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While most sources above 10^5Lsun have already formed an Ultracompact HIIregion (UCHII), this is not necessarily the case for sources of lowerluminosity. Characterizing sources in the transition phase, i.e., very luminousobjects without any detectable free-free emission, is important for a generalunderstanding of massive star formation. Therefore, we observed the luminousHigh-Mass Protostellar Object IRAS23151+5912 with the Submillimeter Array at875mum in the submm continuum and spectral line emission at sub-arcsecondresolution. The 875mum submm continuum emission has been resolved into at leasttwo condensations. The previously believed driving source of one of theoutflows, the infrared source IRS1, is ~0.9'' offset from the main submm peak.Over the entire 4GHz bandwidth we detect an intermediate dense spectral lineforest with 27 lines from 8 different species, isotopologues orvibrationally-torsionally excited states. Temperature estimates based on theCH3OH line series result in values of T(Peak1)~150+-50K and T(Peak2)~80~30K forthe two submm peak positions, respectively. The SiO(8-7) red- and blue-shiftedline maps indicate the presence of two molecular outflows. In contrast, thevibrationally-torsionally excited CH3OH line exhibits a velocity gradientapproximately perpendicular to one of the outflows. With a size ofapproximately 5000AU and no Keplerian rotation signature, this structure doesnot resemble a genuine accretion disk but rather a larger-scale rotating toroidthat may harbor a more common accretion disk at its so far unresolved center.

The 10^5Lsun High-Mass Protostellar Object IRAS23151+5912