PHOTOMETRIC SYSTEMS FOR QUANTITATIVE STUDIES OF WHITE-DWARFS

The suitability of the Stromgren uvby system for quantitative studies of white dwarfs is examined. For the cooler DA's the system yields useful indicators of the atmospheric parameters but is inadequate for gravity determinations for Teff > 15 000 K. An alternative intermediate band system is suggested which allows determinations of Teff and g over the observed colour range. The hydrogen deficient DB white dwarfs are also discussed. The uvby system is found to be unsuitable for quantitative studies of these stars and alternative methods are suggested. Masses and radii of cool DA white dwarfs for which reliable absolute magnitudes are available are derived from Graham's uvby photometry. No significant discrepancy with theoretical mass-radius relations for heavy element interior compositions (He -> Fe) is found. The scatter due to probable errors in the observational data, in particular the absolute magnitude determinations, is, however, very large. © Royal Astronomical Society.