AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 68. The Young Ones 1: Star Formation, Disks and Jets
Display, Wednesday, June 2, 1999, 10:00am-6:30pm, Southwest Exhibit Hall

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[68.06] Examining Disk-Regulated Rotation: The Rotation Period Distribution of Pre-Main Sequence Stars In and Around the Orion Nebula

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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