OBSERVATIONS OF THE PLASMA-FLOW IN COMET P SWIFT-TUTTLE/

We present direct ground based observations of the plasma flow sunward and tailward of the nucleus of comet P/Swift-Tuttle. The observations are long-slit high resolution spectra of the H2O+ emission centered a t 6199 angstrom with a velocity resolution of about 7 km s-1 (FWHM) an d a spatial resolution of about 10(4) km at the comet. Emission is vis ible from just inside the predicted position of the cometopause on the sunward side of the nucleus out to 5 x 10(5) km on the tailward side. The deceleration of the solar plasma on the sunward side is clearly o bserved as is the acceleration of cometary ions into the tail. These o bservations show the effectiveness of ground based methods for the sys tematic study of cometary plasmas and point to the need for a better t heoretical understanding of their acceleration mechanisms.