Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986umas.rept.....i&link_type=abstract
Semiannual Status Report, 1 Jun. - 30 Nov. 1985 Massachusetts Univ., Amherst.
Astronomy and Astrophysics
Astronomy
Astronomical Spectroscopy, Halley'S Comet, Planetary Atmospheres, Radiative Transfer, Radio Observation, Astronomical Observatories, Cometary Atmospheres, Hydroxyl Radicals, Line Spectra, Signal To Noise Ratios
Scientific paper
The research emphasis during the period of this report has been on radio observations of comets, related to the International Halley Watch. Observations of the 18 cm lambda-doublet of OH have been carried out monthly. Both of the 1667 and 1665 MHz lines have been repeatedly detected for Comets Halley, Giacobini-Zinner, Thiele, and Hartley-Good. The first astronomical detection of the weak satellite line at 1720 MHz was made for P/Halley. These data promise to supply the highest signal-to-noise-ratio data over an extended period ever obtained for cometary radio observations. Analysis will provide gas production rates as a function of heliocentric distance and allow for detailed comparisons with the OH excitation model involving ultraviolet pumping. In the case of Halley, the lines appear quite symmetric, usually being centered within 0.1 km/s with respect to the nominal nuclear velocity. Line widths have been typically within 10% of 2 km/s. There is thus little evidence for asymmetric emission in the data obtained to date. It seems likely that non-steady-state models of the coma will be required to interpret the data. Evidence for significant departures from the LTE hyperfine ratios was found for Comet Giacobini-Zinner. Smaller, but nonetheless significant, deviations have been found for Comet Halley.
Irvine William M.
Schloerb Peter F.
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