AGS-FIRP Track 3: Solar Eclipse Observations with the Airborne Coronal Emission Surveyor (ACES)

Smithsonian Institution Astrophysical Observatory, Cambridge MA

Investigators

Abstract

This project is a Track-3 deployment to commission a new imaging Fourier transform spectrometer with an observation of the solar corona from the NSF/NCAR Gulfstream V (GV) during the 2024 total solar eclipse across North America. The Airborne Coronal Emission Surveyor (ACES), currently under construction on NSF award AGS-MRI #2117582, will survey the 1–4 μm wavelength region to look for lines that may be viable candidates for measuring the coronal magnetic field and plasma diagnostics at large solar radii. ACES is a new focal plane instrument enabled by the Airborne Stabilized Platform for InfraRed Experiments (ASPIRE, AGS-MRI #1919809), commissioned in 2021 with observations from the GV. It builds on the success of ASPIRE and the Airborne InfraRed Spectrometer (AIR-Spec, AGS- MRI #1531549 & AGS #1822314) to expand the infrared window for thermal and magnetic studies of the Sun’s outer atmosphere. The eclipse campaign and data reduction effort are modeled on the very successful AIR-Spec missions to observe the 2017 and 2019 total solar eclipses. Following deployment, the instrument will be delivered to NCAR as a resource for the solar physics community. Two REU students and one graduate student will be trained. The team is a diverse group of early to mid-career scientists and engineers and is led by a female PI. During its six-minute commissioning observation from the GV, ACES will observe from an altitude of 14 km with a spectral resolution of 0.5 cm−1 and a spatial plate scale of 20" across a field of view of 2000"×100". The instrument will search for more than twenty forbidden lines of ionized magnesium, aluminum, silicon, sulfur, argon, calcium, iron, and nickel, at least half of which have never before been observed. The novel research goals include: identifying the brightest spectral lines; documenting their widths and higher order properties of the line profiles; measuring contributions from collisional versus radiative excitation; documenting the variations of all of the above as a function of the features observed and projected radius. The science questions probe the diagnostic potential of emission lines in the 1–4 μm range, the variation of plasma density and temperature with radial distance, the ratio of radiative to collisional excitation as a function of radius, and the variation of elemental abundances across the corona. The solar feed for ACES will be provided by ASPIRE, which was constructed with NSF award AGS-MRI #1919809 and commissioned in December 2021. ASPIRE enables the large aperture, high altitude, and image stability (6 arcsec RMS in a 1-s exposure) necessary to measure the infrared corona with high sensitivity. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.