LUMINOSITY AND RELATED PARAMETERS OF DELTA-SCUTI STARS FROM HIPPARCOSPARALLAXES - GENERAL-PROPERTIES OF LUMINOSITY

The absolute magnitudes of delta Scuti stars derived from parallaxes m easured by the Hipparcos astrometric satellite are discussed and compa red with the previous estimates based on photometric uvby beta indices . There are significant differences which are related to photometric e ffects of metallicity and rotational velocity, but the possible effect of a close companion on the measured apparent magnitude should be als o taken into account. The possibility of different groupings of delta Scuti stars based on the absolute magnitudes is briefly discussed. Som e high amplitude delta Scuti stars with intermediate or normal metalli city and small and uncertain parallax have apparently a very low lumin osity; this could be a systematic effect related to the observational errors.