Studies of evolved stars. I. Plume mixing in S and N stars.
Abstract
A detailed hydrodynamic model for mixing in evolved stars in the mass range 3-10 M0 is presented. This model is based on meteorological models of terrestrial maintained plumes. These plumes transport carbon and heavy elements from the region between the hydrogen and helium shell sources during the helium shell flashes to the base of the convective envelope on a time scale of 1 year. The motion is driven by the energy from the 12C(p, y)'3N(fl+)13C(p, y)14N reaction sequence. The CN abundances approach but fall considerably short of the steady-state ratios. The mass fraction ratio of 12C/13C is between 2.7 and 4.0 just as the plumes enter the convective envelope. Very little 14N is produced, however. Lithium-7 is produced in the plumes from 3He in the form of 7Be as proposed by Cameron and Cameron and Fowler. The plumes are shown to be capable of converting an M star to a carbon star in 50200 shell flashes. Stellar population statistics support the identification of these models as S and N stars. Subject headings: carbon stars - convection - interiors, stellar
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 1973
- DOI:
- 10.1086/152216
- Bibcode:
- 1973ApJ...183..151S