Alignment of rotational axes in asynchronous late type binaries

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, i_r, of the primaries and the orbital inclinations, i_o, are independently determined to test the alignment between the equatorial and the orbital planes. The observed difference Delta i=| {i_o} - {i_r}| 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 Delta i can be studied only by statistical methods. The distribution of the observed Delta i is compared wih the expected values of Delta i() e 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. The appendix is available only electronically with the on-line publication at http://link.springer.de/link/service/journals/00230