Some processes of mixing in the atmospheres of cold giants. Observed evidence of burning of hydrogen

Gorbanyeva, TI, Mishenina, TV, Soubiran, C, Kantsen, LE, Korotin, SA
Kinemat. fiz. nebesnyh tel (Online) 2004, 20(4):300-312
Language: Russian
Abstract: 

Some atmosphere parameters (Teff, lgg, [Fe/H], Vt) and the abundances of 21 elements for 19 giants of the disk are determined. The gravity is determined through three methods, namely, by condition of ionization balance for atoms of iron, with the use of parallaxes (and masses) and the adjustment of wings of the Ca I λ 616.217 nm line. The abundances of the carbon, nitrogen and oxygen are determined from a molecular synthetic spectrum, the abundances of the magnesium and natrium are deduced in the assumption of NLTE, and the abundance of europium is determined from a sophisticated consideration of hyperfine structure. The study of the evidence of stellar evolution and mixing in the stellar atmospheres is carried out. The average values for the abundances of elements of the CNO-group are obtained. They point to the under abundance of the carbon, overabundance of nitrogen and «normal» abundance of the oxygen, which is indicative of the reactions of the CNO-cycle of hydrogen burning and subsequent transfer of the enriched material on a surface. A small surplus of the natrium and a trend of its abundance with lgg are found. A similar trend is revealed in the case of the nitrogen as well. This, probably, points to reactions of burning of hydrogen also in NeNa-cycle where additional Ne can be obtained during a number of transformations from nitrogen.

Keywords: cold giants, stellar atmospheres, stellar evolution