Spectroscopic Study of C, N, O, and S Abundances in a Field Horizontal-Branch Star HD 161817

Details Spectroscopic Study of C, N, O, and S Abundances in a Field Horizontal-Branch Star HD 161817 Spectroscopic Study of C, N, O, and S Abundances in a Field Horizontal-Branch Star HD 161817

Oct 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997pasj...49..571t&link_type=abstract

Publications of the Astronomical Society of Japan, v.49, p.571-581.

Astronomy and Astrophysics

Astronomy

6

Stars: Abundances, Stars: Atmospheres, Stars: Horizontal Branch, Stars: Individual (Hd 161817, 20 Cvn), Stars: Population Ii

Scientific paper

A detailed non-LTE analysis of neutral C, N, O, and S lines was performed based on a set of CCD spectra in the red and near-IR wavelength regions for a field Pop II horizontal-branch star HD 161817 (along with 20 CVn included for a comparison), in order to establish the photospheric abundances of these elements. It turned out that [O/Fe] and [S/Fe] show a mild excess, amounting to 0.4--0.5 dex, which agrees quantitatively well with that of typical halo dwarfs corresponding to [Fe/H] ~ -1.5 (the metallicity of HD 161817), suggesting that the original composition is retained unaltered for oxygen and sulfur (alpha -elements). Meanwhile, the resulting abundances of carbon and nitrogen ([C/Fe] ~ -0.2 and [N/Fe] ~ + 0.5) indicate a mixing of CN-cycle products, when compared with [C/Fe] =~ [N/Fe] =~ 0 (a typical value occasionally quoted for dwarfs in the halo). It was also found that the microturbulent velocity tends to increase with height in the atmosphere of HD 161817, which may be the cause for the discrepancy between the value established from blue metallic lines (2--3 \kms ) and that from Oi 7771--5 (4 \kms ).

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