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301. Abundances of non-variable red and blue HB stars
ID:
ivo://CDS.VizieR/J/AJ/140/1694
Title:
Abundances of non-variable red and blue HB stars
Short Name:
J/AJ/140/1694
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a new detailed abundance study of field red horizontal branch (RHB) and blue horizontal branch (BHB) non-variable stars. High resolution and high signal-to-noise ratio echelle spectra of 11 RHB and 12 BHB were obtained with the McDonald 2.7m telescope, and the RHB sample was augmented by reanalysis of spectra of 25 stars from a recent survey. We derived stellar atmospheric parameters based on spectroscopic constraints and computed relative abundance ratios for 24 species of 19 elements.
302. Abundances of ONC X-ray PMS stars
ID:
ivo://CDS.VizieR/J/ApJ/660/1462
Title:
Abundances of ONC X-ray PMS stars
Short Name:
J/ApJ/660/1462
Date:
21 Oct 2021
Publisher:
CDS
Description:
Following the Chandra Orion Ultradeep Project (COUP) observation, we have studied the chemical composition of the hot plasma in a sample of 146 X-ray-bright pre-main-sequence stars in the Orion Nebula Cluster (ONC). We report measurements of individual element abundances for a subsample of 86 slightly absorbed and bright X-ray sources, using low-resolution X-ray spectra obtained from the Chandra ACIS instrument.
303. Abundances of open cluster stars
ID:
ivo://CDS.VizieR/J/MNRAS/428/2321
Title:
Abundances of open cluster stars
Short Name:
J/MNRAS/428/2321
Date:
21 Oct 2021
Publisher:
CDS
Description:
The first generation of large-scale chemical tagging surveys, in particular the High Efficiency and Resolution Multi-Element Spectrograph (HERMES)/Galactic Archaeology with HERMES million star survey, promises to vastly expand our understanding of the chemical and dynamical evolution of the Galaxy. This, however, is contingent on our ability to confidently perform chemical tagging on such a large data set. Chemical homogeneity has been observed across a range of elements within several Galactic open clusters, yet the level to which this is the case globally, and particularly in comparison to the scatter across clusters themselves, is not well understood. The patterns of elements in coeval cluster members, occupying a complex chemical abundance space, are rooted in the evolution, ultimately the nature of the very late stages, of early generations of stars. The current astrophysical models of such stages are not yet sufficient to explain all observations, combining with our significant gaps in the understanding of star formation, makes this a difficult arena to tackle theoretically. Here, we describe a robust pair-wise metric used to gauge the chemical difference between two stellar components. This metric is then applied to a data base of high-resolution literature abundance sources to derive a function describing the probability that two stars are of common evolutionary origin. With this cluster probability function, it will be possible to report a confidence, grounded in empirical observational evidence, with which clusters are detected, independent of the group finding methods. This formulation is also used to probe the role of chemical dimensionality, and that of individual chemical species, on the ability of chemical tagging to differentiate coeval groups of stars.
304. Abundances of {phi} Her
ID:
ivo://CDS.VizieR/J/ApJ/655/1046
Title:
Abundances of {phi} Her
Short Name:
J/ApJ/655/1046
Date:
21 Oct 2021
Publisher:
CDS
Description:
Observations of the mercury-manganese star phi Her with the Navy Prototype Optical Interferometer (NPOI) conclusively reveal the previously unseen companion in this single-lined binary system. The NPOI data were used to predict a spectral type of A8 V for the secondary star phi Her B. This prediction was subsequently confirmed by spectroscopic observations obtained at the Dominion Astrophysical Observatory. phi Her B is rotating at 50+/-3km/s, in contrast to the 8 km/s lines of phi Her A. Recognizing the lines from the secondary permits one to separate them from those of the primary. The abundance analysis of phi Her A shows an abundance pattern similar to those of other HgMn stars, with Al being very under-abundant and Sc, Cr, Mn, Zn, Ga, Sr, Y, Zr, Ba, Ce, and Hg being very overabundant.
305. Abundances of 42 Pisces-Eridanus stream stars
ID:
ivo://CDS.VizieR/J/MNRAS/496/2422
Title:
Abundances of 42 Pisces-Eridanus stream stars
Short Name:
J/MNRAS/496/2422
Date:
21 Oct 2021
Publisher:
CDS
Description:
Recently, a new cylindrical-shaped stream of stars, up to 700pc long, was discovered hiding in the Galactic disk using kinematic data enabled by the Gaia mission. This curious stream of stars, dubbed the Pisces-Eridanus stream, was initially thought to be as old as 1Gyr, yet its stars shared a rotation period distribution consistent with the 120-Myr-old Pleiades cluster. In this work, we explore the detailed chemical nature of this stellar stream. We carried out high-resolution spectroscopic follow-up of 42 Pisces-Eridanus stream stars using McDonald Observatory, and combined these data with information for 40 members observed with the low-resolution LAMOST spectroscopic survey. Together, these data enabled us to measure the abundance distribution of light/odd-Z (Li, C, Na, Al, Sc, V), {alpha} (Mg, Si, Ca, Ti), Fe-peak (Cr, Mn, Fe, Co, Ni, Zn), and neutron capture (Sr, Y, Zr, Ba, La, Nd, Eu) elements across the Pisces-Eridanus stream. We find that the stream is (1) near solar metallicity with [Fe/H] = -0.03 dex and (2) has a metallicity spread of 0.07 dex (or 0.04 dex when removing outliers). We also find that (3) the abundance of Li indicates that Pisces-Eridanus is ~120Myr old, consistent with the gyrochronology result. We find that (4) the stream has a [X/Fe] abundance spreads of 0.06<{sigma}_[X/Fe]_<0.20dex in most elements, and (5) no significant abundance gradients across its major axis except a potentially weak gradient in [Si/Fe]. These results together show that the Pisces-Eridanus stream is a uniquely close, young, chemically interesting laboratory for testing our understanding of star and planet formation.
306. Abundances of PNe in NGC 300
ID:
ivo://CDS.VizieR/J/A+A/552/A12
Title:
Abundances of PNe in NGC 300
Short Name:
J/A+A/552/A12
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have obtained deep spectroscopy of 26 planetary nebulae (PNe) and 9 compact HII regions in the nearby spiral galaxy NGC 300, and analyzed them together with the giant HII regions observed by Bresolin et al. (2009ApJ...700..309B). We have determined the physical properties of all those objects and their content in He, N, O, Ne, S and Ar in a consistent way. We find that compact HII regions have abundances similar to those of giant HII regions, while PNe have systematically larger N/O ratios and similar Ne/O and Ar/O ratios. We demonstrate that this nitrogen enhancement in PNe cannot be due to second dredge-up in the progenitor stars, since their initial masses are around 2-2.5M_{sun}_. An extra mixing process is required, perhaps be driven by rotation. Concerning the radial abundance distribution, PNe behave differently from HII regions: In the central parts, they show an average O/H smaller by 0.15dex. Their abundance dispersion at any galactocentric radius is significantly larger than for HII regions and many of them have O/H values higher than HII regions at the same galactocentric distance, suggesting that oxygen production in the PN progenitors in NGC 300 is common. PN abundance gradients in O/H, Ne/H and Ar/He are significantly shallower than those of HII regions. We argue that this indicates a steepening of the metallicity gradient in NGC 300 during the last Gr, rather than the effect of radial stellar motions.
307. Abundances of PN towards Galactic bulge
ID:
ivo://CDS.VizieR/J/A+A/380/300
Title:
Abundances of PN towards Galactic bulge
Short Name:
J/A+A/380/300
Date:
21 Oct 2021
Publisher:
CDS
Description:
In this work we report spectrophotometric observations of a planetary nebula sample towards the galactic bulge. A total of 45 PNe was observed and their physical parameters (electron density and temperature) were derived. Ionic abundances were calculated using a three-level atom model and abundances were derived through ionisation correction factors. Results show low abundance objects at high galactic latitudes, indicating a possible vertical gradient inside the bulge. A few objects with low N/O ratio were found, which could have originated from old, low mass progenitors.
308. Abundances of Population II stars in NGC 6397
ID:
ivo://CDS.VizieR/J/A+A/490/777
Title:
Abundances of Population II stars in NGC 6397
Short Name:
J/A+A/490/777
Date:
21 Oct 2021
Publisher:
CDS
Description:
Evolutionary trends in the surface abundances of heavier elements have recently been identified in the globular cluster NGC 6397 ([Fe/H]=-2), indicating the operation of atomic diffusion in these stars. Such trends constitute important constraints for the extent to which diffusion modifies the internal structure and surface abundances of solar-type, metal-poor stars. We perform an independent check of the reality and size of abundance variations within this metal-poor globular cluster. Observational data covering a large stellar sample, located between the cluster turn-off point and the base of the red giant branch, are homogeneously analysed. The spectroscopic data were obtained with the medium-high resolution spectrograph FLAMES/GIRAFFE on VLT-UT2 (R~27000). We derive independent effective-temperature scales from profile fitting of Balmer lines and by applying colour-Teff calibrations to Stroemgren uvby and broad-band BVI photometry. An automated spectral analysis code is used together with a grid of MARCS model atmospheres to derive stellar surface abundances of Mg, Ca, Ti, and Fe.
309. Abundances of red clump & RGB stars with APOGEE
ID:
ivo://CDS.VizieR/J/ApJ/872/137
Title:
Abundances of red clump & RGB stars with APOGEE
Short Name:
J/ApJ/872/137
Date:
21 Oct 2021
Publisher:
CDS
Description:
Internal mixing on the giant branch is an important process which affects the evolution of stars and the chemical evolution of the galaxy. While several mechanisms have been proposed to explain this mixing, better empirical constraints are necessary. Here, we use [C/N] abundances in 26097 evolved stars from the SDSS-IV/APOGEE-2 DR14 to trace mixing and extra mixing in old field giants with -1.7<[Fe/H]<0.1. We show that the APOGEE [C/N] ratios before any dredge-up occurs are metallicity dependent, but that the change in [C/N] at the first dredge-up is metallicity independent for stars above [Fe/H]~-1. We identify the position of the red giant branch (RGB) bump as a function of metallicity, note that a metallicity-dependent extra mixing episode takes place for low-metallicity stars ([Fe/H]{<}-0.4) 0.14dex in logg above the bump, and confirm that this extra mixing is stronger at low metallicity, reaching {Delta}[C/N]=0.58dex at [Fe/H]=-1.4. We show evidence for further extra mixing on the upper giant branch, well above the bump, among the stars with [Fe/H]{<}-1.0. This upper giant branch mixing is stronger in the more metal-poor stars, reaching 0.38 dex in [C/N] for each 1.0dex in logg. The APOGEE [C/N] ratios for red clump (RC) stars are significantly higher than for stars at the tip of the RGB, suggesting additional mixing processes occur during the helium flash or that unknown abundance zero points for C and N may exist among the RC sample. Finally, because of extra mixing, we note that current empirical calibrations between [C/N] ratios and ages cannot be naively extrapolated for use in low-metallicity stars specifically for those above the bump in the luminosity function.
310. Abundances of 7 red giant members of BootesI
ID:
ivo://CDS.VizieR/J/ApJ/763/61
Title:
Abundances of 7 red giant members of BootesI
Short Name:
J/ApJ/763/61
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a double-blind analysis of high-dispersion spectra of seven red giant members of the Bootes I ultrafaint dwarf spheroidal galaxy, complemented with re-analysis of a similar spectrum of an eighth-member star. The stars cover [Fe/H] from -3.7 to -1.9 and include a CEMP-no star with [Fe/H]=-3.33. We conclude from our chemical abundance data that Bootes I has evolved as a self-enriching star-forming system, from essentially primordial initial abundances. This allows us uniquely to investigate the place of CEMP-no stars in a chemically evolving system, in addition to limiting the timescale of star formation. The elemental abundances are formally consistent with a halo-like distribution, with enhanced mean [{alpha}/Fe] and small scatter about the mean. This is in accord with the high-mass stellar initial mass function in this low-stellar-density, low-metallicity system being indistinguishable from the present-day solar neighborhood value. There is a non-significant hint of a decline in [{alpha}/Fe] with [Fe/H]; together with the low scatter, this requires low star formation rates, allowing time for supernova ejecta to be mixed over the large spatial scales of interest. One star has very high [Ti/Fe], but we do not confirm a previously published high value of [Mg/Fe] for another star. We discuss the existence of CEMP-no stars, and the absence of any stars with lower CEMP-no enhancements at higher [Fe/H], a situation that is consistent with knowledge of CEMP-no stars in the Galactic field. We show that this observation requires there be two enrichment paths at very low metallicities: CEMP-no and "carbon-normal."

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