- ID:
- ivo://CDS.VizieR/J/ApJ/875/89
- Title:
- Metal-poor stars with APF. I. LAMOST CEMP stars
- Short Name:
- J/ApJ/875/89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the discovery of five carbon-enhanced metal-poor (CEMP) stars in the metallicity range of -3.3<[Fe/H]{<}-2.4. These stars were selected from the LAMOST DR3 low-resolution (R~2000) spectroscopic database as metal-poor candidates and followed up with high-resolution spectroscopy (R~110000) with the Lick/APF. Stellar parameters and individual abundances for 25 chemical elements (from Li to Eu) are presented for the first time. These stars exhibit chemical abundance patterns that are similar to those reported in other literature studies of very and extremely metal-poor stars. One of our targets, J2114-0616, shows high enhancement in carbon ([C/Fe]=1.37), nitrogen ([N/Fe]=1.88), barium ([Ba/Fe]=1.00), and europium ([Eu/Fe]=0.84). Such chemical abundance pattern suggests that J2114-0616 can be classified as CEMP-r/s star. In addition, the star J1054+0528 can be classified as a CEMP-rI star, with [Eu/Fe]=0.44 and [Ba/Fe]=-0.52. The other stars in our sample show no enhancements in neutron-capture elements and can be classified as CEMP-no stars. We also performed a kinematic and dynamical analysis of the sample stars based on Gaia DR2 data. The kinematic parameters, orbits, and binding energy of these stars show that J2114-0616 is member of the outer-halo population, while the remaining stars belong to the inner-halo population but with an accreted origin. Collectively, these results add important constraints on the origin and evolution of CEMP stars as well as on their possible formation scenarios.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/882/27
- Title:
- Metal-poor stars with APF obs. II. MW halo stars
- Short Name:
- J/ApJ/882/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we study the chemical compositions and kinematic properties of six metal-poor stars with [Fe/H]{<}-2.5 in the Galactic halo. From high-resolution (R~110000) spectroscopic observations obtained with the Lick/Automated Planet Finder, we determined individual abundances for up to 23 elements, to quantitatively evaluate our sample. We identify two carbon-enhanced metal-poor stars (J1630+0953 and J2216+0246) without enhancement in neutron-capture elements (CEMP-no stars), while the rest of our sample stars are carbon-intermediate. By comparing the light-element abundances of the CEMP stars with predicted yields from nonrotating zero-metallicity massive-star models, we find that the possible progenitors of J1630+0953 and J2216+0246 could be in the 13-25M_{sun}_ mass range, with explosion energies (0.3-1.8)x10^51^erg. In addition, the detectable abundance ratios of light and heavy elements suggest that our sample stars are likely formed from a well-mixed gas cloud, which is consistent with previous studies. We also present a kinematic analysis, which suggests that most of our program stars likely belong to the inner-halo population, with orbits passing as close as ~2.9kpc from the Galactic center. We discuss the implications of these results on the critical constraints on the origin and evolution of CEMP stars, as well as the nature of the Population III progenitors of the lowest-metallicity stars in our Galaxy.
- ID:
- ivo://CDS.VizieR/J/A+A/422/527
- Title:
- Metal-poor star uvby-beta photometry. X.
- Short Name:
- J/A+A/422/527
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (uvby) and H-beta photometry has been obtained for an additional 411 very metal-poor stars selected from the HK survey, and used to derive basic parameters such as interstellar reddenings, metallicities, photometric classifications, distances, and relative ages.
- ID:
- ivo://CDS.VizieR/J/A+AS/136/519
- Title:
- Mg2 indices for early-type galaxies
- Short Name:
- J/A+AS/136/519
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 210 new measurements of the central absorption line-strength Mg_2_ index for 87 early-type galaxies drawn from the Prugniel & Simien (1996, Cat. <J/A+A/309/749>) sample. 28 galaxies were not observed before. The results are compared to measurements published previously as available in HYPERCAT, and rescaled to the Lick system. The mean individual internal error on these measurements is 0.009mag+/-0.003mag and the mean external error is 0.012mag+/-0.002mag for this series of measurements. These data are also available from HYPERCAT.
- ID:
- ivo://CDS.VizieR/J/ApJ/883/84
- Title:
- MIKE obs. of 2 metal-poor stars in Sylgr stream
- Short Name:
- J/ApJ/883/84
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We observe two metal-poor main-sequence stars that are members of the recently discovered Sylgr stellar stream. We present radial velocities, stellar parameters, and abundances for 13 elements derived from high-resolution optical spectra collected using the Magellan Inamori Kyocera Echelle spectrograph. The two stars have identical compositions (within 0.13 dex or 1.2{sigma}) among all elements detected. Both stars are very metal-poor ([Fe/H]=-2.92+/-0.06). Neither star is highly enhanced in C ([C/Fe]<+1.0). Both stars are enhanced in the {alpha} elements Mg, Si, and Ca ([{alpha}/Fe]=+0.32+/-0.06), and the ratios among Na, Al, and all Fe-group elements are typical for other stars in the halo and ultra-faint and dwarf spheroidal galaxies at this metallicity. Sr is mildly enhanced ([Sr/Fe]=+0.22+/-0.11), but Ba is not enhanced ([Ba/Fe]{<}-0.4), indicating that these stars do not contain high levels of neutron-capture elements. The Li abundances match those found in metal-poor unevolved field stars and globular clusters (GCs) (log{epsilon}(Li)=2.05+/-0.07), which implies that environment is not a dominant factor in determining the Li content of metal-poor stars. The chemical compositions of these two stars cannot distinguish whether the progenitor of the Sylgr stream was a dwarf galaxy or a GC. If the progenitor was a dwarf galaxy, the stream may originate from a dense region such as a nuclear star cluster. If the progenitor was a GC, it would be the most metal-poor GC known.
- 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/568/A7
- Title:
- Model SDSS colors for halo stars
- Short Name:
- J/A+A/568/A7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze a sample of tens of thousands of spectra of halo turnoff stars, obtained with the optical spectrographs of the Sloan Digital Sky Survey (SDSS), to characterize the stellar halo population "in situ" out to a distance of a few tens of kpc from the Sun. In this paper we describe the derivation of atmospheric parameters. We also derive the overall stellar metallicity distribution based on F-type stars observed as flux calibrators for the Baryonic Oscillations Spectroscopic Survey (BOSS). Our analysis is based on an automated method that determines the set of parameters of a model atmosphere that best reproduces each observed spectrum. We use an optimization algorithm and evaluate model fluxes by means of interpolation in a pre-computed grid. In our analysis, we account for the spectrograph's varying resolution as a function of fiber and wavelength. Our results for early SDSS (pre-BOSS upgrade) data compare well with those from the SEGUE Stellar Parameter Pipeline (SSPP), except for stars at logg (cgs units) lower than 2.5. An analysis of stars in the globular cluster M13 reveals a dependence of the inferred metallicity on surface gravity for stars with logg<2.5, confirming the systematics identified in the comparison with the SSPP. We find that our metallicity estimates are significantly more precise than the SSPP results. We also find excellent agreement with several independent analyses. We show that the SDSS color criteria for selecting F-type halo turnoff stars as flux calibrators efficiently excludes stars with high metallicities, but does not significantly distort the shape of the metallicity distribution at low metallicity. We obtain a halo metallicity distribution that is narrower and more asymmetric than in previous studies. The lowest gravity stars in our sample, at tens of kpc from the Sun, indicate a shift of the metallicity distribution to lower abundances, consistent with that expected from a dual halo system in the Milky Way.
- ID:
- ivo://CDS.VizieR/J/ApJ/762/26
- Title:
- Most metal-poor stars. II. 190 Galactic halo stars
- Short Name:
- J/ApJ/762/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a homogeneous chemical abundance analysis of 16 elements in 190 metal-poor Galactic halo stars (38 program and 152 literature objects). The sample includes 171 stars with [Fe/H]<=-2.5, of which 86 are extremely metal poor, [Fe/H]<=-3.0. Our program stars include 10 new objects with [Fe/H]<=-3.5. We identify a sample of "normal" metal-poor stars and measure the trends between [X/Fe] and [Fe/H], as well as the dispersion about the mean trend for this sample. Using this mean trend, we identify objects that are chemically peculiar relative to "normal" stars at the same metallicity. These chemically unusual stars include CEMP-no objects, one star with high [Si/Fe], another with high [Ba/Sr], and one with unusually low [X/Fe] for all elements heavier than Na. The Sr and Ba abundances indicate that there may be two nucleosynthetic processes at lowest metallicity that are distinct from the main r-process. Finally, for many elements, we find a significant trend between [X/Fe] versus T_eff_, which likely reflects non-LTE and/or three-dimensional effects. Such trends demonstrate that care must be exercised when using abundance measurements in metal-poor stars to constrain chemical evolution and/or nucleosynthesis predictions.
- ID:
- ivo://CDS.VizieR/J/ApJ/762/27
- Title:
- Most metal-poor stars. III. 86 [Fe/H]<=-3.0 stars
- Short Name:
- J/ApJ/762/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the metallicity distribution function (MDF) and fraction of carbon-enhanced metal-poor (CEMP) stars in a sample that includes 86 stars with [Fe/H]<=-3.0, based on high-resolution, high signal-to-noise spectroscopy, of which some 32 objects lie below [Fe/H]=-3.5. After accounting for the completeness function, the "corrected" MDF does not exhibit the sudden drop at [Fe/H]=-3.6 that was found in recent samples of dwarfs and giants from the Hamburg/ESO survey. Rather, the MDF decreases smoothly down to [Fe/H]=-4.1. Similar results are obtained from the "raw" MDF. We find that the fraction of CEMP objects below [Fe/H]=-3.0 is 23%+/-6% and 32%+/-8% when adopting the Beers & Christlieb (2005ARA&A..43..531B) and Aoki et al. (2007, J/ApJ/655/492) CEMP definitions, respectively. The former value is in fair agreement with some previous measurements, which adopt the Beers & Christlieb criterion.
- ID:
- ivo://CDS.VizieR/J/A+A/435/1087
- Title:
- Nebular abundances of southern symbiotic stars
- Short Name:
- J/A+A/435/1087
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have calculated relative element abundances for a sample of 43 symbiotic stars. Helium abundances and the relative elemental abundances N/O, Ne/O, Ar/O were derived from new spectra collected in the optical range through low dispersion spectroscopy. The He ionic abundances were derived taking into account self-absorption effects in Balmer lines. We found that the symbiotic stars in the galactic bulge have heavy element abundances showing the same wide distribution as other bulge objects. In the galactic disk, the symbiotic stars follow the abundance gradient as derived from different kinds of objects.
