THE EMISSION OF THE RS CVN BINARIES IN THE IRAS PASSBANDS

In the Literature, there is an ambiguity pertaining to the existence o f a far-IR excess in RS CVn systems. In the current paper we undertook a study of the behaviour of 103 such systems in the IRAS passbands. W e found 72 acceptable detections in the 12 mu m band, and 40 in the 25 mu m band (50% more than the IRAS Point Source Catalog). Although our findings may be interpreted as indicating towards the existence of an excess beyond 12 mu m for some systems, the evidence is not conclusiv e in all but two cases. These are systems GX Lib and HR 7428, with Cap ella being the only system where the IRAS fluxes in all four bands ori ginate from the stellar photosphere. Given the accuracy of the data we did not find 12 mu m excess for any system. We argue that the IRAS da ta alone cannot settle the issue, as their uncertainty is, in many cas es, higher than what the Signal-to-Noise ratio of each observation imp lies. Furthermore, at the higher wavelength bands the IRAS angular res olution drops from 0.5' at 12 mu m to 2' at 100 mu m and the backgroun d becomes very complex, so one cannot be certain about the origin of t he observed flux. The existence of IR excess in the RS CVn stars is im portant as far as the evolutionary scenarios for these systems are con cerned. Future missions such as the Infrared Space Observatory will re turn more sensitive and accurate measurements and the ambiguity can be removed. The fluxes we quote will be helpful when planning these futu re observations, as we provide more accurate photometry and for a larg er selection of sources than the IRAS Point Source Catalog.