The emission of the RS CVn binaries in the IRAS passbands

C.K. Mitrou, J.G. Doyle, M. Mathioudakis and E. Antonopoulou

In the literature, there is an ambiguity pertaining to the existance of 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. We found 72 acceptable detections in the 12mu band, and 40 in the 25mu band (50% more than the IRAS Point Source Catalog). Although our findings may be interpreted as indicating towards the existence of an excess beyond 12mu for some systems, the evidence is not conclusive in all but two cases. These are systems GX Lib and Hr 7428, with Capella being the only system where the IRAS fluxes in all four bands originate from the stellar photosphere. Given the accuracy of the data we did not find 12mu excess for any system. We argue that the IRAS alone cannot settle the issue, as their uncertainty is, in many cases, than what the Signal-to-Noise ratio on each observation implies. Furthermore, at the higher wavelength bands the IRAS angular resolution drops from 0.5 arcmin at 12mu to 2 arcmin at 100mu and the background becomes very complex so one cannot be certain about the origin of the observed flux. The existence of IR excess in the RS CVn stars is important as far as the evolutionary scenarios for these systems are concerned. Future missions such as the Infrared Space Observatory will return more sensitive and accurate measurements and the ambiguity can be removed. The fluxes we quote will be helped when planning these future observations, as we provide more accurate photometry and for a larger selection of sources than the IRAS Point Source Catalog.