2019MNRAS.486.5614I

Comet-centaur 29P/Schwassmann-Wachmann 1 was observed in CO⁺ emission and continuum during 2007-2009 using the 6-m Big Telescope Alt-azimuth at the Special Astrophysical Observatory of the Russian Academy of Sciences. We analysed the morphology of the CO⁺ and dust coma. The distributions of dust and CO⁺ ions in the coma are not similar and vary depending on the level of comet activity. CO⁺ ions are more concentrated towards the nucleus than the dust continuum. The column density of the CO⁺ was derived and found to vary from 3.7 x 10⁹ to 4.3 x 10¹⁰ ions cm^–2. The production rate of CO⁺ was estimated to be from (7.01 ± 2.7) x 10²⁴ to (1.15 ± 0.5) x 10²⁶ ions s^–1. We discuss possible mechanisms for the ionization of cometary material and show that impact ionization by solar wind particles is probably the main ionization mechanism at large heliocentric distances.