Other
Scientific paper
Mar 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008sptz.prop50082r&link_type=abstract
Spitzer Proposal ID #50082
Other
Scientific paper
We propose to obtain deep spectra of the outer region of the Orion Nebula. The area of particular interest is SE of the Bar where archival Spitzer spectra have shown high signal-to-noise lines of [S IV] 10.5 and [Ne III] 15.6 microns. We were staggered with astonishment to see such S/N in high ionization species well beyond the Bright Bar, given the conventional view of the Bar as the boundary between ionized and photodissociated regions (PDR). Previous IR missions observed only the inner few arcmin, the so-called Huygens region. The extreme sensitivity of Spitzer's IRS short-high (SH) and long-high (LH) modules in the 10-37 micron spectral range will permit us to measure the above lines and many others of interest to much larger distances from the exciting star theta1 Ori C. Orion is the benchmark for studies of the interstellar medium, particularly for elemental abundances. In the case of the Orion Nebula, the best way to obtain abundances from observations has been through detailed photoionization modeling. These new Spitzer spectra will provide a unique, legacy dataset for new science, including improved current and future models of Orion. Indeed we will use our own modeling codes for this purpose, one of which self-consistently treats the H II region and the PDR. The Orion Bar is the defining interface by which all H+ - H0 - H2 regions are judged. Because there must be extra emission along this sight line, we need to understand this contribution and remove what is not physically a part of the Bar. Our program will permit a more reliable set of line emission that actually arises from the Bar that can rigorously be used to define the interface problem. Our spectra will be the deepest ever taken in these outer regions of Orion over the 10-37 micron range. Tracking the changes in ionization structure via the line emission to larger distances provides much more leverage for understanding the far less studied outer regions. The outer Veil is likely to provide a new, benchmark HIIR-PDR interface.
Colgan Sean
Erickson Edwin
Ferland Gary
O'Dell Charles Robert
Rubin Robert
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