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

Hipparcos parallaxes of high–amplitude δ 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. Comparisonswith several P–L relations from the literature show satisfactory agreement, and all deviations from theHipparcosmean relation canbe explainedby 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 δ Scuti stars, it is concluded that this sample is homogeneous and has similar basic physical properties as the “normal” low–amplitude δ 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 δ Scuti stars can be used to check fundamental distance determinations to e.g. globular clusters, the Galactic bulge and the Magellanic Clouds.