- ID:
- ivo://CDS.VizieR/J/A+A/587/A124
- Title:
- Metal-poor stars towards the Galactic bulge
- Short Name:
- J/A+A/587/A124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive chemical abundance analysis of five red giants and two horizontal branch (HB) stars towards the south- ern edge of the Galactic bulge, at (l, b)~(0{deg}, -11{deg}). Based on high-resolution spectroscopy obtained with the Magellan/MIKE spectrograph, we derived up to 23 chemical element abundances and identify a mixed bag of stars, representing various populations in the central regions of the Galaxy. Although cosmological simulations predict that the inner Galaxy was host to the first stars in the Universe, we see no chemical evidence of the ensuing massive supernova explosions: all of our targets exhibit halo-like, solar [Sc/Fe] ratios, which is in contrast to the low values predicted from Population III nucleosynthesis. One of the targets is a CEMP-s star at [Fe/H]=-2.52dex, and another target is a moderately metal-poor ([Fe/H]=-1.53dex) CH star with strong enrichment in s-process elements (e.g., [Ba/Fe]=1.35). These individuals provide the first contenders of these classes of stars towards the bulge. Four of the carbon-normal stars exhibit abundance patterns reminiscent of halo star across a metallicity range spanning -2.0 to -2.6dex, i.e., enhanced {alpha}-elements and solar Fe-peak and neutron-capture elements, and the remaining one is a regular metal-rich bulge giant. The position, distance, and radial velocity of one of the metal-poor HB stars coincides with simulations of the old trailing arm of the disrupted Sagittarius dwarf galaxy. While their highly uncertain proper motions prohibit a clear kinematic separation, the stars' chemical abundances and distances suggest that these metal-poor candidates, albeit located towards the bulge, are not of the bulge, but rather inner halo stars on orbits that make them pass through the central regions. Thus, we caution similar claims of detections of metal-poor stars as true habitants of the bulge.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/445/939
- Title:
- Metal-poor stars uvby-beta photometry. XI.
- Short Name:
- J/A+A/445/939
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New uvby-beta data are provided for 442 high-velocity and metal-poor stars; 90 of these stars have been observed previously by us, and 352 are new. When combined with our previous two photometric catalogues, the data base is now made up of 1533 high-velocity and metal-poor stars, all with photometry and complete kinematic data. Hipparcos, plus a new photometric calibration for M_v_ also based on the Hipparcos parallaxes, provide distances for nearly all of these stars; our previous photometric calibrations give values for E(b-y) and [Fe/H]. The [Fe/H],V(rot) diagram allows us to separate these stars into different Galactic stellar population groups, such as old-thin-disk, thick-disk, and halo. The X histogram, where X is our stellar-population discriminator combining V(rot) and [Fe/H], and contour plots for the [Fe/H],V(rot) diagram both indicate two probable components to the thick disk.
- 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.
- 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/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.
