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R. B. Makidon (STScI), M. T. Adams (Univ. of Texas, McDonald Observatory), L. M. Rebull (NASA/JPL), S. E. Strom (NOAO)
We present the results of a study of periodic and non-periodic variability of pre-Main Sequence (PMS) stars in the NGC 2264 OB Association. Our I-band time-series photometry, obtained with the McDonald Observatory's 0.76-m telescope, is complemented by UBVRIJHK photometry and R=1000 spectroscopy. Of the 4974 stars observed, 118 are periodic variables, with periods ranging from 0.25d to 25d, while 277 are non-periodic variables. Such objects comprise nearly 80 of a proper-motion selected sample, and based on their location in the I/(V-I) Color-Magnitude diagram, span ages from < 0.3 Myr to 3.0 Myr. This suggests variability - both periodic and non-periodic - may be an excellent diagnostic of PMS cluster membership.
We examine correlations pertaining both to the evolution of stellar angular momentum and stellar activity with age.