Structure of the Radio Nebula W49 and OH Emission.

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view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Structure of the Radio Nebula W49 and OH Emission. Hughes, V. A. Abstract The object of the paper is to show the results of some new observations of the radio nebula W49 (3C398) obtained at the wavelength of 2.85 cm with the 150 ft radio telescope at the Algonquin Radio Observatory, and to suggest a mechanism for the formation of OH. The region is seen to consist of the two sources previously resolved by Mezger, the thermal source A and the nonthermal source B, contours being resolved down to an antenna temperature of 0.1 0K. The possibility that source B is a supernova is indicated by the possible presence of a disturbance propagating into source A. Source A can be resolved into at least two dense regions of ionization, Al and A2, which are coincident in position with the sources of intense anomalous OH emission at 1665 Mc/sec as measured by A. E. E. Rogers et al. (Astrophys. J. 147,1369,1965). An analysis shows that the ionization density in the two sources is about 10~ electrons/cc in agreement with the independent suggestion by Mezger. The particle density in the H I region surrounding the source is probably of the same value. The formation of OH in the excited (A 2~) state as a two-body process has been observed in the laboratory with the emission of 3064 A radiation by Spindler et al. (Spindler, G., Ticktin, S., and Schiff, H. I., Nature 214, 1006, 1967) at a rate given by I=K[HJ[OJ where the value for the rate factor K is approximately 10-20 molecules cm-3 sec~' at room temperature. It is suggested that this process is taking place in the pressure wave ahead of a D-type ionization front which forms the boundary of the intense H II regions. An increase in density of 40 times is possible in the front which leads to the formation of OH at the rate of 3 X 10-12 molecules cm-3 sec-', assuming the ratio of H to 0 of 10~. For a front velocity of 10 km/sec and a distance traveled by the front of 1 pc, the density of OH molecules will be 18 cm-3. Since the OH is formed in an excited state, this could provide the pumping mechanism for laser action, which requires an excess population in the upper state of 10-1 cm-3. The two-body process is amenable to observation since it produces optical radiation at the wavelength of 3064 A. Publication: The Astronomical Journal Pub Date: September 1967 DOI: 10.1086/110319 Bibcode: 1967AJ.....72..805H full text sources ADS |