- ID:
- ivo://CDS.VizieR/J/A+A/606/A94
- Title:
- Chemical abundances of 1059 FGK stars
- Short Name:
- J/A+A/606/A94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To understand the formation and evolution of the different stellar populations within our Galaxy it is essential to combine detailed kinematical and chemical information for large samples of stars. The aim of this work is to explore the chemical abundances of neutron capture elements which are a product of different nucleosynthesis processes taking place in diverse objects in the Galaxy, such as massive stars, asymptotic giant branch (AGB) stars and supernovae (SNe) explosions. We derive chemical abundances of Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd, and Eu for a large sample of more than 1000 FGK dwarf stars with high-resolution (R~115000) and high-quality spectra from the HARPS-GTO program. The abundances are derived by a standard local thermodynamic equilibrium (LTE) analysis using measured equivalent widths (EWs) injected to the code MOOG and a grid of Kurucz ATLAS9 atmospheres. Results. We find that thick disc stars are chemically disjunct for Zn and Eu and also show on average higher Zr but lower Ba and Y than the thin disc stars. We also discovered that the previously identified high-alpha metal-rich population is also enhanced in Cu, Zn, Nd, and Eu with respect to the thin disc but presents lower Ba and Y abundances on average, following the trend of thick disc stars towards higher metallities and further supporting the different chemical composition of this population. By making a qualitative comparison of O (pure alpha), Mg, Eu (pure r-process), and s-process elements we can distinguish between the contribution of the more massive stars (SNe II for alpha and r-process elements) and the lower mass stars (AGBs) whose contribution to the enrichment of the Galaxy is delayed, due to their longer lifetimes. The ratio of heavy-s to light-s elements of thin disc stars presents the expected behaviour (increasing towards lower metallicities) and can be explained by a major contribution of low-mass AGB stars for s-process production at disc metallicities. However, the opposite trend found for thick disc stars suggests that intermediate-mass AGB stars play an important role in the enrichment of the gas from where these stars formed. Previous works in the literature also point to a possible primary production of light-s elements at low metallicities to explain this trend. Finally, we also find an enhancement of light-s elements in the thin disc at super-solar metallicities which could be caused by the contribution of metal-rich AGB stars. This work proves the utility of homogeneous and high-quality data of modest sample sizes. We find some interesting trends that might help to differentiate thin and thick disc population (such as [Zn/Fe] and [Eu/Fe] ratios) and that can also provide useful constraints for Galactic chemical evolution models of the different populations in the Galaxy.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/450/1900
- Title:
- Chemical abundances of 257 giant stars
- Short Name:
- J/MNRAS/450/1900
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We performed a uniform and detailed abundance analysis of 12 refractory elements for a sample of 257 G- and K-type evolved stars from the CORALIE planet search program. This sample, being homogeneously analyzed, can be used as a comparison sample for other planet-related studies, as well as for different type of studies related to stellar and Galaxy astrophysics. The abundances of the chemical elements were determined using an LTE abundance analysis relative to the Sun, with the spectral synthesis code MOOG and a grid of Kurucz ATLAS9 atmospheres. To separate the Galactic stellar populations both a purely kinematical approach and a chemical method were applied.
- ID:
- ivo://CDS.VizieR/J/A+A/547/A36
- Title:
- Chemical abundances of 87 KOIs
- Short Name:
- J/A+A/547/A36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent studies showed that at low metallicities Doppler-detected planet-hosting stars have preferably high alpha-content and belong to the thick disk.We used the reconnaissance spectra of 87 Kepler planet candidates and data available from the HARPS planet search survey to explore this phenomena. Using the traditional spectroscopic abundance analysis methods we derived Ti, Ca, and Cr abundances for the Kepler stars. In the metallicity region -0.65<[Fe/H]<-0.3dex the fraction of Ti-enhanced thick-disk HARPS planet harboring stars is 12.3+/-4.1% and for their thin-disk counterparts this fraction is 2.2+/-1.3%. The binomial statistics gives a probability of 0.008 that this could have occurred by chance. Combining the two samples (HARPS + Kepler) reinforces the significance of this result (P~99.97%). Since most of these stars are harboring small-mass/size planets we can assume that, although terrestrial planets can be found at low-iron regime, they are mostly enhanced by alpha-elements. This implies that early formation of rocky planets could get started in the Galactic thick disk, where the chemical conditions for their formation were more favorable.
- ID:
- ivo://CDS.VizieR/J/A+A/449/127
- Title:
- Chemical abundances of 32 mildly metal-poor stars
- Short Name:
- J/A+A/449/127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present photospheric abundances of the O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Ni, and Ba elements for 32 mildly metal-poor stars with [Fe/H]~-0.7. High resolution and high signal-to-noise ratio spectra were obtained with the Coude Echelle Spectrograph mounted on the 2.16m telescope at the National Astronomical Observatories (Xinglong, China) on 10 nights during 1999. Effective temperatures were estimated from colour indices, and surface gravities from Hipparcos parallaxes. Stellar abundances were determined from a differential LTE analysis. Our element abundance results extend and confirm previous works. The oxygen and other alpha-elements (Mg, Si, Ca, and Ti) abundances of thin and thick disk stars show distinct trends at [Fe/H]<-0.60. The [Al/Fe] behaviour is exactly as an alpha-element, although the separation for [Na/Fe] of thin and thick disk stars is not clear. The elements V, Cr, and Ni follow Fe very closely, and there is no offset between thin and thick disk stars, but the Sc and Mn abundance trends of the thin and thick disk stars are different, and [Ba/Fe] of thin disk and thick disk stars shows different behaviour.
- ID:
- ivo://CDS.VizieR/J/A+A/423/199
- Title:
- Chemical abundances of planetary nebulae
- Short Name:
- J/A+A/423/199
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we report new observations and derive chemical abundances for a sample of 26 planetary nebulae (PN) located in the anti-center direction. Most of these nebulae are far away objects, located at galactocentric distances greater than about 8kpc, so that they are particularly useful for the determination of the radial gradients at large distances from the galactic center.
- ID:
- ivo://CDS.VizieR/J/A+A/497/563
- Title:
- Chemical abundances of 451 stars
- Short Name:
- J/A+A/497/563
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a uniform study of the chemical abundances of 12 elements (Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Na, Mg, and Al) derived from the spectra of 451 stars observed as part of one of the HARPS GTO planet search programs. Sixty eight of these are planet-bearing stars. The main goals of our work are: i) the investigation of possible differences between the abundances of stars with and without planets; ii) the study of the possible differences in the abundances of stars in the thin and the thick disc. We confirm that there is a systematically higher metallicity in planet host stars, when compared to non planet-hosts, common to all studied species. We also found that there is no difference in the galactic chemical evolution trends of the stars with and without planets. Stars that harbour planetary companions simply appear to be in the high metallicity tail of the distribution. We also confirm that Neptunian and super-Earth class planets may be easier to find at lower metallicities. A statistically significative abundance difference between stars of the thin and the thick disc was found for [Fe/H]<0. However, the populations from the thick and the thin disc cannot be clearly separated.
- 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.
- ID:
- ivo://CDS.VizieR/J/ApJ/773/33
- Title:
- Chemical analysis of the metal-poor subgiant BD+44 493
- Short Name:
- J/ApJ/773/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present detailed chemical abundances for the bright carbon-enhanced metal-poor (CEMP) star BD+44{deg}493, previously reported on by Ito et al. (2009ApJ...698L..37I). Our measurements confirm that BD+44{deg}493 is an extremely metal-poor ([Fe/H]=-3.8) subgiant star with excesses of carbon and oxygen. No significant excesses are found for nitrogen and neutron-capture elements (the latter of which place it in the CEMP-no class of stars). Other elements that we measure exhibit abundance patterns that are typical for non-CEMP extremely metal-poor stars. No evidence for variations of radial velocity has been found for this star. These results strongly suggest that the carbon enhancement in BD+44{deg}493 is unlikely to have been produced by a companion asymptotic giant-branch star and transferred to the presently observed star, nor by pollution of its natal molecular cloud by rapidly-rotating, massive, mega metal-poor ([Fe/H]<-6.0) stars. A more likely possibility is that this star formed from gas polluted by the elements produced in a "faint" supernova, which underwent mixing and fallback, and only ejected small amounts of elements of metals beyond the lighter elements. The Li abundance of BD+44{deg}493 (A(Li)=log(Li/H)+12=1.0) is lower than the Spite plateau value, as found in other metal-poor subgiants. The upper limit on Be abundance (A(Be)=log(Be/H)+12<-1.8) is as low as those found for stars with similarly extremely-low metallicity, indicating that the progenitors of carbon- (and oxygen-) enhanced stars are not significant sources of Be, or that Be is depleted in metal-poor subgiants with effective temperatures of ~5400K.
- ID:
- ivo://CDS.VizieR/J/MNRAS/359/865
- Title:
- Chemical composition of delta Sct
- Short Name:
- J/MNRAS/359/865
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present chemical abundances in the photosphere of delta Scuti (delta Sct) - a prototype of the class of pulsating variables - determined from the analysis of a spectrum obtained by using the 2-m telescope at the Peak Terskol Observatory and a high-resolution spectrometer with R=52000, a signal-to-noise ratio 250 and from International Ultraviolet Explorer spectra. The abundance pattern of delta Sct consists of 49 chemical elements. The abundances of 19 elements have not been investigated previously. The abundances of Pr and Nd obtained from the lines of the second and third spectra are equal. The abundances of heavy elements indicate the overabundances with respect to the solar system values up to 1dex. The abundance pattern of delta Sct is similar to the abundance patterns of Am-Fm or delta Del type stars. A splitting of the cores of all clean lines is observed for the spectra of Sct and HD 57749. This can signify evidence of non-radial pulsations in these stars
- 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.
