Possibility of mass loss in the red-giant stage from H-R diagrams of galactic clusters

A statistical research on evolved stars beyond hydrogen exhaustion is performed by comparing the H-R diagrams of about 60 open clusters with a set of isochronous curves without mass loss derived from Iben's evolutionary tracks and time scales for Population I stars. Interpreting the difference in magnitude between the theoretical positions thus calculated and the observed ones as due to mass loss, when negative, the results indicate that this loss may be conspicuous only for very massive and red stars. However, a comparison with an analogous work of Lindoff reveals that the uncertainties connected with the bolometric and colour corrections may invalidate by a large amount the conclusions which might be drawn from such research.Presented at the Trieste Colloquium on Mass Loss from Stars, September 12–16, 1968.