The spatial distribution of gaseous atomic sodium in the comae of comets: Evidence for direct nucleus and extended plasma sources

Observations of Comet Kohoutek (1973f) in the spectral region between 1200 and 3200 angstroms were made from an Aerobee rocket on 5.1 January 1974 universal time. The strongest features observed were the Lyman alpha line of neutral atomic hydrogen at 1216 angstroms and the hydroxyl (OH) bands at 3090 and 3142 angstroms. Atomic oxygen and atomic carbon were also detected, and their luminosity implies a production rate (of carbon monoxide or carbon dioxide) commensurate with that of water vapor.

Rocket ultraviolet spectrophotometry of comet Kohoutek (1973f).

Absolute spectrophotometry of the coma of Comet Kohoutek 1973f during post-perihelion period has been presented for seven nights in January 1984. Moderately wide range of heliocentric distance (0.436–0.799 AU) covered during observations allowed us to study the flux variation of emission bands with heliocentric distance. The emission features of CN, CH, C2, C3, and NaI have been identified in this comet. The abundances of CN and C2 have been estimated and the production rates of CN, C2 and C3 have been derived. Production rates of CN and C2 seem to vary as r
−0.33 and r
−3.50 respectively. The continuum of the comet became more and more redder as the heliocentric distance of the comet increased and phase angle decreased.

Absolute spectrophotometry of Comet kohoutek 1973f during post-perihelion passage

Emission fluxes of CN, C2 and C3 species observed in the coma of some comets are analysed in the framework of Haser model. CN, C2 and C3 production rates are determined using recently derived fluorescence efficiencies and dependence of CN, C2 and C3 production rates on the heliocentric distance is studied. Evidence for a burst type activity around January 15, 1974 in the post-perihelion period of comet Kohoutek (1973f) is observed.

Haser model CN, C2 and C3 production rates in some comets

Outbursts of comets - the case of 1P/Halley

Spectrum scans have been obtained of the head of Comet Austin on six nights at helio-centric distances (r) from 0.70 to 0.87 AU. The useful spectral region is λλ330–750nm. Strong emission features of CN (388 nm) and Swan band sequence of C2 (474, 516, and 563 nm) were identified. Weak emission features of CH + C2(436 nm), C2(600 nm), CN(420 nm) and CH + C3(405 nm) have also been found present. There is a change in the ratio of CN(388 nm) to C2(516 nm) emission strength with increasing heliocentric distance. An estimate of the CN and C2 abundances has been made and their production rates have been derived. The continuum of the comet is strongly reddened with reference to Sun. The continuum matches the scattered continuum of solar radiation according to λ2 law (Mie scattering) closely.

Spectrophotometry of Comet Austin (1982g) during post-perihelion period

The results of photometric measurements (in UBV filters) of Comet P/Halley during four nights in January 1986 have been presented. Rapid recurring increases of P/Halley's brightness were observed during these four nights. This phenomenon seemed to occur at a time interval of about 23.7 ± 0.3 hr. The maximum variation of brightness during an individual night amounts to δU ~ 0.m70; δB ~ 0.m, 65 and δV ~ 0.m66 in U, B, and V filters, respectively. Rapid irregular short-lived fluctuations of brightness of the order of 0.m1 were also found present during an individual night. The present observations show the active nature of P/Halley.

Rapid changes of brightness in P/Halley

We present spectrophotometric studies of comet Hartley-Good (1985l) in the spectral region λλ3200–7000 A. The emission features of molecules CN, CH, C2, and C3 are observed. The variation of the emission strength of different species has been studied as a function of heliocentric distance. The abundances (N) and production rates (Q) of the molecules are also estimated.

Spectrophotometry of Comet Hartley-Good (1985l)

Spectral scans of the head of periodic Comet Halley (1982i) have been presented in the optical region (λλ3200–7000 A) for six nights. Emission features due to NH, CN, CH, C3, C2 and NH2 molecules have been identified. It is found that the comet exhibits night-to-night variation of emission bands. The abundances and production rates of CN and C2 species have been derived.

P. S. Goraya

Papers

Absolute spectrophotometry of Comet kohoutek 1973f during post-perihelion passage

Spectrophotometry of Comet Austin (1982g) during post-perihelion period

Rapid changes of brightness in P/Halley

Spectrophotometry of Comet Hartley-Good (1985l)

Spectrophotometry of P/Halley (1982i)