SIMBAD references

1996A&A...311..127F - Astronomy and Astrophysics, volume 311, 127-134 (1996/7-1)

On the width of the theoretical lower main sequence. Consequences for the determination of the {DELTA}Y/{DELTA}Z ratio in the solar neighbourhood.

FERNANDES J., LEBRETON Y. and BAGLIN A.

Abstract (from CDS):

We discuss the relation between the main sequence thickness and chemical composition variations. With the help of theoretical zero-age main sequence models between 0.7 and 1.0M, computed with an advanced physical description of the stellar interiors, in a range of metallicities typical from Population I stars (0.008≤Z≤0.034), we establish a theoretical relation between the relative helium to metal enrichment, {DELTA}Y/{DELTA}Z, and the main-sequence broadening, represented in this work by {DELTA}Mbol. The locus in the Hertzsprung-Russell diagram of 69 low mass stars closer than 25pc is analyzed, taking into account the present available metallicities for 25 of them. Models show that {DELTA}Y/{DELTA}Z should be higher than 2.0 in the solar neighbourhood to account for the observational main sequence width. As a consequence an helium abundance lower limit of Y=0.246 is found in the solar neighbourhood. This value is presently loosely constrained by the observational uncertainties. A new step towards the {DELTA}Y/{DELTA}Z determination is expected in the very near future, when accurate values of the stellar luminosities as determined by Hipparcos will permit more definite conclusions.

Abstract Copyright:

Journal keyword(s): Galaxy: solar neighbourhood - stars: abundances - stars: low mass - stars: HR diagram - Galaxy: abundances

Simbad objects: 25

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