Gas and dust production by comet P/Halley (1910 II)

Selected long-slit spectrograms of comet P/Halley, photographed during the postperihelion period between 1910 April 16 and June 3 by V. M. Slipher of Lowell Observatory, have been quantitatively analyzed for comparison with the 1985/86 apparition. Using the Fe-V-Na spark spectrum which Slipher employed for his wavelength calibration, we have determined characteristic curves for these plates and applied flux calibrations based on contemporaneous broad-band photometric measurements. We computed Haser model production rates for C₂ and values Afp for each of the nights selected and compared them with the photometric observations obtained by Schleicher et al. during the comparable postperihelion period of the 1985/86 apparition. As they found for the 1985/86 apparition, the gas and dust production in 1910 varied in phase, but the rates of production were higher than observed in 1986 by a small but statistically significant amount. Using the postperihelion heliocentric dependence derived by Schleicher et al., we deduced a value of log (Q) = 27.55 ± 0.22 for C₂ at 1 AU, which is larger than the equivalent measurement in 1986 by 0.45. The gas-to-dust ratio was independent of heliocentric distance in the range of the 1910 observations, yielding a mean value of log(Q/Afp) = 22.52 + 0.13.