CN, C2 radicals and dust in Comets Shoemaker–Levy 1991 T2 and P/deVico 1995 S1

The results of the multiaperture photometry of Comet Shoemaker–Levy 1991 T2 in the pre-perihelion and P/deVico in the post-perihelion period with the narrowband CN, C2 and Blue Continuum (BC) IHW filters are presented. A Haser model of the molecular coma was used for the determination of the parent and daughter scale-lengths and production rates of the radicals. The comets showed some substantial differences between their parent scale-lengths. The CN parent scale-length (at 1.0 AU) was 16 × 10 3  km for Comet Shoemaker–Levy and 39 × 10 3 for P/deVico, the C2 parent scale-lengths were respectively 29 × 10 3 and 54 × 10 3  km . Such divergences could be interpreted in the frame of different scenarios of emission of cometary parents, either from a nucleus or from a volume source. The daughter scale-lengths for these comets were quite similar, namely: 306 × 10 3 and 318 × 10 3  km for CN and 69 × 10 3 and 66 × 10 3  km for C2. We determined the Afρ parameter for apertures of different radii. A Monte Carlo model of the dust coma was used to obtain the dust ejection velocity. It was of the order of 0.1 km s−1 for both comets. The power index of the distribution of the β-parameter of dust particles (ratio of light pressure to the solar gravitation) was of the order of 3 for C/Shoemaker–Levy and close to 2 for P/deVico. The dependence on heliocentric distance ( r h ) of the radical and dust production rates for P/deVico in the range of 0.7–1.0 AU was described by the power law function r h − α with a power index equal to: 5.55 ± 0.14 for CN, 5.70 ± 0.24 for C2 and 5.22 ± 0.19 for dust. Relative abundances of the dynamically new Comet Shoemaker–Levy and short-period P/deVico were quite similar with an enhancement of C2 comparing with standard values taken from AʹHearn et al. (1995).