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MEC: The MKID Exoplanet Camera for High Speed Focal Plane Control at the Subaru Telescope

  • Author(s): Walter, Alexander Bryce
  • Advisor(s): Mazin, Benjamin A
  • et al.

Direct Imaging of exoplanets from the ground is one of the most technically difficult techniques used to study exoplanets, but holds immense promise for not just detecting but characterizing planets around the nearest stars. Ambitious instruments at the world’s largest telescopes have been built to carry out this science: the Gemini Planet Imager (GPI), SPHERE at VLT, SCExAO at Subaru, and the P1640 and Stellar Double Coronagraph (SDC) at Palomar. These instruments share a common archetype consisting of an extreme AO system feeding a coronagraph for on-axis stellar light rejection followed by a focal plane Integral Field Spectrograph (IFS). They are currently limited by uncontrolled scattered and diffracted light which produces a coherent speckle halo in the image plane. A number of differential imaging schemes exist to mitigate these issues resulting in star-planet contrast ratios as deep as ∼10^-6 at low angular separations. Surpassing this contrast limit requires high speed active speckle nullification from a focal plane wavefront sensor (FPWS) and new processing techniques.

MEC, the Microwave Kinetic Inductance Detector (MKID) Exoplanet Camera, is a J-band IFS module behind Subaru Telescope’s SCExAO system. MEC is capable of producing an image cube several thousand times a second without the read noise that dominates conventional high speed IFUs. This enables it to integrate with SCExAO as an extremely fast FPWS while eliminating non-common path aberrations by doubling as a science camera. Key science objectives can be further explored if longer wavelengths (H and K band) are simultaneously sent to CHARIS for high resolution spectroscopy. MEC, commissioned in March 2018, is the second MKID IFS for high contrast imaging following DARKNESS’ debut at Palomar in July 2016.

MEC is designed to follow up on young planets and debris disks discovered in the SEEDS survey or by Project 1640 as well as discover self-luminous massive planets. The increased sensitivity, combined with the advanced coronagraphs in SCExAO which have inner working angles (IWAs) as small as 0.03" at 1.2 μm, allows young Jupiter-sized objects to be imaged as close as 4 AU from their host star. If the wavefront control enabled by MEC is fully realized, it may begin to probe the reflected light of giant planets around some nearby stars, opening a new parameter space for direct imaging targeting older stars. While direct imaging of reflected light exoplanets is the most challenging of the scientific goals, it is a promising long-term path towards characterization of habitable planets around nearby stars using Extremely Large Telescopes (ELTs). With diameters >∼30 m, an ELT can resolve the habitable zones of nearby M-type stars, for which an Earth-sized planet would be at ∼10^-7 contrast at 1μm. This will complement future space-based high contrast optical imaging targeting the wider habitable zones of sun-like stars for ∼10^-10 contrast earth analogs.

This thesis presents the motivation, design, and commissioning of MEC including initial lab and on-sky characterization and results. We include detail on technological advances in cryogenic microwave engineering and a new algorithm for discriminating speckles from exoplanets in post-processing.

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