DY/DZ from fine structure in the Main Sequence based on Hipparcos parallaxes

Abstract

The slope Delta Y/Delta Z is a quantity of interest in relation to stellar evolution, the initial mass function and the determination of the primordial helium abundance. In this paper we estimate Delta Y/Delta Z from fine structure in the Main Sequence of nearby stars from Hipparcos data for stars with Z \leq Zsun and find a value of about 3, which is consistent with what has been found in extragalactic H II regions and with stellar models for suitable upper limits to the initial masses of supernovae according to the IMF slope adopted.

6 pages (MNRAS LaTeX macro) and 4 figures (EPS) submitted to MNRAS November 1997

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