The Solar Minimum Corona from Differential Emission Measure Tomography

Abstract

We present results derived from a dual-spacecraft tomographic reconstruction of the solar corona’s three-dimensional (3D) extreme ultraviolet (EUV) emissivity. We use simultaneously taken STEREO A and B spacecraft EUVI images from Carrington rotation 2077 (2008, November 20 06:56 UT through December 17 14:34 UT). During this period, the spacecraft view-angles were separated by an average 85.4◦ which allowed for the reconstruction to be performed with data gathered in about 3/4 of a full solar rotational time. The EUV reconstructions provide the 3D emissivity in each of the three EUVI Fe bands, in the range of heights 1.00 to 1.25 Rs . We use this information to perform local differential emission measure (LDEM) analysis. Taking moments of the so-derived LDEM distributions gives the 3D values of the electron density, temperature and temperature spread. We determine relationships between the moments of the LDEM and the coronal magnetic field by making longitudinal averages of the moments, and relating them to the global-scale structures of a potential field source surface (PFSS) magnetic field model. In this way, we determine how the electron density, mean temperature, and temperature spread vary for different coronal structures. We draw conclusions about the relationship between the LDEM moments and the sources of the fast and slow solar winds, and the transition between the two regimes.