Observations of interstellar H/sub 2/O emission at 183 Gigahertz
Line emission at 183 GHz by the 3/sub 13/--2/sub 20/ rotational transition of water vapor has been detected from the Orion Nebula with the NASA Kuiper Airborne Observatory 91 cm telescope. The peak antenna temperature of the line is 15 K, its LSR velocity is 8 km s/sup -1/, and its width is 15 km s/sup -1/. The velocity profile has characteristics similar to those for CO:a narrow (approx.4 km s/sup -1/) ''spike'' centered at 9.5 km s/sup -1/ and a broad ''plateau'' with flaring wings centered at approx.8 km s/sup -1/. Our 7'.5 antenna beam did not resolve the source. The 183 GHz H/sub 2/O plateau emission appears enhanced above that expected for thermal excitation if it originates from the no greater than 1' region characteristic of plateau emission from all other observed molecules. The spike emission is consistent with an optically thick source of the approximated size of the well-known molecular ridge in Orion having the H/sub 2/O in thermal equilibrium at Tapprox. =50 K. If this is the case, then the H/sub 2/O column density giving rise to the spike is N/sub H/2/sub O/> or =3 x 10/sup 17/ cm/sup -2/. An excitation calculation implies N/sub H/2/sub O/approx. =10/sup 18/ cm/sup -2/ for a source the size of the molecular ridge. These results imply that H/sub 2/O is one of the more abundant species in the Orion Molecualr Cloud.H/sub 2/O emission at 183 GHz was not detected in Sgr A, Sgr B2, W3, W43, W49, W51, DR 21, NGC 1333, NGC 7027, GL 2591, or the rho Oph cloud; it may have been detected in M17.
- Research Organization:
- Jet Propulsion Laboratory, California Institute of Technology
- OSTI ID:
- 5461156
- Journal Information:
- Astrophys. J.; (United States), Vol. 235:1
- Country of Publication:
- United States
- Language:
- English
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