Sodium Velocities and Sources in Hale–Bopp

Abstract

We use spatially resolved high-resolution spectra of the 5890 and 5896 Å sodium D lines in the nuclear regions of Comet Hale–Bopp to determine the sources of cometary sodium. Comparison of the data to a Monte Carlo model of sodium dynamics suggests that the intensities and velocities of sodium in Hale–Bopp can be explained if 55% of the observed sodium is produced at the nucleus, the remaining 45% is produced in an extended source, and the sodium is accelerated by solar radiation pressure. Observations of H_2O^+in Hale–Bopp and subsequent modeling of a plasma-derived sodium source show that this source produces sodium at higher velocities than those observed; any contribution from such a source must be small. The combined nucleus and extended sources of sodium which fit our data best would create a sodium tail at a scale 100 times larger than that of these observations identical in morphology and velocity to that observed in Hale–Bopp.