Occultation observations of compact radio sources through comet Halley's plasma tail

Abstract

Enhancement in scintillations of radio sources attributable to plasma irregularities in the cometary tail have been reported for comet Kohoutek1 and recently for comet Halley2,3. The radio sources suitable for studying the plasma tail of a comet must have a significant fraction of their flux density in the sub-arc second structure, so a set of 30 sources lying within 2° of the path of comet Halley and with a flux density of S408≳ 0.8 Jy were chosen from the Molonglo Catalogue4 and interplanetary scintillation (IPS) observations of them were made with the Ooty Radio Telescope at 327 MHz during January 19865. From these, four were found to be suitable for cometary scintillation observations; these were done between February and April 1986. We monitored nearly simultaneously other scintillating sources outside the tail for comparison and, in contrast with earlier claims of positive detection, found no significant increase in the level of turbulence that could be attributed to the plasma tail.