On-sky Performance and Results of the Recently Upgraded ALES Integral Field Spectrograph

Abstract

The Arizona Lenslets for Exoplanet Spectroscopy (ALES) is an integral field spectrograph implemented with a modular design comprising magnifiers, a lenslet array, and direct-vision prisms all installed in filterwheels within the LBTI/LMIRCam instrument. ALES is unique among high-contrast instruments for providing spatially resolved spectroscopy out to 5 microns. ALES has been operating with an upgraded lenslet array and prism assembly since late 2018. The new lenslet array includes larger lenslets to reduce diffraction losses and spatial crosstalk in the data. The lenslet array is fabricated with a unique sag surface for each lenslet, correcting for rotating off-axis astigmatism in the magnified intermediate focal plane. The result is tighter lenslet spots and better data. The new prism assembly provides increased spectral resolution in the 2.9 to 4.2 micron wavelength range. Here we characterize the performance of upgraded ALES, and report initial results probing the atmospheres of high-contrast companions to nearby stars. A calibration and data pre-processing strategy unique to the upgraded instrument is discussed. We also report laboratory tests of additional future upgrades including prism and blocking filter pairs for added bandpasses and magnification modes to facilitate Fizeau interferometry with LMIRCam and ALES. © 2022 SPIE.