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2791. Chemical evolution of the UMi dSph
ID:
ivo://CDS.VizieR/J/ApJ/719/931
Title:
Chemical evolution of the UMi dSph
Short Name:
J/ApJ/719/931
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an abundance analysis based on high-resolution spectra of 10 stars selected to span the full range in metallicity in the Ursa Minor (UMi) dwarf spheroidal (dSph) galaxy. We find that [Fe/H] for the sample stars ranges from -1.35 to -3.10 dex. Combining our sample with previously published work for a total of 16 luminous UMi giants, we establish the trends of abundance ratios [X/Fe] as functions of [Fe/H] for 15 elements. In key cases, particularly for the {alpha}-elements, these trends resemble those for stars in the outer part of the Galactic halo, especially at the lowest metallicities probed. The neutron-capture elements show an r-process distribution over the full range of Fe metallicity reached in this dSph galaxy. This suggests that the duration of star formation in the UMi dSph was shorter than in other dSph galaxies. The derived ages for a larger sample of UMi stars with more uncertain metallicities also suggest a population dominated by uniformly old (~13Gyr) stars, with a hint of an age-metallicity relationship. We note the presence of two UMi giants with [Fe/H]<-3.0 dex in our sample and reaffirm that the inner Galactic halo could have been formed by early accretion of Galactic satellite galaxies and dissolution of young globular clusters, while the outer halo could have formed from those satellite galaxies that accreted somewhat later.
2792. Chemically peculiar stars in the LMC
ID:
ivo://CDS.VizieR/J/A+A/459/871
Title:
Chemically peculiar stars in the LMC
Short Name:
J/A+A/459/871
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present high precision photometric Delta a observations of 417 objects in NGC 2136/7 and its surrounding field, of which five turned out to be bona fide magnetic CP stars. In addition, we discovered two Be/Ae stars. This intermediate band photometric system samples the depth of the 520nm flux depression by comparing the flux at the center with the adjacent regions with bandwidths of 11nm to 23nm. The Delta a photometric system is most suitable for detecting CP2 stars with high efficiency, but is also capable of detecting a small percentage of non-magnetic CP objects. From our investigations of NGC 1711, NGC 1866, NGC 2136/7, their surroundings, and one independent field of the LMC population, we derive an occurrence of classical chemically peculiar stars of 2.2(6)% in the LMC, which is only half the value found in the Milky Way. The mass and age distribution of the photometrically detected CP stars is not different from that of similar objects in galactic open clusters.
2793. Chemical properties of M31 star clusters
ID:
ivo://CDS.VizieR/J/ApJ/797/116
Title:
Chemical properties of M31 star clusters
Short Name:
J/ApJ/797/116
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present ages, [Fe/H] and abundances of the {alpha} elements CaI, SiI, TiI, TiII, and light elements MgI, NaI, and AlI for 31 globular clusters (GCs) in M31, which were obtained from high-resolution, high signal-to-noise ratio >60 echelle spectra of their integrated light (IL). All abundances and ages are obtained using our original technique for high-resolution IL abundance analysis of GCs. This sample provides a never before seen picture of the chemical history of M31. The GCs are dispersed throughout the inner and outer halo, from 2.5kpc<R_M31_<117kpc.
2794. Chemical properties of red MSX sources (RMSs)
ID:
ivo://CDS.VizieR/J/ApJ/833/248
Title:
Chemical properties of red MSX sources (RMSs)
Short Name:
J/ApJ/833/248
Date:
21 Oct 2021
Publisher:
CDS
Description:
Red Midcourse Space Experiment (MSX) Sources (RMSs) are regarded as excellent candidates of massive star-forming regions. In order to characterize the chemical properties of massive star formation, we made a systematic study of 87 RMSs in the southern sky, using archival data taken from the Atacama Pathfinder Experiment Telescope Large Area Survey of the Galaxy (ATLASGAL), the Australia Telescope Compact Array, and the Millimetre Astronomy Legacy Team Survey at 90GHz (MALT90). According to previous multiwavelength observations, our sample could be divided into two groups: massive young stellar objects and HII regions. Combined with the MALT90 data, we calculated the column densities of N_2_H^+^, C_2_H, HC_3_N, and HNC and found that they are not much different from previous studies made in other massive star-forming regions. However, their abundances are relatively low compared to infrared dark clouds (IRDCs). The abundances of N_2_H^+^ and HNC in our sample are at least 1mag lower than those found in IRDCs, indicating chemical depletions in the relatively hot gas. Besides, the fractional abundances of N_2_H^+^, C_2_H, and HC_3_N seem to decrease as a function of their Lyman continuum fluxes (N_L_), indicating that these molecules could be destroyed by UV photons when HII regions have formed inside. We also find that the C_2_H abundance decreases faster than HC_3_N with respect to N_L_. The abundance of HNC has a tight correlation with that of N_2_H^+^, indicating that it may be also preferentially formed in cold gas. We regard our RMSs as being in a relatively late evolutionary stage of massive star formation.
2795. Chemical properties of 89 stars in the LMC disk
ID:
ivo://CDS.VizieR/J/ApJ/761/33
Title:
Chemical properties of 89 stars in the LMC disk
Short Name:
J/ApJ/761/33
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have used high-resolution spectra obtained with the multifiber facility FLAMES at the Very Large Telescope of the European Southern Observatory to derive kinematic properties and chemical abundances of Fe, O, Mg, and Si for 89 stars in the disk of the Large Magellanic Cloud (LMC). The derived metallicity and [{alpha}/Fe], obtained as the average of O, Mg, and Si abundances, allow us to draw a preliminary scheme of the star formation history of this region of the LMC. The derived metallicity distribution shows two main components: one component (comprising ~84% of the sample) peaks at [Fe/H]=-0.48dex and it shows an [{alpha}/Fe] ratio slightly under solar ([{alpha}/Fe]~-0.1dex). This population probably originated in the main star formation event that occurred 3-4Gyr ago (possibly triggered by tidal capture of the Small Magellanic Cloud). The other component (comprising ~16% of the sample) peaks at [Fe/H]~-0dex and it shows an [{alpha}/Fe]~0.2dex. This population was probably generated during the long quiescent epoch of star formation between the first episode and the most recent bursts. Indeed, in our sample we do not find stars with chemical properties similar to the old LMC globular clusters nor to the iron-rich and {alpha}-poor stars recently found in the LMC globular cluster NGC 1718 and also predicted to be in the LMC field, thus suggesting that both of these components are small (<1%) in the LMC disk population.
2796. Chemical sulfur abundances of 719 FGK stars
ID:
ivo://CDS.VizieR/J/A+A/634/A136
Title:
Chemical sulfur abundances of 719 FGK stars
Short Name:
J/A+A/634/A136
Date:
21 Oct 2021
Publisher:
CDS
Description:
Elemental abundances are of prime importance to help us reconstruct the origin and evolution of stars and galaxies in our Universe. Sulfur abundances have not been as heavily studied as other elements, so some details regarding its behaviour are still unclear. We aim to investigate [S/Fe] ratios in stars of the solar neighbourhood in order to analyse the chemical evolution of sulfur and probe for possible differences in abundances of planet host and non-planet host stars. We use the code MOOG to perform spectral synthesis and derive v*sin(i) values and [S/Fe] ratios for 719 FGK stars with high-resolution (R~115000) and high-quality spectra from the HARPS-GTO program. We find the best fit and corresponding parameter values by performing chi-square minimisation of the deviation between synthetic profiles and observational spectra. Our results reveal that sulfur behaves as a typical alpha-element, with low abundances in young thin disk stars and high abundances in old thick disk stars, following what was expected from our understanding of the Galactic chemical evolution (GCE). Nevertheless, further studies into the abundances of sulfur in very metal-poor stars are required as our sample only derived sulfur abundances to stars with metallicity as low as [Fe/H]=-1.13dex. High-alpha metal rich stars are more enhanced in sulfur compared to their thin disk counterparts at the same metallicity. We compare our results to GCE models from other authors in the [S/Fe] vs. [Fe/H] plane. The [S/Fe]-age relationship is a good proxy for time, just like it is the case with other alpha-elements. We report no differences in the abundances of sulfur between stars with and without planetary companions in the metallicity range [Fe/H]>=-0.3dex.
2797. Chemistry in infrared dark clouds
ID:
ivo://CDS.VizieR/J/A+A/527/A88
Title:
Chemistry in infrared dark clouds
Short Name:
J/A+A/527/A88
Date:
21 Oct 2021
Publisher:
CDS
Description:
Massive stars play an important role in shaping the structure of galaxies. Infrared dark clouds (IRDCs), with their low temperatures and high densities, have been identified as the potential birthplaces of massive stars. In order to understand the formation processes of massive stars, the physical and chemical conditions in infrared dark clouds have to be characterized. The goal of this paper is to investigate the chemical composition of a sample of southern infrared dark clouds. One important aspect of the observations is to check, whether the molecular abundances in IRDCs are similar to the low-mass pre-stellar cores, or if they show signatures of more evolved evolutionary stages. We performed observations toward 15 IRDCs in the frequency range between 86 and 93GHz using the 22-m Mopra radio telescope. In total, 13 molecular species comprising N_2_H^+^, ^13^CS, CH_3_CN, HC_3_N, HNC, HCO^+^, HCN, HNCO, C_2_H, SiO, H^13^CO^+^, H^13^CN, and CH_3_C_2_H were observed for all targets. Hence, we included in general species appropriate for elevated densities, where some of them trace the more quiescent gas, while others are sensitive to more dynamical processes.
2798. Chemo-kinematic properties of Aquarius
ID:
ivo://CDS.VizieR/J/A+A/634/A10
Title:
Chemo-kinematic properties of Aquarius
Short Name:
J/A+A/634/A10
Date:
21 Oct 2021
Publisher:
CDS
Description:
Dwarf galaxies found in isolation in the Local Group (LG) are unlikely to have interacted with the large LG spirals, and therefore environmental effects such as tidal and ram-pressure stripping should not be the main drivers of their evolution. We aim to provide insight into the internal mechanisms shaping LG dwarf galaxies by increasing our knowledge of the internal properties of isolated systems. Here we focus on the evolved stellar component of the Aquarius dwarf galaxy, whose kinematic and metallicity properties have only recently started to be explored. Spectroscopic data in the region of the near-infrared Ca~II triplet lines has been obtained with FORS2 at the Very Large Telescope for 53 red giant branch (RGB) stars. These data are used to derive line-of-sight velocities and [Fe/H] of the individual RGB stars. We have derived a systemic velocity of -142.2^+1.8^_-1.8_km/s, in agreement with previous determinations from both the HI gas and stars. The internal kinematics of Aquarius appears to be best modelled by a combination of random motions (l.o.s. velocity dispersion of 10.3^+1.6^_-1.3_km/s) and linear rotation (with a gradient -5.0^+1.6^_-1.9_km/s/arcmin) along a P.A.=139_-27_^+17^deg, broadly consistent with the optical projected major axis. This rotation signal is significantly misaligned or even counter-rotating to that derived from the HI gas. We also find the tentative presence of a mild negative metallicity gradient and indications that the metal-rich stars have a colder velocity dispersion than the metal-poor ones. This work represents a significant improvement with respect to previous measurements of the RGB stars of Aquarius, as it doubles the number of member stars already studied in the literature. We speculate that the misaligned rotation between the HI gas and evolved stellar component might have been the result of recent accretion of HI gas, or re-accretion after gas-loss due to internal stellar feedback.
2799. Chemo-kinematics from MARVELS
ID:
ivo://CDS.VizieR/J/MNRAS/481/3244
Title:
Chemo-kinematics from MARVELS
Short Name:
J/MNRAS/481/3244
Date:
21 Oct 2021
Publisher:
CDS
Description:
Combining stellar atmospheric parameters, such as effective temperature, surface gravity, and metallicity, with barycentric radial velocity data provides insight into the chemo-dynamics of the Milky Way and our local Galactic environment. We analyse 3075 stars with spectroscopic data from the Sloan Digital Sky Survey III MARVELS radial velocity survey and present atmospheric parameters for 2343 dwarf stars using the spectral indices method, a modified version of the equivalent width method. We present barycentric radial velocities for a sample of 2610 stars with a median uncertainty of 0.3km/s. We determine stellar ages using two independent methods and calculate ages for 2335 stars with a maximum-likelihood isochronal age-dating method and for 2194 stars with a Bayesian age-dating method. Using previously published parallax data, we compute Galactic orbits and space velocities for 2504 stars to explore stellar populations based on kinematic and age parameters. This study combines good ages and exquisite velocities to explore local chemo-kinematics of the Milky Way, which complements many of the recent studies of giant stars with the APOGEE survey, and we find our results to be in agreement with current chemo-dynamical models of the Milky Way. Particularly, we find from our metallicity distributions and velocity-age relations of a kinematically defined thin disc that the metal-rich end has stars of all ages, even after we clean the sample of highly eccentric stars, suggesting that radial migration plays a key role in the metallicity scatter of the thin disc. All stellar parameters and kinematic data derived in this work are catalogued and published online in machine-readable form.
2800. Cheshire Cat galaxies: redshifts and magnitudes
ID:
ivo://CDS.VizieR/J/ApJ/806/268
Title:
Cheshire Cat galaxies: redshifts and magnitudes
Short Name:
J/ApJ/806/268
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Cheshire Cat is a relatively poor group of galaxies dominated by two luminous elliptical galaxies surrounded by at least four arcs from gravitationally lensed background galaxies that give the system a humorous appearance. Our combined optical/X-ray study of this system reveals that it is experiencing a line of sight merger between two groups with a roughly equal mass ratio with a relative velocity of ~1350 km/s. One group was most likely a low-mass fossil group, while the other group would have almost fit the classical definition of a fossil group. The collision manifests itself in a bimodal galaxy velocity distribution, an elevated central X-ray temperature and luminosity indicative of a shock, and gravitational arc centers that do not coincide with either large elliptical galaxy. One of the luminous elliptical galaxies has a double nucleus embedded off-center in the stellar halo. The luminous ellipticals should merge in less than a Gyr, after which observers will see a massive 1.2-1.5x10^14^ M_{sun}_ fossil group with an M_r_=-24.0 brightest group galaxy at its center. Thus, the Cheshire Cat offers us the first opportunity to study a fossil group progenitor. We discuss the limitations of the classical definition of a fossil group in terms of magnitude gaps between the member galaxies. We also suggest that if the merging of fossil (or near-fossil) groups is a common avenue for creating present-day fossil groups, the time lag between the final galactic merging of the system and the onset of cooling in the shock-heated core could account for the observed lack of well-developed cool cores in some fossil groups.

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