Electron Coronal Density Irregularity

from Measurements of K-Coronal and Lyman Lines Brightnesses

We plan to use a new technique to derive the coronal density irregularity factor , where n is the electron density. This technique will exploit the unique UVCS capabilities of cotemporal and cospatial measurements of both UV and white-light K-coronal polarized brightness, pB.

The knowledge of the coronal electron density is the cornerstone on which the empirical models of the corona, derived from UV observations, are built. The electron density is obtained from measurements of pB. Some of the methods developed to date to derive the density from pB measurements assume an unstructured, spherically symmetric corona. This can result in unrealistic density profiles if a more structured corona is actually present.

The absolute photometric comparison in the inner corona of the intensity of UV lines with pB provides an unique constraint on the inhomogeneity of the corona. The ratio of the measured H I Lyman (Ly-) line intensity to the resonant-scattering dominated H I Lyman (Ly-) intensity can be used to extract the collisional component of the Ly-. This component yields an estimate of . The quantity is then obtained from the UVCS white-light K-coronal measurements. The use of lines of the same atomic species minimizes the effects due to outflow velocities (i.e., Doppler dimming), and reduces the errors introduced by the uncertainties in the ionization balance, the atomic parameters, and the solar abundances. The knowledge of the coronal inhomogeneity is significant also in getting an insight into the coronal dissipation and heating processes, and in understanding the acceleration of the solar wind in coronal holes (below 1.5 R), and streamers (below 2.5 R).

Electron Coronal Density Irregularity from Measurements of K-Coronal and Lyman Lines Brightnesses