Increased sky coverage for the 23-meter LBT

Twin adaptive secondaries at the Large Binocular Telescope (LBT) enable powerful observing modes. Two of these, imaging (Fizeau) interferometry and nulling interferometry, make the LBT in many respects the first Extremely Large Telescope (ELT) [1]. Science programs that have been conducted using LBT as a 23-meter telescope include measuring habitable-zone dust around nearby stars and imaging planets during early stages of formation [2, 3]. To allow LBT to function as a 23-meter telescope, the light from its two 8.4-meter segments must be combined coherently. To this end, the Large Binocular Telescope Interferometer (LBTI) co-phases the two incoming beams via a piezo-electric path length corrector. This device is controlled by a fringe-tracking system that measures optical path difference in real time. Here we describe an upgrade to this system: the Fizeau Fringe Tracking Camera (FFTCam) [4]. New science will be enabled. For example, the number of exosolar systems in Taurus-Auriga that can be probed down to 3.5 AU^∗ that can be studied with LBTI will increase by nearly two orders of magnitude.