Search for Evidence of Alpha Particle Beams during a Solar Flare

Details Search for Evidence of Alpha Particle Beams during a Solar Flare Search for Evidence of Alpha Particle Beams during a Solar Flare

Jan 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002mwoc.conf..283b&link_type=abstract

Multi-Wavelength Observations of Coronal Structure and Dynamics -- Yohkoh 10th Anniversary Meeting. Proceedings of the conferenc

Computer Science

Scientific paper

We observed NOAA Region 9090 (N13 W39) with SOHO's CDS and EIT between 18:17 and 21:09 UT on 24 July 2000 to search for evidence of alpha particle beams during solar flares. The GOES satellite reports a C3.8 event in this region from 19:57 to 20:05 UT. Theoretically, an alpha particle beam will manifest itself during the impulsive phase of a flare through an enhancement in the red wing of the He II Lyalpha (303.782 AA) emission line, without a corresponding blue wing enhancement. This enhancement is due to downstreaming nonthermal alpha particles undergoing charge exchange with chromospheric neutral hydrogen atoms to form downstreaming nonthermal He II ions. Lyalpha radiation emitted from these downstreaming ions is Doppler-shifted into the red wing of the Lyalpha line. Our CDS observing program acquired high time resolution (9.7 s) 4'' times 4' slit spectra between 590 and 630 AA, where we observed He II Lyalpha in second order (607.564 AA). We fit the spectral background and emission line profiles for each CDS spectrum in our observed sequence. Density- and temperature-insensitive intensity ratios of O IV and Mg X lines generally agree with their theoretical values before and after the flare, but differ significantly from their theoretical values during the flare. This may indicate line blending with unknown components, line blending with second order C IV and Fe XV lines, or loss of ionization equilibrium. Most important, however, we find that although the red wing and blue wing backgrounds for He II Lyalpha remain relatively constant during most of our observation, the blue wing undergoes a more significant enhancement during the flare than does the red wing. This effect is opposite that expected in the presence of an alpha particle beam. Further, blended spectral line features that mimic the expected nonthermal redshifted He II Lyalpha beam signal are understood in terms of well known emission line components. Thus we find no evidence for the presence of alpha particle beams in this case.

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