A Multiyear Photometric Study of IC 348

The extremely young cluster IC 348 has been monitored photometrically over 5observing seasons from Dec 1998 to March 2003 in Cousins I with a 0.6 mtelescope at Van Vleck Observatory. Twenty-eight periodic variables and 16irregular variables have been identified. Among the brighter stars, 14 of the16 known K or M-type WTTS were found to be periodic variables, while all 5 ofthe known CTTS were found to be irregular variables. In the full sample, whichincludes 150 stars with I mag as faint as 18, we find that 40% of the 63 WTTSare detected as variables, nearly all of them periodic, while 55% of the 20CTTS are also detected as variable, with none of them periodic. Our studysuggests that 80-90% of all WTTS in young clusters will be detected as periodicvariables given sufficiently precise and extended monitoring, whereas CTTS willreveal themselves primarily or solely as irregular variables. This has clearconsequences for PMS rotational studies based on photometric periods. Weexamine the stability of the periodic light curves from season to season. Allperiodic stars show modulations of their amplitude, mean brightness and lightcurve shape on time scales of less than 1 yr, presumably due to changes in spotconfigurations and/or physical characteristics. In no case, however, can wefind definitive evidence of a change in period, indicating that differentialrotation is probably much less on WTTS than it is on the Sun. Among thenon-periodic stars, we report the detection of two possible UXors as well as apre-main sequence star, HMW 15, which apparently undergoes an eclipse with aduration exceeding three years