Interpretation of photometry on pulsating stars

Abstract

The observed colour variations of pulsating stars can be attributed to changes in their surface conditions, mainly the effective surface temperature and the surface gravity. Variations in these two quantities can be estimated from the colour variations by predicting a relationship between the two, using model stellar atmospheres. Once these variations are known the fluctuations in the stellar radius can also be determined. The uncertainty in the model atmosphere predictions limits the accuracy of this method. In order to ascertain how significant this uncertainty is, three sets of data on delta Scuti type variable stars were analysed using two different sets of model atmospheres. Each set of data was collected on a different photometric system and one of these sets was analysed at three different values of the assumed average effective temperature for the star. Clear differences between the variations predicted by the two different models were found. Peak-to-peak values varied by as much as 150K for the effective temperature variations and by a factor of two for the radial variations. Some conclusions on the choice of photometric system and the effect of varying the average effective temperature were drawn.