The time sequence of 105 spectra covering one full orbital period of AA Dor has been analyzed .
Direct determination of V \sin i for the sdOB component from 97 spectra outside of the eclipse for the lines Mg II 4481 Å and Si IV 4089 Å clearly indicated a substantially smaller value than estimated before .
Detailed modelling of line profile variations for 8 spectra during the eclipse for the Mg II 4481 Å line , combined with the out-of-eclipse fits , gave V \sin i = 31.8 \pm 1.8 km s ^ { -1 } .
The previous determinations of V \sin i , based on the He II 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 K _ { 1 } and V \sin i lead to the mass ratio q = 0.213 \pm 0.013 which in turn gives K _ { 2 } and thus the masses and radii of both components .
The sdOB component appears to be less massive than assumed before , M _ { 1 } = 0.25 \pm 0.05 M _ { \odot } , but the secondary has its mass–radius parameters close to theoretically predicted for a brown dwarf , M _ { 2 } = 0.054 \pm 0.010 M _ { \odot } and R _ { 2 } = 0.089 \pm 0.005 R _ { \odot } .
Our results do not agree with the recent determination of Vŭcković et al .
( 10 ) based on a K _ { 2 } estimate from line-profile asymmetries .