A Multiyear Photometric Study of IC 348

Abstract

The extremely young cluster IC 348 has been monitored photometrically over 5\nobserving seasons from Dec 1998 to March 2003 in Cousins I with a 0.6 m\ntelescope at Van Vleck Observatory. Twenty-eight periodic variables and 16\nirregular variables have been identified. Among the brighter stars, 14 of the\n16 known K or M-type WTTS were found to be periodic variables, while all 5 of\nthe known CTTS were found to be irregular variables. In the full sample, which\nincludes 150 stars with I mag as faint as 18, we find that 40% of the 63 WTTS\nare detected as variables, nearly all of them periodic, while 55% of the 20\nCTTS are also detected as variable, with none of them periodic. Our study\nsuggests that 80-90% of all WTTS in young clusters will be detected as periodic\nvariables given sufficiently precise and extended monitoring, whereas CTTS will\nreveal themselves primarily or solely as irregular variables. This has clear\nconsequences for PMS rotational studies based on photometric periods. We\nexamine the stability of the periodic light curves from season to season. All\nperiodic stars show modulations of their amplitude, mean brightness and light\ncurve shape on time scales of less than 1 yr, presumably due to changes in spot\nconfigurations and/or physical characteristics. In no case, however, can we\nfind definitive evidence of a change in period, indicating that differential\nrotation is probably much less on WTTS than it is on the Sun. Among the\nnon-periodic stars, we report the detection of two possible UXors as well as a\npre-main sequence star, HMW 15, which apparently undergoes an eclipse with a\nduration exceeding three years.\n