- ID:
- ivo://CDS.VizieR/J/A+A/586/A49
- Title:
- r- and s- process elements in Milky Way disk
- Short Name:
- J/A+A/586/A49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Elements heavier than iron are produced through neutron-capture processes in the different phases of stellar evolution. Asymptotic giant branch (AGB) stars are believed to be mainly responsible for elements that form through the slow neutron-capture process, while the elements created in the rapid neutron-capture process have production sites that are less understood. Knowledge of abundance ratios as functions of metallicity can lead to insight into the origin and evolution of our Galaxy and its stellar populations. We aim to trace the chemical evolution of the neutron-capture elements Sr, Zr, La, Ce, Nd, Sm, and Eu in the Milky Way stellar disk. This will allow us to constrain the formation sites of these elements, as well as to probe the evolution of the Galactic thin and thick disks. Using spectra of high resolution (42000<=R<=65000) and high signal-to-noise (S/N>=200) obtained with the MIKE and the FEROS spectrographs, we determine Sr, Zr, La, Ce, Nd, Sm, and Eu abundances for a sample of 593 F and G dwarf stars in the solar neighborhood. The abundance analysis is based on spectral synthesis using one-dimensional, plane-parallel, local thermodynamic equilibrium (LTE) model stellar atmospheres calculated with the MARCS 2012 code.
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1412. Rare earth abundances
- ID:
- ivo://CDS.VizieR/J/ApJS/182/80
- Title:
- Rare earth abundances
- Short Name:
- J/ApJS/182/80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have derived new abundances of the rare earth elements Pr, Dy, Tm, Yb, and Lu for the solar photosphere and for five very metal-poor, neutron-capture r-process-rich giant stars. The photospheric values for all five elements are in good agreement with meteoritic abundances. For the low-metallicity sample, these abundances have been combined with new Ce abundances from a companion paper, and reconsideration of a few other elements in individual stars, to produce internally consistent Ba, rare earth, and Hf(56<=Z<=72) element distributions. These have been used in a critical comparison between stellar and solar r-process abundance mixes.
- ID:
- ivo://CDS.VizieR/J/ApJ/897/78
- Title:
- RAVE J183013.5-455510 equivalent-width measurements
- Short Name:
- J/ApJ/897/78
- Date:
- 15 Mar 2022 04:12:46
- Publisher:
- CDS
- Description:
- We report on the spectroscopic analysis of RAVE-J183013.5-455510, an extremely metal-poor star, highly enhanced in CNO, and with discernible contributions from the rapid neutron-capture process. There is no evidence of binarity for this object. At [Fe/H]=-3.57, this star has one of the lowest metallicities currently observed, with 18 measured abundances of neutron-capture elements. The presence of Ba, La, and Ce abundances above the solar system r-process predictions suggests that there must have been a non-standard source of r-process elements operating at such low metallicities. One plausible explanation is that this enhancement originates from material ejected at unusually high velocities in a neutron star merger event. We also explore the possibility that the neutron-capture elements were produced during the evolution and explosion of a rotating massive star. In addition, based on comparisons with yields from zero-metallicity faint supernova, we speculate that RAVE-J1830-4555 was formed from a gas cloud pre-enriched by both progenitor types. From analysis based on Gaia DR2 measurements, we show that this star has orbital properties similar to the Galactic metal-weak thick-disk stellar population.
- ID:
- ivo://CDS.VizieR/J/ApJ/844/18
- Title:
- RAVE J203843.2-002333 high-resolution spectroscopy
- Short Name:
- J/ApJ/844/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of RAVE J203843.2-002333, a bright (V=12.73), very metal-poor ([Fe/H]=-2.91), r-process-enhanced ([Eu/Fe]=+1.64 and [Ba/Eu]=-0.81) star selected from the RAVE survey. This star was identified as a metal-poor candidate based on its medium-resolution (R~1600) spectrum obtained with the KPNO/Mayall Telescope, and followed up with high-resolution (R~66000) spectroscopy with the Magellan/Clay Telescope, allowing for the determination of elemental abundances for 24 neutron-capture elements, including thorium and uranium. RAVE J2038-0023 is only the fourth metal-poor star with a clearly measured U abundance. The derived chemical abundance pattern exhibits good agreement with those of other known highly r-process- enhanced stars, and evidence suggests that it is not an actinide-boost star. Age estimates were calculated using U/X abundance ratios, yielding a mean age of 13.0+/-1.1Gyr.
- ID:
- ivo://CDS.VizieR/J/A+A/600/A106
- Title:
- RAVE open cluster pairs, groups and complexes
- Short Name:
- J/A+A/600/A106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Galactic open clusters (OCs) mainly belong to the young stellar population in the Milky Way disk, but are there groups and complexes of OCs that possibly define an additional level in hierarchical star formation? Current compilations are too incomplete to address this question, especially regarding radial velocities (RVs) and metallicities ([M/H]). Here we present the parameters for the final working sample of 432 open clusters, as well as the mean parameters for the 19 detected potential open cluster groupings.
- ID:
- ivo://CDS.VizieR/J/ApJ/737/9
- Title:
- RAVE spectroscopic data of stars in the thick disk
- Short Name:
- J/ApJ/737/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have undertaken the study of the elemental abundances and kinematic properties of a metal-poor sample of candidate thick-disk stars selected from the Radial Velocity Experiment spectroscopic survey of bright stars to differentiate among the present scenarios of the formation of the thick disk. In this paper, we report on a sample of 214 red giant branch, 31 red clump/horizontal branch, and 74 main-sequence/sub-giant branch metal-poor stars, which serves to augment our previous sample of only giant stars. We find that the thick disk [{alpha}/Fe] ratios are enhanced and have little variation (<0.1dex), in agreement with our previous study. The augmented sample further allows, for the first time, investigation of the gradients in the metal-poor thick disk.
- ID:
- ivo://CDS.VizieR/J/AJ/142/193
- Title:
- RAVE stellar elemental abundances (DR1)
- Short Name:
- J/AJ/142/193
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present chemical elemental abundances for 36561 stars observed by the RAdial Velocity Experiment (RAVE), an ambitious spectroscopic survey of our Galaxy at Galactic latitudes |b|>25{deg} and with magnitudes in the range 9<I_DENIS_<13. RAVE spectra cover the Ca-triplet region at 8410-8795{AA} with resolving power R~7500. This first data release of the RAVE chemical catalog is complementary to the third RAVE data release of radial velocities and stellar parameters, and it contains chemical abundances for the elements Mg, Al, Si, Ca, Ti, Fe, and Ni, with a mean error of ~0.2dex, as judged from accuracy tests performed on synthetic and real spectra. Abundances are estimated through a dedicated processing pipeline in which the curve of growth of individual lines is obtained from a library of absorption line equivalent widths to construct a model spectrum that is then matched to the observed spectrum via a {chi}^2^ minimization technique. We plan to extend this pipeline to include estimates for other elements, such as oxygen and sulfur, in future data releases.
- ID:
- ivo://CDS.VizieR/J/ApJS/157/371
- Title:
- Recombination lines in planetary nebulae
- Short Name:
- J/ApJS/157/371
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recombination lines (RLs) of C II, N II, and O II in planetary nebulae (PNs) have been found to give abundances that are much larger in some cases than abundances from collisionally excited forbidden lines (CELs). The origins of this abundance discrepancy are highly debated. We present new spectroscopic observations of O II and C II recombination lines for six planetary nebulae.
- ID:
- ivo://CDS.VizieR/J/ApJ/858/L7
- Title:
- Red clump stars selected from LAMOST and APOGEE
- Short Name:
- J/ApJ/858/L7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Core helium-burning red clump (RC) stars are excellent standard candles in the Milky Way. These stars may have more precise distance estimates from spectrophotometry than from Gaia parallaxes beyond 3kpc. However, RC stars have values of Teff and logg that are very similar to some red giant branch (RGB) stars. Especially for low-resolution spectroscopic studies where Teff, logg, and [Fe/H] can only be estimated with limited precision, separating RC stars from RGB through established methods can incur ~20% contamination. Recently, Hawkins+ (2018ApJ...853...20H) demonstrated that the additional information in single-epoch spectra, such as the C/N ratio, can be exploited to cleanly differentiate RC and RGB stars. In this second paper of the series, we establish a data-driven mapping from spectral flux space to independently determined asteroseismic parameters, the frequency and the period spacing. From this, we identify 210371 RC stars from the publicly available LAMOST DR3 and APOGEE DR14 data, with ~9% of contamination. We provide an RC sample of 92249 stars with a contamination of only ~3%, by restricting the combined analysis to LAMOST stars with S/N_pix_>=75. This demonstrates that high-signal-to-noise ratio (S/N), low-resolution spectra covering a broad wavelength range can identify RC samples at least as pristine as their high- resolution counterparts. As coming and ongoing surveys such as TESS, DESI, and LAMOST will continue to improve the overlapping training spectroscopic-asteroseismic sample, the method presented in this study provides an efficient and straightforward way to derive a vast yet pristine sample of RC stars to reveal the three-dimensional (3D) structure of the Milky Way.
- ID:
- ivo://CDS.VizieR/J/A+A/440/901
- Title:
- Reddening and metallicity of NGC 6752
- Short Name:
- J/A+A/440/901
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Accurate reddenings for Globular Clusters could be obtained by comparing the colour-temperature obtained using temperatures from reddening-free indicator (H{alpha}), with that given by standard colour-temperature calibrations. The large multiplexing opportunity offered by FLAMES at VLT2 allowed us to obtain spectra centered on H{alpha} at a resolution of R=6000 and 5<S/N<50 for 120 stars near the turn-off of NGC 6752 with GIRAFFE from a single 1300 seconds exposure on June 24th, 2004.