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161. Abundances of 156 bulge red giants
ID:
ivo://CDS.VizieR/J/AJ/148/67
Title:
Abundances of 156 bulge red giants
Short Name:
J/AJ/148/67
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present radial velocities and chemical abundances of O, Na, Mg, Al, Si, Ca, Cr, Fe, Co, Ni, and Cu for a sample of 156 red giant branch stars in two Galactic bulge fields centered near (l,b)=(+5.25,-3.02) and (0,-12). The (+5.25,-3.02) field also includes observations of the bulge globular cluster NGC 6553. The results are based on high-resolution (R~20000), high signal-to-noise ration (S/N>~70) FLAMES-GIRAFFE spectra obtained through the European Southern Observatory archive. However, we only selected a subset of the original observations that included spectra with both high S/N and that did not show strong TiO absorption bands. This work extends previous analyses of this data set beyond Fe and the {alpha}-elements Mg, Si, Ca, and Ti. While we find reasonable agreement with past work, the data presented here indicate that the bulge may exhibit a different chemical composition than the local thick disk, especially at [Fe/H]>~-0.5. In particular, the bulge [{alpha}/Fe] ratios may remain enhanced to a slightly higher [Fe/H] than the thick disk, and the Fe-peak elements Co, Ni, and Cu appear enhanced compared to the disk. There is also some evidence that the [Na/Fe] (but not [Al/Fe]) trends between the bulge and local disk may be different at low and high metallicity. We also find that the velocity dispersion decreases as a function of increasing [Fe/H] for both fields, and do not detect any significant cold, high-velocity populations. A comparison with chemical enrichment models indicates that a significant fraction of hypernovae may be required to explain the bulge abundance trends, and that initial mass functions that are steep, top-heavy (and do not include strong outflow), or truncated to avoid including contributions from stars >40M_{sun}_ are ruled out, in particular because of disagreement with the Fe-peak abundance data. For most elements, the NGC 6553 stars exhibit abundance trends nearly identical to comparable metallicity bulge field stars. However, the star-to-star scatter and mean [Na/Fe] ratios appear higher in the cluster, perhaps indicating additional self-enrichment.
162. Abundances of 650 bulge red giants
ID:
ivo://CDS.VizieR/J/A+A/530/A54
Title:
Abundances of 650 bulge red giants
Short Name:
J/A+A/530/A54
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the analysis of the [alpha/Fe] abundance ratios for a large number of stars at several locations in the Milky Way bulge with the aim of constraining its formation scenario. We obtained FLAMES-GIRAFFE spectra (R=22500) at the ESO Very Large Telescope for 650 bulge red giant branch (RGB) stars and performed spectral synthesis to measure Mg, Ca, Ti, and Si abundances. This sample is composed of 474 giant stars observed in 3 fields along the minor axis of the Galactic bulge and at latitudes b=-4{deg}, b=-6{deg}, b=-12{deg}. Another 176 stars belong to a field containing the globular cluster NGC 6553, located at b=-3{deg} and 5{deg} away from the other three fields along the major axis.
163. Abundances of carbon-enhanced metal-poor stars
ID:
ivo://CDS.VizieR/J/A+A/548/A34
Title:
Abundances of carbon-enhanced metal-poor stars
Short Name:
J/A+A/548/A34
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a detailed study of Carbon-Enhanced Metal-Poor (CEMP) stars, based on high-resolution spectroscopic observations of a sample of 18 stars. The stellar spectra for this sample were obtained at the 4.2m William Herschel Telescope (WHT) in 2001 and 2002, using the Utrecht Echelle Spectrograph (UES), at a resolving power R~52000 and S/N~40, covering the wavelength range {lambda}-{lambda}3700-5700{AA}. The atmospheric parameters determined for this sample indicate temperatures ranging from 4750K to 7100K, log g from 1.5 to 4.3, and metallicities -3.0<=[Fe/H]<=-1.7. Elemental abundances for C, Na, Mg, Sc, Ti, Cr, Cu, Zn, Sr, Y, Zr, Ba, La, Ce, Nd, Sm, Eu, Gd, Dy are determined. Abundances for an additional 109 stars were taken from the literature and combined with the data of our sample. The literature sample reveals a lack of reliable abundance estimates for species that might be associated with the r-process elements for about 67% of CEMP stars, preventing a complete understanding of this class of stars, since [Ba/Eu] ratios are used to classify them. Although eight stars in our observed sample are also found in the literature sample, Eu abundances or limits are determined for four of these stars for the first time. From the observed correlations between C, Ba, and Eu, we argue that the CEMP-r/s class has the same astronomical origin as CEMP-s stars, highlighting the need for a more complete understanding of Eu production.
164. Abundances of carbon stars in Galactic halo
ID:
ivo://CDS.VizieR/J/ApJ/658/367
Title:
Abundances of carbon stars in Galactic halo
Short Name:
J/ApJ/658/367
Date:
21 Oct 2021
Publisher:
CDS
Description:
It is known that the carbon-enhanced, extremely metal-poor (CEMP) stars constitute a substantial proportion of the extremely metal-poor (EMP) stars of the Galactic halo, and a by far larger proportion than CH stars among Population II stars. We investigate their origin by taking into account an additional evolutionary path to the surface carbon enrichment, triggered by hydrogen engulfment by the helium flash convection, in EMP stars with [Fe/H]<~-2.5. This process is distinct from the third dredge-up operating in more metal-rich stars and in EMP stars. In binary systems of EMP stars, the secondary stars become CEMP stars through mass transfer from the low- and intermediate- mass primary stars that have developed the surface carbon enhancement. Our binary scenario can predict the variations in the abundances not only for carbon but also for nitrogen and s-process elements and can reasonably explain the observed properties such as the stellar distributions of the carbon abundances, the binary periods, and the evolutionary stages.
165. Abundances of 3 CEMP stars
ID:
ivo://CDS.VizieR/J/A+A/579/A28
Title:
Abundances of 3 CEMP stars
Short Name:
J/A+A/579/A28
Date:
21 Oct 2021
Publisher:
CDS
Description:
In the course of the TOPoS (Turn Off Primordial Stars) survey, aimed at discovering the lowest metallicity stars, we have found several carbon-enhanced metal-poor (CEMP) stars. These stars are very common among the stars of extremely low metallicity and provide important clues to the star formation processes. We here present our analysis of six CEMP stars. We want to provide the most complete chemical inventory for these six stars in order to constrain the nucleosynthesis processes responsible for the abundance patterns.
166. Abundances of 54 Cepheids
ID:
ivo://CDS.VizieR/J/AJ/132/902
Title:
Abundances of 54 Cepheids
Short Name:
J/AJ/132/902
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper reports on the spectroscopic investigation of 54 Cepheids, deriving parameters and abundances. These Cepheids extend previous samples by about 35% in number and increase the amount of the Galactic disk coverage, especially in the direction of l~120{deg}. We find that there exists in the Galactic disk at that longitude and at a solar distance of about 3-4kpc a region that has enhanced abundances, <[Fe/H]>~+0.2, with respect to the local region. A simple linear fit to all Cepheid data now extant yields a gradient d[Fe/H]/dR=-0.068+/-0.003dex/kpc. After consideration of the spatial abundance inhomogeneities in the sample, we conclude that the best current estimate of the overall gradient is d[Fe/H]/dR=-0.06dex/kpc.
167. Abundances of 10 Cepheids
ID:
ivo://CDS.VizieR/J/AJ/128/343
Title:
Abundances of 10 Cepheids
Short Name:
J/AJ/128/343
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of a detailed multiphase spectroscopic analysis of 10 classical Cepheids with pulsation periods between 6 and 10 days. For each star, we have derived phased values of effective temperature, surface gravity, microturbulent velocity, and elemental abundances. We show that the elemental abundance results for intermediate-period Cepheids are consistent for all pulsational phases.
168. Abundances of classical Cepheids
ID:
ivo://CDS.VizieR/J/MNRAS/420/1590
Title:
Abundances of classical Cepheids
Short Name:
J/MNRAS/420/1590
Date:
21 Oct 2021
Publisher:
CDS
Description:
We propose a statistical method for decomposition of contributions to iron production from various sources: Type II supernovae and the subpopulations of Type Ia supernovae, prompt (their progenitors are short-lived stars with ages lower than >100Myr) and tardy (their progenitors are long-lived stars with ages >100Myr). To do that, we develop a theory of oxygen and iron synthesis that takes into account the influence of the spiral arms on the amount of the above elements synthesized by both Type II supernovae and prompt Type Ia supernovae. In the framework of the theory, we processed statistically the new, more precise, observational data on Cepheid abundances, which, as is well known, demonstrate non-trivial radial distributions of oxygen and iron in the Galactic disc with bends in the gradients.
169. Abundances of disk and bulge giants
ID:
ivo://CDS.VizieR/J/A+A/625/A141
Title:
Abundances of disk and bulge giants
Short Name:
J/A+A/625/A141
Date:
21 Oct 2021
Publisher:
CDS
Description:
The formation and evolution of the Galactic bulge and the Milky Way is still a debated subject. Observations of the X-shaped bulge, cylindrical stellar motions, and the presumed existence of a fraction of young stars in the bulge have suggested that it formed through secular evolution of the disk and not through gas dissipation and/or mergers, as thought previously. Our goal was to measure the abundances of six iron-peak elements (Sc, V, Cr, Mn, Co, and Ni) in the local thin and thick disks and in the bulge. These abundances can provide additional observational constraints for Galaxy formation and chemical evolution models, and help us to understand whether the bulge has emerged from the thick disk or not. We use high-resolution optical spectra of 291 K giants in the local disk mostly obtained by the FIES at NOT (signal-to-noise ratio (S/N) of 80-100) and 45K giants in the bulge obtained by the UVES/FLAMES at VLT (S/N of 10-80). The abundances are measured using Spectroscopy Made Easy (SME). Additionally, we apply non-local thermodynamic equilibrium (NLTE) corrections to the ratios [Mn/Fe] and [Co/Fe]. The thin and thick disks were separated according to their metallicity, [Ti/Fe], as well as proper motions and the radial velocities from Gaia DR2. The trend of [V/Fe] vs. [Fe/H] shows a separation between the disk components, being more enhanced in the thick disk. Similarly, the [Co/Fe] vs. [Fe/H] trend shows a hint of an enhancement in the local thick disk. The trends of V and Co in the bulge appear to be even more enhanced, although within the uncertainties. The decreasing value of [Sc/Fe] with increasing metallicity is observed in all the components, while our [Mn/Fe] value steadily increases with increasing metallicity in the local disk and the bulge instead. For Cr and Ni we find a flat trend following iron for the whole metallicity range in the disk and the bulge. The ratio of [Ni/Fe] appears slightly overabundant in the thick disk and the bulge compared to the thin disk, although the difference is minor. The somewhat enhanced ratios of [V/Fe] and [Co/Fe] observed in the bulge suggest that the local thick disk and the bulge might have experienced different chemical enrichment and evolutionary paths. However, we are unable to predict the exact evolutionary path of the bulge solely based on these observations. Galactic chemical evolution models could, on the other hand, allow us to predict them using these results.
170. Abundances of disk giants: O, Mg, Ca and Ti
ID:
ivo://CDS.VizieR/J/A+A/598/A100
Title:
Abundances of disk giants: O, Mg, Ca and Ti
Short Name:
J/A+A/598/A100
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Galactic bulge is an intriguing and significant part of our Galaxy, but it is hard to observe because it is both distant and covered by dust in the disk. Therefore, there are not many high-resolution optical spectra of bulge stars with large wavelength coverage, whose determined abundances can be compared with nearby, similarly analyzed stellar samples. We aim to determine the diagnostically important alpha elements of a sample of bulge giants using high-resolution optical spectra with large wavelength coverage. The abundances found are compared to similarly derived abundances from similar spectra of similar stars in the local thin and thick disks. In this first paper we focus on the solar neighborhood reference sample. We used spectral synthesis to derive the stellar parameters as well as the elemental abundances of both the local and bulge samples of giants. We took special care to benchmark our method of determining stellar parameters against independent measurements of effective temperatures from angular diameter measurements and surface gravities from asteroseismology. In this first paper we present the method used to determine the stellar parameters and elemental abundances, evaluate them, and present the results for our local disk sample of 291 giants. When comparing our determined spectroscopic temperatures to those derived from angular diameter measurements, we reproduce these with a systematic difference of +10K and a standard deviation of 53K. The spectroscopic gravities reproduce those determined from asteroseismology with a systematic offset of +0.10dex and a standard deviation of 0.12dex. When it comes to the abundance trends, our sample of local disk giants closely follows trends found in other works analyzing solar neighborhood dwarfs, showing that the much brighter giant stars are as good abundance probes as the often used dwarfs.

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