Eclipse observations of RS CVn binaries II. A parametric model of extended matter

We have surveyed ten RS CVn binary systems and have detected large regions of extended, prominencelike material which we have shown to be a common feature in these systems. These extended regions are apparent as anomalous absorption features in the spectra when they obscure the disk of the eclipsed star and as weak emission features when they appear with no disk behind. We have constructed a first-generation model to verify the general prominencelike nature of the material and to estimate its extent and its most basic physical characteristics. In this paper we present our results of our modeling on four of the systems in our survey that showed clear signatures of extended material: AW Her, MM Her, SS Boo, and UV Psc. We find that these stellar prominencelike structures are very much larger than their solar counterparts, though their gross physical characteristics (i.e., their electron density and temperature and their general appearance as tenuous, vertically oriented, magnetically confined structures) are similar to those seen in solar prominences. These features appear to evolve fairly rapidly, since moderate- to high-velocity flows ranging from several tens of km/s to 170 km/s are apparent. However, in at least one case (SS Boo) they are recurrent over a time scale of at least a year. We conclude by discussing the implications of this work regarding the nature of close binary star active structures and their evolution.