Meridional circulation and CNO anomalies in red giant stars

Journal Article · Sun Apr 15 04:00:00 EST 1979 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/156996· OSTI ID:6183280

Sweigart, A v; Mengel, J G

The possibility that meridional circulation due to internal rotation might lead to the mixing of CNO-processed material from the vicinity of the hydrogen shell into the envelope of a red giant star has been investigated and found to be generally consistent with the observational data on weak G band and CN-strong stars and on stars with low /sup 12/C//sup 13/C ratios. CNO processing of the red giant envelope by meridional circulation begins on the upper subgiant branch or lower giant branch when the hydrogen shell reaches the hydrogen discontinuity produced by the convective envelope at the time of deepest penetration on the subgiant branch. The main-sequence angular velocity ..omega../sub MS/ needed for substantial CNO processing of the envelope has been computed by assuming that a star retain its interior angular momentum into the red giant phase. If the specific angular momentum is constant within the convective envelope of a red giant star, ..omega../sub MS/ is approx.10/sup -4/ rad s/sup -1/. Such an angular velocity is plausible if one attributes the observed slow rotation rates of the lower main-sequence stars to a spin-down of the outer convective layers. Prohibitively large values of ..omega../sub MS/ are required if the entire convective envelope rotates instead as a solid body. This difficulty can be readily overcome if the inner part of the convective envelope departs from solid-body rotation. Reasons for such a departure are discussed. The distributions of the CNO elements near the hydrogen shell have been computed for several red giant models. The results show that there is a region of significant extent above the hydrogen shell within which carbon has been converted to nitrogen by the CN cycle.

• Research Organization: Laboratory for Astronomy and Solar Physics, NASA Goddard Space Flight Center
• OSTI ID: 6183280
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 229:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640102* -- Astrophysics & Cosmology-- Stars & Quasi-Stellar
Radio & X-Ray Sources
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABUNDANCE
ANGULAR MOMENTUM
ANGULAR VELOCITY
CARBON
CHEMICAL COMPOSITION
CNO CYCLE
ELEMENTS
GIANT STARS
ISOTOPE RATIO
MAIN SEQUENCE STARS
MATHEMATICAL MODELS
MIXING
MOTION
NONMETALS
RED GIANT STARS
ROTATION
STAR BURNING
STAR CLUSTERS
STAR MODELS
STARS
VELOCITY