next up previous contents
Next: Estimates of Line Up: Intensities and Count Previous: Intensities and Count

Introduction

In view of the preparation and interpretation of UVCS/SOHO future observations, it is important to estimate the EUV emission line intensities and profiles to be expected in coronal structures to be observed by this instrument. In this chapter we give some estimates of the intensity values expected for UVCS/SOHO observations of HI Ly- and OVI1032 and 1037, obtained as a function of heliocentric distance for different regions in the extended solar corona.

To calculate the line intensities, we have used models which specify the plasma temperatures, densities and outflow velocities in coronal holes. In this context, it should be kept in mind that there are relatively few empirical values of these quantities for the extended solar corona. As the line intensities depend strongly on the assumed plasma parameters, they are intended only for order-of-magnitude estimates.

Section 3.2 provides intensity values for HI Ly- and OVI in coronal holes. In section 3.2.1 we give the expression used to calculate the intensities and the assumed atomic data for the HI and OVI lines. In section 3.2.2 we describe the densities, velocities and temperatures assumed for the coronal regions considered. The results for the line intensities calculated using the assumptions described in sections 3.2.1 and 3.2.2 are reported in section 3.2.3. Section 3.2.4 provides measured HI Ly-a intensities from sounding rocket and Spartan 201 flights, and a comparison to the calculated intensities. Section 3.3 provides measured streamer intensities for HI Ly-a from Spartan 201 and streamer intensities for OVI 1032 which are scaled from the calculated coronal hole values. Section 3.4 provides a formula for deriving count rates from the estimated intensities and also provides some examples of the expected count rates.



Peter Smith
Fri Jan 17 12:11:15 EST 1997