- ID:
- ivo://CDS.VizieR/J/MNRAS/448/42
- Title:
- Equivalent widths and atomic data for GCs
- Short Name:
- J/MNRAS/448/42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Detailed chemical abundances for five stars in two Galactic globular clusters, NGC 5466 and NGC 5024, are presented from high-resolution optical (from the Hobby-Eberley Telescope) and infrared spectra (from the SDSS-III APOGEE survey). We find [Fe/H]=-1.97+/-0.13 dex for NGC 5466, and [Fe/H]=-2.06+/-0.13 dex for NGC 5024, and the typical abundance pattern for globular clusters for the remaining elements, e.g. both show evidence for mixing in their light element abundance ratios (C, N), and asymptotic giant branch contributions in their heavy element abundances (Y, Ba, and Eu). These clusters were selected to examine chemical trends that may correlate them with the Sgr dwarf galaxy remnant, but at these low metallicities no obvious differences from the Galactic abundance pattern are found. Regardless, we compare our results from the optical and infrared analyses to find that oxygen and silicon abundances determined from the infrared spectral lines are in better agreement with the other {alpha}-element ratios and with smaller random errors.
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- ID:
- ivo://CDS.VizieR/J/A+A/404/187
- Title:
- Equivalent widths for metal-poor stars
- Short Name:
- J/A+A/404/187
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present element-to-element abundance ratios measured from high dispersion spectra for 150 field subdwarfs and early subgiants with accurate Hipparcos parallaxes (errors<20%). For 50 stars new spectra were obtained using the UVES on Kueyen (VLT UT2), the McDonald 2.7m telescope, and SARG at TNG. Additionally, literature equivalent widths were taken from the works by Nissen & Schuster (1997, Cat. <J/A+A/326/751>), Fullbright (2000AJ....120.1841F), and Prochaska et al. (2000AJ....120.2513P) to complement our data. The whole sample includes both thick disk and halo stars (and a few thin disk stars); most stars have metallicities in the range -2<[Fe/H]<-0.6. We found our data, that of Nissen & Schuster, and that of Prochaska to be of comparable quality; results from Fulbright scatter a bit more, but they are still of very good quality and are extremely useful due to the large size of his sample. The results of the present analysis will be used in forthcoming papers to discuss the chemical properties of the dissipational collapse and accretion components of our Galaxy.
- ID:
- ivo://CDS.VizieR/J/ApJ/740/60
- Title:
- Equivalent widths for NGC2419 and NGC7099 RGB stars
- Short Name:
- J/ApJ/740/60
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 2419 is a massive outer halo Galactic globular cluster (GC) whose stars have previously been shown to have somewhat peculiar abundance patterns. We have observed seven luminous giants that are members of NGC 2419 with Keck/HIRES at reasonable signal-to-noise ratio. One of these giants is very peculiar, with an extremely low [Mg/Fe] and high [K/Fe] but normal abundances of most other elements. The abundance pattern does not match the nucleosynthetic yields of any supernova model. The other six stars show abundance ratios typical of inner halo Galactic GCs, represented here by a sample of giants in the nearby GC M30. Although our measurements show that NGC 2419 is unusual in some respects, its bulk properties do not provide compelling evidence for a difference between inner and outer halo GCs.
- ID:
- ivo://CDS.VizieR/J/ApJ/760/86
- Title:
- Equivalent widths for 13 NGC2419 RGB stars
- Short Name:
- J/ApJ/760/86
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new Keck/HIRES observations of six red giants in the globular cluster (GC) NGC 2419. Although the cluster is among the most distant and most luminous in the Milky Way, it was considered chemically ordinary until very recently. Our previous work showed that the near-infrared Ca II triplet line strength varied more than expected for a chemically homogeneous cluster, and that at least one star had unusual abundances of Mg and K. Here, we confirm that NGC 2419 harbors a population of stars, comprising about one-third of its mass, that is depleted in Mg by a factor of eight and enhanced in K by a factor of six with respect to the Mg-normal population. Although the majority, Mg-normal population appears to have a chemical abundance pattern indistinguishable from ordinary, inner-halo GCs, the Mg-poor population exhibits dispersions of several elements. The abundances of K and Sc are strongly anti-correlated with Mg, and some other elements (Si and Ca among others) are weakly anti-correlated with Mg. These abundance patterns suggest that the different populations of NGC 2419 sample the ejecta of diverse supernovae in addition to asymptotic giant branch ejecta. However, the abundances of Fe-peak elements except Sc show no star-to-star variation. We find no nucleosynthetic source that satisfactorily explains all of the abundance variations in this cluster. Because NGC 2419 appears like no other GC, we reiterate our previous suggestion that it is not a GC at all, but rather the core of an accreted dwarf galaxy.
- ID:
- ivo://CDS.VizieR/J/A+A/412/495
- Title:
- Equivalent widths for 6 RS CVn systems
- Short Name:
- J/A+A/412/495
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photospheric parameters and abundances are presented for a sample of single-lined chromospherically active binaries from a differential LTE analysis of high-resolution spectra. Abundances have been derived for 13 chemical species, including several key elements such as Li, Mg, and Ca.
- ID:
- ivo://CDS.VizieR/J/AJ/157/167
- Title:
- Equivalent widths for RSGs in the MW & LMC/SMC
- Short Name:
- J/AJ/157/167
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Red supergiants (RSGs) are evolved massive stars that represent extremes, in both their physical sizes and their cool temperatures, of the massive star population. The effective temperature (T_eff_) is the most critical physical property needed to place an RSG on the Hertzsprung-Russell Diagram, due to the stars' cool temperatures and resulting large bolometric corrections. Several recent papers have examined the potential utility of atomic line equivalent widths (EWs) in cool supergiant (CSG) spectra for determining T_eff_ and other physical properties and found strong correlations between Ti I and Fe I spectral features and T_eff_ in earlier-type CSGs (G and early K) but poor correlations in M-type stars, a spectral subtype that makes up a significant fraction of RSGs. We have extended this work by measuring the EWs of Ti, Fe, and Ca lines in late K- and M-type RSGs in the Milky Way, Large Magellanic Cloud, and Small Magellanic Cloud, and compared these results to the predictions of the theoretical stellar LTE atmosphere models (MARCS) stellar atmosphere models. Our analyses show a poor correlation between T_eff_ and the Fe I and Ti I lines in our observations (at odds with strong correlations predicted by stellar atmosphere models), but do find statistically significant correlations between T_eff_ and the Ca II triplet (CaT) features of Milky Way RSGs, suggesting that this could be a potential diagnostic tool for determining T_eff_ in M-type supergiants. We also examine correlations between these spectral features and other physical properties of RSGs (including metallicity, surface gravity, and bolometric magnitude), and consider the underlying physics driving the evolution of atomic line spectra in RSGs.
- ID:
- ivo://CDS.VizieR/J/A+A/627/A117
- Title:
- Equivalent widths for six M67 stars
- Short Name:
- J/A+A/627/A117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The benchmark open cluster M67 is known to have solar metallicity and similar age as the Sun. It thus provides us a great opportunity to study the properties of solar twins, as well as the evolution of Sun-like stars. Previous spectroscopic studies claimed to detect possible subtle changes in stellar surface abundances throughout the stellar evolutionary phase, namely the effect of atomic diffusion, in M67. In this study we attempt to confirm and quantify the effect of atomic diffusion, as well as to explore the level of chemical (in)homogeneity in M67. We presented a strictly line-by-line differential chemical abundance analysis of two groups of stars in M67: three turn-off stars and three sub-giants. Stellar atmospheric parameters and elemental abundances were obtained with very high precision using the Keck/HIRES spectra. The sub-giants in our sample show negligible abundance variations (<=0.02dex), which implies that M67 was born chemically homogeneous. We note there is a significant abundance difference (~0.1-0.2dex) between sub-giants and turn-off stars, which can be interpreted as the signature of atomic diffusion. Qualitatively stellar models with diffusion agree with the observed abundance results. Some turn-off stars do not follow the general pattern, which suggests that in some cases diffusion can be inhibited. Our results thus pose a challenge for chemical tagging using the turn-off stars since they are likely not chemically homogeneous. Meanwhile, our results suggest that the effect of atomic diffusion could be as large as 0.1-0.2dex, and must be taken into account when using the current surface abundances of stars for chemical tagging.
- ID:
- ivo://CDS.VizieR/J/A+A/588/A120
- Title:
- Equivalent widths in 10 open clusters
- Short Name:
- J/A+A/588/A120
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Open clusters are distributed all across the disk and are convenient tracers of its properties. In particular, outer disk clusters bear a key role for the investigation of the chemical evolution of the Galactic disk. The goal of this study is to derive homogeneous elemental abundances for a sample of ten outer disk OCs, and investigate possible links with disk structures such as the Galactic Anticenter Stellar Structure. We analyse high-resolution spectra of red giants, obtained from the HIRES@Keck and UVES@VLT archives. We derive elemental abundances and stellar atmosphere parameters by means of the classical equivalent width method. We also performed orbit integrations using proper motions. The Fe abundances we derive trace a shallow negative radial metallicity gradient of slope -0.027+/-0.007dex/kpc in the outer 12kpc of the disk. The [alpha/Fe] gradient appears flat, with a slope of 0.006+/-0.007dex/kpc. The two outermost clusters (Be 29 and Sau 1) appear to follow elliptical orbits. Be 20 also exhibits a peculiar orbit with a large excursion above the plane. The irregular orbits of the three most metal-poor clusters (two of which are located at the edge of the Galactic disk), if confirmed by more robust astrometric measurements such as those of the Gaia mission, are compatible with an inside-out formation scenario for the Milky Way, in which extragalactic material is accreted onto the outer disk. We cannot determine if Be 20, Be 29, and Sau 1 are of extragalactic origin, as they may be old genuine Galactic clusters whose orbits were perturbed by accretion events or minor mergers in the past 5Gyr, or they may be representants of the thick disk population. The nature of these objects is intriguing and deserves further investigations in the near future.
- ID:
- ivo://CDS.VizieR/J/AZh/81/658
- Title:
- Equivalent widths of 9 barium stars
- Short Name:
- J/AZh/81/658
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present our analysis of elemental abundances in the atmospheres of 16 classical barium stars derived from high-resolution spectra and model atmospheres. Comparison of the results with analogous data for moderate barium stars and normal red giants shows that the abundance patterns for elements before the iron peak are the same for all three groups of red giants, testifying to a similar origin. For binary systems, we confirm the influence of the orbital period and, hence, the component separation, on the overabundance of s-process elements. The amount of enrichment in s-process elements is also in influenced by mass, metallicity, and evolutionary phase. Any of these parameters can be important in individual objects.
- ID:
- ivo://CDS.VizieR/J/A+A/377/123
- Title:
- Equivalent widths of 6 binaries
- Short Name:
- J/A+A/377/123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We performed a careful differential abundance analysis of individual components of six main sequence binaries with separations of a few hundreds of AU. To reduce analysis concerns, we selected systems with almost equal mass components. We were able to derive differential abundances of several elements with errors down to 0.01dex in the best cases. We found that in four systems the two components have the same chemical composition, within these very severe limits. However, clear differences were found for the two remaining systems (HD 219542 and HD 200466), in both cases the primaries being more Fe-rich than the secondaries, by 0.091+/-0.009 and 0.053+/-0.024dex respectively. Similar differences were found for most of the elements considered in our analysis; however, we found no appreciable difference for volatile elements and a trend for increasing abundance differences with increasing condensation temperature for individual elements, a result similar to that found for some single stars with planets by Smith et al. (2001AJ....121.3207S). Finally, we note that HD 219542A has a Li-abundance comparable to those of Li-rich stars in old open clusters, while no Li is detected in the slightly cooler HD 219542B. We suggest that the primaries of these two systems have accreted rocky planets or the inner dust-rich part of a protoplanetary disk, likely due to gravitational perturbation caused by the presence of the companion.