MRI: Track 1 Development of Multi-Spectral Band Advances for the CHARA Array

The CHARA (Center for High Angular Resolution Astronomy) Array combines the light from six 1-meter optical telescopes as an interferometer that records interference patterns (fringes) to measure the angular size and shape of objects on the sky. CHARA’s angular resolution is ten times higher than the largest single aperture telescopes currently in development. This allows astronomers to resolve the diameters of stars, image stellar surfaces, detect close binary companions, and measure the structure of disks around stars. This program develops a new observing mode that lets the CHARA Array record fringes simultaneously at visible and infrared wavelengths. Collecting data at different wavelengths improves stellar diameter measurements, enables better characterization or exoplanet host stars and transiting exoplanets, and reveals the temperature and structure of star spots, convection cells, and circumstellar disks. To achieve this, upgrades will be made to the telescopes’ adaptive optics systems to operate simultaneously at both visible and infrared wavelengths. A new star-tracking camera will be installed to extend alignment stability to fainter targets. This program also implements a summer internship for undergraduate students in science and engineering, leveraging a unique environment for education and practical work experience in astronomy and instrumentation. The new multi-wavelength imaging mode created by this program directly enhances the open access program at the CHARA Array that provides 100 nights per year of observing time to the US community. The upgrades will optimize performance and sensitivity to provide higher quality data at sub-milliarcsecond resolution. Collecting data simultaneously at visible and infrared wavelengths will yield significant additional information about stellar limb-darkening, which directly impacts both knowledge of stellar structure as well as measurements of stellar diameters and exoplanetary transits. The new mode will be accomplished by replacing the dichroic beam splitters in the adaptive optics systems at the telescopes to minimize the chromatic dispersion between the visible and infrared light transported to the beam-combining lab and upgrading the detector in the star tracking system to extend recent improvements in the alignment stability to fainter targets. The summer internship program brings students to work with CHARA staff and visiting scientists on projects involving instrument design, hardware installation, software development, and detector characterization. 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.