THE PRODUCTION-RATE AND SPATIAL-DISTRIBUTION OF H2O FOR COMET P-HALLEY

Spectroscopic observations of the OI 1D lines for comet P/Halley are used to derive water-production rates. Forty-three exposures during the period 1985 August to 1986 June are reduced. The reduction procedure involves sky subtraction, ratios with solar analog comparison stars, subtraction of contaminating NH2 emissions, and absolute flux calibration. The flux collected within our 2″.5 wide x 151″ long integration aperture is converted to a total comet OI 6300 Å luminosity using a cometary gas outflow model. Spatial OI profiles are extracted and illustrated but are not analyzed in this paper. Water-production rates for 10 preperihelion dates and seven postperihelion dates are derived. An error budget yields an estimated uncertainty of + 30% in H2O production rates with a maximum error of ±50%. For the preperihelion period a good fit of the water-production rate as a function of heliocentric distance can be obtained as Q(H2O) = 4.36 x 1029 x r-2.54. A postperihelion enhancement by about a factor of 1.8, which appears to dissipate by 1986 June, is observed. Several values of enhanced water production agree well with the observed lightcurve of P/Halley. Comparison of our H2O production rates with those deduced by other methods shows quite reasonable agreement.