The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is a high-contrast imaging system installed at the 8-m Subaru Telescope on Maunakea, Hawaii. Due to its unique evolving design, SCExAO is both an instrument open for use by the international scientific community, and a testbed validating new technologies, which are critical to future high-contrast imagers on Giant Segmented Mirror Telescopes (GSMTs). Through multiple international collaborations over the years, SCExAO was able to test the most advanced technologies in wavefront sensors, real-time control with GPUs, low-noise high frame rate detectors in the visible and infrared, starlight suppression techniques or photonics technologies. Tools and interfaces were put in place to encourage collaborators to implement their own hardware and algorithms, and test them on-site or remotely, in laboratory conditions or on-sky. We are now commissioning broadband coronagraphs, the Microwave Kinetic Inductance Detector (MKID) Exoplanet Camera (MEC) for high-speed speckle control, as well as a C-RED ONE camera for both polarization differential imaging and IR wavefront sensing. New wavefront control algorithms are also being tested, such as predictive control, multi-camera machine learning sensor fusion, and focal plane wavefront control. We present the status of the SCExAO instrument, with an emphasis on current collaborations and recent technology demonstrations. We also describe upgrades planned for the next few years, which will evolve SCExAO —and the whole suite of instruments on the IR Nasmyth platform of the Subaru Telescope— to become a system-level demonstrator of the Planetary Systems Imager (PSI), the high-contrast instrument for the Thirty Meter Telescope (TMT).
Polarization Differential Imaging (PDI) is one of the most productive modes of current high-contrast imagers. Dozens of new protoplanetary, transition and debris disks were imaged recently for the first time, helping us understand the processes of planet formation, and giving clues on the mass of potential planets inside these disks, even if they cannot be imaged directly. The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is equipped with a fast visible dual-camera polarimetric module, VAMPIRES, already producing valuable scientific observations of protoplanetary disks and dust shells. In addition, we recently commissioned two new polarimetric modules in the infrared. The first one is a spectro-polarimetric mode using the CHARIS Integral Field Spectrograph (IFS). A Wollaston prism was added in front of the IFS, reducing the field-of-view to 2x1 arcsec to accommodate for the imaging of both polarizations on the same detector without sacrificing the spectral resolution of the instrument, in any of its spectral modes. The second module, similar to VAMPIRES, uses a low-noise high frame rate C-RED ONE camera combined with a Ferroelectric Liquid Crystal (FLC) device to modulate and record the polarization at high-speed, freezing effectively the atmospheric speckles for higher precision. We present on-sky results of the new polarimetric capabilities taken during the commissioning phase. In addition, we show future capabilities that are already scheduled to increase the performance of these modules, especially the addition of non-redundant masks, as well as a polarimetric vector Apodizing Phase Plate (vAPP) coronagraph.
High-contrast optical stellar interferometry generally refers to instruments able to detect circumstellar emission at least a few hundred times fainter than the host star at high-angular resolution (typically within a few λ/D). While such contrast levels have been enabled by classical modal-filtered interferometric instruments such as VLTI/PIONIER, CHARA/FLUOR, and CHARA/MIRC the development of instruments able to filter out the stellar light has significantly pushed this limit, either by nulling interferometry for on-axis observations (e.g., PFN, LBTI, GLINT) or by off-axis classical interferometry with VLTI/GRAVITY. Achieving such high contrast levels at small angular separation was made possible thanks to significant developments in technology (e.g., adaptive optics, integrated optics), data acquisition (e.g., fringe tracking, phase chopping), and data reduction techniques (e.g., nulling self-calibration). In this paper, we review the current status of high-contrast optical stellar interferometry and present its key scientific results. We then present ongoing activities to improve current ground-based interferometric facilities for high-contrast imaging (e.g., Hi-5/VIKING/BIFROST of the ASGARD instrument suite, GRAVITY+) and the scientific milestones that they would be able to achieve. Finally, we discuss the long-term future of high-contrast stellar interferometry and, in particular, ambitious science cases that would be enabled by space interferometry (e.g., LIFE, space-PFI) and large-scale ground-based projects (PFI).
In the coming year, the CHARA 1-meter telescopes will be equipped with Adaptive Optics (AO) systems. This improvement opens the possibility to apply, in the visible domain, the principle of spatial filtering with single mode fibers well demonstrated in the near-infrared. It will clearly open new astrophysical fields by taking benefit of an improved sensitivity and state-of-the-art precision and accuracy on interferometric observables. A demonstrator called FRIEND (Fibered and spectrally Resolved Interferometric Experiment - New Design) has been developed. FRIEND combines the beams coming from 3 telescopes after injection in single mode optical fibers and provides photometric channels as well as some spectral capabilities for characterization purposes. It operates around the R spectral band (from 600nm to 750nm) and uses the fast and sensitive analog detector OCAM2. On sky tests at the focus of the CHARA interferometer have been performed during the last year to get the optimal DIT or an estimation of the stability of the instrumental visibility. Complementary lab tests have permitted to characterize the birefringence of the fibers, and the characteristics of the detector. In this paper, we present the results of these tests.