NH₂ and Its Parent Molecule in the Inner Coma of Comet Hyakutake (C/1996 B2)

Spectroscopic observations of comet Hyakutake (C/1996 B2) in the visible region was performed at Bisei Astronomical Observatory. The obtained spectrum covers the wavelengths from 5800 to 7300 Å and includes several emissions of some NH₂ bands, i.e., the (0, 7, 0), (0, 8, 0), and (0, 9, 0) bands.

Comet Hyakutake was observed when it was fairly close to the Earth; the geocentric distance of the comet was Δ = 0.113 AU. The surface brightness profile of the inner coma in the vicinity of the nucleus was obtained at the sufficient spatial resolution.

The collisions between the molecules are conspicuous in the region near the nucleus (where the nucleocentric distance is less than about 10³ km). The random walk model, considering the collisions between molecules, is used to research the parent molecule of NH₂ in this study. It is possible to examine whether each of the few candidates for the parent molecule of NH₂ can explain the observed NH₂ spatial profile. The result of our simulation supports the fact that NH₃ is most likely to be the parent molecule of NH₂.