CNO abundances in Cepheids and supergiants: theoretical implications

Journal Article · Wed Sep 15 04:00:00 EDT 1982 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/160290· OSTI ID:6577236

Becker, S A; Cox, A N

Models of a 9 M/sub sun/ star have been evolved to see if the observed nitrogen enhancement and the carbon and oxygen depletions in yellow supergiants and Cepheids can be explained. In the standard (first dredge-up phase) evolutionary picture, the normal or near normal CNO abundances for the envelopes of stars on the main sequence are altered when such stars become red giants with deeply mixed convective envelopes prior to core He ignition. While this process does result in a noticeable nitrogen enhancement and a carbon reduction (oxygen is only slightly reduced), the observed changes in the CNO abundances are reported to be much larger. Consequently, other additional mechanisms need to be considered. The effects of primordial abundances, mass loss and transfer, convective overshoot, rotation, and magnetic fields are discussed. It is found that in order to explain the observed O depletion, there must be some form of mixing between the convective hydrogen-burning core and the inner part of the radiative envelope. This additional mixed material is then latter dredged up during the red giant phase. A simplified three-zone model is proposed. Finally, as a consequence of this additional mixing, longer main-sequence lifetimes and more luminous blue loops in the Cepheid region are predicted.

• Research Organization: W. K. Kellogg Radiation Laboratory, California Institute of Technology
• OSTI ID: 6577236
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 260:2; 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
CARBON
CEPHEIDS
CONVECTION
ELEMENTS
GIANT STARS
HYDROGEN BURNING
MAIN SEQUENCE STARS
MATHEMATICAL MODELS
MOTION
NITROGEN
NONMETALS
NUCLEOSYNTHESIS
OXYGEN
PULSATING VARIABLE STARS
RED GIANT STARS
ROTATION
STAR BURNING
STAR EVOLUTION
STAR MODELS
STARS
STELLAR WINDS
SUPERGIANT STARS
VARIABLE STARS