Period Analysis The combination of the X--ray and photometric observations have produced two samples of low mass PMS stars.
At the time that the stars were monitored for rotational modulation, their photometric and spectroscopic properties were not yet known. For this reason, only the stars in each sample which were coincident with X--ray sources and randomly chosen comparison stars had their photometric data extracted and analyzed. By measuring the rotational periods of the stars in the two samples, one can separate out the effects of age on the rotation period from those of other factors such as mass.