First Science Observations with SOFIA/FORCAST: 6 TO 37 micron Imaging of Orion BN/KL

The BN/KL region of the Orion Nebula is the nearest region of high mass star formation in our galaxy. As such, it has been the subject of intense investigation at a variety of wavelengths, which have revealed it to be brightest in the infrared to sub-mm wavelength regime. Using the newly commissioned SOFIA airborne telescope and its 5-40 micron camera FORCAST, images of the entire BN/KL complex have been acquired. The 31.5 and 37.1 micron images represent the highest resolution observations (<=4) ever obtained of this region at these wavelengths. These observations reveal that the BN object is not the dominant brightness source in the complex at wavelengths >31.5 microns, and that this distinction goes instead to the source IRc4. It was determined from these images and derived dust color temperature maps that IRc4 is also likely to be self-luminous. A new source of emission has also been identified at wavelengths >31.5 microns that coincides with the northeastern outflow lobe from the protostellar disk associated with radio source I.

SiO Outflow Signatures Toward Massive Young Stellar Objects with Linearly Distributed Methanol Masers

Methanol masers are often found in linear distributions, and it has been hypothesized that these masers are tracing circumstellar accretion disks around young massive stars. However, recent observations in H2 emission have shown what appear to be outflows at similar angles to the maser distribution angles, not perpendicular as expected in the maser-disk scenario. The main motivation behind the observations presented here is to determine from the presence and morphology of an independent outflow tracer, namely SiO, if there are indeed outflows present in these regions and if they are consistent or inconsistent with the maser-disk hypothesis. For ten sources with H2 emission we obtained JCMT single dish SiO (6-5) observations to search for the presence of this outflow indicator. We followed up those observations with ATCA interferometric mapping of the SiO emission in the (2-1) line in six sources. The JCMT observations yielded a detection in the SiO (6-5) line in nine of the ten sources. All of the sources with bright SiO lines display broad line wings indicative of outflow. A subset of the sources observed with the JCMT have methanol maser velocities significantly offset from their parent cloud velocities, supporting the idea that the masers in these sources are likely not associated with circumstellar disks. The ATCA maps of the SiO emission show five of the six sources do indeed have SiO outflows. The spatial orientations of the outflows are not consistent with the methanol masers delineating disk orientations. Overall, the observations presented here seem to provide further evidence against the hypothesis that linearly distributed methanol masers generally trace the orientations of circumstellar disks around massive young stars.