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K.G. Stassun, R.D. Mathieu (Univ. Wisconsin), T. Mazeh (Wise Obs.), F.J. Vrba (USNO)
Photometrically derived rotation periods are presented for 254 pre-main sequence stars in a 40 \times 80 arcmin area centered on the Orion Nebula. The distribution of rotation periods we determine, sensitive to periods 0.1 < P < 8 days, shows a sharp cutoff for periods P < 0.5 days, which we show is consistent with breakup velocity for these stars. Above 0.5 days, the distribution is consistent with a uniform distribution. The distribution of v\sin i among these stars bears remarkable resemblance to the v\sin i distribution of low-mass Pleiads. Stellar rotation period correlates neither with spectral signatures of active accretion nor with near-infrared signatures of circumstellar disks.
Our results question the paradigm of disk-locking as the dominant mechanism for dissipating stellar angular momentum in the pre-main sequence phase. We show that most stars in our sample require problematically high accretion rates and/or weak magnetic fields to be consistent with the disk-locking scenario. Most significantly, we find many stars rotating at or near breakup velocity---stars that must still shed large quantities of angular momentum---that do not show evidence for disks.
We invite discussion of these results among those studying stellar rotation in low-mass main-sequence stars. New N-band photometry will also be presented. This research is supported by a University of Wisconsin minority graduate fellowship and a grant from the Wisconsin Space Grant Consortium.
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