2.4 Coronal Spectral measurements in the mid-IR during the Solar Eclipse of 2017

As part of the larger ground and airborne project we plan to measure, for the first time, the infrared spectrum of the solar corona from 2 to 12 μ. No such IR spectral survey of the corona has ever been performed, yet some of the most magnetically sensitive spectral lines are theoretically predicted in this region. All of the infrared coronal lines are forbidden lines of magnetic dipole character. We do not know how infrared emission line intensities are distributed in the corona, nor do we know wavelengths accurately enough to determine detrimental effects of telluric absorption on these particular lines.  The project is led by NCAR/HAO, the G-V is operated by NCAR/EOL, the primary airborne instrument is from SAO (Smithsonian Astronomical Observatory) and the ground-based IR survey is by NCAR/ACOM.

The experiments are planned to fly on the Gulfstream V (GV) aircraft to accompany a spectral survey from the ground, producing images of the corona and polarization measurements during the extended eclipse afforded by the aircraft platform. The main science goals are (1) to identify spectral lines ideally suited to measure coronal magnetic fields, (2) to find the range of temperatures spanned by the lines (ions from 6 to 14 times ionized), (3) to identify the typical range of features sampled by the lines (active regions, source regions of fast and slow solar wind) and (4) to find precisely where coronal lines lie relative to telluric absorption features.

Our proposed experiments will collectively provide the information needed to build the next generation of instruments probing the magnetic structure of the solar corona, and thus put the origins of space weather events on a quantitative footing. The National Science Foundation’s (NSF’s) huge investment in the Daniel K. Inouye Solar Telescope (DKIST) and future investment in the COronal Solar Magnetism Observatory (COSMO) will especially benefit from these new experiments. We anticipate publications identifying optimal spectral lines for future work, the origins and nature of noise in coronagraphic polarimetric data by comparison with eclipse data, and analysis of the magnetic and dynamical state of the corona using infrared (IR), X-ray and Extreme Ultraviolet Variability Experiment (EUV) data from operating spacecraft.

Sample template image
Figure 1. Path of total solar eclipse 21 August 2017.

The eclipse will occur on 21 August 2017 near mid-day.  Figure 1 shows the path of totality across the continental US.  The ACOM instrument will be stationed on a mountain top at approximately 2900masl near Casper Wyoming and less then 2km off the path of totality.  The instrument originally designed as a replacement for the long time airborne FTIR program at ACOM will be fitted into a trailer along with solar tracking capability for this experiment.  The instrument shown in Figure 2, is a compact multi-pass Michaelson interferometer designed to operate at variable optical paths to 250cm and acquire spectra from 1.5 to 14 µm using cryogenically cooled detectors.

Sample template image
Figure 2. Compact multi-pass Michaelson interferometer.