High spectral resolution Fabry-Perot interferometer measurements of comet Halley at H-alpha and 6300 A

Abstract

A 40.6 cm Newtonian telescope has been interfaced to the Fabry-Perot interferometer at the Arecibo Observatory to make high spectral resolution measurements of Comet Halley emissions at 6562.72 A (H-alpha) and 6300.3 A (OI). In March 1986 the H-alpha surface brightness for a 5'.9 field of view centered on the comet nucleus decreased from 39+/-7.8 rayleighs on 12 March to 16+/-3.8 rayleighs on 23 March. The atomic hydrogen production rate on 12 March 1986 was 1.62+/-0.5 x 1030 s-1, and on 23 March 1986 it was 6.76+/-2.3 x 1029 s-1. Using spectral resolution of 0.196 A, we found the atomic hydrogen outflow velocity to be approximately 7.9+/-1.0 km s-1. In general, the H-alpha spectra are highly structured, and indicative of a multiple component atomic hydrogen velocity distribution. An isotropic outflow of atomic hydrogen at various velocities is not adequate to explain the spectra measured at H-alpha. The 6300.3 A emission of O(1D) had a surface brightness of 81+/-16 rayleighs on 15 March 1986, and 95+/-11 rayleighs on 17 March 1986. After adjustment for atmospheric extinction, the implied O(1D) production rate on 15 March is 6.44+/-3.0 x 1028 s-1, and the production rate on 17 March is 5.66+/-2.7 x 1028 s-1. These spectra included a feature at 6300.8 A that we attribute to NH2. The brightness of this emission feature was 37+/-11 rayleighs on 15 March.