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À propos de : The mass ratio and the orbital parameters of the sdOB binary AA Doradus        

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  • The mass ratio and the orbital parameters of the sdOB binary AA Doradus
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  • The time sequence of 105 spectra covering one full orbital period of AA Dor has been analysed. 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 eight spectra during the eclipse for the Mg ii 4481 Å line, combined with the out-of-eclipse fits, gave V sin i= 31.8 ± 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 K1 and V sin i 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 ± 0.05 M⊙, but the secondary has its mass-radius parameters close to theoretically predicted for a brown dwarf, M2= 0.054 ± 0.010 M⊙ and R2= 0.089 ± 0.005 R⊙. Our results do not agree with the recent determination of Vŭcković et al. based on a K2 estimate from line-profile asymmetries.
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