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Astron. Astrophys. 329, 1152-1155 (1998)

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

Mark R. Kidger 1, Miquel Serra-Ricart 1, Javier Licandro 2, Ruth Torres 3, Leonid Schulman 4, and José Nicolás González-Pérez 1

1 Instituto de Astrofísica de Canarias c/Via Láctea, s/n E-38200 La Laguna, Tenerife, Spain
2 Departamento de Astronoma - Facultad de Ciencias y Observatorio Astronómico "Los Molinos", Montevideo, Uruguay
3 Departamento de Astrofísica Universidad de La Laguna c/Astrofísico Francisco Sánchez, s/n E-38200 La Laguna, Tenerife, Spain
4 Main Astronomical Observatory National Academy of Sciences Kyiv-22, 252650 Ukraine

Received 2 January 1996 / Accepted 7 May 1996

Abstract

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 [FORMULA], 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.

Key words: comets: Hale-Bopp (1995 O1)

* Observations taken with the IAC-80 Telescope at Teide Observatory, Tenerife, Spain

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© European Southern Observatory (ESO) 1998

Online publication: December 16, 1997
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