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.
The upcoming SCALES instrument for W.M. Keck Observatory will enable coronagraphic imaging and low-/mid-resolution IFS observations over 2-5 micron wavelengths, using two separate HgCdTe Teledyne Imaging H2RG detectors. These detectors are wired for slow-mode readout at a pixel clock rate of ~100kHz, but when operated with a Teledyne Imaging SIDECAR ASIC followed by an AstroBlank/Markury Scientific MACIE controller card, the system can be operated at faster clock rates up to 30MHz, a mode referred to as hybrid fast-slow readout. We perform room-temperature laboratory tests of detector readout to demonstrate feasibility of hybrid readout using a MUX in place of the H2RG, before proceeding into room-temperature and cold tests with the H2RG detector. We test and optimize full-frame data acquisition with pixel clock rates from 5-30 MHz. We discuss the next steps in detector system testing and verification.
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.
Long wavelength infrared (8-13 μm) spectroscopy is invaluable for detecting molecular features in the atmospheres of gas giant and terrestrial exoplanets. The nulling-optimized mid-infrared camera (NOMIC) on the Large Binocular Telescope Interferometer (LBTI) has a low resolution (R∼200) germanium grism that was previously installed but has not been characterized and commissioned for scientific observations. Using a 1.27 mm slit and broadband filter in combination with the grism, the infrared window between 8-13 μm can be captured. We describe initial on sky testing of the LBTI/NOMIC grism mode with adaptive optics to study standard stars and binaries. We discuss the impact of observational strategy and telluric calibration on the spectral reduction process. We infer the impact of existing mid-infrared detectors on NOMIC’s spectroscopic mode and discuss requirements to enable higher resolution 8-13 μm spectroscopy on current and future facilities.
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.
The Slicer Combined with an Array of Lenslets for Exoplanet Spectroscopy (SCALES) instrument is a lenslet-based integral field spectrograph that will operate at 2 to 5 microns, imaging and characterizing colder (and thus older) planets than current high-contrast instruments. Its spatial resolution for distant science targets and/or close-in disks and companions could be improved via interferometric techniques such as sparse aperture masking. We introduce a nascent Python package, NRM-artist, that we use to design several SCALES masks to be non-redundant and to have uniform coverage in Fourier space. We generate high-fidelity mock SCALES data using the scalessim package for SCALES’ low spectral resolution modes across its 2 to 5 micron bandpass. We include realistic noise from astrophysical and instrument sources, including Keck adaptive optics and Poisson noise. We inject planet and disk signals into the mock datasets and subsequently recover them to test the performance of SCALES sparse aperture masking and to determine the sensitivity of various mask designs to different science signals.
We present the design of SCALES (Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy) a new 2-5 micron coronagraphic integral field spectrograph under construction for Keck Observatory. SCALES enables low-resolution (R∼50) spectroscopy, as well as medium-resolution (R∼4,000) spectroscopy with the goal of discovering and characterizing cold exoplanets that are brightest in the thermal infrared. Additionally, SCALES has a 12x12” field-of-view imager that will be used for general adaptive optics science at Keck. We present SCALES’s specifications, its science case, its overall design, and simulations of its expected performance. Additionally, we present progress on procuring, fabricating and testing long lead-time components.
The direct characterization of exoplanetary systems with high contrast imaging is among the highest priorities for the broader exoplanet community. As large space missions will be necessary for detecting and characterizing exo-Earth twins, developing the techniques and technology for direct imaging of exoplanets is a driving focus for the community. For the first time, JWST will directly observe extrasolar planets at mid-infrared wavelengths beyond 5 μm, deliver detailed spectroscopy revealing much more precise chemical abundances and atmospheric conditions, and provide sensitivity to analogs of our solar system ice-giant planets at wide orbital separations, an entirely new class of exoplanet. However, in order to maximise the scientific output over the lifetime of the mission, an exquisite understanding of the instrumental performance of JWST is needed as early in the mission as possible. In this paper, we describe our 55-hour Early Release Science Program that will utilize all four JWST instruments to extend the characterisation of planetary mass companions to ∼15-20 μm as well as image a circumstellar disk in the mid-infrared with unprecedented sensitivity. Our program will also assess the performance of the observatory in the key modes expected to be commonly used for exoplanet direct imaging and spectroscopy, optimize data calibration and processing, and generate representative datasets that will enable a broad user base to effectively plan for general observing programs in future cycles.
HgCdTe detectors with longer wavelength cutoffs were created for extending the lifetime of space-based applications because of their higher operating temperatures compared to arsenic doped silicon (Si:As) detectors. In addition to lower dark currents, the HgCdTe detectors also have higher quantum efficiencies compared to Si:As detectors. We are testing a HgCdTe detector with a 12.8 micron cutoff presented in Cabrera et al 2019 using HAWAII electronics in fast read-out mode to understand this array’s viability in instruments behind future ELT s that will directly image Earth-like planets. An f/100 system is required to operate the detector on a thirty meter diameter telescope without saturating, therefore we are the same f# system on the modified cryostat used to test and characterize the detector. We will present initial results on the detector’s quantum efficiency from 2 to 12 microns, read noise, dark current, and ability to tolerate flux levels that would be seen on future ELTs.
SCALES (Santa Cruz Array of Lenslets for Exoplanet Spectroscopy) is a 2-5 micron high-contrast lenslet integral-field spectrograph (IFS) driven by exoplanet characterization science requirements and will operate at W. M. Keck Observatory. Its fully cryogenic optical train uses a custom silicon lenslet array, selectable coronagraphs, and dispersive prisms to carry out integral field spectroscopy over a 2.2 arcsec field of view at Keck with low (< 300) spectral resolution. A small, dedicated section of the lenslet array feeds an image slicer module that allows for medium spectral resolution (5000 10000), which has not been available at the diffraction limit with a coronagraphic instrument before. Unlike previous IFS exoplanet instruments, SCALES is capable of characterizing cold exoplanet and brown dwarf atmospheres (< 600 K) at bandpasses where these bodies emit most of their radiation while capturing relevant molecular spectral features.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.