- ID:
- ivo://CDS.VizieR/J/AJ/147/136
- Title:
- Stars of very low metal abundance. VI. Abundances
- Short Name:
- J/AJ/147/136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present radial velocities, equivalent widths, model atmosphere parameters, and abundances or upper limits for 53 species of 48 elements derived from high resolution optical spectroscopy of 313 metal-poor stars. A majority of these stars were selected from the metal-poor candidates of the HK Survey of Beers, Preston, and Shectman. We derive detailed abundances for 61% of these stars for the first time. Spectra were obtained during a 10yr observing campaign using the Magellan Inamori Kyocera Echelle spectrograph on the Magellan Telescopes at Las Campanas Observatory, the Robert G. Tull Coude Spectrograph on the Harlan J. Smith Telescope at McDonald Observatory, and the High Resolution Spectrograph on the Hobby-Eberly Telescope at McDonald Observatory. We perform a standard LTE abundance analysis using MARCS model atmospheres, and we apply line-by-line statistical corrections to minimize systematic abundance differences arising when different sets of lines are available for analysis. We identify several abundance correlations with effective temperature. A comparison with previous abundance analyses reveals significant differences in stellar parameters, which we investigate in detail. Our metallicities are, on average, lower by {approx}0.25dex for red giants and {approx}0.04dex for subgiants. Our sample contains 19 stars with [Fe/H]<=-3.5, 84 stars with [Fe/H]<=-3.0, and 210 stars with [Fe/H]<=-2.5. Detailed abundances are presented here or elsewhere for 91% of the 209 stars with [Fe/H]<=-2.5 as estimated from medium resolution spectroscopy by Beers, Preston, and Shectman. We will discuss the interpretation of these abundances in subsequent papers.
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- ID:
- ivo://CDS.VizieR/J/A+A/398/363
- Title:
- Statistical properties of exoplanets II
- Short Name:
- J/A+A/398/363
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Table2 file is an extended version of table 2 in the paper. It contains the stellar parameters as well as the number of FeI and FeII lines used (and the rms around the mean value) in the analysis, the spectrograph used, and the derived stellar masses for each star. Velocity files contains the U, V, and W space velocities for the planet host stars used in Figs. 9 and 10.
- ID:
- ivo://CDS.VizieR/J/A+A/614/A146
- Title:
- Stellar parameters of NGC3201 RGB stars
- Short Name:
- J/A+A/614/A146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The origin of the globular cluster (GC) NGC3201 is under debate. Its retrograde orbit points to an extragalactic origin, but no further chemical evidence supports this idea. Light-element chemical abundances are useful to tag GCs and can be used to shed light in this discussion. Recently it was shown that the CN and CH indices are useful to identify anomalous GCs out of typical Milky Way GCs. A possible origin of anomalous clusters is the merger of two GCs and/or nucleus of a dwarf galaxy. We aim at deriving CN and CH band strengths for red giant stars in NGC3201 and compare with photometric indices and high-resolution spectroscopy and discuss in the context of GC chemical tagging. We measure molecular band indices of S(3839) and G4300 for CN and CH, respectively from low-resolution spectra of red giant stars. Gravity and temperature effects are removed. Photometric indices are used to indicate further chemical information on C+N+O or s-process element abundances, not derived from low-resolution spectra. We found three groups on the CN-CH distribution. A main sequence (S1), a secondary less-populated sequence (S2), and a group of peculiar (pec) CN-weak and CH-weak stars, one of which was previously known. The three groups seem to have different C+N+O and/or s-process element abundances, to be confirmed by high-resolution spectroscopy. These are typical characteristics of anomalous GCs. The CN distribution of NGC3201 is quadrimodal, which is more common in anomalous clusters. However, NGC3201 does not belong to the trend of anomalous GCs in the mass-size relation. NGC3201 shows signs that it can be chemically tagged as anomalous: unusual CN-CH relation, indications that pec-S1-S2 is an increasing sequence of C+N+O or s-process element abundances, and a multimodal CN distribution that seems to correlate with s-process element abundances. The differences are: it has a debatable Fe-spread and it does not follow the trend of mass-size of all anomalous clusters. Three scenarios are postulated here: (i) if the sequence pec-S1-S2 has increasing C+N+O and s-process element abundances, NGC3201 would be the first anomalous GC out of the mass-size relation; (ii) if the abundances are almost constant, NGC3201 would be the first non-anomalous GC with multiple CN-CH anti-correlation groups, or (iii) it would be the first anomalous GC without variations in C+N+O and s-process element abundances. In all cases, the definition of anomalous clusters and the scenario where they have an extragalactic origin must be revised.
- ID:
- ivo://CDS.VizieR/J/PASP/113/1365
- Title:
- Super-metal-rich stars
- Short Name:
- J/PASP/113/1365
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Lick spectral indices for a complete sample of 139 candidate super-metal-rich stars of different luminosity classes (MK type from I to V). For 91 of these stars we were able to identify, in an accompanying paper, the fundamental atmosphere parameters. This confirms that at least 2/3 of the sample consists of stars with [Fe/H] in excess of +0.1 dex. Optical indices for both observations and fiducial synthetic spectra have been calibrated to the Lick system according to Worthey et al. (1994, Cat. <J/ApJS/94/687>) and include the FeI indices of Fe5015, Fe5270, and Fe5335 and the MgI and MgH indices of Mg_2_ and Mg_b_ at 5180{AA}. The internal accuracy of the observations is found to be {sigma}(Fe5015)=10.32{AA}, {sigma}(Fe5270)=10.19{AA}, {sigma}(Fe5335)=10.22{AA}, {sigma}(Mg_2_)=10.004mag, and {sigma}(Mg_b_)=10.19{AA}. This is about a factor of 2 better than the corresponding theoretical indices from the synthetic spectra, the latter being a consequence of the intrinsic limitations in the input physics, as discussed by Chavez et al. (1997, Cat. <J/A+AS/126/267>).
- ID:
- ivo://CDS.VizieR/J/A+A/574/A129
- Title:
- The First CEMP star in the Sculptor dSph
- Short Name:
- J/A+A/574/A129
- Date:
- 04 Feb 2022 11:54:02
- Publisher:
- CDS
- Description:
- he origin of carbon-enhanced metal-poor (CEMP) stars and their possible connection with the chemical elements produced by the first stellar generation is still highly debated. In contrast to the Galactic halo, not many CEMP stars have been found in the dwarf spheroidal galaxies around the Milky Way. Here we present detailed abundances from ESO VLT/UVES high-resolution spectroscopy for ET0097, the first CEMP star found in the Sculptor dwarf spheroidal, which is one of the best studied dwarf galaxies in the Local Group. This star has [Fe/H]=-2.03+/-0.10, [C/Fe]=0.51+/-0.10 and [N/Fe]=1.18+/-0.20, which is the first nitrogen measurement in this galaxy. The traditional definition of CEMP stars is [C/Fe]>=0.70, but taking into account that this luminous red giant branch star has undergone mixing, it was intrinsically less nitrogen enhanced and more carbon-rich when it was formed, and so it falls under the definition of CEMP stars, as proposed by Aoki et al. (2007ApJ...655..492A, Cat. J/ApJ/655/492) to account for this effect.
- ID:
- ivo://CDS.VizieR/J/ApJ/762/25
- Title:
- The most metal-poor stars in HES and SDSS. I.
- Short Name:
- J/ApJ/762/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of 34 stars in the Hamburg/ESO Survey (HES) for metal-poor stars and the Sloan Digital Sky Survey (SDSS) that have [Fe/H]<~-3.0. Their median and minimum abundances are [Fe/H]=-3.1 and -4.1, respectively, while 10 stars have [Fe/H]<-3.5. High-resolution, high signal-to-noise spectroscopic data --equivalent widths and radial velocities-- are presented for these stars, together with an additional four objects previously reported or currently being investigated elsewhere. We have determined the atmospheric parameters, effective temperature (T_eff_), and surface gravity (logg), which are critical in the determination of the chemical abundances and the evolutionary status of these stars. Three techniques were used to derive these parameters. Spectrophotometric fits to model atmosphere fluxes were used to derive T_eff_, logg, and an estimate of E(B-V); H{alpha}, H{beta}, and H{gamma} profile fitting to model atmosphere results provided the second determination of T_eff_and logg; and finally, we used an empirical T_eff_-calibrated H{delta} index, for the third, independent T_eff_determination. The three values of T_eff_ are in good agreement, although the profile fitting may yield systematically cooler T_eff_values, by ~100K. This collective data set will be analyzed in future papers in the present series to utilize the most metal-poor stars as probes of conditions in the early universe.
- ID:
- ivo://CDS.VizieR/J/A+A/650/A194
- Title:
- Titans metal-poor reference stars. I.
- Short Name:
- J/A+A/650/A194
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Several large stellar spectroscopic surveys are producing overwhelming amounts of data that can be used for determining stellar atmospheric parameters and chemical abundances. Nonetheless, the accuracy achieved in the derived astrophysical parameters is still insufficient, mainly because of the paucity of adequate calibrators, particularly in the metal-poor regime ([Fe/H]<=-1.0). Our aim is to increase the number of metal-poor stellar calibrators that have accurate parameters. Here, we introduce the Titans metal-poor reference stars: a sample of 41 dwarf and subgiant stars with accurate, but model-dependent, parameters. Effective temperatures (Teff) were derived by fitting observed H{alpha} profiles with synthetic lines computed using three dimensional (3D) hydrodynamic model atmospheres that take into account departures from the local thermodynamic equilibrium (non-LTE effects). Surface gravities (logg) were computed using evolutionary tracks and parallaxes from Gaia early-data release 3. The same methods recover the Teff values of the Gaia benchmark stars, which are mostly based on interferometric measurements, with a 1{sigma} dispersion of 50K. We assume this to be the accuracy of the H{alpha} profiles computed from 3D non-LTE models for metal-poor dwarfs and subgiants, although this is likely an upper-bound estimate dominated by the uncertainty of the standard Teff values. We achieved an internal precision typically between 30-40K, these errors dominated by instrumental effects. The final total uncertainty for the Teff values of the Titans are thus estimated to be of the order of 1%. The typical error for logg is 0.04dex. In addition, we identified a few members of Gaia-Enceladus, of Sequoia, and of the Helmi stream in our sample. These stars can pave the way for the accurate chemical characterization of these Galactic substructures. Using the Titans as reference, large stellar surveys will be able to improve the internal calibration of their astrophysical parameters. Ultimately, this sample will help users of data from Gaia and large surveys in reaching their goal of redefining our understanding of stars, stellar systems, and the Milky Way.
- ID:
- ivo://CDS.VizieR/J/A+A/658/A36
- Title:
- Transition disks around evolved stars
- Short Name:
- J/A+A/658/A36
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Post-AGB binaries are surrounded by massive disks of gas and dust that are similar to protoplanetary disks surrounding young stars. We assembled a catalog of all known Galactic post-AGB binaries with disks. We explore correlations between the different observables with the aim to learn more about potential disk-binary interactions. We compiled spectral energy distributions of 85 Galactic post-AGB binary systems. We built-up a color-color diagram to differentiate between the different disk morphologies traced by the characteristics of the infrared excess. We categorised different disk types and looked for correlations with other observational characteristics of these systems. 8 to 12% of our targets are surrounded by transition disks, i.e. disks having no or low near-infrared excesses. We find a strong link between these transition disks and the depletion of refractory elements seen on the surface of the post-AGB star. We interpret this correlation as evidence for the presence of a mechanism that stimulates the dust and gas separation within the disk and which also produces the transition disk structure. We propose that such a mechanism can be a giant planet carving a hole in the disk which traps the dust in the outer disk parts. We propose two disk evolutionary scenarios, depending on the presence of such a giant planet in the disk. We advocate that giant planets can successfully explain the correlation between the transition disks and the depletion of refractory materials observed in post-AGB binaries. If the planetary scenario is confirmed, disks around post-AGB binaries could be a unique laboratory to test planet-disk interactions and their influence on the late evolution of binary stars. Whether the planets are first or second generation also remains to be studied. We argue that these disks are the perfect place to study planet formation scenarios in an unprecedented parameter space.
- ID:
- ivo://CDS.VizieR/J/PASP/102/1392
- Title:
- UBV photometry from HK survey. I
- Short Name:
- J/PASP/102/1392
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photoelectric photometry is presented for a sample of 139 halo stars drawn an extension of the HK (Ca II H & K lines) objective-prism survey of Beers, Preston and Shectmann (1988ApJS...67..461) to the Northern Galactic hemisphere. The candidates for which photometry is reported here were selected to span a wide range of types, but are dominated by stars classified as type AB, A, or "metal-poor" (MP).
- ID:
- ivo://CDS.VizieR/J/ApJS/76/1001
- Title:
- UBV photometry of HK survey stars
- Short Name:
- J/ApJS/76/1001
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photoelectric UBV observations of 1782 stars are used to explore properties of the HK objective-prism survey conducted by Beers, Preston, and Shectman with the Curtis-Schmidt telescope of the Cerro Tololo Inter-American Observatory. We construct an intrinsic (U-B)0 versus (B-V)0 relation for blue horizontal branch stars and use it to derive estimates of E(B-V) color excesses in 50 survey fields. Comparison of these with the reddening maps of Burstein and Heiles indicates good agreement except in low-latitude fields toward the Galactic bulge. We describe qualitative features of the stellar content of the HK survey by use of unreddened two-color diagrams and indicate how the photometric data may prove useful in several applications. Finally, we use a halo density model to estimate the variation of completeness with apparent magnitude, B, in our catalog of field horizontal branch star candidates.
