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Astron. Astrophys. 328, 579-585 (1997)

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Alignment of rotational axes in asynchronous late type binaries

R. Gebocki 1 and A. Stawikowski 2

1 Institute of Theoretical Physics and Astrophysics, University of Gdask, ul. Wita Stwosza 57, PL-80952 Gdansk, Poland (fizrg@univ.gda.pl)
2 N. Copernicus Astronomical Center, ul. Rabiaska 8, PL-87100 Toru, Poland (stawik@ncac.torun.pl)

Received 27 January 1997 / Accepted 10 July 1997

Abstract

41 RS CVn and BY Dra type binaries with reliable orbital and physical parameters have been found to rotate asynchronously with the orbital revolution. For this sample inclinations of the rotational axes, [FORMULA], of the primaries and the orbital inclinations, [FORMULA], are independently determined to test the alignment between the equatorial and the orbital planes. The observed difference [FORMULA] measures a deviation from coplanarity of these planes. It turns out that most asynchronous systems prove to be misaligned, especially when the influence of the position angle is taken into account. Thus, the generally accepted assumption that rotational axes are perpendicular to orbital planes is not valid for asynchronous RS CVn and BY Dra type binaries. The influence of the position angle of the observer on the derived values of [FORMULA] can be studied only by statistical methods. The distribution of the observed [FORMULA] is compared wih the expected values of [FORMULA] for two cases: a) the rotational axes are randomly inclined to the orbital planes, and b) the rotational axes are perpendicular to the orbital planes. The best fit to our observed sample of asynchronous binaries is obtained for the case a), while for the synchronous RS CVn and BY Dra type binaries the rotational axes are perpendicular to their orbital planes.

Key words: stars: binaries: close – stars: rotation

Send offprint requests to: A. Stawikowski

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© European Southern Observatory (ESO) 1997

Online publication: March 26, 1998

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