The Slicer Combined with an Array of Lenslets for Exoplanet Spectroscopy (SCALES) will be the first facility-class integral field spectrograph (IFS) to operate between 2-5 microns. Expected to see first light at W. M. Keck Observatory in 2025, SCALES will extend the parameter space of directly imaged exoplanets to those that are colder, and thus older. SCALES will perform high-contrast imaging of these objects and other targets including protoplanetary disks, Solar System objects, and supernovae. Interferometric techniques such as non-redundant aperture masking (NRM) have been demonstrated to improve spatial resolution at high contrasts. Aperture masking turns a telescope into an interferometer by blocking the pupil with an opaque mask with some number of circular holes. Here we present the final designs for the non-redundant masks that will be integrated into SCALES. We outline their design, manufacturing, characterization, and integration processes. We also present the injection and recovery of several planet and disk companion models into mock SCALES science frames to assess the performance of the selected designs.
KEYWORDS: Planets, Stars, Point spread functions, Exoplanets, Speckle, Atmospheres, Spectral resolution, Atmospheric modeling, Simulations, Signal to noise ratio
SCALES (Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy) is a high-contrast lenslet-based integral field spectrograph (IFS) designed to characterize exoplanet atmospheres in the 2 - 5 micron wavelength range. The SCALES medium-resolution mode provides the ability to characterize exoplanets at increased spectral resolution via the use of a lenslet subarray with a 0.34 x 0.36 arcsecond field of view and an image slicer. We use the SCALES simulator scalessim to generate high-fidelity mock observations of planets in the mediumresolution mode that include realistic Keck adaptive optics performance, as well as other atmospheric and instrumental noise effects, to simulate planet detections, and then employ angular differential imaging to extract the planet spectra. Analyzing the recovered spectra from these simulations allows us to quantify the effects of systematic noise sources on planet characterization, in particular residual speckle noise following angular differential data processing. We use these simulated recovered spectra to explore SCALES’ ability to constrain molecular abundances and disequilibrium chemistry in giant exoplanet atmospheres.
SCALES (Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy) is the next-generation, diffraction-limited, thermal infrared, fully cryogenic, coronagraphic exoplanet spectrograph and imager for W.M. Keck Observatory. SCALES is fed by the Keck II Adaptive Optics bench. Both modes use common fore-optics to simplify the optical design and have individual detectors, which are JWST flight spares. The imager mode operates from 1 to 5 microns with selectable narrow- and broadband filters over a field of view 12.3 arcseconds on a side, and the integral field spectrograph mode operates from 2 to 5 microns with both low and mid spectral resolutions (R∼ 100 to R∼ 7500) over a field of view 2.15 arcseconds on a side. The diamond-turned aluminum optics, most of which are already delivered, with the rest being fabricated, provide low distortion, low wavefront error, and high throughput for all modes. The slicing unit, located behind the lenslet array, allows SCALES to reach heretofore unheard-of spatially-resolved spectral resolution for exoplanet and disc observations from the ground with a coronagraphic integral field spectrograph. The SCALES consortium includes UC Observatories, CalTech, W.M. Keck Observatory, the Indian Institute of Astrophysics, and the University of Durham, with over 40 science team members. We report on the overall design and project status during its ongoing fabrication phase, which started in early 2023.
SCALES (Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy) is a 2 micron to 5 micron high-contrast lenslet-based Integral Field Spectrograph (IFS) designed to characterize exoplanets and their atmospheres. The SCALES medium-spectral-resolution mode uses a lenslet subarray with a 0.34 x 0.36 arcsecond field of view which allows for exoplanet characterization at increased spectral resolution. We explore the sensitivity limitations of this mode by simulating planet detections in the presence of realistic noise sources. We use the SCALES simulator scalessim to generate high-fidelity mock observations of planets that include speckle noise from their host stars, as well as other atmospheric and instrumental noise effects. We employ both angular and reference differential imaging as methods of disentangling speckle noise from the injected planet signals. These simulations allow us to assess the feasibility of speckle deconvolution for SCALES medium resolution data, and to test whether one approach outperforms another based on planet angular separations and contrasts.
The Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy (SCALES) is an under-construction thermal infrared high-contrast integral field spectrograph that will be located at the W. M. Keck Observatory. SCALES will detect and characterize planets that are currently inaccessible to detailed study by operating at thermal (2 μm to 5 μm) wavelengths and leveraging integral-field spectroscopy to readily distinguish exoplanet radiation from residual starlight. SCALES’ wavelength coverage and medium-spectral-resolution (R ∼ 4,000) modes will also enable investigations of planet accretion processes. We explore the scientific requirements of additional custom gratings and filters for incorporation into SCALES that will optimally probe tracers of accretion in forming planets. We use ray-traced hydrogen emission line profiles (i.e., Brγ, Brα) and the SCALES end-to-end simulator, scalessim, to generate grids of high-fidelity mock datasets of accreting planetary systems with varying characteristics (e.g., Teff, planet mass, planet radius, mass accretion rate). In this proceeding, we describe potential specialized modes that best differentiate accretion properties and geometries from the simulated observations.
The Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy (SCALES) is a 2 μm to 5 μm, high-contrast Integral Field Spectrograph (IFS) currently being built for Keck Observatory. With both low (R ≲ 250) and medium (R approximately 3500 to 7000) spectral resolution IFS modes, SCALES will detect and characterize significantly colder exoplanets than those accessible with near-infrared (approximately 1 μm to 2 μm) high-contrast spectrographs. This will lead to new progress in exoplanet atmospheric studies, including detailed characterization of benchmark systems that will advance the state of the art of atmospheric modeling. SCALES’ unique modes, while designed specifically for direct exoplanet characterization, will enable a broader range of novel (exo)planetary observations as well as galactic and extragalactic studies. Here we present the science cases that drive the design of SCALES. We describe an end-to-end instrument simulator that we use to track requirements and show simulations of expected science yields for each driving science case. We conclude with a discussion of preparations for early science when the instrument sees first light in approximately 2025.
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