Rotation periods for seven stars in the Trapezium cluster

Abstract

Results of a periodogram analysis of seven stars in the Trapezium cluster in the Orion Nebula are presented. These stars are found to have significant peaks in their power spectra, which are intepreted as the rotation periods of the stars. Periods range from 6.2 to 14.3 d. Three of them have periods longer than any previously detected for premain-sequence objects, and the group average, 8.7 d, is more than twice as long as the average period of previously measured T Tauri stars. A real difference is found in the rotational velocities of Trapezium cluster stars and T Tauri stars in associations, perhaps because the Trapezium cluster stars are extremely young. Selection effects are hindering the discovery of longer rotation periods among T Tauri stars in associations, and selection effects are hindering the discovery of short-period stars in the Trapezium cluster. Classical and weak T Tauri stars clearly coexist in this extremely young cluster, but the classical stars appear to be confined to I magnitudes fainter than 12.5.