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C. M. Johns-Krull, G. H. Fisher (UCB/SSL), J. Varsik, W. Marquette (BBSO)
The role of ~100 keV proton beams in flare energy transport is currently unknown. Claims in the literature range from an energetically negligible role for such protons during flares to claims that 100 keV proton beams carry the majority of the energy released in the corona to the photosphere during a solar flare. Much of the uncertainty concerning protons is due to the fact that 100 keV protons produce very few distinguishable radiative emissions. One such distinguishing emission is the production of linear polarization in the core of the H\alpha emission line during the impulsive phase of a solar flare. This linear polarization is produced as accelerated, directed, protons collide with ambient hydrogen atoms in the solar chromosphere. The geometry of the situation is such that the linear polarization should be strongest at the limb of the Sun and vanish at disk center, while the orientation of the polarization should always be along the line between the flare location and disk center. The expected signal is 5 -- 10% linear polarization at the limb. We have modified the Big Bear Solar Observatory (BBSO) video magnetograph (VMG) to operate in the core of the H\alpha line. Here, we present observations of a handful of solar flares using this system. We show that our sensitivity level is ~1%, and we discuss in detail observations of a long duration GOES class M2 flare observed at the West limb on 5 August 1999.
CMJ-K would like to acknowledge partial funding support of this work by CalSpace.