MRI: Development of An Airborne Infrared Spectrometer (AIR-Spec) for Coronal Emission Line Observation

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Total solar eclipses offer unique opportunities for scientific explorations and discoveries, and also for people of all walks of life and ages to witness one of Nature's most fascinating displays of beauty. On August 21, 2017, a rare total solar eclipse event will occur that will traverse the continental United States, starting in Oregon and ending in South Carolina. The previous such occasion was on 29 July 1878. The purpose of this major research instrumentation project is to design, build, test, and fly a highly advanced imaging spectrometer to make measurements during this eclipse, for the first time, of the solar corona in the infrared spectrum. This opens a new wavelength window for observation of the solar corona that has exiting potential for advancing our understanding of this hard-to-observe region. The Airborne Infra-Red Spectrometer (AIR-Spec) instrument will include a novel image stabilization system to allow it to be deployed on NSF's Gulfstream V aircraft operated by the National Center for Atmospheric Research (NCAR). Flying at an altitude above 49,000 feet makes it possible to get measurements without disturbances from local weather and avoiding most of the absorbing water vapor in the atmosphere that poses a challenge for observations at the ground. The completion of this program will see the delivery to NCAR of a stable commissioned instrument that is certified and available for other scientist to fly on the GV for future research missions. The GV can travel almost anywhere and re-flights at other future eclipses are an obvious possibility to pursue. The July 2, 2019, South Pacific eclipse will be the first chance for another eclipse flight. In addition, the stabilized high resolution observing capability can be used by other experiments for solar and atmospheric observations throughout the world.The project will be carried out in collaboration between the scientists and engineers at the Smithsonian Astrophysical Observatory (SAO) and NCAR's High Altitude Observatory (HAO), each contributing essential expertise and experience to ensure its successful completion. The project will directly contribute to training the next generation of instrumentation scientists while fostering diversity. A Harvard graduate student from the School of Engineering and Applied Sciences will be involved in all aspects of the project, including design, fabrication and test of the AIR-Spec instrument, as well as analysis of the observations, if scientific data are acquired during the eclipse. This will form the basis for her thesis and she will enjoy the benefits of mentoring from scientists and engineers at both SAO and HAO. In addition, the 2017 US solar eclipse is expected to generate a huge amount of interest amongst the general public and the project team will work closely with partners at the National Air and Space Museum, the Boston Museum of Science and the Eclipse Mega-Movie group at HAO on pre and post eclipse outreach events. The AIR-Spec instrumentation includes an image stabilization system, a feed telescope, a grating spectrometer and a slit-jaw imager. It will measure emission line intensity, FWHM, and Doppler shift a set of magnetically sensitive coronal emission lines at a range of coronal positions during the August 21, 2017 "Great American Eclipse". Although high resolution, high sensitivity coronal imaging spectroscopy has never been performed between 1.4 and 4um, this spectral region has great potential for coronal plasma diagnostics, for coronal hole spectroscopy, and as a path finder for observations of coronal magnetic fields. Infrared coronal emission lines are well suited for measuring magnetic field properties using the Zeeman and Hanle effects, but such measurements require high precision spectro-polarimetric instruments that cannot be designed until the candidate emission lines have been characterized. The 2017 eclipse provides a unique opportunity to survey these lines, and AIR-Spec observations can help provide guidance for future ground-based Infrared observations. The AIR-Spec commissioning flight during the 2017 eclipse will target three science goals: (1) Search for high frequency waves in multiple lines at multiple locations in the corona. These waves are candidates for heating and acceleration of the solar wind. (2) Identify large-scale flows in the corona, particularly in polar coronal holes. Three of the lines to be observed are expected to be strong in coronal hole plasmas because they are excited in part by scattered photospheric light. Line profile analysis will probe the origins of the fast and slow solar wind. (3) Complement ground based eclipse observations to provide detailed plasma diagnostics throughout the corona. AIR-Spec will measure IR emission of ions also observed in the visible, giving insight into plasma heating and acceleration at radial distances inaccessible with existing or planned spectrometers. On the technology side, the AIR-Spec stabilization system removes a significant obstacle to airborne observations. The system relies on inertial measurements to stabilize the platform to 1.4 arcsec RMS for the planned 0.3 sec exposure (1.7arcsec RMS per sec), allowing it to be used for a wide range of solar and atmospheric imaging experiments. Finally, for the future there is the possibility for AIR-Spec to be modified to add linear polarization optics for direct measurements of coronal magnetic field direction.