- ID:
- ivo://CDS.VizieR/J/ApJ/847/127
- Title:
- Abundance analyses of V652 Her and HD 144941
- Short Name:
- J/ApJ/847/127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Optical high-resolution spectra of V652 Her and HD 144941, the two extreme helium stars with exceptionally low C/He ratios, have been subjected to a non-LTE abundance analysis using the tools TLUSTY and SYNSPEC. Defining atmospheric parameters were obtained from a grid of non-LTE atmospheres and a variety of spectroscopic indicators including HeI and HeII line profiles, and the ionization equilibrium of ion pairs such as CII/CIII and NII/NIII. The various indicators provide a consistent set of atmospheric parameters: Teff=25000+/-300K, logg=3.10+/-0.12(cgs), and {xi}=13+/-2km/s are provided for V652 Her, and Teff=22000+/-600K, logg=3.45+/-0.15(cgs), and {xi}=10km/s are provided for HD 144941. In contrast to the non-LTE analyses, the LTE analyses-LTE atmospheres and an LTE line analysis-with the available indicators do not provide a consistent set of atmospheric parameters. The principal non-LTE effect on the elemental abundances is on the neon abundance. It is generally considered that these extreme helium stars with their very low C/He ratio result from the merger of two helium white dwarfs. Indeed, the derived composition of V652 Her is in excellent agreement with predictions by Zhang & Jeffery (2012MNRAS.419..452Z), who model the slow merger of helium white dwarfs; a slow merger results in the merged star having the composition of the accreted white dwarf. In the case of HD 144941, which appears to have evolved from metal-poor stars, a slow merger is incompatible with the observed composition but variations of the merger rate may account for the observed composition. More detailed theoretical studies of the merger of a pair of helium white dwarfs are to be encouraged.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/606/A112
- Title:
- Abundance analysis of ALW Carina 8
- Short Name:
- J/A+A/606/A112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Carbon-enhanced metal-poor (CEMP) stars bear important imprints of the early chemical enrichment of any stellar system. While these stars are known to exist in copious amounts in the Milky Way halo, detailed chemical abundance data from the faint dwarf spheroidal (dSph) satellites are still sparse, although the relative fraction of these stars increases with decreasing metallicity. Here, we report the abundance analysis of a metal-poor ([Fe/H]=-2.5dex), carbon-rich ([C/Fe]=1.4dex) star, ALW-8, in the Carina dSph using high-resolution spectroscopy obtained with the ESO/UVES instrument. Its spectrum does not indicate any over-enhancements of neutron capture elements. Thus classified as a CEMP-no star, this is the first detection of this kind of star in Carina. Another of our sample stars, ALW-1, is shown to be a CEMP-s star, but its immediate binarity prompted us to discard it from a detailed analysis. The majority of the 18 chemical elements we measured are typical of Carina's field star population and also agree with CEMP stars in other dSph galaxies. Similar to the only known CEMP-no star in the Sculptor dSph and the weak-r-process star HD 122563, the lack of any strong barium-enhancement is accompanied by a moderate overabundance in yttrium, indicating a weak r-process activity. The overall abundance pattern confirms that, also in Carina, the formation site for CEMP-no stars has been affected by both faint supernovae and by standard core collapse supernovae. Whichever process was responsible for the heavy element production in ALW-8 must be a ubiquitous source to pollute the CEMP-no stars, acting independently of the environment such as in the Galactic halo or in dSphs.
- ID:
- ivo://CDS.VizieR/J/A+A/584/A86
- Title:
- Abundance analysis of HD 140283
- Short Name:
- J/A+A/584/A86
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- HD 140283 is a reference subgiant that is metal poor and confirmed to be a very old star. The abundances of this type of old star can constrain the nature and nucleosynthesis processes that occurred in its (even older) progenitors. The present study may shed light on nucleosynthesis processes yielding heavy elements early in the Galaxy. A detailed abundance analysis of a high-quality spectrum is carried out, with the intent of providing a reference on stellar lines and abundances of a very old, metal-poor subgiant.
- 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.
- 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/A+A/619/A178
- Title:
- Abundance analysis of 4 red giants in NGC 6558
- Short Name:
- J/A+A/619/A178
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 6558 is a bulge globular cluster with a blue horizontal branch (BHB), combined with a metallicity of [Fe/H]~-1.0. It is similar to HP 1 and NGC 6522, which could be among the oldest objects in the Galaxy. Element abundances in these clusters could reveal the nature of the first supernovae. We aim to carry out detailed spectroscopic analysis for four red giants of NGC 6558, in order to derive the abundances of the light elements C, N, O, Na, Al, the {alpha}-elements Mg, Si, Ca, Ti, and the heavy elements Y, Ba, and Eu. High-resolution spectra of four stars with FLAMES-UVES@VLT UT2-Kueyen were analysed. Spectroscopic parameter-derivation was based on excitation and ionization equilibrium of FeI and FeII. This analysis results in a metallicity of [Fe/H]=-1.17+/-0.10 for NGC 6558. We find the expected {alpha}-element enhancements in O and Mg with [O/Fe]=+0.40, [Mg/Fe]=+0.33, and low enhancements in Si and Ca. Ti has a moderate enhancement of [Ti/Fe]=+0.22. The r-element Eu appears very enhanced with a mean value of [Eu/Fe]=+0.63. The first peak s-elements Y and Sr are also enhanced, these results have however to be treated with caution, given the uncertainties in the continuum definition; the use of neutral species (Sr I, YI), instead of the dominant ionized species is another source of uncertainty. Ba appears to have a solar abundance ratio relative to Fe. NGC 6558 shows an abundance pattern that could be typical of the oldest inner bulge globular clusters, together with the pattern in the similar clusters NGC 6522 and HP 1. They show low abundances of the odd-Z elements Na and Al, and of the explosive nucleosynthesis {alpha}-elements Si, Ca, and Ti. The hydrostatic burning {alpha}-elements O and Mg are normally enhanced as expected in old stars enriched with yields from core-collapse supernovae, and the iron-peak elements Mn, Cu, Zn show low abundances, which is expected forMn and Cu, but not for Zn. Finally, the cluster trio NGC 6558, NGC 6522 and HP 1 have relatively high abundances of first-peak heavy elements, variable second-peak element Ba, and the r-element Eu is enhanced. The latter is particularly high in NGC 6558.
- ID:
- ivo://CDS.VizieR/J/A+A/589/A17
- Title:
- Abundance analysis of solar twin HIP 100963
- Short Name:
- J/A+A/589/A17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze and investigate the origin of the abundance pattern of HIP 100963 in detail, in particular the pattern of the light element Li, the volatile and refractory elements, and heavy elements from the s- and r-processes. We confirm that HIP 100963 is a solar twin and demonstrate that its abundance pattern is about solar after corrections for GCE. The star also shows enrichment in s- and r-process elements, as well as depletion in lithium that is caused by stellar evolution.
- ID:
- ivo://CDS.VizieR/J/A+AS/111/17
- Title:
- Abundance analysis of stars in NGC 6522
- Short Name:
- J/A+AS/111/17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The CASPEC echelle spectrograph at the ESO 3.6 m telescope was used to obtain high resolution spectra of Arp 1145 and Arp 2240, two stars of the Baade Window, near the globular cluster NGC 6522. From a detailed analysis using equivalent widths and spectrum synthesis we derive the stellar parameters (T_eff_, log g and [M/H])=(4750,1.2,-0.9) and (5000,2.15,+0.2), respectively for Arp 1145 and Arp 2240.
- 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.
