Differentiating Coronal Holes from the Quiet Sun by He 1083 nm Imaging Spectroscopy

The locations of coronal holes are usually based on equivalent-width images in the He i 1083 nm line. However, it is difficult to differentiate coronal holes from the centers of quiet chromospheric network without complementary data and the skill of an experienced observer. Analysis of imaging spectroscopy shows that line half-width and central intensity are correlated differently in coronal holes and a quiet Sun. This fact can be used to form linear combinations of these images in which coronal holes are better separated from the quiet Sun. Coronal hole borders agree well with SOHO/EIT data but can show significant differences from National Solar Observatory maps.