Instrumentation for Ultraviolet Spectroscopy of the Extended Solar Corona

Abstract

Instrumentation and plasma diagnostic techniques are being developed to obtain a detailed empirical description of solar wind acceleration regions at heights between the coronal base and about 10 solar radii from sun center (R⊙). The goal of this work is to determine a sufficient number of observational parameters to constrain, significantly, theories of solar wind acceleration, coronal heating and solar wind composition. Although a substantial amount of data on the electron density structure of the corona already exists, there are only isolated measurements of other critical plasma parameters, except for observations of regions near the base of the corona. Ultraviolet spectroscopy provides a capability to expand greatly the number of plasma parameters that can be specified by means of remote sensing techniques. Ultraviolet measurements of spectral line profiles determine the random velocity distributions and effective temperature of protons, minor ions and electrons. Ion densities, and chemical abundances are derivable from the collisional component of the observed resonant line intensities. Outflow velocities can be determined from Doppler shifts and Doppler dimming of spectral lines. The instruments which are being developed for remote sensing of the extended corona, consist of an occulted telescope system and a high resolution spectrometer. The basic design was proven on three sounding rocket flights. Initial data on proton temperatures, and solar wind outflow velocities for heliospheric heights between 1.5 and 3.5 solar radii from sun center have been obtained. More powerful instruments are being developed for Spartan (a shuttle deployed subsatellite) and for the SOHO Mission.