Pulsation models of delta Scuti variables. II. delta Scuti stars as precise distance indicators

Abstract

The Hipparcos period-luminosity relation for high-amplitude delta Scuti stars is discussed as an average period-luminosity-colour-metallicity relation comparing the Hipparcos sample of calibrating stars with a more representative sample taken from McNamara (1997). The Hipparcos relation includes systematic effects of both colour and metallicity and agrees with other period-luminosity relations with an accuracy of about +/- 0.10 mag. Direct stellar-evolution and pulsation modelling is used to study effects on the average period-luminosity relation from the location of the high-amplitude variables within the instability strip given as a range in effective temperature (colour term) and the metallicity given as [Fe/H]. Using accurate data for the instability strip given by McNamara precise agreement with the Hipparcos relation is found. By fitting the bolometric magnitude as a function of pulsation period, effective temperature and metallicity an accuracy of 0.02-0.03 mag is obtained both within the narrow high-amplitude strip and including a much broader strip covering most of the full {delta Sct} instability strip. Problems in practical application of this relation are briefly considered. Using uvbybeta narrow-band photometry it seems possible to obtain this accuracy in determinations of distances to e.g. the Galactic Bulge and the Magellanic Clouds.