UVCS/SOHO Search for Coronal Suprathermal Seed Particles: 2011 Campaign
Abstract
The Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric Observatory is being used to measure precise coronal H I Ly-alpha spectral line profiles out to several Doppler half widths. Such observations can be used to reveal the proton velocity distribution along the line-of-sight. Departures from a Maxwellian distribution are believed to be needed for the acceleration of solar energetic particles (SEPs) by coronal mass ejection (CME) shocks. It is generally believed that the seed particle population needed to produce the numbers of SEPs observed in large events would have 0.001 to 0.01 of the particles with speeds that exceed 1000 km/s. Assuming a kappa distribution that is symmetric in the tangential plane and Maxwellian in the radial direction, this would correspond to a distribution with kappa = 3.5 or smaller. We have shown that UVCS observations can distinguish a Gaussian from a kappa exponent of 4 or less. Previously reported observations near solar minimum have not yielded any such distributions, but the sampling of the corona was not very systematic. A new observational campaign was begun on 28 April 2011. Observations are all at a heliographic height of 2.7 solar radii from Sun-center and at a solar position angle of 290 degrees. Observations are made on a continuous basis except during SOHO Keyhole periods when UVCS observations are not possible, and at a few other times. Results of this campaign and some earlier observations will be reported. This work is supported by the National Aeronautics and Space Administration (NASA) under Grant NNX11AM46G to the Smithsonian Astrophysical Observatory.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMSH33D..05K
- Keywords:
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- 7514 SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY / Energetic particles;
- 7549 SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY / Ultraviolet emissions