Observations of ions in comet P/Halley with a focal reducer

Summary

Comet Halley was observed with the ESO 1 m telescope and a dedicated focal reducer instrumentation. Narrowband images of the comet in the light of the $CO_2^ +$ ion at 367.4 nm were obtained for the first time. On these images, the cometary plasma can be observed as close as 10⁴ km to the nucleus. No plasma envelopes are visible. Multislit spectra show emissions of OH⁺, $CO_2^ +$ ,CO⁺, $N_2^ +$ and CH⁺. They indicate the presence of CO⁺ ions in a large halo around the comet, not only in the tail streamers.

Paper based on observations collected at the European Southern Observatory, La Silla, Chile