- 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.
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- ID:
- ivo://CDS.VizieR/J/A+A/546/A57
- Title:
- Spectroscopy of 400 red giants in the Bulge
- Short Name:
- J/A+A/546/A57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The presence of two stellar populations in the Milky Way bulge has been reported recently, based on observations of giant and dwarf stars in the inner an intermediate bulge. We aim at studying the abundances and kinematics of stars in the outer Galactic bulge, thereby providing additional constraints on formation models of the bulge. Spectra of 401 red giant stars in a field at (l,b)=(0,-10) were obtained with the FLAMES-GIRAFFE spectrograph at the VLT. Stars of luminosities down to below the two bulge red clumps are included in the data set. From these spectra we measure general metallicities, abundances of iron and the alpha-elements, and radial velocities of the stars. The abundances are derived from an interpolation and fitting procedure within a grid of COMARCS model atmospheres and spectra. These measurements as well as photometric data are compared to simulations with the Besancon and TRILEGAL models of the Galaxy. We confirm the presence of two populations among our sample stars: i) a metal-rich one at [M/H]~+0.3, comprising about 30% of the sample, with low velocity dispersion and low alpha-abundance, and ii) a metal-poor population at [M/H]~-0.6 with high velocity dispersion and high alpha-abundance. The metallicity difference between the two populations, a systematically and statistically robust figure, is Delta[M/H]=0.87+-0.03. The metal-rich population could be connected to the Galactic bar. We identify this population as the carrier of the double red clump feature. We do not find a significant difference in metallicity or radial velocity between the two red clumps, a small difference in metallicity being probably due to a selection effect and contamination by the metal-poor population. The velocity dispersion agrees well with predictions of the Besancon Galaxy model, but the metallicity of the "thick bulge" model component should be shifted to lower metallicity by 0.2 to 0.3dex to well reproduce the observations. We present evidence that the metallicity distribution function depends on the evolutionary state of the sample stars, suggesting that enhanced mass loss preferentially removes metal-rich stars. We also confirm the decrease of alpha-element over-abundance with increasing metallicity. Conclusions: Our sample is consistent with the existence of two populations, one being a metal-rich bar, the second one being more like a metal-poor classical bulge with larger velocity dispersion.
- 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.
17484. Spectroscopy of Reticulum II
- ID:
- ivo://CDS.VizieR/J/ApJ/808/95
- Title:
- Spectroscopy of Reticulum II
- Short Name:
- J/ApJ/808/95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Magellan/M2FS, Very Large Telescope/GIRAFFE, and Gemini South/GMOS spectroscopy of the newly discovered Milky Way satellite Reticulum II. Based on the spectra of 25 Ret II member stars selected from Dark Energy Survey imaging, we measure a mean heliocentric velocity of 62.8+/-0.5km/s and a velocity dispersion of 3.3+/-0.7km/s. The mass-to-light ratio of Ret II within its half-light radius is 470+/-210M_{sun}_/L_{sun}_, demonstrating that it is a strongly dark matter-dominated system. Despite its spatial proximity to the Magellanic Clouds, the radial velocity of Ret II differs from that of the LMC and SMC by 199 and 83km/s, respectively, suggesting that it is not gravitationally bound to the Magellanic system. The likely member stars of Ret II span 1.3dex in metallicity, with a dispersion of 0.28+/-0.09dex, and we identify several extremely metal-poor stars with [Fe/H]<-3. In combination with its luminosity, size, and ellipticity, these results confirm that Ret II is an ultra-faint dwarf galaxy. With a mean metallicity of [Fe/H]=-2.65+/-0.07, Ret II matches Segue 1 as the most metal-poor galaxy known. Although Ret II is the third-closest dwarf galaxy to the Milky Way, the line-of-sight integral of the dark matter density squared is log_10_(J)=18.8+/-0.6GeV^2^/cm^5^ within 0.2{deg}, indicating that the predicted gamma-ray flux from dark matter annihilation in Ret II is lower than that of several other dwarf galaxies.
- 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.
- ID:
- ivo://CDS.VizieR/J/AJ/144/168
- Title:
- Spectroscopy of Scl 1019417 and UMi 20103
- Short Name:
- J/AJ/144/168
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The most metal-poor stars in dwarf spheroidal galaxies (dSphs) can show the nucleosynthetic patterns of one or a few supernovae (SNe). These SNe could have zero metallicity, making metal-poor dSph stars the closest surviving links to Population III stars. Metal-poor dSph stars also help to reveal the formation mechanism of the Milky Way (MW) halo. We present the detailed abundances from Keck/HIRES spectroscopy for two very metal-poor stars in two MW dSphs. One star, in the Sculptor dSph, has [FeI/H]=-2.40. The other star, in the Ursa Minor dSph, has [FeI/H]=-3.16. Both stars fall in the previously discovered low-metallicity, high-[{alpha}/Fe] plateau. Most abundance ratios of very metal-poor stars in these two dSphs are largely consistent with very metal-poor halo stars. However, the abundances of Na and some r-process elements lie at the lower end of the envelope defined by inner halo stars of similar metallicity. We propose that the metallicity dependence of SN yields is the cause. The earliest SNe in low-mass dSphs have less gas to pollute than the earliest SNe in massive halo progenitors. As a result, dSph stars at -3<[Fe/H]<-2 sample SNe with [Fe/H]{Lt}-3, whereas halo stars in the same metallicity range sample SNe with [Fe/H]~-3. Consequently, enhancements in [Na/Fe] and [r/Fe] were deferred to higher metallicity in dSphs than in the progenitors of the inner halo.
17490. Spectroscopy of Segue 1
- ID:
- ivo://CDS.VizieR/J/ApJ/692/1464
- Title:
- Spectroscopy of Segue 1
- Short Name:
- J/ApJ/692/1464
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Keck/DEIMOS spectroscopy of Segue 1, an ultra-low-luminosity (M_V_=-1.5^+0.6^_-0.8_) Milky Way satellite companion. While the combined size and luminosity of Segue 1 are consistent with either a globular cluster or a dwarf galaxy, we present spectroscopic evidence that this object is a dark matter-dominated dwarf galaxy. We identify 24 stars as members of Segue 1 with a mean heliocentric recession velocity of 206+/-1.3km/s. Although Segue 1 spatially overlaps the leading arm of the Sagittarius stream, its velocity is 100km/s different from that predicted for recent Sagittarius tidal debris at this position. Using spectral synthesis modeling, we derive a metallicity for the single red giant branch star in our sample of [Fe/H]=-3.3+/-0.2dex. We conclude that Segue 1 is the least luminous of the ultra-faint galaxies recently discovered around the Milky Way, and is thus the least-luminous known galaxy.