Measurement of Hydrogen Velocity Distributions in the Extended Solar Corona

Details Measurement of Hydrogen Velocity Distributions in the Extended Solar Corona Measurement of Hydrogen Velocity Distributions in the Extended Solar Corona

Jul 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...465l.141k&link_type=abstract

Astrophysical Journal Letters v.465, p.L141

Astronomy and Astrophysics

Astronomy

50

Sun: Corona, Sun: Solar Wind, Sun: Uv Radiation

Scientific paper

H I Ly alpha spectral line profiles have been measured in polar regions of the solar corona at projected heliocentric heights of 1.8--3.5 Rsolar. Observations were made with the Ultraviolet Coronal Spectrometer on the Spartan 201 satellite from 16:52 to 04:04 UT on 1993 April 11--12 (south pole) and from 12:28 to 22:09 UT on 1993 April 12 (north pole). In general, the coronal profiles cannot be accurately curve-fitted with a single-Gaussian function. The fits with two Gaussians yield most probable velocities of 158 and 322 km s-1 (south) and 98 and 266 km s-1 (north). These parameters vary by less than 10% (1 sigma ) over the observed heights. The observations are consistent with a line-of-sight model that attributes the narrow component to background streamers and to sites within polar coronal holes or a surrounding diffuse corona, and the broad component to the polar coronal holes and/or plumes. This interpretation suggests that there are regions within the observed coronal holes that have hydrogen and proton kinetic temperatures of (4--6) x 106 K, which is 4--10 times higher than the expected electron temperatures at the same heights. However, other models with, for example, local non-Maxwellian velocity distributions are also consistent with the observations.

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