34th Solar Physics Division Meeting, June 2003
Session 14 RHESSI Results I
Oral, Wednesday, June 18, 2003, 9:00am-12:00noon, Auditorium

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[14.07] High Resolution Spectroscopy of Nuclear De-excitation Lines Observed in the 23 July 2002 Flare

D. M. Smith (Space Sciences Laboratory, U. C. Berkeley), G. H. Share, R. J. Murphy (Naval Research Laboratory), R. A. Schwartz (NASA/GSFC), A. Y. Shih, R. P. Lin (Dept. of Physics and Space Sciences Laboratory, U. C. Berkeley)

We will present the first high-resolution spectra of nuclear de-excitation lines from a solar flare, taken with the \it Reuven Ramaty High Energy Solar Spectroscopy Imager (RHESSI) \rm during the X4.8 flare of 23 July 2002. Lines from neon, magnesium, silicon, iron, carbon, and oxygen were observed. The flare occurred at a heliocentric angle of 73 degrees, yet the redshifts of the de-excitation lines are large (0.1-0.8%, varying inversely with the mass of the excited nucleus). These redshifts would be expected for a heliocentric angle of 30-40 degrees if the interacting ions have a pitch-angle distribution isotropic in the downward hemisphere and zero in the upward hemisphere. Either the interacting ions are beamed almost directly downwards instead, or else the magnetic field at the base of the loops containing the accelerated ions is not perpendicular to the solar surface, but rather inclined so as to be more nearly parallel to our line of sight.

We will also discuss the relative intensities of the de-excitation lines and how the intensity and lineshape measurements together can constrain the spectral shape of the interacting ions, their alpha/proton ratio, and the composition (e.g. photospheric to coronal) of the medium in which they interact.

This work was funded by NASA contract NAS 5-98033.


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