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.
Highlights
The chromosphere is the physical interface between the high-pressure photosphere and very low-pressure corona
The longer-wavelength G1.43 and G1.73 spectrometers were both fed via optical fibers from a single telescope comprising a 250 mm focal length (FL) lens of 50 mm aperture, and a 100 mm FL negative lens in a telephoto configuration, yielding an effective FL of 1200 mm
By fitting the slope of the measured fluxes to the area-weighted center-to-limb intensity functions tabulated by Allen (1973), we found that the NCAR Airborne Interferometer” (NAI) instrument clock was 21 ± 1 s behind UT
Summary
The chromosphere is the physical interface between the high-pressure photosphere and very low-pressure corona. The present paper has two objectives: first, to analyze photospheric and chromospheric data obtained at high time resolution and at wavelengths previously unobserved; second, to test a modified “flash spectrum” technique designed to optimize photometric precision at the expense of spatial information along the solar limb. This is one of two papers analyzing data from the eclipse of 2017 August 21 involving seven different instruments.
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