History of the chemical evolution of the primary component of the binary system υ Sagittarius

Details History of the chemical evolution of the primary component of the binary system υ Sagittarius History of the chemical evolution of the primary component of the binary system υ Sagittarius

Jan 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998astl...24...39l&link_type=abstract

Astronomy Letters, Volume 24, Issue 1, January 1998, pp.39-47; Pis'ma v Astronomicheskii Zhurnal, Vol. 24, p. 45

Astronomy and Astrophysics

Astronomy

4

Scientific paper

We propose a model of evolution of the internal structure of the peculiar binary system nu Sgr, which accounts for the observed anomalous chemical composition of its atmosphere [X(H) = 10^4, X(He) = 0.844, X(C) = 0.013, X(N) = 0.042]. We assume that five million years ago the primary component of the system was in the stage of nuclear hydrogen burning in the shell that surrounded the helium core at the center of which helium-to-carbon conversion reactions proceeded. Convective mixing caused the produced carbon to diffuse into the hydrogen-burning zone, where it became a catalyst of the CN-cycle reactions resulting in the anomalously high nitrogen abundance. The subsequent ejection of the star's outer layers exposed the shell mentioned above, which is currently the atmosphere of the primary component with the observed chemical anomalies. The elemental abundances that we calculated using our model are in good agreement with observations. We placed quantitative constraints on the density and temperature in the corresponding layers and on the mixing parame- ters. We show that the best agreement with observations is obtained, if 0.25 of the mass of the matter from the helium-burning zone penetrates into the helium envelope. The ratio of the mass fractions He/C in this matter must be equal to 2, and the fraction of mass that diffuses into the hydrogen-burning shell source can vary in the range 1/3 to 1/4 of the shell mass.

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