On-Sky Operations with the ALES Integral Field Spectrograph

TL;DR

This paper describes the on-sky operation procedures and observational strategies for the ALES integral field spectrograph, enabling 2-5 μm spectroscopy of directly imaged exoplanets with the LBTI.

Contribution

It introduces the operational setup, calibration, and observing techniques for ALES, facilitating high-contrast exoplanet spectroscopy.

Findings

Successful collection of multiple datasets of exoplanets.

Optimized observing procedures for sky background and alignment.

Effective calibration and nodding strategies implemented.

Abstract

The integral field spectrograph configuration of the LMIRCam science camera within the Large Binocular Telescope Interferometer (LBTI) facilitates 2 to 5 $\mu$m spectroscopy of directly imaged gas-giant exoplanets. The mode, dubbed ALES, comprises magnification optics, a lenslet array, and direct-vision prisms, all of which are included within filter wheels in LMIRCam. Our observing approach includes manual adjustments to filter wheel positions to optimize alignment, on/off nodding to track sky-background variations, and wavelength calibration using narrow band filters in series with ALES optics. For planets with separations outside our 1"x1" field of view, we use a three-point nod pattern to visit the primary, secondary and sky. To minimize overheads we select the longest exposure times and nod periods given observing conditions, especially sky brightness and variability. Using this strategy we collected several datasets of low-mass companions to nearby stars.