with temperatures in excess of $10^{6}$K. In stars that have reached the zero age main sequence (ZAMS) or older, the driving mechanism for this magnetic activity is thought to be a stellar dynamo: stars with convective envelopes and rapid rotation are relatively luminous X-ray sources compared with slower rotating stars of similar spectral type. There is now a well-founded age-rotation-activity paradigm (ARAP – see Jeffries 1999; Randich 2000), established via observations of many open clusters with ages from 50Myr to several Gyr (e.g. Stauffer et al. 1994; Stern, Schmitt & Kahabka 1995; Jeffries, Thurston & Pye 1997), whereby younger stars tend to be more rapidly rotating and hence exhibit strong X-ray emission up to a saturated level, where the ratio of X-ray to bolometric flux, $L_{\rm x}/L_{\rm bol} \simeq 10^{-3}$. As stars get older, they lose angular momentum and eventually spin down to rotation rates where $L_{\rm x}/L_{\rm bol}<10^{-3}$ and decreases further thereafter.

For very young stars in star forming regions with ages $<10$Myr, a direct connection between rotation and X-ray activity is much less clear and the presence of an (accretion) disc may play a role in either stimulating or inhibiting the observed levels of X-ray activity (see Feigelson 