The expected stable point spread function, wide field of view, and sensitivity of the NIRCam instrument on the James Webb Space Telescope (JWST) will allow a simple, classical Lyot coronagraph to detect warm Jovian-mass companions orbiting young stars within 150 pc as well as cool Jupiters around the nearest low-mass stars. The coronagraph can also be used to study protostellar and debris disks. At λ = 4.5 µm, where young planets are particularly bright relative to their stars, and at separations beyond ~0.5 arcseconds, the low space background gives JWST significant advantages over ground-based telescopes equipped with adaptive optics. We discuss the scientific capabilities of the NIRCam coronagraph, describe the technical features of the instrument, and present end-to-end simulations of coronagraphic observations of planets and circumstellar disks.
The NIRCam instrument on the James Webb Space Telescope will provide coronagraphic imaging from λ=1-5 µm of high contrast sources such as extrasolar planets and circumstellar disks. A Lyot coronagraph with a variety of circular and wedge-shaped occulting masks and matching Lyot pupil stops will be implemented. The occulters approximate grayscale transmission profiles using halftone binary patterns comprising wavelength-sized metal dots on anti-reflection coated sapphire substrates. The mask patterns are being created in the Micro Devices Laboratory at the Jet Propulsion Laboratory using electron beam lithography. Samples of these occulters have been successfully evaluated in a coronagraphic testbed. In a separate process, the complex apertures that form the Lyot stops will be deposited onto optical wedges. The NIRCam coronagraph flight components are expected to be completed this year.
Cross‐borehole, radio‐frequency geotomographs were made across two different‐sized, operating, experimental, underground, in‐situ, oil‐shale retorts. The tomographs taken of the smaller retort were of a plane 16.7 m wide by 18.0 m high bisecting the retort. The measurements were taken at a frequency of 25 MHz and showed excellent correlation of high signal attenuation with the high‐temperature zones. Measured attenuation coefficients (inverse skin depth) at 25 MHz ranged from [Formula: see text] across the cool, unrubbled, sill‐pillar, and between [Formula: see text] for the high‐temperature 370–700° C zone. Image resolution was approximately 1 m. The signal attenuation across the lower retort region was also found to correlate well with the movement and concentration of condensed water. The conventional algebraic deconvolution method (ART) was modified for limited perspective and finite beam width, and gave results which were in good agreement with thermocouple data. The measurements made on the larger retort were taken over a period of 33 days of retort burn and mapped the attenuation coefficients in a vertical plane 90 m wide by 48 m high at a frequency of 1.5 MHz. At this frequency, attenuation coefficients in the cool, dry retort regions were between 0.12 and [Formula: see text], while regions containing a high moisture content had coefficients of from 0.15 to [Formula: see text]. In the regions encompassing the retorting and combustion zones, attenuation coefficients were between 0.15 and [Formula: see text]. Some additional effects on the attenuation measurements were observed due to nearby thermocouple piping. The movement of the contours of attenuation coefficient with time followed temperature changes, though the paucity of thermocouples in the tomographic plane only allowed a marginal correlation to be made. Overall results suggest that radio‐frequency geotomography can be a useful tool for mapping in‐situ moisture concentrations and temperature fronts in an operating in‐situ oil‐shale retort.
Abstract. SAO has set up a testbed to study coronagraphic techniques, starting with Labeyrie's multi-step speckle reduction technique. This technique expands the general concept of a coronagraph by incorporating a speckle corrector (phase and/or amplitude) in combination with a second occulter for speckle light suppression. The correction function is derived applying the phase diversity method on images taken in focus and slightly out-of-focus. The occulter masks for the testbed will initially be produced lithographically. However, in a parallel program we are studying a new manufacturing method. This method utilizes focussed ion beams and will directly mill the mask shape into absorbing material deposited on a transparent substrate.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.