- ID:
- ivo://CDS.VizieR/J/A+A/285/247
- Title:
- Molecules in O- and C-rich envelopes
- Short Name:
- J/A+A/285/247
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observations of 10 microwave transitions of the molecules SiO, HCN, HNC, SiS, HC_3_N, CS, SO, and ^13^CO are presented in a total sample of 47 evolved stars. The studied sources are mainly O- and C-rich standard AGB stars, as well as O-rich red supergiants, S-type stars, protoplanetary nebulae and detached envelopes. We also take into account observations of these transitions, as well as of ^12^CO J=1-0, from the literature. The observations were carried out during May and September 1991 and June 1992 with the IRAM 30-m radiotelescope at Pico de Veleta (Spain); the resolution is 1MHz for 3mm data (100GHz) and 2 MHz for 2 and 1mm data (150 to 300GHz).
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- ID:
- ivo://CDS.VizieR/J/AJ/151/49
- Title:
- M6 open cluster: star members properties
- Short Name:
- J/AJ/151/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present here the first abundance analysis of 44 late B-, A-, and F-type members of the young open cluster M6 (NGC 6405, age about 75 Myr). Low- and medium-resolution spectra, covering the 4500-5840 {AA} wavelength range, were obtained using the FLAMES/GIRAFFE spectrograph attached to the ESO Very Large Telescopes. We determined the atmospheric parameters using calibrations of the Geneva photometry and by adjusting the H_{beta}_ profiles to synthetic ones. The abundances of up to 20 chemical elements, from helium to mercury, were derived for 19 late B, 16 A, and 9 F stars by iteratively adjusting synthetic spectra to the observations. We also derived a mean cluster metallicity of [Fe/H]=0.07+/-0.03 dex from the iron abundances of the F-type stars. We find that for most chemical elements, the normal late B- and A-type stars exhibit larger star-to-star abundance variations than the F-type stars probably because of the faster rotation of the B and A stars. The abundances of C, O, Mg, Si, and Sc appear to be anticorrelated with that of Fe, while the opposite holds for the abundances of Ca, Ti, Cr, Mn, Ni, Y, and Ba as expected if radiative diffusion is efficient in the envelopes of these stars. In the course of this analysis, we discovered five new peculiar stars: one mild Am, one Am, and one Fm star (HD 318091, CD-32 13109, GSC 07380-01211, CP1), one HgMn star (HD 318126, CP3), and one He-weak P-rich (HD 318101, CP4) star. We also discovered a new spectroscopic binary, most likely a SB2. We performed a detailed modeling of HD 318101, the new He-weak P-rich CP star, using the Montreal stellar evolution code XEVOL which self-consistently treats all particle transport processes. Although the overall abundance pattern of this star is properly reproduced, we find that detailed abundances (in particular the high P excess) resisted modeling attempts even when a range of turbulence profiles and mass-loss rates were considered. Solutions are proposed which are still under investigation.
- ID:
- ivo://CDS.VizieR/J/ApJ/762/26
- Title:
- Most metal-poor stars. II. 190 Galactic halo stars
- Short Name:
- J/ApJ/762/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a homogeneous chemical abundance analysis of 16 elements in 190 metal-poor Galactic halo stars (38 program and 152 literature objects). The sample includes 171 stars with [Fe/H]<=-2.5, of which 86 are extremely metal poor, [Fe/H]<=-3.0. Our program stars include 10 new objects with [Fe/H]<=-3.5. We identify a sample of "normal" metal-poor stars and measure the trends between [X/Fe] and [Fe/H], as well as the dispersion about the mean trend for this sample. Using this mean trend, we identify objects that are chemically peculiar relative to "normal" stars at the same metallicity. These chemically unusual stars include CEMP-no objects, one star with high [Si/Fe], another with high [Ba/Sr], and one with unusually low [X/Fe] for all elements heavier than Na. The Sr and Ba abundances indicate that there may be two nucleosynthetic processes at lowest metallicity that are distinct from the main r-process. Finally, for many elements, we find a significant trend between [X/Fe] versus T_eff_, which likely reflects non-LTE and/or three-dimensional effects. Such trends demonstrate that care must be exercised when using abundance measurements in metal-poor stars to constrain chemical evolution and/or nucleosynthesis predictions.
- ID:
- ivo://CDS.VizieR/J/ApJ/762/27
- Title:
- Most metal-poor stars. III. 86 [Fe/H]<=-3.0 stars
- Short Name:
- J/ApJ/762/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the metallicity distribution function (MDF) and fraction of carbon-enhanced metal-poor (CEMP) stars in a sample that includes 86 stars with [Fe/H]<=-3.0, based on high-resolution, high signal-to-noise spectroscopy, of which some 32 objects lie below [Fe/H]=-3.5. After accounting for the completeness function, the "corrected" MDF does not exhibit the sudden drop at [Fe/H]=-3.6 that was found in recent samples of dwarfs and giants from the Hamburg/ESO survey. Rather, the MDF decreases smoothly down to [Fe/H]=-4.1. Similar results are obtained from the "raw" MDF. We find that the fraction of CEMP objects below [Fe/H]=-3.0 is 23%+/-6% and 32%+/-8% when adopting the Beers & Christlieb (2005ARA&A..43..531B) and Aoki et al. (2007, J/ApJ/655/492) CEMP definitions, respectively. The former value is in fair agreement with some previous measurements, which adopt the Beers & Christlieb criterion.
- ID:
- ivo://CDS.VizieR/J/AJ/124/234
- Title:
- M31 outer halo UBVRI photometry and metallicity
- Short Name:
- J/AJ/124/234
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present first results from a spectroscopic survey designed to examine the metallicity and kinematics of individual red giant branch stars in the outer halo of the Andromeda spiral galaxy (M31). This study is based on multislit spectroscopy with the Keck II 10m telescope and Low Resolution Imaging Spectrograph of the Ca II near-infrared triplet in 99 M31 halo candidates in a field at R=19kpc on the southeast minor axis with brightnesses from 20<I<22.
- ID:
- ivo://CDS.VizieR/J/A+A/602/A112
- Title:
- M31 PHAT star clusters
- Short Name:
- J/A+A/602/A112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This study is the fifth of a series that investigates the degeneracy and stochasticity problems present in the determination of physical parameters such as age, mass, extinction, and metallicity of partially resolved or unresolved star cluster populations in external galaxies when using HST broad-band photometry. In this work we aim to derive parameters of star clusters using models with fixed and free metallicity based on the HST WFC3+ACS photometric system. The method is applied to derive parameters of a subsample of 1363 star clusters in the Andromeda galaxy observed with the HST. Following Paper III (de Meulenaer et al., 2015A&A...574A..66D), we derive the star cluster parameters using a large grid of stochastic models that are compared to the six observed integrated broad-band WFC3+ACS magnitudes of star clusters. We show that the age, mass, and extinction of the M31 star clusters, derived assuming fixed solar metallicity, are in agreement with previous studies. We also demonstrate the ability of the WFC3+ACS photometric system to derive metallicity of star clusters older than ~1 Gyr. We show that the metallicity derived using broad-band photometry of 36 massive M31 star clusters is in good agreement with the metallicity derived using spectroscopy.
- ID:
- ivo://CDS.VizieR/J/MNRAS/464/2730
- Title:
- M28 red giant branch stars abundances
- Short Name:
- J/MNRAS/464/2730
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the abundance analysis for a sample of 17 red giant branch stars in the metal-poor globular cluster M28 based on high-resolution spectra. This is the first extensive spectroscopic study of this cluster. We derive abundances of O, Na, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Ba, La, Ce, and Eu. We find a metallicity of [Fe/H]=-1.29+/-0.01 and an {alpha}-enhancement of +0.34+/-0.01 (errors on the mean), typical of halo globular clusters in this metallicity regime. A large spread is observed in the abundances of light elements O, Na, and Al. Mg also shows an anti-correlation with Al with a significance of 3{sigma}. The cluster shows a Na-O anti-correlation and a Na-Al correlation. This correlation is not linear but 'segmented' and that the stars are not distributed continuously, but form at least three well-separated sub-populations. In this aspect, M28 resembles NGC 2808 that was found to host at least five sub-populations. The presence of a Mg-Al anti-correlation favour massive AGB stars as the main polluters responsible for the multiple-population phenomenon.
- ID:
- ivo://CDS.VizieR/J/MNRAS/444/1812
- Title:
- M54 red giants abundances
- Short Name:
- J/MNRAS/444/1812
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The cosmological Li problem is the observed discrepancy between Li abundance (A(Li)) measured in Galactic dwarf, old and metal-poor stars (traditionally assumed to be equal to the initial value A(Li)_0_), and that predicted by standard big bang nucleosynthesis (BBN) calculations (A(Li)_BBN_). Here, we attack the Li problem by considering an alternative diagnostic, namely the surface Li abundance of red giant branch stars that in a colour-magnitude diagram populate the region between the completion of the first dredge-up and the red giant branch bump. We obtained high-resolution spectra with the FLAMES facility at the Very Large Telescope for a sample of red giants in the globular cluster M54, belonging to the Sagittarius dwarf galaxy. We obtain A(Li)=0.93+/-0.11dex, translating - after taking into account the dilution due to the dredge-up - to initial abundances (A(Li)_0_) in the range 2.35-2.29 dex, depending on whether or not atomic diffusion is considered. This is the first measurement of Li in the Sagittarius galaxy and the more distant estimate of A(Li)_0_ in old stars obtained so far. The A(Li)_0_ estimated in M54 is lower by ~0.35dex than A(Li)_BBN_, hence incompatible at a level of ~3{sigma}. Our result shows that this discrepancy is a universal problem concerning both the Milky Way and extragalactic systems. Either modifications of BBN calculations, or a combination of atomic diffusion plus a suitably tuned additional mixing during the main sequence, need to be invoked to solve the discrepancy.
- ID:
- ivo://CDS.VizieR/J/A+A/645/A115
- Title:
- 346 M31 star clusters and their parameters
- Short Name:
- J/A+A/645/A115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Determining the metallicities and ages of M31 clusters is fundamental to the study of the formation and evolution of M31 itself. The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) has carried out a systematic spectroscopic campaign of clusters and candidates in M31. We constructed a catalogue of 346 M31 clusters observed by LAMOST. By combining the information of the LAMOST spectra and the multi-band photometry, we developed a new algorithm to estimate the metallicities and ages of these clusters. We distinguish young clusters from old using random forest classifiers based on a empirical training data set selected from the literature. Ages of young clusters are derived from the spectral energy distribution fits of their multi-band photometric measurements. Their metallicities are estimated by fitting their observed spectral principal components extracted from the LAMOST spectra with those from the young metal-rich single stellar population (SSP) models. For old clusters we built non-parameter random forest models between the spectral principal components and/or multi-band colours and the parameters of the clusters based on a training data set constructed from the SSP models. The ages and metallicities of the old clusters are then estimated by fitting their observed spectral principal components extracted from the LAMOST spectra and multi-band colours from the photometric measurements with the resultant random forest models. We derived parameters of 53 young and 293 old clusters in our catalogue. Our resultant parameters are in good agreement with those from the literature. The ages of ~30 catalogued clusters and metallicities of ~40 sources are derived for the first time.
- ID:
- ivo://CDS.VizieR/J/MNRAS/465/3515
- Title:
- M13 stars radial velocities
- Short Name:
- J/MNRAS/465/3515
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use radial velocities from spectra of giants obtained with the WIYN telescope, coupled with existing chemical abundance measurements of Na and O for the same stars, to probe the presence of kinematic differences among the multiple populations of the globular cluster (GC) M13. To characterize the kinematics of various chemical subsamples, we introduce a method using Bayesian inference along with a Markov chain Monte Carlo algorithm to fit a six-parameter kinematic model (including rotation) to these subsamples. We find that the so-called extreme population (Na-enhanced and extremely O-depleted) exhibits faster rotation around the centre of the cluster than the other cluster stars, in particular, when compared with the dominant `intermediate' population (moderately Na-enhanced and O-depleted). The most likely difference between the rotational amplitude of this extreme population and that of the intermediate population is found to be 4km/s , with a 98.4 per cent probability that the rotational amplitude of the extreme population is larger than that of the intermediate population. We argue that the observed difference in rotational amplitudes, obtained when splitting subsamples according to their chemistry, is not a product of the long-term dynamical evolution of the cluster, but more likely a surviving feature imprinted early in the formation history of this GC and its multiple populations. We also find an agreement (within uncertainties) in the inferred position angle of the rotation axis of the different subpopulations considered. We discuss the constraints that these results may place on various formation scenarios.
