Herschel Search for O2 Toward the Orion Bar
Gary J. Melnick, Volker Tolls, Paul F. Goldsmith, Michael J. Kaufman,, David J. Hollenbach, John H. Black, Pierre Encrenaz, Edith Falgarone,, Maryvonne Gerin, {\AA}ke Hjalmarson, Di Li, Dariusz C. Lis, Ren\'e Liseau,, David A. Neufeld, Laurent Pagani, Ronald L. Snell

TL;DR
This study used Herschel observations to search for molecular oxygen in the Orion Bar, setting upper limits on its abundance and discussing implications for astrochemical models and the physical conditions of the region.
Contribution
First observational upper limits on O2 in the Orion Bar using Herschel, challenging existing models of molecular oxygen abundance in photodissociation regions.
Findings
No O2 lines detected, upper limit on column density < 4×10^15 cm^-2
Observed column density is significantly below model predictions
Discrepancies suggest possible factors like ice adsorption energy or clumpy structure
Abstract
We report the results of a search for molecular oxygen (O2) toward the Orion Bar, a prominent photodissociation region at the southern edge of the HII region created by the luminous Trapezium stars. We observed the spectral region around the frequency of the O2 N_J = 3_3 - 1_2 transition at 487 GHz and the 5_4 - 3_4 transition at 774 GHz using the Heterodyne Instrument for the Far Infrared on the Herschel Space Observatory. Neither line was detected, but the 3sigma upper limits established here translate to a total line-of-sight O2 column density < 1.5 10^16 cm^-2 for an emitting region whose temperature is between 30K and 250 K, or < 1 10^16 cm^-2 if the O2 emitting region is primarily at a temperature of ~< 100 K. Because the Orion Bar is oriented nearly edge-on relative to our line of sight, the observed column density is enhanced by a factor estimated to be between 4 and 20 relative…
Peer Reviews
No public reviews on file for this paper yet. If you reviewed it on a platform where reviews are public (OpenReview, ICLR, NeurIPS, ICML), you can paste yours below so the community can read it here.
Videos
No videos yet. Explain this paper in a talk, walkthrough, or lecture? Add one.
