- ID:
- ivo://CDS.VizieR/J/ApJ/719/996
- Title:
- Effects of binarity in SEGUE pipeline
- Short Name:
- J/ApJ/719/996
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the effects that unresolved binaries have on the determination of various stellar atmospheric parameters for targets from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) using numerical modeling, a grid of synthetic spectra, and the SEGUE Stellar Parameter Pipeline (SSPP). The SEGUE survey, a component of the Sloan Digital Sky Survey-II (SDSS-II) project focusing on Galactic structure, provides medium resolution spectroscopy for over 200000 stars of various spectral types over a large area on the sky. To model undetected binaries that may be in this sample, we use a variety of mass distributions for the primary and secondary stars in conjunction with empirically determined relationships for orbital parameters to determine the fraction of G-K dwarf stars, defined by SDSS color cuts as having 0.48<=(g-r)_0_<=0.75, that will be blended with a secondary companion. We focus on the G-K dwarf sample in SEGUE as it records the history of chemical enrichment in our galaxy. To determine the effect of the secondary on the spectroscopic parameters, specifically effective temperature, surface gravity, metallicity, and [{alpha}/Fe], we synthesize a grid of model spectra from 3275 to 7850K and [Fe/H]=-0.5 to -2.5 from MARCS model atmospheres using TurboSpectrum. These temperature and metallicity ranges roughly correspond to a stellar mass range of 0.1-1.0M_{sun}_. We assume that both stars in the pair have the same metallicity. We analyze both "infinite" signal-to-noise ratio (S/N) models and degraded versions of the spectra, at median S/N of 50, 25, and 10.
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- ID:
- ivo://CDS.VizieR/J/A+A/650/A203
- Title:
- Effects of IMG on Galactic chemical enrichment
- Short Name:
- J/A+A/650/A203
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We have been seeing mounting evidence that the stellar initial mass function (IMF) might extend far beyond the canonical Mi~100M_{sun}_ limit, but the impact of such a hypothesis on the chemical enrichment of galaxies is yet to be clarified. We aim to address this question by analysing the observed abundances of thin- and thick-disc stars in the Milky Way with chemical evolution models that account for the contribution of very massive stars dying as pair instability supernovae. We built new sets of chemical yields from massive and very massive stars up to Mi~350M_{sun}_ by combining the wind ejecta extracted from our hydrostatic stellar evolution models with explosion ejecta from the literature. Using a simple chemical evolution code, we analysed the effects of adopting different yield tables by comparing predictions against observations of stars in the solar vicinity. After several tests, we set our focus on the [O/Fe] ratio that best separates the chemical patterns of the two Milky Way components. We nd that with a standard IMF, truncated at Mi~100M_{sun}_, we can reproduce various observational constraints for thin-disc stars; however, the same IMF fails to account for the [O/Fe] ratios of thick-disc stars. The best results are obtained by extending the IMF up to Mi=350M_{sun}_; while including the chemical ejecta of very massive stars in the form of winds and pair instability supernova (PISN) explosions. Our study indicates that PISN may have played a significant role in shaping the chemical evolution of the thick disc of the Milky Way. Including their chemical yields makes it easier to reproduce not only the level of the a-enhancement, but also the observed slope of thick-disc stars in the [O/Fe] versus [Fe/H] diagram. The bottom line is that the contribution of very massive stars to the chemical enrichment of galaxies is potentially quite important and should not be neglected in models of chemical evolution.
- ID:
- ivo://CDS.VizieR/J/A+A/354/899
- Title:
- Elemental abundance analyses IV.
- Short Name:
- J/A+A/354/899
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using new CASLEO echelle spectrograms, we extended our elemental abundances of the sharp-lines Mercury-Manganese star {mu} Lep, 14 Hya, {kappa} Cnc, HR 4487, 28 Her, and HR 7245, the closely related star 3 CenA, and 7 Sex an A0V star with population I abundances, but with Population II star space motion. The {lambda}{lambda}4500-6200 region contains a sufficient number of lines to derive high-quality abundances of these stars. For most stars, the new spectra provide additional lines for the analyses which improve their quality as well as help fill in the periodic table.
- ID:
- ivo://CDS.VizieR/J/AN/329/4
- Title:
- Elemental abundance analyses of nu Her & 41 Cyg
- Short Name:
- J/AN/329/4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This series of high quality elemental abundance analyses of mostly Main Sequence normal and peculiar B, A, and F stars defines their properties and provides data for the comparison with analyses of somewhat similar stars and with theoretical predictions. Most use high dispersion and high S/N (greater than or equal to 200) spectrograms obtained with CCD detectors at the long camera of the 1.22-m Dominion Astrophysical Observatory telescope's coude spectrograph. Here we expand the range of stars examined to include two relatively quiescent F supergiants. nu Her (F2 II) and 41 Cyg (F5 Ib-II) are analyzed as consistently as possible with previous studies. These LTE fine analyses use the ATLAS9 and the WIDTH9 programs of R.L. Kurucz. High signal-to-noise spectrograms and high quality atomic data were employed. The derived values of these photometrically constant stars are somewhat different with the abundances of nu Her being somewhat metal-poor and those of 41 Cyg being crudely solar-like. Our analyses indicate that the basic results of Luck and Wepfer who also studied nu Her and 41 Cyg are not likely to be significantly changed by new studies of all their stars.
- ID:
- ivo://CDS.VizieR/J/A+A/447/685
- Title:
- Elemental abundance analyses. XXIX.
- Short Name:
- J/A+A/447/685
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We performed elemental abundances analyses of the mercury-manganese (HgMn) stars 53 Tau, {beta} Tau, and {gamma} Crv consistent with previous studies of similar stars in this series.
- ID:
- ivo://CDS.VizieR/J/MNRAS/356/1256
- Title:
- Elemental abundance analysis of HR 8216
- Short Name:
- J/MNRAS/356/1256
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed the abundance analysis of the cool magnetic CP star HR 8216 (=HD 204411) using 2.4{AA}/mm Dominion Astrophysical Observatory Reticon exposures covering ll 3830-4770{AA} with a typical signal-to-noise ratio of 200. The spectrograms were measured interactively with the graphics computer program REDUCE. We performed a fine analysis with an ATLAS9 metal-rich model atmosphere whose predictions best matched the optical region fluxes and the Hg profile. HR 8216's anomalies are primarily an enhancement of many iron peak elements with the rare earths elements much less enhanced than for many similar cool magnetic CP stars .Using the results of the fine analysis we synthetized the spectrum. Comparison with the observed spectrum showed that agreement is better.
- ID:
- ivo://CDS.VizieR/J/A+A/371/1078
- Title:
- Elemental abundance of 4 normal B and A stars
- Short Name:
- J/A+A/371/1078
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Elemental abundances analysis of the superficially normal B and A stars {alpha} Dra (A0 III), {tau} Her (B5 IV), {gamma} Lyr (B9 III), and HR 7926 (B8 II-III) are performed consistent with previous studies of this series using spectrograms obtained with Reticon and CCD detectors. Comparisons of the first two analysis with those of the same stars performed earlier in this series which used mostly coadded photographic plates show the general consistency of the derived elemental abundances. A slight increase in the adopted effective temperature produces a corresponding increase in the derived abundances. In these stars the He/H ratios are found to be close to solar. Except for {gamma} Lyr the metals show for the most part marginally subsolar abundance values. But this star has Al, Ca, Sc, and Sr abundances that are substantially underabundant as well as other underabundant values.
- ID:
- ivo://CDS.VizieR/J/MNRAS/367/1329
- Title:
- Elemental abundances for 176 stars
- Short Name:
- J/MNRAS/367/1329
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed an abundance analysis for F- and G- dwarfs of the Galactic thick-disc component. A sample of 176 nearby (d<=150pc) thick-disc candidate stars was chosen from the Hipparcos catalogue and subjected to a high-resolution spectroscopic analysis. Using accurate radial velocities combined with the Hipparcos astrometry, kinematics (U, V and W) and Galactic orbital parameters were computed. We estimate the probability for a star to belong to the thin disc, the thick disc or the halo. With a probability P>=70 per cent taken as certain membership, we assigned 95 stars to the thick disc, 13 to the thin disc, and 20 to the halo. The remaining 48 stars in the sample cannot be assigned with reasonable certainty to one of the three components. Abundances of C, O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Ba, Ce, Nd and Eu have been obtained.
- ID:
- ivo://CDS.VizieR/J/MNRAS/364/272
- Title:
- Elemental abundances in Blanco 1
- Short Name:
- J/MNRAS/364/272
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High-resolution spectroscopy is used to determine the detailed chemical abundances of a group of eight F- and G-type stars in the young open cluster Blanco 1. An average [Fe/H] of +0.04+/-0.02 (internal error)+/-0.04 (external error) is found, considerably lower than a previous spectroscopic estimate for this cluster. The difference is due mainly to our adoption of significantly cooler temperatures that are consistent with both photometric and spectroscopic constraints. Blanco 1 exhibits subsolar [Ni/Fe](0.18+/-0.01+/-0.01), [Si/Fe](0.09+/-0.02+/-0.03), [Mg/Fe](0.14+/-0.02+/-0.03) and [Ca/Fe](0.09+/-0.03+/-0.03); ratios that are not observed among nearby field stars.
- ID:
- ivo://CDS.VizieR/J/AJ/118/1245
- Title:
- Elemental abundances in five stars in M54
- Short Name:
- J/AJ/118/1245
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Chemical abundances in five stars in M54, a globular cluster associated with the Sagittarius dwarf galaxy, have been determined using high-resolution echelle spectra. We find the cluster to have [Fe/H] = -1.55 and possibly halo-normal abundance patterns, although the [O/Fe] and [{alpha}/Fe] ratios lie between solar and the normal halo values. One star shows the combination of low oxygen and enhanced Na and Al, symptomatic of deep mixing of ON-cycle and other proton-capture products; a second star shows a lesser degree of O depletion unaccompanied by Na and Al excesses. In the cluster Eu is also enhanced, indicating that about 30% of the Ba in the cluster is due to the r-process. In general, M54 is similar to globulars of comparable metallicity in the inner Galactic halo, despite its clear association with the Sagittarius dwarf spheroidal.