Hipparcos Parallaxes and Period--Luminosity Relations of High--Amplitude

Abstract

. Hipparcos parallaxes of high-amplitude ffi Scuti stars are used to derive a period-luminosity relation with a scatter of about \Sigma0.1 mag, which is independent from photometric calibrations to absolute luminosities. Comparisons with several P--L relations from the literature show satisfactory agreement, and all deviations from the Hipparcos mean relation can be explained by uncertainties in the data available before Hipparcos. Hipparcos data for a few stars of relatively small and uncertain parallaxes indicate that they may have systematically very low luminosity. However, briefly discussing Lutz--Kelker corrections and considering the full sample of high--amplitude ffi Scuti stars, it is concluded that this sample is homogeneous and has similar basic physical properties as the "normal" low--amplitude ffi Scuti stars. It is emphasized that the Hipparcos P--L relation defines a new distance scale which is independent from those of the classical Cepheids and RR Lyrae stars. Theref..