Spectroscopic Observation of Comet P/de Vico: Comparison with P/Halley and P/Brorsen-Metcalf

A spectroscopic observation of Comet P/de Vico in the visible region was made at Bisei Astronomical Observatory on 1995 October 11. The obtained spectrum covers the wavelengths from 5200 to 7200 Å, and includes several emissions, such as C2, NH2, and [OI]. The ratios of the gas-production rates of C2 and NH2 relative to that of H2O, Q(C2)/Q(H2O), and Q(NH2)/Q(H2O), were determined from our observation based on the Haser model. The production-rate ratio and gas-to-dust ratio were: Q(C2)/Q(H2O) = 0.25%, Q(NH2)/Q(H2O) = 0.14%, and log10[ Q(H2O)/Af ρ] = 26.9 at the time of observation. Comet P/de Vico was similar to P/Halley from the viewpoint of the chemical composition (C2 and NH2 relative to the H2O), and P/de Vico was comparable to P/Brorsen-Metcalf concerning the gas-to-dust ratio. P/de Vico was one of the most gas-rich comets ever known.