UVCS/SOHO Observations of H I Lyman Alpha Line Profiles in Coronal Holes at Heliocentric Heights Above 3.0 R⊙ |
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Authors: | R M Suleiman JL Kohl A V Panasyuk A Ciaravella SR Cranmer LD Gardner R Frazin R Hauck PL Smith G Noci |
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Institution: | (1) Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA;(2) Università di Firenze, I-50125 Firenze, Italy |
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Abstract: | The Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO) has been used to measure
spectral line profiles for H I Lyα in the south polar coronal hole at projected heliocentric heights from 3.5 to 6.0 R⊙ during 1998 January 5–11. Observations from 1.5 to 2.5 R⊙ were made for comparison. The H I Lyα profile is the only one observable with UVCS above 3.5 R⊙ in coronal holes. Within this region the outflowing coronal plasma becomes nearly collisionless and the ionization balance
is believed to become frozen.
In this paper, the 1/e half widths of the coronal velocity distributions are provided for the observed heights. The velocity
distributions include all motions contributing to the velocities along the line of sight (LOS). The observations have been
corrected for instrumental effects and interplanetary H I Lyα. The half widths were found to increase with projected heliographic
height from 1.5 to 2.5 R⊙ and decrease with height from 3.5 to 5 R⊙.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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Keywords: | corona coronal holes solar wind UV radiation spectroscopy line profiles |
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