- ID:
- ivo://CDS.VizieR/J/A+A/623/A128
- Title:
- Galactic halo CEMP stars abundances & kinematics
- Short Name:
- J/A+A/623/A128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Carbon-enhanced metal-poor (CEMP) stars span a wide range of stellar populations, from bona fide second-generation stars to later-forming stars that provide excellent probes of binary mass transfer and stellar evolution. Here we analyse 11 metal-poor stars (8 of which are new to the literature), and demonstrate that 10 are CEMP stars. Based on high signal-to-noise ratio (S/N) X-Shooter spectra, we derive abundances of 20 elements (C, N, O, Na, Mg, Ca, Sc, Ti, Cr, Mn, Fe, Ni, Sr, Y, Ba, La, Ce, Pr, Nd, and Eu). From the high-S/N spectra, we were able to trace the chemical contribution of the rare earth elements (REE) from various possible production sites, finding a preference for metal-poor low-mass asymptotic giant branch (AGB) stars of 1.5M_{sun}_ in CEMP-s stars, while CEMP-r/s stars may indicate a more massive AGB contribution (2-5M_{sun}_). A contribution from the r-process -- possibly from neutron star--neutron star mergers (NSM) -- is also detectable in the REE stellar abundances, especially in the CEMP-r/s sub-group rich in both slow(s)\ and rapid(r) neutron-capture elements. Combining spectroscopic data with Gaia DR2 astrometric data provides a powerful chemodynamical tool for placing CEMP stars in the various Galactic components, and classifying CEMP stars into the four major elemental-abundance sub-groups, which are dictated by their neutron-capture element content. The derived orbital parameters indicate that all but one star in our sample (and the majority of the selected literature stars) belong to the Galactic halo. These stars exhibit a median orbital eccentricity of 0.7, and are found on both prograde and retrograde orbits. We find that the orbital parameters of CEMP-no and CEMP-s stars are remarkably similar in the 98 stars we study. A special case is the CEMP-no star HE 0020-1741, with very low Sr and Ba content, which possesses the most eccentric orbit among the stars in our sample, passing close to the Galactic centre. Finally, we propose an improved scheme to sub-classify the CEMP stars, making use of the Sr/Ba ratio, which can also be used to separate very metal-poor stars from CEMP stars. We explore the use of [Sr/Ba] versus [Ba/Fe] in 93 stars in the metallicity range -4.2<~[Fe/H]<-2. We show that the Sr/Ba ratio can also be successfully used for distinguishing CEMP-s, CEMP-r/s, and CEMP-no stars. Additionally, the Sr/Ba ratio is found to be a powerful astro-nuclear indicator, since the metal-poor AGB stars exhibit very different Sr/Ba ratios compared to fast-rotating massive stars and NSM, and is also reasonably unbiased by NLTE and 3D corrections.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/352/117
- Title:
- Galactic lithium evolution revisited
- Short Name:
- J/A+A/352/117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This tabular material describes the data-set we use in order to constrain the results of our chemical evolution model.
- ID:
- ivo://CDS.VizieR/J/A+A/434/275
- Title:
- Galactic thin disk [Th/Eu] abundance ratios
- Short Name:
- J/A+A/434/275
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The objective of this work is the determination of the age of the Galactic disk using Th/Eu nucleocosmochronology. To achieve this objective, it is necessary to obtain the abundances of Th and Eu through spectral synthesis, and to perform the synthesis it is necessary to know the atmospheric parameters and chemical abundances of contaminating elements.
- ID:
- ivo://CDS.VizieR/J/A+A/394/187
- Title:
- {gamma} Ser & 101 Her elemental abundances
- Short Name:
- J/A+A/394/187
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Elemental abundances analysis of the superficially normal stars {gamma} Ser (F6 V) and 101 Herculis (A7 V) consistent with previous studies of this series using photographic region spectrograms obtained with Reticon and CCD detectors produced derived values that are generally solar except for Al which is very underabundant and the rare earths which do not have the solar pattern. Similar discrepancies from solar values are seen in other superficially normal stars of this series with similar temperatures. Our results for {gamma} Ser are in acceptable agreement with other recent studies based on different techniques and spectral regions.
- ID:
- ivo://CDS.VizieR/J/AJ/107/1577
- Title:
- Halo red giants reddening
- Short Name:
- J/AJ/107/1577
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Updated uvby observations for a larger sample of metal-deficient red giants are presented and combined with a select sample of data from the literature transformed to a common system. Using the reddening maps of Burstein & Heiles [AJ, 87, 1165 (1982)], new absolute magnitudes, distances, metallicities, and reddenings are derived for each star. The metallicities are determined with a revised calibration of the m1, (b-y) diagram based upon comparison to a compilation of recent spectroscopic abundances transformed to a common system. The photometric abundances agree very well with the spectroscopic; the dispersion among the residuals for 58 giants is +/-0.16dex. The dereddened indices are used to show that for red giants with [Fe/H]<-1.5, there is a well-defined relation in the c0, (b-y)0 diagram which exhibits only a weak dependence upon metallicity. Use of the standard relations allows one to obtain reddening estimates for normal halo field giants and globular clusters in the appropriate metallicity range.
- ID:
- ivo://CDS.VizieR/J/ApJ/778/56
- Title:
- Hamburg/ESO Survey extremely metal-poor stars
- Short Name:
- J/ApJ/778/56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From detailed abundance analysis of >100 Hamburg/ESO candidate extremely metal-poor (EMP) stars we find 45 with [Fe/H]<-3.0dex. We identify a heretofore unidentified group: Ca-deficient stars with sub-solar [Ca/Fe] ratios and the lowest neutron-capture abundances; the Ca-deficient group comprises ~10% of the sample, excluding Carbon stars. Our radial velocity distribution shows that the carbon-enhanced stars with no s-process enhancements, CEMP-no, and which do not show C_2_ bands are not preferentially binary systems. Ignoring Carbon stars, approximately 15% of our sample are strong (>=5{sigma}) outliers in one or more elements between Mg and Ni; this rises to ~19% if very strong (>=10{sigma}) outliers for Sr and Ba are included. Examples include: HE0305-0554 with the lowest [Ba/H] known; HE1012-1540 and HE2323-0256, two (non-velocity variable) C-rich stars with very strong [Mg,Al/Fe] enhancements; and HE1226-1149, an extremely r-process rich star.
- ID:
- ivo://CDS.VizieR/J/A+AS/137/227
- Title:
- HD 133029 & HD 192913 elemental abundances
- Short Name:
- J/A+AS/137/227
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Fine analyses of the silicon stars HD 133029 and HD 192913 are presented using ATLAS9 model atmospheres whose predictions fit the optical region spectrophotometry and H{gamma} profiles and have the same bulk metallicity as the deduced abundances. Both are very He poor stars. The light elements are mostly solar except for silicon, and all the heavier elements, except nickel in HD 133029 which is solar, are greatly overabundant. The iron peak elements are typically 10 times overabundant. SrYZr are of order of 100 times solar. The rare earths are 1000 or more times overabundant.
- ID:
- ivo://CDS.VizieR/J/A+A/569/A43
- Title:
- HE 2252-4225 abundance analysis
- Short Name:
- J/A+A/569/A43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Studies of the r-process enhanced stars are important for better understanding the nature and origin of the r-process. We present a detailed abundance analysis of a very metal-poor giant star discovered in the HERES project, HE 2252-4225, which exhibits overabundances of the r-process elements, with [r/Fe]=+0.80. We determined the stellar atmosphere parameters, Teff=4710K, logg=1.65, and [Fe/H]=-2.63, and chemical abundances by analysing the high-quality VLT/UVES spectra. The surface gravity was calculated from the non-local thermodynamic equilibrium (NLTE) ionisation balance between FeI and FeII. Accurate abundances for a total of 38 elements, including 22 neutron-capture elements beyond Sr and up to Th, were determined in HE 2252-4225. For every chemical species, the dispersion in the single line measurements around the mean does not exceed 0.12dex. This object is deficient in carbon, as expected for a giant star with Teff<4800K. The stellar Na-Zn abundances are well fitted by the yields of a single supernova of 14.4M_{sun}_. For the neutron-capture elements in the Sr-Ru, Ba-Yb, and Os-Ir regions, the abundance pattern of HE 2252-4225 is in excellent agreement with the average abundance pattern of the strongly r-process enhanced stars CS 22892-052, CS 31082-001, HE 1219-0312, and HE 1523-091. This suggests a common origin of the first, second, and third r-process peak elements in HE 2252-4225 in the classical r-process. We tested the solar r-process pattern based on the most recent s-process calculations of Bisterzo, Travaglio, Gallino, Wiescher, and Kappeler and found that elements in the range from Ba to Ir match it very well. No firm conclusion can be drawn about the relationship between the first neutron-capture peak elements, Sr to Ru, in HE 2252-4225 and the solar r-process, due to the uncertainty in the solar r-process. The investigated star has an anomalously high Th/Eu abundance ratio, so that radioactive dating results in a stellar age of {tau}=1.5+/-1.5Gyr that is not expected for a very metal-poor halo star.
- ID:
- ivo://CDS.VizieR/J/ApJ/724/975
- Title:
- Heavy elements abundances of metal-poor stars
- Short Name:
- J/ApJ/724/975
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To better characterize the abundance patterns produced by the r-process, we have derived new abundances or upper limits for the heavy elements zinc (Zn, Z=30), yttrium (Y, Z=39), lanthanum (La, Z=57), europium (Eu, Z=63), and lead (Pb, Z=82). Our sample of 161 metal-poor stars includes new measurements from 88 high-resolution and high signal-to-noise spectra obtained with the Tull Spectrograph on the 2.7m Smith Telescope at the McDonald Observatory, and other abundances are adopted from the literature. We use models of the s-process in asymptotic giant branch stars to characterize the high Pb/Eu ratios produced in the s-process at low metallicity, and our new observations then allow us to identify a sample of stars with no detectable s-process material.
- ID:
- ivo://CDS.VizieR/J/A+A/439/129
- Title:
- HERES II. Spectroscopic analysis
- Short Name:
- J/A+A/439/129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of analysis of "snapshot" spectra of 253 metal-poor halo stars -3.8<=[Fe/H]<=-1.5 obtained in the HERES survey. The snapshot spectra have been obtained with VLT/UVES and have typically S/N~54 per pixel (ranging from 17 to 308), R~20000, lambda=3760-4980{AA}. This sample represents the major part of the complete HERES sample of 373 stars; however, the CH strong content of the sample is not dealt with here.
