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L. Rebull (University of Chicago)
We present an optical study of four 45\arcmin\times45\arcmin fields centered ~35\arcmin north, south, east, and west of the Orion Nebula Cluster center. We have measured V and I\rm C photometry for ~5000 stars in three of these fields, and U photometry for ~1600 of those. We have obtained spectral classifications for ~300 of the stars with UVI\rm C photometry plus an additional ~200 stars located outside the area of our photometric survey. Based on these data, we find ~230 active accretion disk candidates. We have also obtained time-series data for stars in each of these four fields, and ~300 periods derived from these data will be presented and discussed. In recent months, several investigators have presented rotation rates for stars in the Trapezium and its immediate environs. The paradigm (e.g. Choi and Herbst 1996) until now has been that the slow rotators are still (magnetically) locked to their disks, and that the fast rotators have dissipated their disks sufficiently as to allow spinup. Herbst et al. (2000) claim they see a bimodal distribution of rotators in Orion; Stassun et al. (1999) claim not to see such a distribution in a very similar region, and in fact cast doubt on the bimodality of the original distribution. Different selection effects (as well as different numbers of stars) are likely to be affecting these conclusions; the addition of data presented here will clarify the issues.
This research has made use of data taken at McDonald Observatory (by R. Makidon and M. Adams), data taken at the KPNO 0.9m (with B. Patten and C. Pavlovsky), data taken through the WIYN-Queue program, software written by B. Patten, and partial funding via NASA Origins Grants (L. Hillenbrand and S. Strom).