The Hipparcos distances of open clusters and their implication on the local variations of the ΔY/ΔZ ratio.

Abstract

Arguments are collected to demonstrate that recent Hipparcos results on the distances of open clusters are in agreement with previous estimates in the Russian literature which have pointed to a shorter distance scale. Evidence of the absence of a universal correlation between helium and metal abundances is given. It is suggested that violations of this correlation may explain the apparent contradictions between the relative positions of the main sequences of open clusters found from the Hipparcos distances.