A jet-related colour change in the inner coma of comet Hale-Bopp (1995 O1)?

Kidger, Mark R.; Serra-Ricart, Miquel; Licandro, Javier; Torres, Ruth; Schulman, Leonid; Gonzalez-Perez, Jose Nicolas
Bibliographical reference

Astronomy and Astrophysics, v.329, p.1152-1155 (1998)

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Comet Hale-Bopp (1995 O1) has been intensely monitored with the 82cm IAC-80 Telescope at Teide Observatory, Tenerife, Spain. Multicolour photometry taken on various nights in mid-August 1995 shows that the inner coma was redder than solar colours, with a power law spectrum of index ~ -3.5, consistent with dust scattering. A large change in the colour indices to a rather bluer colour and much flatter spectrum was observed simultaneous with an increase in the brightness of the inner coma. This occurred shortly before the August jet event was detected. Extrapolation of the jet expansion back to the origin suggests that the brightening and colour change may have been the initial stages of the formation of the jet. We suggest that it was due to a change in the scattering properties of the circumnuclear region, caused by the ejection event of small, icy grains and/or an increment in the gas to dust ratio. Observations taken with the IAC-80 Telescope at Teide Observatory, Tenerife, Spain