Fabry-Perot observations of NH₂ emission from Comet Halley

Fabry-Perot spectra of Comet Halley emissions near 6300 Å were obtained at a spectral resolution of 0.2 (10 km sec^-1), which was high enough to isolate cometary NH₂ ((0,8,0) band) lines from cometary [OI]6300 emission and terrestial [OI]6300 and OH emissions. The NH₂ spectra were used to obtain the NH₂ production rate Q(NH₂), which was compared with the H₂O production rate QH₂O), obtained from the [OI]6300 observations. Assuming that NH₃ is the major source of NH₂, then our NH₂ emission measurements limit the abundance of NH₃ relative to H₂O. Our results depend on the value of the NH₂ (0,8,0) band fluorescence efficiency factor g_B. Using the M.F. A'Hearn (1982, In Comets (L. Wilkening, Ed.), Univ. of Arizona Press, Tucson) value for g_B, we find that the NH₃ abundance is about 0.1% that of H₂O. If we use the recently revised value of g_B calculated by S. Tegler and S. Wyckoff (1989, Astrophys. J., in press) the relative NH₃ abundance increases to about 0.4%. In either case, our results indicate a low Comet Halley NH₃ abundance relative to H₂O.