[Previous] | [Session 49] | [Next]
P.T. Kondratko (Lawrence University), S.S. Doeleman, C.J. Lonsdale (MIT-Haystack Observatory), C.R. Predmore (University of Mass. - Amherst), L.J. Greenhill (Harvard Smithsonian Center for Astrophysics)
The Orion-KL nebula is the closest (450pc) site of high-mass star formation and exhibits powerful outflows associated with protostars. These stars, however, are deeply embedded within a parent molecular cloud and can be seen only at Radio, and sometimes IR, wavelengths. We present VLBI images of the SiO masers in the Orion-KL nebula which trace the outlines of an outflow at distances of 18 to 67 AU from a central protostar. In three different SiO maser transitions (v=1 J=2-1, v=1 J=1-0, v=2 J=1-0) the maser emission displays an ``X" morphology suggesting two conical outflows to the NW and SE. High resolution maps of the two J=1-0 transitions (43 GHz) show some regions of clear spatial overlap, but the bulk of the emission in these two lines is separate with the v=2 transition situated closer to the outflow axis than the v=1. A lower resolution map of the J=2-1 transition at 86 GHz shows emission even farther from the protostar and spatially distinct from the two 43 GHz transitions. Each maser transition has a different excitation energy and all are probably excited via both radiative and collisional mechanisms. The observed inter-transitional separations therefore suggest that within the outflow, each maser line traces a region of specific physical conditions and chemistry. The images reveal complex structures exhibiting turbulent motions on many scales as well as more organized bulk motions. Efforts to model the outflow which reproduce the more general SiO maser characteristics are discussed.