A new reference spectrum for the EUV irradiance of the quiet Sun: 1. Emission measure formulation

Abstract

We present a quiet Sun irradiance spectrum from 50–1200 Å based primarily on intensities computed from a newly constructed quiet Sun emission measure distribution. We derive the emission measure from a spectrum of a portion of the quiet solar disk measured with the Harvard instrument on Skylab and recent compilations of atomic data. For some specific emission lines and continua which are not optically thin and cannot be computed using an emission measure, we either use intensities from the Harvard spectrum directly or infer them from other observations. Application of a simple center‐to‐limb variation converts the intensities to equivalent full‐disk quiet Sun fluxes.