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Astron. Astrophys. 357, 359-366 (2000)

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CO emission mechanisms in C/1995 O1 (Hale-Bopp)

M.T. Capria, A. Coradini, M.C. De Sanctis and R. Orosei

Istituto di Astrofisica Spaziale (IAS), CNR, Area di Ricerca di Tor Vergata, Via del Fosso del Cavaliere 100, 00133 Rome, Italy

Received 11 October 1999 / Accepted 14 March 2000

Abstract

The subject of this paper is the attempt to reproduce the CO observed production rate curve of comet Hale-Bopp with a numerical model of the nucleus thermal evolution and chemical differentiation. Three possible mechanisms can contribute to the total measured CO production: 1) sublimation of CO from the nucleus; 2) release of gas of CO trapped in the amorphous water ice in the nucleus; 3) emission of CO from grains in the inner coma (diffuse source). To match production rate observations with a numerical model we need an interplay between these emission mechanisms: success (and failure) in reproducing observed curve gives us useful information about the relative importance of these mechanisms and the depth of sublimation front. Using a numerical model of the nucleus we were able to match the observed CO production curve using quite standard initial parameters. We verified that it is impossible to reproduce the observed CO production curve taking solely into account sublimation of CO from ice contained in the nucleus or the release of gas of CO trapped in the amorphous water ice: if amorphous ice is not present immediately below the surface, we have to invoke some other physical process resulting in a perihelion CO production peak, such as a distributed source in the coma and/or the release of some of the trapped CO during water ice sublimation.

Key words: comets: individual: C/1995 O1 Hale-Bopp – comets: general

Send offprint requests to: M.T. Capria

Correspondence to: capria@ias.rm.cnr.it

This article contains no SIMBAD objects.

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© European Southern Observatory (ESO) 2000

Online publication: May 3, 2000
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