- 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.
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- 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.
- ID:
- ivo://CDS.VizieR/J/A+A/574/A124
- Title:
- Spectroscopy of solar twins and analogues
- Short Name:
- J/A+A/574/A124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Many large stellar surveys have been and are still being carried out, providing huge amounts of data, for which stellar physical parameters will be derived. Solar twins and analogues provide a means to test the calibration of these stellar catalogues because the Sun is the best-studied star and provides precise fundamental parameters. Solar twins should be centred on the solar values. This spectroscopic study of solar analogues selected from the Geneva-Copenhagen Survey (GCS) at a resolution of 48000 provides effective temperatures and metallicities for these stars. We test whether our spectroscopic parameters, as well as the previous photometric calibrations, are properly centred on the Sun. In addition, we search for more solar twins in our sample. The methods used in this work are based on literature methods for solar twin searches and on methods we developed in previous work to distinguish the metallicity-temperature degeneracies in the differential comparison of spectra of solar analogues versus a reference solar reflection spectrum.
- ID:
- ivo://CDS.VizieR/J/ApJ/705/1481
- Title:
- Spectroscopy of stars in 6 globular clusters
- Short Name:
- J/ApJ/705/1481
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Intermediate resolution spectra at the CaII triplet have been obtained for 55 candidate red giants in the field of the globular cluster M22 with the VLT/FORS2 instrument. Spectra were also obtained for a number of red giants in standard globular clusters to provide a calibration of the observed line strengths with overall abundance [Fe/H]. For the 41 M22 member stars that lie within the V-V_HB_ bounds of the calibration, we find an abundance distribution that is substantially broader than that expected from the observed errors alone. We argue that this broad distribution cannot be the result of differential reddening. Instead, we conclude that, as has long been suspected, M22 is similar to {omega} Cen in having an intrinsic dispersion in heavy element abundance. The observed M22 abundance distribution rises sharply to a peak at [Fe/H]~-1.9 with a broad tail to higher abundances: the highest abundance star in our sample has [Fe/H] ~-1.45dex. If the unusual properties of {omega} Cen have their origin in a scenario in which the cluster is the remnant nucleus of a disrupted dwarf galaxy, then such a scenario likely also applies to M22.
- ID:
- ivo://CDS.VizieR/J/AJ/149/204
- Title:
- Spectroscopy of 25 stars in M68
- Short Name:
- J/AJ/149/204
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we present a detailed high-resolution spectroscopic study of post main sequence stars in the globular cluster (GC) M68. Our sample, which covers a range of 4000K in T_eff_, and 3.5dex in log(g), is comprised of members from the red giant, red horizontal, and blue horizontal branch, making this the first high-resolution GC study covering such a large evolutionary and parameter space. Initially, atmospheric parameters were determined using photometric as well as spectroscopic methods, both of which resulted in unphysical and unexpected T_eff_, log(g), {xi}_t_, and [Fe/H] combinations. We therefore developed a hybrid approach that addresses most of these problems, and yields atmospheric parameters that agree well with other measurements in the literature. Furthermore, our derived stellar metallicities are consistent across all evolutionary stages, with <[Fe/H]>=-2.42 ({sigma}=0.14) from 25 stars. Chemical abundances obtained using our methodology also agree with previous studies and bear all the hallmarks of GCs, such as a Na-O anti-correlation, constant Ca abundances, and mild r-process enrichment.
1279. Spectroscopy of Terzan 5
- ID:
- ivo://CDS.VizieR/J/ApJ/726/L20
- Title:
- Spectroscopy of Terzan 5
- Short Name:
- J/ApJ/726/L20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the chemical abundance analysis of 33 red giant stars belonging to the complex stellar system Terzan 5. We confirm the discovery of two stellar populations with distinct iron abundances: a relatively metal-poor component with [Fe/H]=-0.25+/-0.07rms and another component with [Fe/H]=+0.27+/-0.04rms, exceeding in metallicity any known Galactic globular cluster (GC). The two populations also show different [{alpha}/Fe] abundance ratios. The metal-poor component has an average [{alpha}/Fe]=+0.34+/-0.06rms, consistent with the canonical scenario for rapid enrichment by core collapse supernovae (SNe). The metal-rich component has [{alpha}/Fe]=+0.03+/-0.04rms, suggesting that the gas from which it formed was polluted by both type II and type Ia SNe on a longer timescale. Neither of the two populations shows evidence of the [Al/Fe] over [O/Fe] anti-correlation that is typically observed in Galactic GCs. Because these chemical abundance patterns are unique, we propose that Terzan 5 is not a true GC, but a stellar system with a much more complex history of star formation and chemical enrichment.
- ID:
- ivo://CDS.VizieR/J/A+A/635/A107
- Title:
- Spectroscopy of the Eri 2 cluster
- Short Name:
- J/A+A/635/A107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It has been shown that the ultra-faint dwarf galaxy Eridanus 2 may host a stellar cluster in its centre. If this cluster is shown to exist, it can be used to set constraints on the mass and abundance of massive astrophysical compact halo objects (MACHOs) as a form of dark matter. Previous research has shown promising expectations in the mass range of 10-100M_{sun}_, but lacked spectroscopic measurements of the cluster. We aim to provide spectroscopic evidence regarding the nature of the putative star cluster in Eridanus 2 and to place constraints on MACHOs as a constituent of dark matter. We present spectroscopic observations of the central square arcminute of Eridanus 2 from MUSE-Faint, a survey of ultrafaint dwarf galaxies with the Multi Unit Spectroscopic Explorer on the Very Large Telescope. We derived line-of-sight velocities for possible member stars of the putative cluster and for stars in the centre of Eridanus 2. We discuss the existence of the cluster and determine new constraints for MACHOs using the Fokker-Planck diffusion approximation. Out of 182 extracted spectra, we identify 26 member stars of Eridanus 2, seven of which are possible cluster members. We find intrinsic mean line-of-sight velocities of 79.7^+3.1^_3.8_km/s and 76.0^+3.2^_3.7_km/s for the cluster and the bulk of Eridanus 2, respectively, as well as intrinsic velocity dispersions of <7.6km/s (68-% upper limit) and 10.3^+3.9^_3.2_km/s, respectively. This indicates that the cluster most likely exists as a distinct dynamical population hosted by Eridanus 2 and that it does not have a surplus of dark matter over the background distribution. Among the member stars in the bulk of Eridanus 2, we find possible carbon stars, alluding to the existence of an intermediate-age population.We derived constraints on the fraction of dark matter that can consist of MACHOs with a given mass between 1-10^5^M_{sun}_. For dark matter consisting purely of MACHOs, the mass of the MACHOs must be less than 7.6M_{sun}_ and 44M_{sun}_ at a 68- and 95-% confidence level, respectively.
