- ID:
- ivo://CDS.VizieR/J/ApJ/704/385
- Title:
- M31 integrated light abundances
- Short Name:
- J/ApJ/704/385
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the first detailed chemical abundances for five globular clusters (GCs) in M31 from high-resolution (R~25000) spectroscopy of their integrated light (IL). These GCs are the first in a larger set of clusters observed as part of an ongoing project to study the formation history of M31 and its GC population. The data presented here were obtained with the HIRES echelle spectrograph on the Keck I telescope and are analyzed using a new IL spectra analysis method that we have developed. In these clusters, we measure abundances for Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Y, and Ba, ages >=10Gyr, and a range in [Fe/H] of -0.9 to -2.2. As is typical of Milky Way GCs, we find these M31 GCs to be enhanced in the {alpha}-elements Ca, Si, and Ti relative to Fe.
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- ID:
- ivo://CDS.VizieR/J/ApJ/858/28
- Title:
- Mixing-length parameter for a sample of KIC stars
- Short Name:
- J/ApJ/858/28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stellar models typically use the mixing-length approximation as a way to implement convection in a simplified manner. While conventionally the value of the mixing-length parameter, {alpha}, used is the solar-calibrated value, many studies have shown that other values of {alpha} are needed to properly model stars. This uncertainty in the value of the mixing-length parameter is a major source of error in stellar models and isochrones. Using asteroseismic data, we determine the value of the mixing-length parameter required to properly model a set of about 450 stars ranging in logg, Teff, and [Fe/H]. The relationship between the value of {alpha} required and the properties of the star is then investigated. For Eddington atmosphere, non-diffusion models, we find that the value of {alpha} can be approximated by a linear model, in the form of {alpha}/{alpha}_{sun}_=5.426-0.101, log(g)-1.071, log(Teff)+0.437([Fe/H]). This process is repeated using a variety of model physics, as well as compared with previous studies and results from 3D convective simulations.
- ID:
- ivo://CDS.VizieR/J/AJ/131/2949
- Title:
- Mn abundances in cluster and field stars
- Short Name:
- J/AJ/131/2949
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have derived Mn abundances for more than 200 stars in 19 globular clusters. In addition, Mn abundance determinations have been made for a comparable number of halo field and disk stars possessing an overlapping range of metallicities and stellar parameters. Our primary data set was comprised of high-resolution spectra previously acquired at the McDonald, Lick, and Keck Observatories. To enlarge our data pool, we acquired globular and open cluster spectra from several other investigators. Data were analyzed using synthetic spectra of the 6000{AA} Mn I triplet. Hyperfine structure parameters were included in the synthetic spectra computations.
- ID:
- ivo://CDS.VizieR/J/MNRAS/454/1585
- Title:
- Mn abundances of Galactic disc stars
- Short Name:
- J/MNRAS/454/1585
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we present and discuss the observations of the Mn abundances for 247 FGK dwarfs, located in the Galactic disc with metallicity -1<[Fe/H]<+0.3. The observed stars belong to the substructures of the Galaxy thick and thin disks, and to the Hercules stream. The observations were conducted using the 1.93m telescope at Observatoire de Haute-Provence (OHP, France) equipped with the echelle-type spectrographs ELODIE and SOPHIE. The abundances were derived under the LTE approximation, with an average error for the [Mn/Fe] ratio of 0.10dex. For most of the stars in the sample, Mn abundances are not available in the literature. We obtain an evolution of [Mn/Fe] ratio with the metallicity [Fe/H] consistent with previous data compilations. In particular, within the metallicity range covered by our stellar sample, the [Mn/Fe] ratio is increasing with the increase of metallicity. This due to the contribution to the Galactic chemical evolution of Mn and Fe from thermonuclear supernovae. We confirm the baseline scenario where most of the Mn in the Galactic disc and in the Sun is made by thermonuclear supernovae. In particular, the effective contribution from core-collapse supernovae to the Mn in the Solar system is about 10-20 per cent. However, present uncertainties affecting the production of Mn and Fe in thermonuclear supernovae are limiting the constraining power of the observed [Mn/Fe] trend in the Galactic discs on, e.g. the frequency of different thermonuclear supernovae populations. The different production of these two elements in different types of thermonuclear supernovae needs to be disentangled by the dependence of their relative production on the metallicity of the supernova progenitor.
- ID:
- ivo://CDS.VizieR/J/ApJ/813/97
- Title:
- M62 (NGC 6266) giant branch stars abundances
- Short Name:
- J/ApJ/813/97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have collected UVES-FLAMES high-resolution spectra for a sample of 6 asymptotic giant branch (AGB) and 13 red giant branch (RGB) stars in the Galactic globular cluster (GC) M62 (NGC 6266). Here we present the detailed abundance analysis of iron, titanium, and light elements (O, Na, Mg, and Al). For the majority (five out of six) of the AGB targets, we find that the abundances of both iron and titanium determined from neutral lines are significantly underestimated with respect to those obtained from ionized features, the latter being, instead, in agreement with those measured for the RGB targets. This is similar to recent findings in other clusters and may suggest the presence of nonlocal thermodynamic equilibrium (NLTE) effects. In the O-Na, Al-Mg, and Na-Al planes, the RGB stars show the typical correlations observed for GC stars. Instead, all the AGB targets are clumped in the regions where first-generation stars are expected to lie, similar to what was recently found for the AGB population of NGC6752. While the sodium and aluminum abundances could be underestimated as a consequence of the NLTE bias affecting iron and titanium, the oxygen line used does not suffer from the same effects, and the lack of O-poor AGB stars therefore is a solid result. We can thus conclude that none of the investigated AGB stars belongs to the second stellar generation of M62. We also find an RGB star with extremely high sodium abundance ([Na/Fe]=+1.08dex).
- ID:
- ivo://CDS.VizieR/J/ApJS/207/7
- Title:
- Modeling Galactic extinction with dust and PAH
- Short Name:
- J/ApJS/207/7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the remarkable apparent variety of galactic extinction curves by modeling extinction profiles with core-mantle grains and a collection of single polycyclic aromatic hydrocarbons. Our aim is to translate a synthetic description of dust into physically well-grounded building blocks through the analysis of a statistically relevant sample of different extinction curves. All different flavors of observed extinction curves, ranging from the average galactic extinction curve to virtually "bumpless" profiles, can be described by the present model. We prove that a mixture of a relatively small number (54 species in 4 charge states each) of polycyclic aromatic hydrocarbons can reproduce the features of the extinction curve in the ultraviolet, dismissing an old objection to the contribution of polycyclic aromatic hydrocarbons to the interstellar extinction curve. Despite the large number of free parameters (at most the 54x4 column densities of each species in each ionization state included in the molecular ensemble plus the 9 parameters defining the physical properties of classical particles), we can strongly constrain some physically relevant properties such as the total number of C atoms in all species and the mean charge of the mixture. Such properties are found to be largely independent of the adopted dust model whose variation provides effects that are orthogonal to those brought about by the molecular component. Finally, the fitting procedure, together with some physical sense, suggests (but does not require) the presence of an additional component of chemically different very small carbonaceous grains.
- ID:
- ivo://CDS.VizieR/J/ApJ/857/46
- Title:
- Modelled vs observed abundances of EMP stars
- Short Name:
- J/ApJ/857/46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compare the elemental abundance patterns of ~200 extremely metal-poor (EMP; [Fe/H]{<}-3) stars to the supernova yields of metal-free stars, in order to obtain insights into the characteristic masses of the first (Population III or Pop III) stars in the universe. The supernova yields are prepared with nucleosynthesis calculations of metal-free stars with various initial masses (M=13, 15, 25, 40 and 100M_{sun}_) and explosion energies (E_51_=E/10^51^[erg]=0.5-60), to include low-energy, normal-energy, and high-energy explosions. We adopt the mixing-fallback model, to take into account possible asymmetry in the supernova explosions, and the yields that best fit the observed abundance patterns of the EMP stars are searched by varying the model parameters. We find that the abundance patterns of the EMP stars are predominantly best- fitted by the supernova yields with initial masses M<40M_{sun}_, and that more than than half of the stars are best-fitted by the M=25M_{sun}_ hypernova (E_51_=10) models. The results also indicate that the majority of the primordial supernovae have ejected 10^-2^-10^-1^M_{sun}_ of ^56^Ni, leaving behind a compact remnant (either a neutron star or a black hole), with a mass in the range of ~1.5-5M_{sun}_. These results suggest that the masses of the first stars responsible for the first metal enrichment are predominantly <40M_{sun}_. This implies that the higher-mass first stars were either less abundant, directly collapsed into a black hole without ejecting heavy elements, or a supernova explosion of a higher-mass first star inhibits the formation of the next generation of low-mass stars at [Fe/H]{<}-3.
- ID:
- ivo://CDS.VizieR/J/A+A/358/257
- Title:
- Molecular clouds SO and CS obs. II.
- Short Name:
- J/A+A/358/257
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We here analyse the observational SO and CS data presented in Nilsson et al. (2000A&AS..144..441N). The SO/CS integrated intensity ratio maps are presented for 19 molecular clouds, together with tables of relevant ratios at strategic positions, where w e have also observed ^34^SO and/or C^34^S.
- ID:
- ivo://CDS.VizieR/J/A+A/646/A97
- Title:
- Molecular emission from the Perseus cloud
- Short Name:
- J/A+A/646/A97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The traditional technique to characterize the structure of molecular clouds is mapping their line emission. We aim to test and apply a sampling technique that can characterize the line emission from a molecular cloud more efficiently than mapping. We have sampled the molecular emission from the Perseus cloud using the H_2_ column density as a proxy. We have divided the cloud into 10 logarithmically- spaced column density bins, and we have selected 10 random positions from each bin. The resulting 100 cloud positions have been observed with the IRAM 30m telescope covering the 3mm-wavelength band and parts of the 2mm and 1mm bands. We focus our analysis on the eleven molecular species (plus isotopologs) detected toward most column density bins. In all cases, the line intensity is tightly correlated with the H_2_ column density. For the CO isotopologs, the correlation is relatively flat, while for most dense gas tracers, the correlation is approximately linear. To reproduce these trends, we have developed a cloud model in which most species have abundance profiles characterized by an outer photo-dissociation edge and an inner freeze-out drop. With this model we determine that the intensity behavior of the dense gas tracers arises from a combination of excitation effects and molecular freeze out, with some modulation from optical depth. The quasi-linear dependence of the dense-gas tracer emission with H_2_ column density makes the gas at low column densities dominate the cloud- integrated emission. It also makes this emission proportional to the cloud mass inside the photodissociation edge. Stratified random sampling is an efficient technique to characterize the emission from molecular clouds. Despite its complex appearance, the molecular emission from Perseus presents a relatively simple behavior that, from a limited comparison with other clouds, seems to reflect a general pattern.
- ID:
- ivo://CDS.VizieR/J/ApJ/780/85
- Title:
- Molecular line study of infrared dark clouds
- Short Name:
- J/ApJ/780/85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is currently assumed that infrared dark clouds (IRDCs) represent the earliest evolutionary stages of high-mass stars (>8M_{sun}_). Submillimeter and millimeter-wave studies performed over the past 15yr show that IRDCs possess a broad variety of properties, and hence a wide range of problems and questions that can be tackled. In this paper, we report an investigation of the molecular composition and chemical processes in two groups of IRDCs. Using the Mopra, APEX, and IRAM radio telescopes over the last four years, we have collected molecular line data for CO, H_2_CO, HNCO, CH_3_CCH, CH_3_OH, CH_3_CHO, CH_3_OCHO, and CH_3_OCH_3_. For all of these species we estimated molecular abundances. We then undertook chemical modeling studies, concentrating on the source IRDC028.34+0.06, and compared observed and modeled abundances. This comparison showed that to reproduce observed abundances of complex organic molecules, a zero-dimensional gas-grain model with constant physical conditions is not sufficient. We achieved greater success with the use of a warm-up model, in which warm-up from 10K to 30K occurs following a cold phase.
