Weighing exo-atmospheres: a novel mid-resolution spectral mode for SCALES

Abstract

SCALES (Slicer Combined with an Array of Lenslets for Exoplanet Spectroscopy) is a 2 -5 micron high-contrast lenslet-based integral field spectrograph (IFS) designed to characterize exoplanets and their atmospheres. Like other lenslet-based IFSs, SCALES produces a short micro-spectrum of each lenslet's micro-pupil. We have developed an image slicer that sits behind the lenslet array & dissects and rearranges a subset of micro-pupils into a pseudo-slit. The combination lenslet array and slicer (or slenslit) allows SCALES to produce much longer spectra, thereby increasing the spectral resolution by over an order of magnitude and allowing for comparisons to atmospheric modeling at unprecedented resolution. This proceeding describes the design and performance of the slenslit.

SCALES on Keck: optical design

“…The SCALES slenslit optical and mechanical design is described in detail in Stelter. 3,4 Following the smaller 17 × 18 spaxel IFU is a second pinhole grid which serves as the object plane for an input relay to the slicer, converting the beam from the f/8 of the lenslet into the f/64 demanded by the slicer module. The slicer stack consists of 18 slices, one for each column of spaxels.…”

“…SCALES has adopted a novel approach to obtaining moderate spectral resolutions over large bandpasses. We are implementing an image slicer developed by Stelter 3,4 to reformat the pupil grid produced by the microlens array into a set of three interleaved pseudoslits, which are dispersed across the full length of the detector by gratings. The medium resolution configuration is shown on the lower panel of Figure 1.…”

Designing custom medium resolution observing modes to trace planet accretion with SCALES

“…SCALES' baseline medium resolution modes will cover each of the K, L, and M bands with spectral resolution determined by available detector space (see Table 1). Stelter et al (2022), 5 also Stelter et al (2023) in these proceedings, 6 has a full discussion of the SCALES medium-resolution design. These modes at thermal infrared wavelengths meet high-level science requirements to constrain molecular abundances of methane, ammonia, carbon monoxide, and water vapor in exoplanet atmospheres.…”

Simulating medium-spectral-resolution exoplanet characterization with SCALES angular/reference differential imaging

“…Exoplanet characterization may be carried out at increased spectral resolution using the SCALES medium-spectral-resolution mode, which uses a lenslet subarray with a 0.34 x 0.36 arcsecond field of view in series with an image slicer. 1 Exploring the sensitivity limitations of the SCALES medium-resolution mode is advantageous as it allows us to assess the feasibility of planet characterization using this mode, as well as to quantify of the effects of various systematic noise sources. We simulate planet detections in the presence of realistic noise sources using the SCALES simulator scalessim to generate high-fidelity mock observations of planets while varying planet temperature, planet-star separations, and number of parallactic angles (η).…”