Far-ultraviolet and X-ray emission of the long period RS CVn star sigma Geminorum.
Linsky, J. L.; Kjeldseth-Moe, O.; Westergaard, N. J.; Ayres, T. R.; Schnopper, H. W.; Engvold, O.; Elgaroy, O.; Jensen, E.; Joras, P. B.
Norway, United States
Abstract
The new UV and X-ray observations of σ Gem support the theory that large active regions associated with starspots are responsible for the enhanced line emission commonly seen in RS CVn systems. The rotational modulation of the UV line fluxes increases with temperature of the line-forming region. The X-ray emission from the stellar corona, on the other hand, shows only a barely detectable variation with rotational phase. One may infer that the coronal active regions of the system are not co-spatial with the activity in the transition region below, and/or occupy a significantly larger surface area. An equally probable explanation, however, is that the X-ray emission is emitted from huge, stellar sized loops.