Hipparcos parallaxes and period-luminosity relations of high-amplitude δ Scuti stars

Hipparcos parallaxes of high-amplitude delta Scuti stars are used to derive a period-luminosity relation with a scatter of about +/-0.1 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 delta Scuti stars, it is concluded that this sample is homogeneous and has similar basic physical properties as the "normal" low-amplitude delta 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. Therefore, observations of high-amplitude delta Scuti stars can be used to check fundamental distance determinations to e.g. globular clusters, the Galactic bulge and the Magellanic Clouds.