Stellar evolution at high mass with semiconvective mixing according to the Schwarzschild criterion

Journal Article · Mon Mar 01 04:00:00 EST 1976 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/154191· OSTI ID:7354788

Stothers, R; Chin, C

New evolutionary sequences of models for stars of 5--60 M/sub sun/ with four different initial chemical compositions have been constructed with the use of the Schwarzschild criterion for convection. This criterion leads to semiconvection outside the convective core just after the zero-age main-sequence stage for masses greater than approx.12 M/sub sun/ and just before the stage of central hydrogen exhaustion for masses greater than approx.6M/sub sun/. The base of the semiconvective zone thereafter becomes fully convective, with the result that the hydrogen profile in the intermediate zone acquires a local plateau. Competition between the effects of the hydrogen plateau, of the envelope opacity, and of the luminosity-to-mass ratio provides the reason why the post--main-sequence evolutionary tracks on the H-R diagram are found to vary widely as a function of initial chemical composition for masses less than approx.17 M/sub sun/ and why, for higher masses, the tracks invariably reach the red region of the H-R diagram only toward the end of core helium burning. The tracks for the more massive stars are found to be relatively insensitive to the uncertainties in the nuclear reaction rates. Small differences among the sequences computed by different authors are probably due mostly to slight differences in the opacities adopted. It is found that the rather cool range of effective temperatures predicted for stable blue supergiants with masses above approx.20 M/sub sun/ is not in agreement with the observations. An observational test utilizing the surface hydrogen abundance of stellar remnants in binary systems is at present inconclusive in deciding whether the Schwarzschild criterion or the Ledoux criterion is the correct criterion for convection to use. It is strongly suggested that neither criterion with any reasonable adopted initial chemical composition can at present lead to model predictions that satisfy all the observational requirements. (AIP)

• Research Organization: Institute for Space Studies, Goddard Space Flight Center, NASA
• OSTI ID: 7354788
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 204:2; 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
BINARY STARS
CHEMICAL COMPOSITION
CONVECTION
CRYOGENIC FLUIDS
DIAGRAMS
ELEMENTS
ENERGY TRANSFER
FLUIDS
GIANT STARS
HEAT TRANSFER
HELIUM
HERTZSPRUNG-RUSSELL DIAGRAM
HYDROGEN
LUMINOSITY
MASS
NONMETALS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RARE GASES
STAR EVOLUTION
STARS
SUPERGIANT STARS