NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
Tests of two convection theories for red giant and red supergiant envelopesTwo theories of stellar envelope convection are considered here in the context of red giants and red supergiants of intermediate to high mass: Boehm-Vitense's standard mixing-length theory (MLT) and Canuto & Mazzitelli's new theory incorporating the full spectrum of turbulence (FST). Both theories assume incompressible convection. Two formulations of the convective mixing length are also evaluated: l proportional to the local pressure scale height (H(sub P)) and l proportional to the distance from the upper boundary of the convection zone (z). Applications to test both theories are made by calculating stellar evolutionary sequences into the red zone (z). Applications to test both theories are made by calculating stellar evolutionary sequences into the red phase of core helium burning. Since the theoretically predicted effective temperatures for cool stars are known to be sensitive to the assigned value of the mixing length, this quantity has been individually calibrated for each evolutionary sequence. The calibration is done in a composite Hertzsprung-Russell diagram for the red giant and red supergiant members of well-observed Galactic open clusters. The MLT model requires the constant of proportionality for the convective mixing length to vary by a small but statistically significant amount with stellar mass, whereas the FST model succeeds in all cases with the mixing lenghth simply set equal to z. The structure of the deep stellar interior, however, remains very nearly unaffected by the choices of convection theory and mixing lenghth. Inside the convective envelope itself, a density inversion always occurs, but is somewhat smaller for the convectively more efficient MLT model. On physical grounds the FST model is preferable, and seems to alleviate the problem of finding the proper mixing length.
Document ID
19950041422
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Stothers, Richard B.
(NASA Goddard Inst. for Space Studies, New York, NY United States)
Chin, Chao-Wen
(NASA Goddard Inst. for Space Studies, New York, NY United States)
Date Acquired
August 16, 2013
Publication Date
February 10, 1995
Publication Information
Publication: Astrophysical Journal, Part 1
Volume: 440
Issue: 1
ISSN: 0004-637X
Subject Category
Astrophysics
Distribution Limits
Public
Copyright
Other
No Preview Available