- ID:
- ivo://CDS.VizieR/J/A+A/413/159
- Title:
- Galactic abundance gradient. V.
- Short Name:
- J/A+A/413/159
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper reports on the spectroscopic investigation of 12 Cepheids which are situated in the crucial region of galactocentric distances from 9kpc to 12kpc, where according to our previous results (Andrievsky et al., 2002, Cat. <J/A+A/392/491>; Luck et al., 2003A&A...401..939L) the radial metallicity distribution experiences an obvious change. In particular, the wriggle in the iron abundance distribution is found to fall approximately at galactocentric distances 10-11kpc (assuming galactocentric distance of the Sun kpc). Within the transition zone from 10 to 11kpc the relative-to-solar iron abundance decreases approximately to -0.2dex. The new sample of stars, analyzed in present paper, gives results supporting the previous conclusion about the multimodal character of the metallicity distribution in galactic disc. Using a quite simple consideration of galactic chemical evolution we show that the observed distribution can be explained in the framework of a model which includes the spiral arms. In particular, the wriggle feature associated with 11 kpc can be interpreted as a change of metallicity level in the vicinity of the galactic corotation resonance.
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- ID:
- ivo://CDS.VizieR/J/A+A/418/551
- Title:
- Galactic disk stars abundances and velocities
- Short Name:
- J/A+A/418/551
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed the detailed analysis of 174 high-resolution spectra of FGK dwarfs obtained with the ELODIE echelle spectrograph at the Observatoire de Haute-Provence. Abundances of Fe, Si and Ni have been determined from equivalent widths under LTE approximation, whereas abundances of Mg have been determined under NLTE approximation using equivalent widths of 4 lines and profiles of 5 lines. Spatial velocities with an accuracy better than 1kms, as well as orbits, have been computed for all stars.
- 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.
- 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/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/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.
- ID:
- ivo://CDS.VizieR/J/A+A/484/721
- Title:
- HES survey. IV. Candidate metal-poor stars
- Short Name:
- J/A+A/484/721
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the quantitative methods used for selecting candidate metal-poor stars in the Hamburg/ESO objective-prism survey (HES). The selection is based on the strength of the CaII K line, B-V colors (both measured directly from the digital HES spectra), as well as J-K colors from the 2 Micron All Sky Survey. The KP index for CaII K can be measured from the HES spectra with an accuracy of 1.0{AA}, and a calibration of the HES B-V colors, using CCD photometry, yields a 1-sigma uncertainty of 0.07mag for stars in the color range 0.3<B-V<1.4.
- ID:
- ivo://CDS.VizieR/J/AJ/156/179
- Title:
- Highly r-process-enhanced field stars kinematics
- Short Name:
- J/AJ/156/179
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the kinematics of 35 highly r-process-enhanced ([Eu/Fe]>=+0.7) metal-poor (-3.8<[Fe/H]< -1.4) field stars. We calculate six-dimensional positions and velocities, evaluate energies and integrals of motion, and compute orbits for each of these stars using parallaxes and proper motions from the second Gaia data release (Cat. I/345) and published radial velocities. All of these stars have halo kinematics. Most stars (66%) remain in the inner regions of the halo (<13 kpc), and many (51%) have orbits that pass within 2.6 kpc of the Galactic center. Several stars (20%) have orbits that extend beyond 20 kpc, including one with an orbital apocenter larger than the Milky Way virial radius. We apply three clustering methods to search for structure in phase space, and we identify eight groups. No abundances are considered in the clustering process, but the [Fe/H] dispersions of the groups are smaller than would be expected by random chance. The orbital properties, clustering in phase space and metallicity, and the lack of highly r-process-enhanced stars on disk-like orbits, indicate that such stars likely were accreted from disrupted satellites. Comparison with the galaxy luminosity-metallicity relation suggests M_V_>~-9 for most of the progenitor satellites, characteristic of ultra-faint or low-luminosity classical dwarf spheroidal galaxies. Environments with low rates of star formation and Fe production, rather than the nature of the r-process site, may be key to obtaining the [Eu/Fe] ratios found in highly r-process-enhanced stars.
