NH2 and NH spatial intensity distribution in the coma of Halley’s comet Original Research Article

In this work, the NH2 and NH radial emission profiles in the sunward coma of Halley’s comet are studied. Spectra in the near UV and visible region, registered from the three-channel spectrometer (TKS) on board the VEGA-2 interplanetary station, on 9 March 1986, are used. The intensity of the observed species is determined from narrow spectral intervals, in which their emissions are predominant. The following wavelength intervals are used: for NH (0, 0) – λλ 3349–3374 Å (pixels 262–265); for NH2 – (0, 9 ,0) 598 nm (λλ 5975–5999 Å, pixels 699–702), (0, 9, 0) 606 nm (λλ 6058–6064 Å, pixel 713), (0, 8, 0) 634 nm (λλ 6330–6348 Å, pixels 759–761), (0, 8, 0) 631 nm (λλ 6306–6312 Å, pixel 755), (0, 10, 0) 573 nm (λλ 5702–5744 Å, pixels 653–659), (0, 7, 0) 662 nm (λλ 6618–6630 Å, pixels 808–809). An improved method is applied to subtract the dust continuum in the UV part of the spectra. The intensities are corrected for the optical depth in the near-nucleus region. Theoretical curves using a Haser model are computed and the data and model are compared. The applicability of the recommended parameters to the TKS data is discussed and the most suitable ones are chosen. In the frames of the TKS experiment the Haser model is found to describe well the obtained dependences of the NH and NH2 column intensities on the distance p of the line of sight to the nucleus, termed the projected distance or p-parameter. A comparison with the results for other neutrals by the TKS spectra, as well as with the results for NH2 and NH published so far, is made, and a similarity is found. The scanning of TKS allowed for the construction of spatial intensity distributions. From the seven obtained distributions, composite intensity distributions for each examined emission are constructed, covering a larger space region. The NH and NH2 intensity spatial distributions are studied, in comparison with other neutral compounds.