Analysis of two CH/CN-strong very metal-poor stars.
Abstract
Two very metal-deficient stars, BPS CS 22948-27 and BPS CS 29497-34, recently identified in the HK objective-prism/interference-filter survey of Beers and collaborators, which exhibit, at low resolution, strong CH and CN bands and metallicities [Fe/H]~-3 , have been observed at high spectral resolution and high S/N at the NTT at ESO with the EMMI echelle spectrograph. A preliminary analysis of these spectra shows that these objects are very unusual. The high-resolution work confirms the very low metallicity of these stars and indicates: (i) effective temperatures T_eff_~4000K and surface gravities logg~0.0 to 1.5; (ii) a very large overabundance of carbon and nitrogen, by ~2dex with respect to iron; (iii) a similar overabundance of a few neutron-capture elements, in particular Ba, La and Nd, also by ~2dex; (iv) a low isotopic ratio ^12^C/^13^C; (v) a variable radial velocity for one of the stars (CS 22948-27). These findings suggest that the two stars are extreme cases of CH stars. The spectra are considerably richer in molecular bands than the spectrum of the remarkable star CS-22892-52, identified in the same survey and studied by Sneden et al.. The determination of the ratio of s-process to r-process elements in these two stars must await observations in the blue spectral region.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- January 1997
- Bibcode:
- 1997A&A...317L..63B
- Keywords:
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- STARS: ABUNDANCES;
- STARS: POPULATION II