Observing the solar corona with a tunable Fabry-Perot filter

Abstract

A solid Fabry-Perot etalon with a 0.16 Å passband was used during the 180 s solar eclipse of 2006 for rapid scans of an emission line of the solar corona. The etalon was a Y-cut lithium niobate wafer coated with reflective and conductive (ITO) layers. Voltage applied perpendicular to the etalon face produced a passband shift of 0.0011 Å V^−1. During the eclipse, 18 filtergrams were obtained at six 0.22 Å steps across the profile of the forbidden [Fe X] spectral emission line at 6374.4 Å, which results from the 106 K coronal plasma. The 9.3×9.3 arcmin field of view showed the structure of the corona above a newly emerged sunspot region. We discuss tests performed on the etalon before and after the eclipse. We also discuss the coronal observations, which show some features with 10 km s^−1 velocities in the line of sight.