Large Binocular Telescope Interferometer Adaptive Optics: On-sky performance and lessons learned
Abstract
The Large Binocular Telescope Interferometer is a high contrast imager and interferometer that sits at the combined bent Gregorian focus of the LBT's dual 8.4~m apertures. The interferometric science drivers dictate 0.1'' resolution with 103-104 contrast at 10~μ m, while the 4~μ m imaging science drivers require even greater contrasts, but at scales >0.2''. In imaging mode, LBTI's Adaptive Optics system is already delivering 4~μ m contrast of 104-105 at 0.3''-0.75'' in good conditions. Even in poor seeing, it can deliver up to 90\% Strehl Ratio at this wavelength. However, the performance could be further improved by mitigating Non-Common Path Aberrations. Any NCPA remedy must be feasible using only the current hardware: the science camera, the wavefront sensor, and the adaptive secondary mirror. In preliminary testing, we have implemented an ``eye doctor'' grid search approach for astigmatism and trefoil, achieving 5\% improvement in Strehl Ratio at 4~μ m, with future plans to test at shorter wavelengths and with more modes. We find evidence of NCPA variability on short timescales and discuss possible upgrades to ameliorate time-variable effects
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