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

New V I-C CCD photometry, obtained with integration times of 20 s, 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 2. 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 non-local thermodynamic equilibrium 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 to 2.2 mum. However, there are differences at individual wavelengths in the derived albedo, which may indicate a redistribution of flux from shorter wavelengths into the V and I-C passbands.