- 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.
Number of results to display per page
Search Results
- 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/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.
- ID:
- ivo://CDS.VizieR/J/A+A/533/A69
- Title:
- Spectroscopy of 124 RGB stars in NGC 1851
- Short Name:
- J/A+A/533/A69
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed chemical tagging of individual stellar populations in the Galactic globular cluster (GC) NGC 1851. Abundances are derived from FLAMES spectra for the largest sample of giants (124) and the widest number of elements ever analysed in this peculiar GC. The chemistry is characterised using homogeneous abundances of proton-capture (O, Na, Mg, Al, Si), {alpha}-capture (Ca, Ti), Fe-peak (Sc, V, Mn, Co, Ni, Cu), and neutron-capture elements (Y, Zr, Ba, La, Ce, Nd, Eu, Dy). We confirm the presence of an [Fe/H] spread larger than the observational errors in this cluster, but too small to clearly separate different sub-populations. We instead propose a classification scheme using a combination of Fe and Ba (which is much more abundant in the more metal-rich group) by means of a cluster analysis. With this approach, we separated stars into two components of a metal-rich (MR) and a metal-poor (MP) population. Each component displays a Na-O anticorrelation, which is a signature of a genuine GC, but has different ratios of primordial (FG) to polluted (SG) stars. Moreover, clear (anti)correlations of Mg and Si with Na and O are found for each component. The level of [{alpha}/H] tracks iron and is higher in the MR population, which might therefore have received an additional contribution from core-collapse supernovae. When considering all s-process elements, the MR population shows a larger enrichment than the MP one. This is probably due to the contribution of intermediate-low mass stars, because we find that the level of heavy s-process elements is higher than that of light s-process nuclei in the MR stars; however, a large contribution from low mass stars is unlikely, because it would likely cancel the O-Na anticorrelation. Finally, we confirm the presence of correlations between the amount of proton-capture elements and the level of s-process elements previously found by other investigations, at least for the MR population. This finding apparently requires a quite long delay for the second generation of the MR component. Scenarios for the formation of NGC 1851 appear complex, and are not yet well understood. A merger of two distinct GCs in a parent dwarf galaxy, each cluster with a different Ba level and an age difference of ~1Gyr, might explain (i) the double subgiant branch, (ii) a possible difference in C content between the two original GCs, and (iii) the Stromgren photometry of this peculiar cluster. However, the correlation existing between p-capture and n-capture elements within the MR population requires the additional assumption of a long delay for its second generation. More observations are required to fully understand the formation of this GC.
- ID:
- ivo://CDS.VizieR/J/AJ/154/150
- Title:
- Spectroscopy of RGB stars in {omega} Centauri
- Short Name:
- J/AJ/154/150
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present [Fe/H] and [Ca/Fe] of ~600 red giant branch (RGB) members of the globular cluster Omega Centauri ({omega} Cen). We collect medium-resolution (R~2000) spectra using the Blanco 4 m telescope at the Cerro Tololo Inter-American Observatory equipped with Hydra, the fiber-fed multi-object spectrograph. We demonstrate that blending of stellar light in optical fibers severely limits the accuracy of spectroscopic parameters in the crowded central region of the cluster. When photometric temperatures are taken in the spectroscopic analysis, our kinematically selected cluster members, excluding those that are strongly affected by flux from neighboring stars, include relatively fewer stars at intermediate metallicity ([Fe/H]~-1.5) than seen in the previous high-resolution survey for brighter giants in Johnson & Pilachowski (2010, J/ApJ/722/1373). As opposed to the trend of increasing [Ca/Fe] with [Fe/H] found by those authors, our [Ca/Fe] estimates, based on Ca II H & K measurements, show essentially the same mean [Ca/Fe] for most of the metal-poor and metal-intermediate populations in this cluster, suggesting that mass- or metallicity-dependent SN II yields may not be necessary in their proposed chemical evolution scenario. Metal-rich cluster members in our sample show a large spread in [Ca/Fe], and do not exhibit a clear bimodal distribution in [Ca/Fe]. We also do not find convincing evidence for a radial metallicity gradient among RGB stars in {omega} Cen.
