- ID:
- ivo://CDS.VizieR/J/A+A/554/A84
- Title:
- Abundances of evolved stars
- Short Name:
- J/A+A/554/A84
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Currently, the core accretion model has its strongest observational evidence on the chemical signature of mostly main sequence stars with planets. We aim to test whether the well-established correlation between the metallicity of the star and the presence of giant planets found for main sequence stars still holds for the evolved and generally more massive giant and subgiant stars. Although several attempts have been made so far, the results are not conclusive since they are based on small or inhomogeneous samples. We determine in a homogeneous way the metallicity and individual abundances of a large sample of evolved stars, with and without known planetary companions, and discuss their metallicity distribution and trends. Our methodology is based on the analysis of high-resolution echelle spectra (R~67000) from 2-3 meter class telescopes. It includes the calculation of the fundamental stellar parameters (effective temperature, surface gravity, microturbulent velocity, and metallicity) by applying iron ionisation and excitation equilibrium conditions to several isolated FeI and FeII lines, as well as, calculating individual abundances of different elements such as Na, Mg, Si, Ca, Ti, Cr, Co, or Ni.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/865/44
- Title:
- Abundances of evolved stars from IGRINS. I.
- Short Name:
- J/ApJ/865/44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have derived elemental abundances of three field red horizontal branch stars using high-resolution (R~45000), high signal-to-noise ratio (S/N>~200) H- and K-band spectra obtained with the Immersion Grating Infrared Spectrograph (IGRINS). We have determined the abundances of 21 elements, including {alpha} (Mg, Si, Ca, S), odd-Z (Na, Al, P, K), Fe-group (Sc, Ti, Cr, Co, Ni), neutron-capture (Ce, Nd, Yb), CNO-group elements. S, P, and K are determined for the first time in these stars. H- and K-band spectra provide a substantial number of S I lines, which potentially can lead to a more robust exploration of the role of sulfur in the cosmochemical evolution of the Galaxy. We have also derived ^12^C/^13^C ratios from synthetic spectra of the first-overtone ^12^CO (2-0) and (3-1) and ^13^CO (2-0) lines near 23440{AA} and ^13^CO (3-1) lines at about 23730{AA}. Comparison of our results with the ones obtained from the optical region suggests that the IGRINS high-resolution H- and K-band spectra offer more internally self-consistent line abundances of the same species for several elements, especially the {alpha}-elements. This in turn provides more reliable abundances for the elements with analytical difficulties in the optical spectral range.
- ID:
- ivo://CDS.VizieR/J/A+A/511/A56
- Title:
- Abundances of five open clusters
- Short Name:
- J/A+A/511/A56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The present number of Galactic open clusters that have high resolution abundance determinations, not only of [Fe/H], but also of other key elements, is largely insufficient to enable a clear modeling of the Galactic disk chemical evolution. To increase the number of Galactic open clusters with high quality measurements, we obtained high resolution (R~30000), high quality (S/N~50-100 per pixel), echelle spectra with the fiber spectrograph FOCES, at Calar Alto, Spain, for three red clump stars in each of five Open Clusters. We used the classical equivalent width analysis method to obtain accurate abundances of sixteen elements: Al, Ba, Ca, Co, Cr, Fe, La, Mg, Na, Nd, Ni, Sc, Si, Ti, V, and Y. We also derived the oxygen abundance using spectral synthesis of the 6300{AA} forbidden line.
- ID:
- ivo://CDS.VizieR/J/MNRAS/492/1164
- Title:
- Abundances of Gaia DR2 wide binaries
- Short Name:
- J/MNRAS/492/1164
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- One of the high-level goals of Galactic archaeology is chemical tagging of stars across the Milky Way to piece together its assembly history. For this to work, stars born together must be uniquely chemically homogeneous. Wide binary systems are an important laboratory to test this underlying assumption. Here we present the detailed chemical abundance patterns of 50 stars across 25 wide binary systems comprised of main-sequence stars of similar spectral type identified in Gaia DR2 with the aim of quantifying their level of chemical homogeneity. Using high-resolution spectra obtained with McDonald Observatory, we derive stellar atmospheric parameters and precise detailed chemical abundances for light/odd-Z (Li, C, Na, Al, Sc, V, Cu), alpha (Mg, Si, Ca), Fe-peak (Ti, Cr, Mn, Fe, Co, Ni, Zn), and neutron capture (Sr, Y, Zr, Ba, La, Nd, Eu) elements. Results indicate that 80% (20 pairs) of the systems are homogeneous in [Fe/H] at levels below 0.02dex. These systems are also chemically homogeneous in all elemental abundances studied, with offsets and dispersions consistent with measurement uncertainties. We also find that wide binary systems are far more chemically homogeneous than random pairings of field stars of similar spectral type. These results indicate that wide binary systems tend to be chemically homogeneous but in some cases they can differ in their detailed elemental abundances at a level of [X/H]~0.10dex, overall implying chemical tagging in broad strokes can work.
- ID:
- ivo://CDS.VizieR/J/A+A/513/A35
- Title:
- Abundances of Galactic red giants
- Short Name:
- J/A+A/513/A35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The formation and evolution of the Galactic bulge and its relationship with the other Galactic populations is still poorly understood. To establish the chemical differences and similarities between the bulge and other stellar populations, we performed an elemental abundance analysis of alpha- (O, Mg, Si, Ca, and Ti) and Z-odd (Na and Al) elements of red giant stars in the bulge as well as of local thin disk, thick disk and halo giants. We use high-resolution optical spectra of 25 bulge giants in Baade's window and 55 comparison giants (4 halo, 29 thin disk and 22 thick disk giants) in the solar neighborhood. All stars have similar stellar parameters but cover a broad range in metallicity (-1.5<[Fe/H]<+0.5). A standard 1D local thermodynamic equilibrium analysis using both Kurucz and MARCS models yielded the abundances of O, Na, Mg, Al, Si, Ca, Ti and Fe. Our homogeneous and differential analysis of the Galactic stellar populations ensured that systematic errors were minimized.
- ID:
- ivo://CDS.VizieR/J/A+A/430/255
- Title:
- Abundances of HD221170
- Short Name:
- J/A+A/430/255
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the abundance determination in the atmosphere of the bright halo star HD 221170. The spectra were taken with the Terskol Observatory's 2.0-m telescope with a resolution R=45000 and signal-to-noise ratio up to 250 in the wavelength region 3638-10275{AA}. The abundances of 43 chemical elements were determined with the method of spectrum synthesis.
- ID:
- ivo://CDS.VizieR/J/ApJ/836/5
- Title:
- Abundances of LAMOST giants from APOGEE DR12
- Short Name:
- J/ApJ/836/5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this era of large-scale spectroscopic stellar surveys, measurements of stellar attributes ("labels," i.e., parameters and abundances) must be made precise and consistent across surveys. Here, we demonstrate that this can be achieved by a data-driven approach to spectral modeling. With The Cannon, we transfer information from the APOGEE survey to determine precise T_eff_, logg, [Fe/H], and [{alpha}/M] from the spectra of 450000 LAMOST giants. The Cannon fits a predictive model for LAMOST spectra using 9952 stars observed in common between the two surveys, taking five labels from APOGEE DR12 as ground truth T_eff_, logg, [Fe/H], [{alpha}/M], and K-band extinction A_k_. The model is then used to infer T_eff_, logg, [Fe/H], and [{alpha}/M] for 454180 giants, 20% of the LAMOST DR2 stellar sample. These are the first [{alpha}/M] values for the full set of LAMOST giants, and the largest catalog of [{alpha}/M] for giant stars to date. Furthermore, these labels are by construction on the APOGEE label scale; for spectra with S/N>50, cross-validation of the model yields typical uncertainties of 70K in T_eff_, 0.1 in logg, 0.1 in [Fe/H], and 0.04 in [{alpha}/M], values comparable to the broadly stated, conservative APOGEE DR12 uncertainties. Thus, by using "label transfer" to tie low-resolution (LAMOST R~1800) spectra to the label scale of a much higher-resolution (APOGEE R~22500) survey, we substantially reduce the inconsistencies between labels measured by the individual survey pipelines. This demonstrates that label transfer with The Cannon can successfully bring different surveys onto the same physical scale.
- ID:
- ivo://CDS.VizieR/J/ApJ/882/177
- Title:
- Abundances of 4 member stars of Tucana III
- Short Name:
- J/ApJ/882/177
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a chemical abundance analysis of four additional confirmed member stars of Tucana III, a Milky Way satellite galaxy candidate in the process of being tidally disrupted as it is accreted by the Galaxy. Two of these stars are centrally located in the core of the galaxy while the other two stars are located in the eastern and western tidal tails. The four stars have chemical abundance patterns consistent with the one previously studied star in Tucana III: they are moderately enhanced in r-process elements, i.e., they have <[Eu/Fe]>~+0.4dex. The non-neutron-capture elements generally follow trends seen in other dwarf galaxies, including a metallicity range of 0.44 dex and the expected trend in {alpha}-elements, i.e., the lower metallicity stars have higher Ca and Ti abundances. Overall, the chemical abundance patterns of these stars suggest that Tucana III was an ultra-faint dwarf galaxy, and not a globular cluster, before being tidally disturbed. As is the case for the one other galaxy dominated by r-process enhanced stars, Reticulum II, Tucana III's stellar chemical abundances are consistent with pollution from ejecta produced by a binary neutron star merger, although a different r-process element or dilution gas mass is required to explain the abundances in these two galaxies if a neutron star merger is the sole source of r-process enhancement.
- ID:
- ivo://CDS.VizieR/J/ApJ/821/37
- Title:
- Abundances of metal-poor star HD 94028
- Short Name:
- J/ApJ/821/37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed analysis of the composition and nucleosynthetic origins of the heavy elements in the metal-poor ([Fe/H]=-1.62+/-0.09) star HD 94028. Previous studies revealed that this star is mildly enhanced in elements produced by the slow neutron-capture process (s process; e.g., [Pb/Fe]=+0.79+/-0.32) and rapid neutron-capture process (r process; e.g., [Eu/Fe]=+0.22+/-0.12), including unusually large molybdenum ([Mo/Fe]= +0.97+/-0.16) and ruthenium ([Ru/Fe]=+0.69+/-0.17) enhancements. However, this star is not enhanced in carbon ([C/Fe]=-0.06+/-0.19). We analyze an archival near-ultraviolet spectrum of HD 94028, collected using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, and other archival optical spectra collected from ground-based telescopes. We report abundances or upper limits derived from 64 species of 56 elements. We compare these observations with s-process yields from low-metallicity AGB evolution and nucleosynthesis models. No combination of s- and r-process patterns can adequately reproduce the observed abundances, including the super-solar [As/Ge] ratio (+0.99+/-0.23) and the enhanced [Mo/Fe] and [Ru/Fe] ratios. We can fit these features when including an additional contribution from the intermediate neutron-capture process (i process), which perhaps operated through the ingestion of H in He-burning convective regions in massive stars, super-AGB stars, or low-mass AGB stars. Currently, only the i process appears capable of consistently producing the super-solar [As/Ge] ratios and ratios among neighboring heavy elements found in HD 94028. Other metal-poor stars also show enhanced [As/Ge] ratios, hinting that operation of the i process may have been common in the early Galaxy.
- ID:
- ivo://CDS.VizieR/J/A+A/645/A61
- Title:
- Abundances of 25 metal-poor stars
- Short Name:
- J/A+A/645/A61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Among carbon-enhanced metal-poor (CEMP) stars, some are found to be enriched in slow-neutron capture (s-process) elements (and are then tagged CEMP-s), some have overabundances in rapid-neutron capture (r-process) elements (tagged CEMP-r), and some are characterized by both s- and r-process enrichments (tagged CEMP-rs). The current distinction between CEMP-s and CEMP-rs is based on their [Ba/Fe] and [Eu/Fe] ratios, since barium and europium are predominantly produced by the s- and the r-process, respectively. The origin of the abundance differences between CEMP-s and CEMP-rs stars is presently unknown. It has been claimed that the i-process, whose site still remains to be identified, could better reproduce CEMP-rs abundances than the s-process. We propose a more robust classification method for CEMP-s and CEMP-rs stars using additional heavy elements other than Ba and Eu. Once a secure classification is available, it should then be possible to assess whether the i-process or a variant of the s-process better fits the peculiar abundance patterns of CEMP-rs stars. We analyse high-resolution spectra of 24 CEMP stars and one r-process enriched star without carbon-enrichment, observed mainly with the high-resolution HERMES spectrograph mounted on the Mercator telescope (La Palma) and also with the UVES spectrograph on VLT (ESO Chile) and HIRES spectrograph on KECK (Hawaii). Stellar parameters and abundances are derived using MARCS model atmospheres. Elemental abundances are computed through spectral synthesis using the TURBOSPECTRUM radiative transfer code. Stars are re-classified as CEMP-s or -rs according to a new classification scheme using eight heavy element abundances. Within our sample of 25 objects, the literature classification is globally confirmed, except for HE 1429-0551 and HE 2144-1832, previously classified as CEMP-rs and now as CEMP-s stars. The abundance profiles of CEMP-s and CEMP-rs stars are compared in detail, and no clear separation is found between the two groups; it seems instead that there is an abundance continuum between the two stellar classes. There is an even larger binarity rate among CEMP-rs stars than among CEMP-s stars, indicating that CEMP-rs stars are extrinsic stars as well. The second peak s-process elements (Ba, La, Ce) are slightly enhanced in CEMP-rs stars with respect to first-peak s-process elements (Sr, Y, Zr), when compared to CEMP-s stars. Models of radiative s-process nucleosynthesis during the interpulse phases reproduce well the abundance profiles of CEMP-s stars, whereas those of CEMP-rs stars are explained well by low-metallicity 1M_{sun}_ models experiencing proton ingestion. The global fitting of our i-process models to CEMP-rs stars is as good as the one of our s-process models to CEMP-s stars. Stellar evolutionary tracks of an enhanced carbon composition (consistent with our abundance determinations) are necessary to explain the position of CEMP-s and CEMP-rs stars in the Hertzsprung-Russell (HR) diagram using Gaia DR2 parallaxes; they are found to lie mostly on the red giant branch (RGB). CEMP-rs stars present most of the characteristics of extrinsic stars such as CEMP-s, CH, barium, and extrinsic S stars; they can be explained as being polluted by a low-mass, low-metallicity thermally-pulsing asymptotic giant branch (TP-AGB) companion experiencing i-process nucleosynthesis after proton ingestion during its first convective thermal pulses. As such, they could be renamed CEMP-sr stars, since they represent a particular manifestation of the s-process at low-metallicities. For these objects a call for an exotic i-process site may not necessarily be required anymore.
