Blue loops during core helium burning as the consequence of moderate convective envelope overshooting in stars of intermediate to high mass

Journal Article · Sat Jun 01 04:00:00 EDT 1991 · Astrophysical Journal; (United States)

DOI:https://doi.org/10.1086/170117· OSTI ID:5588297

Stothers, R B; Chin, Chao-Wen ^[1]

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1. NASA, Goddard Institute for Space Studies, New York (USA)

New calculations of stellar evolutionary sequences without semiconvection in any phase have unexpectedly turned up, for stars in the mass range 3-30 solar masses, an irregular pattern of blue loops on the H-R diagram during the core helium-burning phase. Blue loops occur for 3 and 10 solar masses, but not for 5, 7, 15, and 30 solar masses. It is found, however, that the models near the bottom of the red supergiant branch are only marginallly stable against small inward displacements of the former base of the outer convection zone when it was deepest, for the stellar mass range 5-15 solar masses. As a consequence, convective envelope overshooting need only penetrate a distance of about 0.3 of a local pressure scale height to promote a delayed blue loop in these particular sequences. In conformity with previous work, the triggering mechanism for the blue loop appears to be proximity of the hydrogen-burning shell to the hydrogen discontinuity at the former base of the outer convection zone. 27 refs.

• OSTI ID: 5588297
• Journal Information: Astrophysical Journal; (United States), Journal Name: Astrophysical Journal; (United States) Vol. 374; ISSN ASJOA; ISSN 0004-637X
• 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
COLOR
CONVECTION
DIAGRAMS
ELEMENTS
ENERGY TRANSFER
FLUIDS
GASES
GIANT STARS
HEAT TRANSFER
HELIUM
HELIUM BURNING
HERTZSPRUNG-RUSSELL DIAGRAM
HYDROGEN BURNING
MASS
MASS TRANSFER
MATHEMATICAL MODELS
NONMETALS
OPTICAL PROPERTIES
ORGANOLEPTIC PROPERTIES
PHYSICAL PROPERTIES
RARE GASES
RED GIANT STARS
STAR BURNING
STAR EVOLUTION
STAR MODELS
STARS
SUPERGIANT STARS