New VI photometry of the sdOB binary AA Dor and an improved photometric model

Abstract

New VI CCD photometry, obtained with integration times of 20s, of the sdOB+degenerate-dwarf eclipsing binary system AA Dor has provided new complete light curves with an rms scatter about a mean curve of +/-0.004 mag. These data are analysed with an improved Light2 light curve synthesis code to yield more accurate determinations of the radii of both stars, the orbital inclination, and the flux ratio between the two components. These radii are only a little different from the values derived 25 years ago from less complete data, but the uncertainties on these values are improved by a factor of two. The apparent discrepancy remains between the surface gravity of the sdOB primary star obtained from the light-curve solution with the published spectroscopic orbit and that obtained from NLTE analysis of high-resolution spectra of the sdOB star. The substantial reflection effect in the system is adequately represented by the Light2 code with a bolometric albedo of unity in light curves extending from 0.35 microns to 2.2 microns. However there are differences at individual wavelengths in the derived albedo, which may indicate redistribution of flux from shorter wavelengths into the V and I passbands.