| Description |
Observations carried out to date for the Herschel Oxygen Project (HOP) indicate that the abundance of a potentially major oxygen-bearing species, O2 (molecular oxygen), predicted to be as high as 1e-4, is less than 1e-7. One extremely interesting exception is Orion. We have 2 hours of integration on the 487 Ghz and 774 GHz O2 transitions, and see statistically significant emission in two velocity features, at virgul 6 km/s and virgul 12 km/s. These data were taken at the Peak 1 position of strong H2 vibrational emission, approximately 40 from the KL/hot core position. Plambeck and Wright (1987) found that the Peak A position near the hot core is a strong source of HDO emission at virgul12 km/s. Since HDO is thought to be released from recently warmed grains, this may be intimately connected with the low O2 abundance being a result of atomic oxygen being frozen on cold grains and hydrogenated to water ice. When released after grain heating, it produces a significant gas-phase abundance of water and molecular oxygen. The HOP project did not include the KL/hot core position (Peak A is within 5) due to concerns about line confusion. However, data from the HEXOS survey confirms that the the O2 lines are in relatively windows, and shows O2 emission at the same 6 km/s and 12 km/s velocities. The line intensities are a factor virgul 5 stronger than at the H2 Peak 1 position, although noise is very large due to limited integration time. This suggests that the emission is from the hot core (6 km/s) and Peak A (12 km/s). We thus request 12 hours of time to carry out deep integrations at the frequencies of the 487, 774, and 1121 GHz, O2 lines, pointing at a position that includes the hot core and Peak A. This will confirm the identification as molecular oxygen (with three transitions at matching pair of velocities) and give a good handle on the temperature of the region producing O2 emission and its total column density. The total time requested is 12.1 hours. |
