Nulling Data Reduction and On-Sky Performance of the Large Binocular Telescope Interferometer

TL;DR

The paper discusses the LBTI's nulling mode for high-contrast infrared imaging, demonstrating a record null accuracy that advances the study of exozodiacal dust and planetary systems.

Contribution

It presents the first on-sky performance results of the LBTI nulling mode, including data reduction techniques and achieving a new null accuracy record.

Findings

Achieved 0.05% null accuracy over three hours on beta Leo

Set a new record for high-contrast mid-infrared interferometry

Demonstrated capability to detect exozodiacal dust at 15-30 zodi levels

Abstract

The Large Binocular Telescope Interferometer (LBTI) is a versatile instrument designed for high-angular resolution and high-contrast infrared imaging (1.5-13 microns). In this paper, we focus on the mid-infrared (8-13 microns) nulling mode and present its theory of operation, data reduction, and on-sky performance as of the end of the commissioning phase in March 2015. With an interferometric baseline of 14.4 meters, the LBTI nuller is specifically tuned to resolve the habitable zone of nearby main-sequence stars, where warm exozodiacal dust emission peaks. Measuring the exozodi luminosity function of nearby main-sequence stars is a key milestone to prepare for future exoEarth direct imaging instruments. Thanks to recent progress in wavefront control and phase stabilization, as well as in data reduction techniques, the LBTI demonstrated in February 2015 a calibrated null accuracy of 0.05% over a three-hour long observing sequence on the bright nearby A3V star beta Leo. This is equivalent to an exozodiacal disk density of 15 to 30 zodi for a Sun-like star located at 10pc, depending on the adopted disk model. This result sets a new record for high-contrast mid-infrared interferometric imaging and opens a new window on the study of planetary systems.