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Astron. Astrophys. 316, 487-492 (1996)

A search for 3He enhancements in SEP and CIR-associated events with Ulysses/HI-SCALE

D.A. Biesecker

School of Physics and Space Research, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK

Received 1 April 1996 / Accepted 15 May 1996

Abstract. We identify 17 solar energetic particle (SEP) events with enhanced abundances of 3He relative to 4He detected by the Heliosphere Instrument for Spectra, Composition, and Anisotropy at Low Energies (HI-SCALE) on the Ulysses spacecraft. These events were all detected while Ulysses was within 5 of the ecliptic plane, but at distances from the Sun of 1-5 AU. We compare these results to those obtained with the ONR-604 instrument on the Combined Release and Radiation Effects Satellite (CRRES) mission (Chen et al. 1995). Chen et al. found 13 events with enhancements of 3He above normal solar abundances at energies >50 MeV/nucleon. The HI-SCALE instrument measures He ions with energies between 0.3 and 3.1 MeV/nucleon. We identify flux increases in the HI-SCALE data which correspond to 6 of the CRRES events, but we find an enhancement in 3He in only one of these events. We believe this single coincident detection to be a chance occurrence. We use these results, together with the multitude of previous results at different energies, to discuss the overall picture of 3He-rich events as a function of energy. We also analyze the data for 3He enhancements in high latitude co-rotating interaction region (CIR)-associated events observed while the spacecraft was in the southern solar hemisphere above the streamer belt. We find, within the sensitivity of the HI-SCALE instrument, that there is no 3He enhancement in these CIR-associated events. We then briefly discuss how this relates to particle acceleration mechanisms in solar flares.

Key words: Sun: abundances - Sun: flares - Sun: particle emission

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Last change: December 30, 1996
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