Infrared photometry with 'wall-eyed' pointing at the Large Binocular Telescope

Abstract

The brightness and variability of the atmosphere in the thermal infrared poses obstacles to precision photometry measurements. The need to remove atmospheric effects calls for the use of a comparison star, but it is usually impossible to fit both science and comparison targets on current long-wavelength (>2 µm) detectors. We present a new pointing mode at the Large Binocular Telescope, which has twin 8.4-m primary mirrors that can be pointed up to ∼2 arcminutes apart and allow the placement of both targets on a small-field infrared detector. We present an observation of the primary transit of an exoplanet in front of its host star, and use it to provide preliminary constraints on the attainable photometric precision.

Precision Time-series Photometry in the Thermal Infrared with a “Wall-eyed” Pointing Mode at the Large Binocular Telescope

“…Interpolations of transmission spectra based on the recorded airmass and SMT PWV values show that the general level of transmission changed considerably during this observation, over a total range of >5% (Spalding et al 2016). However, proof of the culpability of windborne PWV variations would require a better understanding of the connection between ground-level windspeed, changing wind profiles at higher altitudes, and the time-dependent behavior of differential PWV values along the lines-of-sight.…”