X-rays obs. in 8 young open star clusters

This may suggest a nearly uniform X-ray activity in the PMS low mass stars of ages ~4--14Myr. These observed values of L_X)/L_bol_ are found to have a mean value of 10^-3.6^+/-0.4, which is below the X-ray saturation level. The L_X_/L_bol_ values for the PMS low mass stars are well correlated with their bolometric luminosities, that implies its dependence on the internal structure of the low mass stars.

The difference between the X-ray luminosity distributions of the intermediate mass stars and the PMS low mass stars has not been found to be statistically significant. Their L_X_/L_bol_ values, however have been found to be significantly different from each other with a confidence level greater than 99.999% and the strength of X-ray activity in the intermediate mass stars is found to be lower compared to the low mass stars.

However, the possibility of X-ray emission from the intermediate mass stars due to a low mass star in close proximity of the intermediate mass star can not be ruled out.