Poster abstract

We describe the initial results of the deep Chandra/ACIS-I observation of h Persei, a young (13 Myr) cluster at the transition between the Pre Main Sequence and the Zero Age Main Sequence phases. This is crucial age at which the stars should reach the fastest rotation, since the contraction has finished and there has not been enough time for losing significant angular momentum via magnetic braking. Taking advantage of the long Chandra observation (~200 ks), we detected 1010 X-ray sources, 800 of which have been identified as photometric members of the cluster on the basis of the observations taken during the Monitor program. The detected members have $L_x$ is in the range 29.3-31.8 erg/sec. We have analysed $L_x/L_{bol}$ for our sources, finding we have reached the unsaturated regime for solar mass stars, while we have observed just the tail of the distribution for lower mass stars.