The Extreme Ultraviolet (EUV) Rotation-activity Relation for Late-Type Stars

We present results on an optically selected sample of 44 main sequence stars, including 18 EUV sources not previously reported, detected with the Extreme Ultraviolet Explorer (EUVE) satellite. The sample covers a broad range of spectral types (early F to late M) with known rotation periods from 0.4 days to 50 days. A comparison of the EUV fluxes with activity related parameters shows that the dynamo related Rossby number is the best parameter for describing the levels of coronal activity. This is in agreement with the conclusion of Noyes et al. (ApJ, 279,763) for the chromosphere. The saturated levels of coronal activity are discussed. This work has been supported by NASA contract NAS5-30180.