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We present new 7mm continuum observations of Orion BN/KL with the VLA. Weresolve the emission from the protostar radio Source I and BN at severalepochs. Source I is highly elongated NW-SE, and remarkably stable in fluxdensity, position angle, and overall morphology over nearly a decade. Thisfavors the extended emission component arising from an ionized disk rather thana jet. We have measured the proper motions of Source I and BN for the firsttime at 43 GHz. We confirm that both sources are moving at high speed (12 and26 km/s, respectively) approximately in opposite directions, as previouslyinferred from measurements at lower frequencies. We discuss dynamical scenariosthat can explain the large motions of both BN and Source I and the presence ofdisks around both. Our new measurements support the hypothesis that a close(~50 AU) dynamical interaction occurred around 500 years ago between Source Iand BN as proposed by Gomez et al. From the dynamics of encounter we argue thatSource I today is likely to be a binary with a total mass on the order of 20Msun, and that it probably existed as a softer binary before the closeencounter. This enables preservation of the original accretion disk, thoughtruncated to its present radius of ~50 AU. N-body numerical simulations showthat the dynamical interaction between a binary of 20 Msun total mass (I) and asingle star of 10 Msun mass (BN) may lead to the ejection of both and binaryhardening. The gravitational energy released in the process would be largeenough to power the wide-angle flow traced by H2 and CO emission in the BN/KLnebula. Assuming the proposed dynamical history is correct, the smaller massfor Source I recently estimated from SiO maser dynamics (>7 Msun) by Matthewset al., suggests that non-gravitational forces (e.g. magnetic) must play animportant role in the circumstellar gas dynamics.

astrophysical journal/the astrophysical journal

A Multi-Epoch Study of the Radio Continuum Emission of Orion Source I:  Constraints on the Disk Evolution of a Massive YSO and the Dynamical History  of Orion BN/KL