RS CVN VERSUS ALGOL-TYPE BINARIES - A COMPARATIVE-STUDY OF THEIR X-RAY-EMISSION

We have compiled a list of 59 RS CVn binaries and 29 Algol-type binari es with well-known orbital parameters and which have been observed wit h the ROSAT PSPC detector in order to find out whether there is any de tectable influence of mass transfer on the x-ray emission properties o f these two types of active binaries. If there were, one might expect the RS CVn binaries (which typically are expected to have negligible m ass exchange) and the semidetached ''Algol'' binaries (which have well -established mass exchange between the two components) to exhibit syst ematic differences in the x-ray region. We have studied the statistica l correlations between (a) the x-ray luminosity (L(x)) and the Roche-l obe filling fraction (Gamma(2)) for the active star, (b) L(x) and the rotation period (P), and (c) the x-ray surface flux (S-x) and P. In ge neral, we find that the RS CVn and Algol binaries do not have similar L(x) distributions. There is a tendency for the Algol binaries to be s imilar to 3-4 times less luminous compared to RS CVns with the same pe riod. This is the exact opposite of what might have been expected if m ass transfer rates influenced x-ray emission levels, since in that cas e the Algol binaries would be more x-ray luminous than the RS CVn bina ries. A highly significant correlation is found between log S-x and lo g P in both of the two types of binaries, while a weak correlation tha t is observed between log L(x) and log Gamma(2) in the RS CVn binaries is likely to be due to correlations of these quantities with the stel lar radii. (C) 1996 American Astronomical Society.