On the Subgiant Components of Eclipsing Binary Systems.

Abstract

A recent paper by Parenago (1950) on the subgiant components of "single-line" eclipsing binary systems of the Algol type has been studied in the light of a result by Struve (1953), showing statistically that the luminosities of the subgiant secondaries depend not only on their masses and radii but on the mass ratio of the components. This mass ratio is directly related to the size of the zerovelocity surface passing through the inner Lagrangian point of the system, which sets an upper limit to the size of the star. From the photometric rad of the secondaries it was possible to obtain an upper limit to their masses. Those with mass limit less than 1 0 were classified as definitely abnormal subgiants. These stars were found to lie, as a group, very near their maximum size. An evolutionary mechanism is proposed, relating the advanced "biological age" of these stars to the fact that they fill the inner zero-velocity surface.