertain and are available for only a small number of metal-poor stars. Here we present the first results of a pilot program aimed at deriving precise masses, ages and chemical abundances for metal-poor halo giants using asteroseismology, and high-resolution spectroscopy. We obtained high-resolution UVES spectra for four metal-poor RAVE stars observed by the K2 satellite. Seismic data obtained from K2 light curves helped improving spectroscopic temperatures, metallicities and individual chemical abundances. Mass and ages were derived using the code PARAM, investigating the effects of different assumptions (e.g. mass loss, [alpha/Fe]-enhancement). Orbits were computed using Gaia DR2 data. {The stars are found to be "normal" metal-poor halo stars (i.e. non C-enhanced), with an abundance pattern typical of old stars (i.e. alpha and Eu-enhanced), and with masses in the 0.80-1.0M_{sun}_ range. The inferred model-dependent stellar ages are found to range from 7.4 to 13.0Gyr, with uncertainties of ~30%-35%. We also provide revised masses and ages for metal-poor stars with Kepler seismic data from APOGEE survey and a set of M4 stars. The present work shows that the combination of asteroseismology and high-resolution spectroscopy provides precise ages in the metal-poor regime. Most of the stars analysed in the present work (covering the metallicity range of [Fe/H]~-0.8 to -2dex), are very old >9Gyr (14 out of 19 stars), and all of them are older than >5Gyr (within the 68 percentile confidence level).
- 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/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.
