Relationships between simultaneous plasma wave, magnetic field, and energetic heavy ion data obtained by the International Cometary Explorer (ICE) spacecraft in the large-scale solar wind particle pickup region surrounding comet Giacobini-Zinner are examined. In particular, we investigate the conditions under which electrostatic emissions at frequencies of a few kilohertz and electromagnetic waves at a few tens of hertz are observed. It is shown that the data are consistent with the view that the kilohertz electrostatic emissions result from a beam-type instability excited by the pickup photoelectron population when the angle &agr; between the magnetic field and the plasma velocity vectors is not too large (&agr;60¿). ¿ American Geophysical Union 1989