2009MNRAS.395.2299R

The time sequence of 105 spectra covering one full orbital period of AA Dor has been analysed. Direct determination of Vsini for the sdOB component from 97 spectra outside of the eclipse for the lines Mgii 4481 Å and Siiv 4089 Å clearly indicated a substantially smaller value than estimated before. Detailed modelling of line-profile variations for eight spectra during the eclipse for the Mgii 4481 Å line, combined with the out-of-eclipse fits, gave Vsini = 31.8±1.8km/s. The previous determinations of Vsini, based on the Heii 4686 Å line, appear to be invalid because of the large natural broadening of the line. With the assumption of the solid-body, synchronous rotation of the sdOB primary, the measured values of the semi-amplitude K₁ and Vsini lead to the mass ratio q = 0.213±0.013 which in turn gives K₂ and thus the masses and radii of both components. The sdOB component appears to be less massive than assumed before, M₁= 0.25±0.05M_☉, but the secondary has its mass-radius parameters close to theoretically predicted for a brown dwarf, M₂= 0.054±0.010M_☉ and R₂= 0.089 ±0.005R_☉. Our results do not agree with the recent determination of V{ubreve}ckovi{cacute} et al. based on a K₂ estimate from line-profile asymmetries.