- ID:
- ivo://CDS.VizieR/J/ApJ/862/174
- Title:
- Spectroscopy obs. of RAVE J094921.8-161722
- Short Name:
- J/ApJ/862/174
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a high-resolution (R~35000), high signal-to-noise ratio (S/N>200) Magellan/MIKE spectrum of the star RAVE J094921.8-161722, a bright (V=11.3) metal-poor red giant star with [Fe/H]=-2.2, identified as a carbon-enhanced metal-poor (CEMP) star from the RAVE survey. We report its detailed chemical abundance signature of light fusion elements and heavy neutron-capture elements. We find J0949-1617 to be a CEMP star with s-process enhancement that must have formed from gas enriched by a prior r-process event. Light neutron-capture elements follow a low-metallicity s-process pattern, while the heavier neutron-capture elements above Eu follow an r-process pattern. The Pb abundance is high, in line with an s-process origin. Thorium is also detected, as expected from an r-process origin, as Th is not produced in the s-process. We employ nucleosynthesis model predictions that take an initial r-process enhancement into account, and then determine the mass transfer of carbon and s-process material from a putative more massive companion onto the observed star. The resulting abundances agree well with the observed pattern. We conclude that J0949-1617 is the first bonafide CEMP-r+s star identified. This class of objects has previously been suggested to explain stars with neutron-capture element patterns that originate from neither the r- nor the s-process alone. We speculate that J0949-1617 formed in an environment similar to those of ultra-faint dwarf galaxies like TucanaIII and ReticulumII, which were enriched in r-process elements by one or multiple neutron star mergers at the earliest times.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/735/L46
- Title:
- Spectroscopy of 64 K red giants
- Short Name:
- J/ApJ/735/L46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on high-resolution spectra obtained with the MIKE spectrograph on the Magellan telescopes, we present detailed elemental abundances for 20 red giant stars in the outer Galactic disk, located at Galactocentric distances between 9 and 13kpc. The outer disk sample is complemented with samples of red giants from the inner Galactic disk and the solar neighborhood, analyzed using identical methods. For Galactocentric distances beyond 10kpc, we only find chemical patterns associated with the local thin disk, even for stars far above the Galactic plane. Our results show that the relative densities of the thick and thin disks are dramatically different from the solar neighborhood, and we therefore suggest that the radial scale length of the thick disk is much shorter than that of the thin disk. We make a first estimate of the thick disk scale length of L_thick_=2.0kpc, assuming L_thin_=3.8kpc for the thin disk. We suggest that radial migration may explain the lack of radial age, metallicity, and abundance gradients in the thick disk, possibly also explaining the link between the thick disk and the metal-poor bulge.
- ID:
- ivo://CDS.VizieR/J/ApJ/657/241
- Title:
- Spectroscopy of Leo I red giants
- Short Name:
- J/ApJ/657/241
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present low-resolution spectroscopy of 120 red giants in the Galactic satellite dwarf spheroidal (dSph) Leo I, obtained with GeminiN GMOS and Keck DEIMOS. We find stars with velocities consistent with membership of Leo I out to 1.3 King tidal radii. By measuring accurate radial velocities with a median measurement error of 4.6km/s, we find a mean systemic velocity of 284.2km/s with a global velocity dispersion of 9.9km/s. The dispersion profile is consistent with being flat out to the last data point.
- ID:
- ivo://CDS.VizieR/J/ApJ/679/1549
- Title:
- Spectroscopy of metal-poor star CS 17435-00532
- Short Name:
- J/ApJ/679/1549
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first detailed abundance analysis of the metal-poor giant HKII 17435-00532. This star was observed as part of the University of Texas long-term project Chemical Abundances of Stars in the Halo (CASH). A spectrum was obtained with the High Resolution Spectrograph (HRS) on the Hobby-Eberly Telescope with a resolving power of R~15000. Our analysis reveals that this star may be located on the red giant branch, red horizontal branch, or early asymptotic giant branch. We find that this metal-poor ([Fe/H]=-2.2) star has an unusually high lithium abundance [log{epsilon}(Li)=+2.1], mild carbon ([C/Fe]=+0.7) and sodium ([Na/Fe]=+0.6) enhancement, as well as enhancement of both s-process ([Ba/Fe]=+0.8) and r-process ([Eu/Fe]=+0.5) material.
- ID:
- ivo://CDS.VizieR/J/AJ/149/15
- Title:
- Spectroscopy of NGC 7789
- Short Name:
- J/AJ/149/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained high-resolution spectra of 32 giants in the open cluster NGC 7789 using the Wisconsin-Indiana-Yale-NOAO Hydra spectrograph. We explore differences in atmospheric parameters and elemental abundances caused by the use of the linelist developed for the Gaia-ESO Survey (GES) compared to one based on Arcturus used in our previous work. [Fe/H] values decrease when using the GES linelist instead of the Arcturus-based linelist; these differences are probably driven by systematically lower (~-0.1dex) GES surface gravities. Using the GES linelist we determine abundances for 10 elements--Fe, Mg, Si, Ca, Ti, Na, Ni, Zr, Ba, and La. We find the cluster's average metallicity [Fe/H]=0.03+/-0.07dex, in good agreement with literature values, and a lower [Mg/Fe] abundance than has been reported before for this cluster (0.11+/-0.05dex). We also find the neutron-capture element barium to be highly enhanced--[Ba/Fe]=+0.48+/-0.08--and disparate from cluster measurements of neutron-capture elements La and Zr (-0.08+/-0.05 and 0.08+/-0.08, respectively). This is in accordance with recent discoveries of supersolar Ba enhancement in young clusters along with more modest enhancement of other neutron-capture elements formed in similar environments.
- ID:
- ivo://CDS.VizieR/J/MNRAS/411/1536
- Title:
- Spectroscopy of of IC4499 red giants
- Short Name:
- J/MNRAS/411/1536
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present radial velocity and metallicity measurements for the far southern Galactic globular cluster IC 4499. We selected several hundred target red giant stars in and around the cluster from the 2MASS point source catalogue, and obtained spectra at the near-infrared calcium triplet using the AAOmega spectrograph. Observations of giants in globular clusters M4, M22 and M68 were taken to provide radial velocity and metallicity comparison objects.
- ID:
- ivo://CDS.VizieR/J/MNRAS/393/272
- Title:
- Spectroscopy of red giants in 12 open clusters
- Short Name:
- J/MNRAS/393/272
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Near-infrared spectra of 133 red giant stars from 10 Galactic open clusters and two Galactic globular clusters spanning 2.2dex in metallicity and 11Gyr in age are presented. We combine this sample with 10 clusters from Cole and collaborators (2004MNRAS.347..367C) to investigate the CaII triplet line strengths and their relation to cluster metallicity and position along the red giant branch. We show that characterizing the stellar surface gravity using K_s_-band photometry (relative to the horizontal branch) taken from the Two Micron All-Sky Survey allows for metallicity measurements at least as precise as those derived using V- or I-band data. This has the great advantage that uniform photometry and reliable astrometry are available for a large number of clusters. Using K_s_-band photometry also reduces the effect of differential reddening within a given cluster. We find no significant evidence for age or metallicity effects to the linear CaII triplet-metallicity relationship over the small range in magnitudes studied when homogeneous reference metallicities are used. We derive the first spectroscopic metallicity and new radial velocity estimates for five open clusters: Berkeley 81, Berkeley 99, IC 1311, King 2 and NGC7044. King2 has an anomalous radial velocity compared with the local disc population. We discuss the possibility that it is part of the Monoceros tidal stream.
- ID:
- ivo://CDS.VizieR/J/AJ/129/1465
- Title:
- Spectroscopy of red giants in the LMC bar
- Short Name:
- J/AJ/129/1465
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report metallicities and radial velocities derived from spectra at the near-infrared calcium triplet for 373 red giants in a 200arcmin^2^ area at the optical center of the LMC bar. These are the first spectroscopic abundance measurements of intermediate-age and old field stars in the high surface brightness heart of the LMC. The metallicity distribution is sharply peaked at the median value [Fe/H]=-0.40, with a small tail of stars extending down to [Fe/H]<=-2.1; 10% of the red giants are observed to have [Fe/H]<=-0.7.
- ID:
- ivo://CDS.VizieR/J/ApJ/731/64
- Title:
- Spectroscopy of 300 RGBs in {omega} Cen
- Short Name:
- J/ApJ/731/64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Omega Centauri is no longer the only globular cluster known to contain multiple stellar populations, yet it remains the most puzzling. Due to the extreme way in which the multiple stellar population phenomenon manifests in this cluster, it has been suggested that it may be the remnant of a larger stellar system. In this work, we present a spectroscopic investigation of the stellar populations hosted in the globular cluster {omega} Centauri to shed light on its still puzzling chemical enrichment history. With this aim, we used FLAMES+GIRAFFE@VLT to observe 300 stars distributed along the multimodal red giant branch of this cluster, sampling with good statistics the stellar populations of different metallicities. We determined chemical abundances for Fe, Na, O, and n-capture elements Ba and La. We confirm that {omega} Centauri exhibits large star-to-star variations in iron with [Fe/H] ranging from ~-2.0 to ~-0.7dex. Barium and lanthanum abundances of metal-poor stars are correlated with iron, up to [Fe/H]~-1.5, while they are almost constant (or at least have only a moderate increase) in the more metal-rich populations. There is an extended Na-O anticorrelation for stars with [Fe/H]<~-1.3 while more metal-rich stars are almost all Na-rich. Sodium was found to mildly increase with iron over the entire metallicity range.
- ID:
- ivo://CDS.VizieR/J/AJ/156/257
- Title:
- Spectroscopy of RGB stars in Draco & Ursa Minor
- Short Name:
- J/AJ/156/257
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Measuring the frequency of binary stars in dwarf spheroidal galaxies (dSphs) requires data taken over long time intervals. We combine radial velocity measurements from five literature sources taken over the course of ~30 years to yield the largest multi-epoch kinematic sample for stars in the dSphs Draco and Ursa Minor. With this data set, we are able to implement an improved version of the Bayesian technique described in Spencer et al. (2017, J/AJ/153/254) to evaluate the binary fraction of red giant stars in these dwarf galaxies. Assuming Duquennoy & Mayor (1991A&A...248..485D) period and mass ratio distributions, the binary fractions in Draco and Ursa Minor are 0.50_-0.06_^+0.04^ and 0.78_-0.08_^+0.09^, respectively. We find that a normal mass ratio distribution is preferred over a flat distribution, and that log-normal period distributions centered on long periods ({mu}_logP_>3.5) are preferred over distributions centered on short ones. We reanalyzed the binary fractions in Leo II, Carina, Fornax, Sculptor, and Sextans, and find that there is <1% chance that binary fraction is a constant quantity across all seven dwarfs, unless the period distribution varies greatly. This indicates that the binary populations in Milky Way dSphs are not identical in regard to their binary fractions, period distributions, or both. We consider many different properties of the dwarfs (e.g., mass, radius, luminosity, etc.) and find that binary fraction might be larger in dwarfs that formed their stars quickly and/or have high velocity dispersions.
