Measurement of Hydrogen Velocity Distributions in the Extended Solar Corona
Abstract
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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 1996
- DOI:
- 10.1086/310145
- Bibcode:
- 1996ApJ...465L.141K
- Keywords:
-
- SUN: CORONA;
- SUN: SOLAR WIND;
- SUN: UV RADIATION