Towards controlled Fizeau observations with the Large Binocular Telescope

Abstract

The Large Binocular Telescope Interferometer (LBTI) can perform Fizeau interferometry in the focal plane, which accesses spatial information out to the LBT's full 22.7-m edge-to-edge baseline. This mode has previously been used to obtain science data, but has been limited to observations where the optical path difference (OPD) between the two beams is not controlled, resulting in unstable fringes on the science detectors. To maximize the science return, we are endeavoring to stabilize the OPD and tip-tilt variations and make the LBTI Fizeau mode optimized and routine. Here we outline the optical configuration of LBTI's Fizeau mode and our strategy for commissioning this observing mode.

Review and scientific prospects of high-contrast optical stellar interferometry

“…It is currently being matured for routine operations. 65,66 Currently, one of the main limitations for for precision, high-fidelity, and high-contrast interferometric imaging with a 23-m equivalent aperture is the limited sensitivity of the PhaseCam fringe tracker 67 (limiting magnitude K ∼ 4.5). PhaseCam is currently equipped with a PICNIC detector and an upgrade to a SAPHIRA detector is in preparation (funded, PI: J.…”

A two-band approach to nλ phase error corrections with LBTI's PHASECam

“…Furthermore, as previously described, for Fizeau interferometry and NRM, there is not a method such as observing the null telemetry for us to quickly detect fringe jumps. They can be seen if one closely examines the images of the fringes, 23 but it is easily missed if one is not consistently watching.…”

“…With the successful conclusion of HOSTS observations during the 2018A observing season, 15 the LBTI has begun the transition to commissioning controlled Fizeau imaging. 23 Active, reliable phase control is critical to maintaining 0 OPD alignment of the Fizeau coherence envelopes for the duration of the observation. The grism-dispersed Fizeau fringes both immediately after the initial finding of the coherence envelope on the LMIRCam detector, as well as after minimization of the OPD, can be seen in Figure 1.…”

An Empirical Mass–Radius Relation for Cool Giant Planets

“…Alternatively, an interferometer can be used to effectively suppress starlight. In contrast to a co-axial beam combiner, which is used for the Keck Interferometer (Millan-Gabet et al 2011;Mennesson et al 2014) and the Large Binocular Telescope Interferometer (Ertel et al 2018(Ertel et al , 2020, a multi-axial beam combiner maximizes the spatial resolution, e.g., the Palomar fiber nuller (PFN, Haguenauer & Serabyn 2006;Mennesson et al 2011;Serabyn et al 2019) and the Fizeau imaging mode at LBT (Spalding et al 2018). We will focus on the multi-axial interferometry because of its enhanced spatial resolution and its potential of feeding a high resolution spectrograph with a single-mode fiber.…”