Production and kinematics of sodium atoms in the coma of comet Hale-Bopp

High-resolution spectra of sodium D line emission in comet Hale-Bopp (C/1995 O1) were obtained at the Observatoire de Haute-Provence, France, on 25-27 March and on 15-17 April, 1997. The observations have been used to measure the velocity of sodium atoms in the coma within 2 10(5) km from the nucleus. A comparison between the March and April data provides an illustration of the influence of the heliocentric radial velocity on the strength of the fluorescence (Swings effect), and on the velocity of Na atoms achieved by solar radiation pressure acceleration. Evidence for the presence of a distributed source in the coma is found from the relatively high tailward velocities on the sunward side of the coma, in addition to the sunward extent of sodium emission up to 1.4 10(5) km in April.