Precision Time-series Photometry in the Thermal Infrared with a 'Wall-Eyed' Pointing Mode at the Large Binocular Telescope

TL;DR

This paper introduces a novel method for thermal infrared time-series photometry using the Large Binocular Telescope's unique pointing mode, enabling simultaneous observation of science and calibration stars in a small field.

Contribution

The paper presents a new differential photometry technique leveraging the LBT's binocular design to observe science and calibration stars simultaneously in the thermal infrared.

Findings

Achieved percent-level scatter in L-band photometry for bright targets.

Demonstrated the feasibility of simultaneous dual-target observations in the thermal IR.

Potential for improved precision with increased sampling and systematics analysis.

Abstract

Time-series photometry taken from ground-based facilities is improved with the use of comparison stars due to the short timescales of atmospheric-induced variability. However, the sky is bright in the thermal infrared (3-5 um), and the correspondingly small fields-of-view of available detectors make it highly unusual to have a calibration star in the same field as a science target. Here we present a new method of obtaining differential photometry by simultaneously imaging a science target and a calibrator star, separated by <2 amin, onto a 10x10 asec field-of-view detector. We do this by taking advantage of the LBT's unique binocular design to point the two co-mounted telescopes apart and simultaneously obtain both targets in three sets of observations. Results indicate that the achievable scatter in Ls-band (3.3 um) is at the percent level for bright targets, and possibly better with heavier sampling and characterization of the systematics.