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1. Differencing and Coadding JWST Images with Matched Point-spread Function

   https://doi.org/10.3847/1538-3881/ad36cb  

   Hu, Lei; Wang, Lifan (April 2024, The Astronomical Journal)

   Abstract We present an algorithm to derive difference images for data taken with JWST with matched point-spread functions (PSFs). It is based on the saccadic fast Fourier transform method but with revisions to accommodate the rotations and spatial variations of the PSFs. It allows for spatially varying kernels in B-spline form with separately controlled photometric scaling and Tikhonov kernel regularization for harnessing the ultimate fitting flexibility. We present this method using the JWST/NIRCam images of galaxy cluster Abell 2744 acquired in JWST Cycle 1 as the test data. The algorithm can be useful for time-domain source detection and differential photometry with JWST. It can also coadd images of multiple exposures taken at different field orientations. The coadded images preserve the sharpness of the central cores of the PSFs, and the positions and shapes of the objects are matched precisely with B-splines across the field. 

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2. Enhanced resolution dispersion optimized multiphoton microscopy with spatial frequency modulation imaging

   https://doi.org/10.1117/12.2650490  

   Scarbrough, Daniel; Thomas, Anna; Field, Jeffrey; Bartels, Randy; Squier, Jeff (April 2023, PROCEEDINGS OF SPIE)

   Periasamy, Ammasi; So, Peter T.; König, Karsten (Ed.)

   Using the structured illumination, single pixel detection imaging technique SPatIal Frequency modulation Imaging (SPIFI), we demonstrate a cascaded Wavelength Domain and Spatial Domain (WD-SD-SPIFI) system enabling real-time, in-line, second order dispersion compensation optimization for multiphoton imaging. Enhanced resolution is demonstrated by imaging a sub-diffractive 140 nm fluorescent nanodiamond with Two Photon Excitation Fluorescence (2PEF) to measure the Point Spread Function (PSF). With a 1034 nm pulsed laser through a Numerical Aperture (NA) of 0.5, a PSF Full Width at Half Max (FWHM) of 780 nm was measured with minimal post processing analysis that only requires Fast Fourier Transforms (FFTs). 

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3. Efficiently Searching for Close-in Companions Around Young M Dwarfs Using a Multiyear PSF Library

   https://doi.org/10.3847/1538-3881/ad769f  

   Sanghi, Aniket; Xuan, Jerry_W; Wang, Jason_J; Mawet, Dimitri; Bowler, Brendan_P; Ngo, Henry; Bryan, Marta_L; Ruane, Garreth; Absil, Olivier; Huby, Elsa (October 2024, The Astronomical Journal)

   Abstract We present Super-RDI, a unique framework for the application of reference star differential imaging (RDI) to Keck/NIRC2 high-contrast imaging observations with the vortex coronagraph. Super-RDI combines frame selection and signal-to-noise ratio (S/N) optimization techniques with a large multiyear reference point-spread function (PSF) library to achieve optimal PSF subtraction at small angular separations. We compile an ∼7000 frame reference PSF library based on a set of 288 new Keck/NIRC2 $L\prime$sequences of 237 unique targets acquired between 2015 and 2019 as part of two planet-search programs designed for RDI, one focusing on nearby young M dwarfs and the other targeting members of the Taurus star-forming region. For our data set, synthetic companion injection-recovery tests reveal that frame selection with the mean-squared error metric combined with Karhunen–Loève Image-Processing-based PSF subtraction using 1000–3000 frames and ≲500 principal components yields the highest average S/N for injected synthetic companions. We uniformly reduce targets in the young M-star survey with both Super-RDI and angular differential imaging (ADI). For the typical parallactic angle rotation of our data set (∼10°), Super-RDI performs better than a widely used implementation of ADI-based PSF subtraction at separations ≲0.″4 (≈5λ/D), gaining an average of 0.25 mag in contrast at 0.″25 and 0.4 mag in contrast at 0.″15. This represents a performance improvement in separation space over RDI with single-night reference star observations (∼100 frame PSF libraries) applied to a similar Keck/NIRC2 data set in previous work. We recover two known brown dwarf companions and provide detection limits for 155 targets in the young M-star survey. Our results demonstrate that increasing the PSF library size with careful selection of reference frames can improve the performance of RDI with the Keck/NIRC2 vortex coronagraph in $L\prime$. 

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4. Photometric Monitoring of MCG–06-30-15

   https://doi.org/10.3847/2515-5172/adcba4  

   Tipton, Ben; Bentz, Misty C (April 2025, Research Notes of the AAS)

   Abstract We describe photometric monitoring of the Seyfert 1 galaxy MCG–06-30-15 with the Las Cumbres Observatory network. Using theVfilter, 496 images were collected between 2023 December and 2024 June from observatories in Chile, South Africa, and Australia. We created light curves of the active galactic nucleus continuum emission using aperture photometry and image subtraction methods. We find that the typical magnitude difference between the two light curves is ΔV ≈ 1.9 mag, indicating that the host galaxy contributes approximately 85% of the total flux through the photometric aperture. The amplitude of variation is significantly enhanced when the host galaxy is removed: ΔV = 0.1 mag from aperture photometry compared to ΔV = 0.5 mag with image subtraction. Future work will compare the continuum light curve with the broad emission-line flux variations to provide insight into the physical parameters of the broad-line region in MCG–06-30-15 and the mass of the central supermassive black hole. 

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5. The Giant Accreting Protoplanet Survey (GAPlanetS): Optimization Techniques for Robust Detections of Protoplanets

   https://doi.org/10.3847/1538-3881/aca60d  

   Adams Redai, Jéa I.; Follette, Katherine B.; Wang 王, Jason 劲飞; Leonard, Clare; Balmer, William; Close, Laird M.; Dacus, Beck; Males, Jared R.; Morzinski, Katie M.; Palmo, Joseph; et al (January 2023, The Astronomical Journal)

   Abstract High-contrast imaging has afforded astronomers the opportunity to study light directly emitted by adolescent (tens of megayears) and “proto” (<10 Myr) planets still undergoing formation. Direct detection of these planets is enabled by empirical point-spread function (PSF) modeling and removal algorithms. The computational intensity of such algorithms, as well as their multiplicity of tunable input parameters, has led to the prevalence of ad hoc optimization approaches to high-contrast imaging results. In this work, we present a new, systematic approach to optimization vetted using data of the high-contrast stellar companion HD 142527 B from the Magellan Adaptive Optics Giant Accreting Protoplanet Survey (GAPlanetS). More specifically, we present a grid search technique designed to explore three influential parameters of the PSF subtraction algorithmpyKLIP: annuli, movement, and KL modes. We consider multiple metrics for postprocessed image quality in order to optimally recover at Hα(656 nm) synthetic planets injected into contemporaneous continuum (643 nm) images. These metrics include peak (single-pixel) signal-to-noise ratio (S/N), average (multipixel average) S/N, 5σcontrast, and false-positive fraction. We apply continuum-optimized KLIP reduction parameters to six Hαdirect detections of the low-mass stellar companion HD 142527 B and recover the companion at a range of separations. Relative to a single-informed, nonoptimized set of KLIP parameters applied to all data sets uniformly, our multimetric grid search optimization led to improvements in companion S/N of up to 1.2σ, with an average improvement of 0.6σ. Since many direct imaging detections lie close to the canonical 5σthreshold, even such modest improvements may result in higher yields in future imaging surveys. 

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