A Variability Study of Pre–Main-Sequence Stars in the Extremely Young Cluster IC 348

Abstract

The extremely young cluster IC 348 has been monitored in the Cousins I band with a 0.6 m telescope at Wesleyan's Van Vleck Observatory. Photometry of 150 stars was obtained on 76 images taken on 27 separate nights during the period December, 1998, through March, 1999. As expected, spectral characteristics largely determine the nature of a star's variability in this cluster. None of the stars with H-alpha in absorption were found to be variables. On the other hand, all 16 stars identified as CTTS by their H-alpha emission equivalent widths and the majority of the 49 WTTS in the part of the cluster we monitored showed evidence of variability. Nineteen stars were found to be periodic, with periods ranging from 2.24 to 16.2 days and masses ranging from 0.35 to 1.1 M-sun. Seventeen of these are WTTS and the other 2 are of unknown spectral class. The period distribution is remarkably similar to what is found in the Orion Nebula Cluster for stars in the same mass range. Namely, it is bimodal with peaks at 2-3 days and 7-8 days, although there are not enough periods known to define these features significantly by the IC 348 data alone. The three fastest rotators are also the three most massive stars in the periodic sample.