Observational data relevant to understanding synchronization and circularization in chromospherically active binaries

Abstract

Twenty chromospherically active binaries which promise to be useful in understanding the synchronization and circularlzation problem are listed in Table I with a synopsis of relevant data. Included are all those for which the orbital period exceeds 60 days and/or the orbital eccentricity is 0. I or more and/or the rotational and orbital periods differ by more than 10%. BY Dra, HR 7578, and BD +24°692 would be considered BY Dra-type systems But most of the rest would be considered RS CVntype binaries. HR 1362 and HD 217188 are not yet proven to be binaries but we are tentatively presuming they are. In Table I the first column gives a familiar designation for each binary. The second column gives the orbital period taken from Batten et al. (1978) or from more recent published sources or in one case (HD 8357) from Fekel (1985). The third column is the orbital eccentricity, where the asterisk means Lucy and Sweeney (1971) concluded that the orbit could be considered circular. The fourth column is the rotational period, in every case except one (Capella) deduced from the photometric period by assuming variability is produced by the chromospherieally active (presumably spotted) star. Rotational periodsdeduced in this way can be far more accurate than those deduced from rotationally broadened llne profiles; spectroscopically deduced rotation speeds require knowledge of the absolute radius of the star and the orbital inclination and~ moreover, are meaningless when rotation is very slow and the broadening correspondingly very small. For 93 Leo and HR 7428 the photometric period was not derived explicitly but a wave did appear in the light curve when the photometry was plotted modulo the known orbital period. Two values of P(rot.) are given for BM Cam, corresponding to the two spot groups found by Hall and Osborn (1985). In two cases (33 Psc and HR 7428) a component of the photometric variability has tentatively been ascribed to the ellipticity effect, not to starspots. The fifth column is the total range of photometric variation in the V bandpass, although in any one year the peak-to-peak amplitude of the wave was generally less. The sixth column is a reference for the photometric data, where the abbreviation ASS stands for Astrophysics and Space Science. The last column is the ratio of the rotational to the orbital period~ where of course a value near unity indicates synchronization. For two of the BY Dra systems (BY Dra and BD +24°692) the orbital eccentricity and asynchronous rotation has been interpreted, in terms of theory developed by Zahn (1977), as a consequence of young age (Bopp et al. 1980). For the RS CVn binaries, however, it is clear that no very simple interpretation connects the data in Table I. We see synchronous rotation associated with orbital periods as long as 80 days but