Rotation periods of T Tauri stars in the Orion Nebula Cluster - A bimodal frequency distribution

CCD photometric monitoring of 11 fields in the Orion Nebula Cluster (ONC) was carried out at Van Vleck Observatory during the 1991/92 Milky Way season. More than 180 variable stars were detected and analysis of their light curves has led to the discovery of 35 rotation periods for premain-sequence stars, more than doubling the existing all-sky sample. Our data reveal a distinct bimodality in the frequency distribution of rotation periods of the ONC stars. There is a 'rapid rotator' group with a mean period of 2.2 days and a dispersion of about 1 day, and a 'slow rotator' group with mean period around 8.5 days and dispersion of about 2.5 days. A comparison is made between the ONC results and the previously known rotation period distribution for stars in T associations, which is also bimodal. The ONC sample has an enhanced long period tail and more long period stars relative to short period stars; both differences could be the result of selection effects influencing the T association sample. The significance of these results for studies of angular momentum evolution in low mass stars is briefly discussed.

Hali tarjima qilinmagan