- ID:
- ivo://CDS.VizieR/J/AJ/140/2109
- Title:
- Metallicites of open clusters NGC7160 and NGC2232
- Short Name:
- J/AJ/140/2109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a moderate-resolution spectroscopic analysis of the 10-25Myr clusters NGC 7160 and NGC 2232 using observations obtained with the WIYN 3.5m telescope. Both NGC 7160 and NGC 2232 are found to have super-solar metallicities, with a mean [Fe/H]=0.16+/-0.03(s.e.m.) for NGC 7160, and 0.22+/-0.09(s.e.m.) or 0.32+/-0.08 for NGC 2232, depending on the adopted temperature scale. NGC 7160 exhibits solar distributions of Na, Fe-peak, and alpha-elements. NGC 2232 is underabundant in light elements Al and Si, by ~0.25 and ~0.15dex, respectively; [Ni/Fe] is roughly solar. The abundance of lithium in NGC 2232 stars is in agreement with undepleted values reported for other cluster main-sequence stars. Our abundances are similar to other metal-rich open clusters and Galactic thin and thick disk stars.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/755/89
- Title:
- Metallicities of damped Ly{alpha} systems
- Short Name:
- J/ApJ/755/89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present chemical abundance measurements for 47 damped Ly{alpha} (DLA) systems, 30 at z>4, observed with the Echellette Spectrograph and Imager and the High Resolution Echelle Spectrometer on the Keck telescopes. H I column densities of the DLAs are measured with Voigt profile fits to the Ly{alpha} profiles, and we find an increased number of false DLA identifications with Sloan Digital Sky Survey at z>4 due to the increased density of the Ly{alpha} forest. Ionic column densities are determined using the apparent optical depth method, and we combine our new metallicity measurements with 195 from previous surveys to determine the evolution of the cosmic metallicity of neutral gas. We find the metallicity of DLAs decreases with increasing redshift, improving the significance of the trend and extending it to higher redshifts, with a linear fit of -0.22+/-0.03 dex per unit redshift from z=0.09-5.06. The metallicity "floor" of {approx}1/600 solar continues out to z~5, despite our sensitivity for finding DLAs with much lower metallicities. However, this floor is not statistically different from a steep tail to the distribution. We also find that the intrinsic scatter of metallicity among DLAs of ~0.5dex continues out to z~5. In addition, the metallicity distribution and the {alpha}/Fe ratios of z>2 DLAs are consistent with being drawn from the same parent population with those of halo stars. It is therefore possible that the halo stars in the Milky Way formed out of gas that commonly exhibits DLA absorption at z>2.
- ID:
- ivo://CDS.VizieR/J/ApJ/819/73
- Title:
- Metallicity evolution of COSMOS BCD sample
- Short Name:
- J/ApJ/819/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present oxygen abundance measurements for 74 blue compact dwarf (BCD) galaxies in the redshift range of [0.2, 0.5] using the strong-line method. The spectra of these objects are taken using Hectospec on the Multiple Mirror Telescope. More than half of these BCDs had dust attenuation corrected using the Balmer decrement method. For comparison, we also selected a sample of 2023 local BCDs from the Sloan Digital Sky Survey (SDSS) database. Based on the local and intermediate-z BCD samples, we investigated the cosmic evolution of the metallicity, star formation rate (SFR), and D_n_(4000) index. Compared with local BCDs, the intermediate-z BCDs had a systematically higher R23 ratio but a similar O32 ratio. Interestingly, no significant deviation in the mass-metallicity (MZ) relation was found between the intermediate-z and local BCDs. Besides the metallicity, the intermediate-z BCDs also exhibited an SFR distribution that was consistent with local BCDs, suggesting a weak dependence on redshift. The intermediate-z BCDs seemed to be younger than the local BCDs with lower D_n_(4000) index values. The insignificant deviation in the mass-metallicity and mass-SFR relations between intermediate-z and local BCDs indicates that the relations between the global parameters of low-mass compact galaxies may be universal. These results from low-mass compact galaxies could be used to place important observational constraints on galaxy formation and evolution models.
- ID:
- ivo://CDS.VizieR/J/A+A/567/A55
- Title:
- Metallicity of the {gamma} Vel cluster
- Short Name:
- J/A+A/567/A55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Knowledge of the abundance distribution of star forming regions and young clusters is critical to investigate a variety of issues, from triggered star formation and chemical enrichment by nearby supernova explosions to the ability to form planetary systems. In spite of this, detailed abundance studies are currently available for relatively few regions. In this context, we present the analysis of the metallicity of the Gamma Velorum cluster, based on the products distributed in the first internal release of the Gaia-ESO Survey. The Gamma Velorum candidate members have been observed with FLAMES, using both UVES and Giraffe, depending on the target brightness and spectral type. In order to derive a solid metallicity determination for the cluster, membership of the observed stars must be first assessed. To this aim, we use several membership criteria including radial velocities, surface gravity estimates, and the detection of the photospheric lithium line. Out of the 80 targets observed with UVES, we identify 14 high-probability members. We find that the metallicity of the cluster is slightly sub-solar, with a mean [Fe/H]=-0.057+/-0.018dex. Although J08095427-4721419 is one of the high-probability members, its metallicity is significantly larger than the cluster average. We speculate about its origin as the result of recent accretion episodes of rocky bodies of about 60 Msun hydrogen-depleted material from the circumstellar disc.
- ID:
- ivo://CDS.VizieR/J/ApJ/781/40
- Title:
- Metal-poor stars from HES survey. II. Spectroscopy
- Short Name:
- J/ApJ/781/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the discovery of seven low-metallicity stars selected from the Hamburg/ESO Survey, six of which are extremely metal-poor (EMP, [Fe/H]{<=}-3.0), with four having [Fe/H]{<=}-3.5. Chemical abundances or upper limits are derived for these stars based on high-resolution (R~35000) Magellan/MIKE spectroscopy, and are in general agreement with those of other very and extremely metal-poor stars reported in the literature. Accurate metallicities and abundance patterns for stars in this metallicity range are of particular importance for studies of the shape of the metallicity distribution function of the Milky Way's halo system, in particular for probing the nature of its low-metallicity tail. In addition, taking into account suggested evolutionary mixing effects, we find that six of the program stars (with [Fe/H]{<=}-3.35) possess atmospheres that were likely originally enriched in carbon, relative to iron, during their main-sequence phases. These stars do not exhibit overabundances of their s-process elements, and hence may be, within the error bars, additional examples of the so-called CEMP-no class of objects.
- ID:
- ivo://CDS.VizieR/J/AJ/154/52
- Title:
- Metal-poor stars from SDSS/SEGUE. I Unevolved stars
- Short Name:
- J/AJ/154/52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present elemental abundances for eight unevolved extremely metal-poor (EMP) stars with T_eff_>5500K, among which seven have [Fe/H]{<}-3.5. The sample is selected from the Sloan Digital Sky Survey/Sloan Extension for Galactic Understanding and Exploration (SDSS/SEGUE) and our previous high-resolution spectroscopic follow-up with the Subaru Telescope. Several methods to derive stellar parameters are compared, and no significant offset in the derived parameters is found in most cases. From an abundance analysis relative to the standard EMP star G64-12, an average Li abundance for stars with [Fe/H]<-3.5 is A(Li)=1.90, with a standard deviation of {sigma}=0.10dex. This result confirms that lower Li abundances are found at lower metallicity, as suggested by previous studies, and demonstrates that the star-to-star scatter is small. The small observed scatter could be a strong constraint on Li-depletion mechanisms proposed for explaining the low Li abundance at lower metallicity. Our analysis for other elements obtained the following results: (i) a statistically significant scatter in [X/Fe] for Na, Mg, Cr, Ti, Sr, and Ba, and an apparent bimodality in [Na/Fe] with a separation of ~0.8dex, (ii) an absence of a sharp drop in the metallicity distribution, and (iii) the existence of a CEMP-s star at [Fe/H]{simeq}-3.6 and possibly at [Fe/H]{simeq}-4.0, which may provide a constraint on the mixing efficiency of unevolved stars during their main-sequence phase.
- 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.
- 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/AJ/106/1839
- Title:
- Metal-rich halo A stars
- Short Name:
- J/AJ/106/1839
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of spectrophotometry of the Ca II K and Balmer lines and radial velocity measurements for stars earlier than type F0, with 10<V<15.5 in fields at (l;b)=(90deg, 270deg; -45deg) are reported. Slit spectroscopy of 320 stars shows that in this magnitude range there are ~80 stars with [Fe/H]>-0.5. The metal-rich population has a vertical scale height of ~600pc and a space density at the Sun equal to 1/225 of the young thin disk A star population. The metal-rich A stars have V_rot_=210+/-60km/s with decreasing angular momentum as a function of distance from the Galactic plane. The line-of-sight velocity dispersion is 40+/-3km/s indicating an anomalous relation between structure and kinematics. There is strong evidence that these stars are identical in properties to the metal-rich extended populations found by Perry [1969AJ.....74..139P] at the NGP and Rodgers [1971ApJ...165..581R] at the SGP.
