Thayne Currie
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Overview

My science interests focus on discovering and characterizing the atmospheres of directly imaging extrasolar planets around nearby stars, primarily with the Subaru Coronagraphic Extreme Adaptive Optics project (SCExAO) coupled with the CHARIS integral field spectrograph.  

I also work on new instrumentation and new methods for image processing to better detect and extract spectra for exoplanets.

Longer-term, I am focused on directly imaging true solar system analogues, including habitable zone Earth-like exoplanets, with NASA missions and with 30m-class telescopes, such as the Thirty Meter Telescope and Giant Magellan Telescope.

Exoplanet Direct Imaging Science

The Subaru Coronagraphic Extreme Adaptive Optics Project

The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) Project is a cutting-edge extreme adaptive optics platform designed to image and characterize the spectra of young jovian planets at never before seen solar system-like scales.  

 SCExAO includes a 2000-actuator deformable mirror driven by modulated Pyramid wavefront sensor/EMCCD camera correcting for over 1000 modes at speeds of 2--3.5 kHz.   SCExAO achieves over 90% Strehl (at 1.65 microns) for bright stars and extreme AO corrections on stars as faint as R = 12.  Sharpened starlight is then suppressed by a suite of coronagraphs and fed to instruments like the CHARIS integral field spectrograph, which yields not just images of planets but their near-infrared spectra.   SCExAO implements new, additional advances in wavefront control to optimize its planet-imaging capabilities, including "predictive control" and focal plane wavefront sensing techniques like "speckle nulling".  Longer term, coupling SCExAO to an ultra-low-noise detector design called MEC will drive focal plane wavefront sensing at high speed and accuracy.



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(Top) SCExAO on the Nasmyth platform at Subaru. (Bottom) SCExAO/CHARIS images of the kappa And and HR 8799 planetary systems.
PictureDirectly-imaged planets discovered with SCExAO/CHARIS: the AB Aurigae b protoplanet (left; Currie et al. 2022, Nature Astronomy) and the superjovian planet HIP 99770 b (Currie et al. 2023, Science).
Exoplanet Discovery Space with SCExAO

We are now starting a dedicated survey to discover and characterize nearby jovian exoplanets with SCExAO/CHARIS.   Our targets are primarily nearby young field stars showing evidence for an astrometric acceleration identified from Gaia data and plausibly due to an unseen planet.   We also identify protoplanets embedded in disks of gas and dust around infant stars in more distant star-forming regions.  SCExAO is sensitive to young Jupiter-mass planets orbiting on solar system-like scales (5-30 au) around nearby young stars.  Future upgrades to SCExAO will improve its planet discovery capabilities, approaching the performance needed to image some mature exoplanets in reflected light.

Characterizing Exoplanet Atmospheres with SCExAO

While transit studies have yielded detailed constraints on the atmospheres of mature, close-separation jovian planets, direct imaging best clarifies the atmospheric properties of jovian planets at ages when they are undergoing substantial evolution in cloud structure, effective temperature, and surface gravity (10--100 Myr).   With exoplanet photometry obtained with conventional AO, Adam Burrows and I showed that young exoplanets like HR 8799 bcde have thicker clouds than do field brown dwarfs of the same temperatures (left panel).  
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With spectra from SCExAO/CHARIS, we can further constrain the temperature, chemistry, and gravity of exoplanets.  Young exoplanets show evidence for a lower surface gravity than field brown dwarfs of the same temperatures.   SCExAO/CHARIS is capable of tracing multiple gravity indicators, such as the H band continuum shape (e.g. for kappa And b; right panel).

Exoplanet Direct Imaging Instrumentation and Data Analysis

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Wavefront Control

I am interested in advanced wavefront sensing capabilities at the focal plane that will be critical to the success of exoplanet imaging with TMT.   At NASA-Ames, I conducted experiments further developing a new high-contrast wavefront control method called "Linear Dark Field Control" (LDFC; middle/right panels), which LDFC corrects for changes in the "dark field" (deep contrast region within which we can image planets) by measuring corresponding intensity changes within the "bright field" (uncorrected region).  The consequences should be dramatic: LDFC will increase direct imaging contrast and sensitivity, allowing us to discover and characterize lower mass, more solar system-like exoplanets.  

In our recent paper, we demonstrated the efficacy of LDFC at the Ames Coronagraph Experiment laboratory at contrasts relevant for imaging extrasolar planets in reflected light.   Follow-up studies are demonstrating LDFC with simulated turbulence and with on-sky data.   Read more about LDFC here and see our first paper demonstrating LDFC here.    

At UTSA, I plan to develop a new high-contrast imaging laboratory focused on technology development. My goal is to use the laboratory and time on the SCExAO optical bench to explore and hone wavefront control algorithms that will be needed to someday image solar system-like planets in reflected light using ground-based telescopes.

Coronagraphy

With SCExAO, I investigated the performance of the Shaped Pupil Coronagraph, an advanced design planned for use with the upcoming Roman-CGI mission, verifying its durability to low-order aberrations (left panel).   We are designing new shaped-pupils on SCExAO plus other designs such as the PIAACMC (also under consideration for a future NASA flagship mission) and vortex coronagraphs.

Image Processing

To directly image planets, I've built an exoplanet direct imaging pipeline including advanced PSF subtraction techniques called ``adaptive" LOCI or A-LOCI.  A-LOCI is a sort of 'hybrid' of the Locally Optimized Combination of Images (LOCI) and Karhunen-Lo'eve Eigen-Images Projection (KLIP) algorithms.  It employs ``speckle filtering" (`on-the-fly' correlation-based frame selection),  a moving pixel mask (Currie et al 2012b), and a varying SVD cutoff to model individual modes of speckle noise structure, etc.   As a result, it often achieves deeper contrast than LOCI or KLIP methods.  Equally important, A-LOCI now provides much better precision in extracting useful planet spectra and astrometry, through forward modeling.  I plan to incorporate more wrinkles into this approach in the future.

Papers describing A-LOCI PSF subtraction and forward-modeling are here, here, and here.

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Keck/NIRC2 data for HR 8799 reduced with three different methods: (left) a 'classical' ADI-based PSF subtraction method, (middle) LOCI, and (right) A-LOCI. LOCI and (especially) A-LOCI yield a significant contrast gain, allowing us to image faint planets deeply embedded in the stellar halo.