Linear Polarization as Diagnostics of Accelerated Particles in Solar Flares

Y. Hanaoka (National Astronomical Observatory of Japan)

In solar flares, the magnetic energy released by magnetic reconnection
is converted to the energy of accelerate particles.  In contrast to
accelerated electrons, which emit hard X-rays, it is very difficult to 
detect accelerated ions, particularly protons, even though
they are considered to have a large part of energy as well as
electrons.  However, the particles bombarding the chromosphere,
whichever electrons or protons, excite hydrogen atoms and they emit
linearly polarized light.  Therefore, polarization observation of
flare kernels in chromospheric lines, particularly in the H-alpha
line, is one of important diagnostics of the accelerated particles in
solar flares.  However, only small number of polarization observations
have been reported so far.  Then, we started a regular observation of
the polarization in solar flares for a systematic study of the
polarization in 2002, and recently we replaced the polarimeter with a
new, higher-precision one using ferroelectric liquid crystals.  We
will report the results of the systematic study of the polarization of
solar flares at the conference.