Luminosity and related parameters of δ Scuti stars from HIPPARCOS parallaxes. General properties of luminosity.

Abstract

The absolute magnitudes of δ Scuti stars derived from parallaxes measured by the Hipparcos astrometric satellite are discussed and compared with the previous estimates based on photometric uvbyβ indices. There are significant differences which are related to photometric effects of metallicity and rotational velocity, but the possible effect of a close companion on the measured apparent magnitude should be also taken into account. The possibility of different groupings of δ Scuti stars based on the absolute magnitudes is briefly discussed. Some high amplitude δ Scuti stars with intermediate or normal metallicity and small and uncertain parallax have apparently a very low luminosity; this could be a systematic effect related to the observational errors.