Rotation Periods and Variability of Trapezium Cluster Stars

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Session 48 -- Young Stars
Display presentation, Tuesday, 10, 1995, 9:20am - 6:30pm

[48.10] Rotation Periods and Variability of Trapezium Cluster Stars

W. Herbst, N. L. Eaton (Wesleyan U.), L. A. Hillenbrand (UMass)

Results from the fourth season (1993/94) of monitoring the Trapezium cluster in the Cousin's I band at Van Vleck Observatory are reported. Data were obtained on thirty nights with multiple exposures on most. The periodogram technique described by Horne and Baliunas (ApJ 302, 757) based on Scargle's method was used to search for periods. False alarm probablities must be carefully assessed when the sampling intervals are distributed in the manner of this study. With a conservative criterion, we now have rotation periods for nineteen cluster members; ten are confirmations of periods reported by Mandel and Herbst (ApJ 383, L75) and/or Attridge and Herbst (ApJ 398, L61). One of these, JW 710 has an amplitude of variation exceeding 1.5 mag. which is indicative of a hot (accretion) spot. The bimodal period distribution discovered in the Orion Nebular Cluster by Attridge and Herbst is now clearly seen even within the Trapezium cluster, itself. We also identify fourteen large amplitude irregular variables; most show the light curve characteristics of typical classical T Tauri stars; one is a much slower, FUor-like, variable; three have UXor-like variations mimicing eclipsing variables (one or more of these may, in fact, BE an eclipsing variable but no periods have been found); and one star underwent an outburst of 1.5 mag on one night, highly unusual behavior in I. VIJHK photometry has been obtained for most of these objects and spectral types are available for many. Correlations between rotation periods, location on the HR diagram and presence or absence of IR excesses indicative of disks will be presented and discussed.

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