Helium gravitational settling in the envelopes of evolving main-sequence A and F stars

Details Helium gravitational settling in the envelopes of evolving main-sequence A and F stars Helium gravitational settling in the envelopes of evolving main-sequence A and F stars

Sep 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992apjs...82..329r&link_type=abstract

Astrophysical Journal Supplement Series (ISSN 0067-0049), vol. 82, no. 1, Sept. 1992, p. 329-349. Research supported by NSERC an

Astronomy and Astrophysics

Astrophysics

16

A Stars, F Stars, Helium, Main Sequence Stars, Stellar Envelopes, Stellar Gravitation, Gaseous Diffusion, Lithium, Stellar Convection, Stellar Cores, Stellar Evolution, Stellar Models

Scientific paper

A two-step envelop-diffusion program is set forth for modeling the envelope structure of A and F stars for the case in which the gravitational settling of helium occurs. The primary input for the technique is the Teff-luminosity history of a homogeneous star, and the model generates an inhomogeneous star with an envelope that includes the effects of the diffusion of helium. The coupling between diffusion and evolution is simulated by alternating between diffusion calculations in a fixed envelop and readjustments of the envelope structure based on the diffusion-based abundance profiles. The evolution of A and F stars with helium settling in the envelopes is described, and when the value of alpha is determined to fit the sun Teff models at about 6700 K have uniquely fixed properties. Changes in Z do not alter the Teff/temperature relation at the bottom of the convection zone; this suggests that only models that fit the sun can be used to determine the Teff at which the Li gap is observed in F stars.

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