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Astron. Astrophys. 336, 769-775 (1998)

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Probing 5-minute oscillations in the solar wind with comet Hale-Bopp (C/1995 O1)

Sebastian Steffens and Dieter Nürnberger

Astronomisches Institut der Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany (steffens@astro.uni-wuerzburg.de; nurnberg@astro.uni-wuerzburg.de)

Received 15 December 1997 / Accepted 16 April 1998

Abstract

This study aims at short-period fluctuations of the solar wind by using comet Hale-Bopp (C/1995 O1) as a probe. The comet's intensity fluctuations due to changes in the reflectivity and emission of molecular lines are investigated both in the coma and the tails at about 1 AU heliocentric distance. The existence of oscillations with periods of a few minutes as an already suggested by Isserstedt & Schlosser (1975) on the basis of observations of comet 1973f (Kohoutek). We focus here on the time scale of the solar p-modes (5 min.); Thomson et al. (1995) have recently claimed to observe these periods in the flux density of the solar wind.

Both in the comet's coma and in the ion tail we found oscillations on the time scale of minutes if mainly the stimulated emission of the C3 line was observed through a `narrow-band' filter. No comparable oscillations were seen through a `broad band' filter where reflected sunlight dominates the intensity. We show that the observed fluctuations are neither induced by the earth's atmosphere nor due to genuine comet activity.

Key words: solar wind – Sun: oscillations – comets: individual: Hale Bopp

Send offprint requests to: S. Steffens

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© European Southern Observatory (ESO) 1998

Online publication: July 20, 1998
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