Search for Line Emission from Interstellar OH Radicals.

Abstract

view Abstract Citations (8) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Search for Line Emission from Interstellar OH Radicals. Penzias, A. A. Abstract A search for 1667-Mc OH line emission from the galactic plane was carried out using a fixed horn-reflector antenna and a multichannel radiometer. The antenna was oriented so that its beam would drift through the galactic plane at longitude 580 and at the anticenter. From a plot of the average of twelve 24-h scans no emission was detected, with sensitivities of 0.05 0K and 0.15 0K for the two longitudes respectively. (The measurements at the anticenter were less sensitive because of the proximity of the sun to this direction during the period of observations.) These measurements allow us to place an upper limit of 10-~ on non/nn for the regions investigated, provided that the excitation temperature of the transition is much larger than the background temperature. The principal excitation of this OH transition comes from an interaction between the fields of passing ions and the permanent electric dipole moment of the radical. The cross section for this process, computed from a Fourier analysis of the interaction, is 3 X lO-~~ cm2 for a particle velocity of 10~ cm/sec. We obtain an excitation temperature of approximately 500K from this process, for an ion density of 5X10-3 per cm3. A comparison of our result with recent successful OH absorption measurements indicates that the typical value of the OH excitation temperature is probably closer to 100K, suggesting that the actual ion density in interstellar clouds is substantially smaller than the generally accepted value employed above. Publication: The Astronomical Journal Pub Date: 1964 DOI: 10.1086/109430 Bibcode: 1964AJ.....69R.146P full text sources ADS |