Journal Article

The mass ratio and the orbital parameters of the sdOB binary AA Doradus

Slavek M. Rucinski

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 395, issue 4, pages 2299-2303
Published in print June 2009 | ISSN: 0035-8711
Published online May 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.14709.x
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.

Keywords: binaries: close; binaries: eclipsing; stars: individual: AA Dor

Journal Article.  4403 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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