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.