- ID:
- ivo://CDS.VizieR/J/A+A/561/A63
- Title:
- The chemically peculiar binary HD 161701
- Short Name:
- J/A+A/561/A63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We perform a complete study of the HgMn binary HD 161701, including the determination of physical parameters and photospheric chemical abundances. We analyzed time series of high-resolution FEROS and HARPS spectroscopic observations in addition to a near-IR spectrum obtained with CRIRES. Radial velocity curves were combined with additional spectroscopic information to estimate absolute stellar parameters. A spectral separation technique was applied, which enabled us to conduct a detailed spectral analysis of both components. The primary is a HgMn star with overabundances of P, Mn, Ga, Y, Xe, and Hg. The secondary is an Ap star showing strong (2-5dex) overabundances of Sr, Y, and rare-earth elements. We detected line profile variations in both stellar companions, indicating a non uniform surface distribution of chemical composition. The secondary presents a remarkable chemical pattern with Ti and rare-earths pemanently facing the binary companion, and Fe concentrated on the far side. The primary star shows weak profile variations in Mn and Cr spectral lines. The coincidence of chemical spots with the position of the binary companion suggests a possible connection between the presence of the companion and the origin of chemical anomalies.
Number of results to display per page
Search Results
- 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/339/165
- Title:
- The red spectrum of HD 101065
- Short Name:
- J/A+A/339/165
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Wavelength list for Przybylski's star (a rapidly rotation Ap star) including a measurement of the line depths.
- 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.
- ID:
- ivo://CDS.VizieR/J/ApJ/847/142
- Title:
- Ultra-metal-poor stars LTE and NLTE abundances
- Short Name:
- J/ApJ/847/142
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new ultra-metal-poor stars parameters with [Fe/H] < -4.0 based on line-by-line non-local thermodynamic equilibrium (NLTE) abundances using an up-to-date iron model atom with a new recipe for non-elastic hydrogen collision rates. We study the departures from LTE in their atmospheric parameters and show that they can grow up to ~1.00dex in [Fe/H], ~150K in Teff and ~0.5dex in logg toward the lowest metallicities. Accurate NLTE atmospheric stellar parameters, in particular [Fe/H] being significantly higher, are the first step to eventually providing full NLTE abundance patterns that can be compared with Population III supernova nucleosynthesis yields to derive properties of the first stars. Overall, this maximizes the potential of these likely second-generation stars to investigate the early universe and how the chemical elements were formed.
- ID:
- ivo://CDS.VizieR/J/A+A/367/597
- Title:
- ups Her, phi Her & HR 7018 abundances
- Short Name:
- J/A+A/367/597
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Elemental abundances analyses are performed for the Mercury-Manganese stars {upsilon} Her, {phi} Her, and HR 7018 consistent with previous studies of this series using spectrograms obtained with Reticon and CCD detectors. Comparisons of the first two analyses with those performed using coadded photographic plates show the general consistency of the derived elemental abundances. For {upsilon} Her and for {phi} Her, abundances were newly found for O, and for Al, V, Zn, and Ce, respectively. HR 7018 is discovered to be a single-lined spectroscopic binary. Its Sc abundance is the smallest of any class member with derived abundances and its Sr abundance the largest of any known HgMn star. A correlation analysis of the most complete abundance sets for 20 HgMn stars shows that the abundances of some elements are correlated with one another and some are functions of the stellar effective temperature.
