High-cadence Visible and Infrared Spectra of the Sun during Eclipse

Abstract

Abstract We study novel spectra from 310 nm to 5.5 μm obtained during the 2017 August 21 eclipse. Four spectrometers were deployed at Camp Wyoba (altitude 2402 m) on Casper Mountain, WY. Three low-resolution ( ≲ 1000) Avantes spectrometers obtained useful spectra from 310 nm to 2.3 μm, at cadences from 8 to 500 ms. To maximize photometric precision, these instruments were fed with optical fibers placed in the pupil planes of two small (D = 5 cm) telescopes, thereby integrating all light from the field of view. We also acquired higher-resolution ( ≈ 30000) spectra with a new infrared Fourier Transform Spectrometer, fed by a Sun-tracking heliostat, at a 2.5 s cadence. We calibrate the fluxes using counts obtained during partial eclipse, with known limb-darkened photospheric intensities. Fluxes of chromospheric lines, including Ca ii H, K, and Hα, obtained near third contact, were measured every 20 ms, a sampling in height above the limb of 5.6 km. The behavior found corresponds to that found in traditional (image-plane) flash spectra. Two unknown chromospheric emission lines are noted. Based upon our measurements and earlier calculations, we propose new eclipse experiments to uncover clues to the origin and structure of spicules.