GALEX photometric data for 193 ROSAT giant stars

Correlations are sought between several chromospheric and coronal activity indicators for giants that were detected in soft X-rays by the ROentgen SATellite. There is an evident correlation between log(L_X_L_bol_) and log(F_MgII_/F_bol_), where LX is the X-ray luminosity and FMgII is the flux from MgIIh and k emission lines, although there is substantial scatter.

Using GALEX far-ultraviolet (FUV) magnitudes, the relationship between an FUV-excess parameter (a proxy for chromospheric and transition-region emission lines) and X-ray luminosity is documented. Correlations found herein are not strong, and may be linked to binarity. There is a varied range of FUV emission among CHeB stars, indicating that giants in this phase may be exhibiting differences or cycles in outer atmospheric activity.