High cadence visible and infrared spectra of the Sun during eclipse

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Friday, February 1, 2019

We study visible and infrared spectra, from 310 nm to 5 microns, obtained during the 21st August 2017 eclipse. The instruments were situated at Camp Wyoba (altitude 2402 m) on Casper Mountain, WY.

Graph of visible and infrared spectra
Raw counts are plotted against wavelength in air for spectral lines of interest in the 1-5 μm, from the NAI Fourier trans- form spectrometer. The data are shown at full spectral resolution. Several emission lines of hydrogen are shown with the regions sur- rounding non-detected coronal lines. Each panel shows nine sep- arate scans of 2.5 seconds length, as the second contact was ap- proached, centered between 19 and 2 seconds prior to second con- tact at 17:45:37.2 UT. Important molecular absorbers are listed for each wavelength region on the figure.

Three low-resolution spectrographs, loaned to us by Avantes corporation, were used to obtain data with cadences from 8 to 500 milliseconds, as the moon covered and uncovered the solar atmo- sphere close to second and third contact. These data are combined with photospheric data obtained close to second contact from a ground-based infrared Fourier Transform spectrometer (NAI), to help understand the effects of telluric absorption at infrared wavelengths. The Avantes spectrographs were fed via optical fibers from a pupil plane, by two small (D = 5 cm) telescopes. The spectra thus accu- mulate all light from the eclipsed Sun, except that a field stop of width 100” was placed at prime focus in the visible G0.70 spectrograph. The spectral intensities reported here are placed on a crude abso- lute scale, assuming a certain average geometry for the solar corona. All measurements are mutually consistent and compatible with more sensitive observations from the Air-Spec airborne spectrometer recently reported by Samra and associates. Two unknown but strong chromospheric emission lines are noted. The experiments suggest that non-imaging high-cadence eclipse data can reveal new clues to the nature of spicules and the connection of the corona to the chromosphere, when higher quality eclipse spectra can be acquired in future.

Publication Name: ApJ First HAO

Author's Name: Philip Judge

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