An Initial Attempt to Measure Suprathermal Tails in Coronal Proton Velocity Distributions

Details An Initial Attempt to Measure Suprathermal Tails in Coronal Proton Velocity Distributions An Initial Attempt to Measure Suprathermal Tails in Coronal Proton Velocity Distributions

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsh44a..05k&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #SH44A-05

Astronomy and Astrophysics

Astrophysics

2114 Energetic Particles (7514), 7500 Solar Physics, Astrophysics, And Astronomy, 7513 Coronal Mass Ejections (2101), 7549 Ultraviolet Emissions

Scientific paper

Test observations made with the Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO in August 2005 are being used to make an initial assessment of the possibility of measuring suprathermal tails in the proton velocity distribution functions. Any successful theory of solar energetic particle (SEP) production by CME shocks must account for the large observed variations in SEP spectral characteristics and elemental abundances. Some have proposed that this variability arises from an inherently variable population of suprathermal seed particles (e.g., Mason et al. 2005): some that exist all the time in the solar wind (with varying properties depending on wind speed) and some that are associated with prior flares and CME shocks (e.g., Kahler 2004; Tylka et al. 2005). As yet, though, the suprathermal particle population in the solar corona has never been measured. The seed particle number density predicted for typical gradual SEP events is about 0.002 - 0.01 times the thermal population (e.g., Lee 2005), and should, in at least some cases, correspond to a measurable enhancement in the wing of the H I Ly-alpha profile. In August 2005, the Ly-alpha channel of UVCS was recommissioned and used to observe HI Ly-alpha line profiles at 2.0 solar radii in coronal holes, helmet streamers, above active regions and after a CME. The holographically ruled diffraction grating provides the low stray light level needed to observe the tail of the line profile out to about 0.5 nm from line center. New observations as well as measurements from the original UVCS laboratory calibration and in flight measurements from earlier in the mission are being used to characterize the instrument response to monochromatic light so such instrument effects can be removed. Initial results will be reported. This work is supported by NASA Grant NNG05GG38G to the Smithsonian Astrophysical Observatory Kahler, S. W. 2004, ApJ, 603, 330. Lee, M. A. 2005, ApJ Supp., 158, 38. Mason, G., Desai, M., Mazur, J., & Dwyer, J. 2005, COSPAR 35th Scientific Assemly, p. 1596. Tylka, A. J., et al. 2005, ApJ, 625, 474.

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