A ray-trace simulation of the light-field camera is used to calculate point source responses as a function of 3D source positions. Each point source location yields a unique and well-determined ...segmented-pupil pattern in the lenslet array's focal plane, with lateral object offsets changing the pattern's location and symmetry, and defocus distances altering the pattern's diameter. Segmented-pupil images can thus be used to infer point sources' 3D locations. Numerical simulations show that the centroids and widths of segmented pupil images can be used to deduce lateral image positions to the size of a detector pixel, and image defocus to the accuracy of the lenslet focal length. In sparse-source cases, such as, e.g., fluorescence microscopy or particle tracking, 3D point-source locations can thus be accurately determined from the observed point source response patterns. The degree of pupil segmentation also directly constrains the ability to refocus light-field images-for image defocus distances large enough that the number of pupil segments exceeds the number of pixels within a "whole" pupil behind a single lenslet, the image can no longer be brought to focus numerically, thus defining the light-field camera's depth of field. This constraint implies a depth of field larger than the usual imaging depth of focus by a factor of the number of detector pixels per lenslet, consistent with the general expectation.
Three exoplanets around the star HR 8799 have recently been discovered by means of differential imaging with large telescopes. Bright scattered starlight limits high-contrast imaging to large angular ...offsets, currently of the order of ten diffraction beamwidths, 10 /D, of the star (where is the wavelength and D is the aperture diameter). Imaging faint planets at smaller angles calls for reducing the starlight and associated photon and speckle noise before detection, while efficiently transmitting nearby planet light. To carry out initial demonstrations of reduced-angle high-contrast coronagraphy, we installed a vortex coronagraph capable of reaching small angles behind a small, well-corrected telescope subaperture that provides low levels of scattered starlight. Here we report the detection of all three HR 8799 planets with the resultant small-aperture (1.5 m) system, for which only 2 /D separate the innermost planet from the star, with a final noise level within a factor of two of that given by photon statistics. Similar well-corrected small-angle coronagraphs should thus be able to detect exoplanets located even closer to their host stars with larger ground-based telescopes, and also allow a reduction in the size of potential space telescopes aimed at the imaging of very faint terrestrial planets.
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Context. Transition disks offer the extraordinary opportunity to look for newly born planets and to investigate the early stages of planet formation. Aim. In this context we observed the Herbig A5 ...star MWC 758 with the L′-band vector vortex coronagraph installed in the near-infrared camera and spectrograph NIRC2 at the Keck II telescope, with the aim of unveiling the nature of the spiral structure by constraining the presence of planetary companions in the system. Methods. Our high-contrast imaging observations show a bright (ΔL′ = 7.0 ± 0.3 mag) point-like emission south of MWC 758 at a deprojected separation of ~20 au (r = 0.′′111 ± 0.′′004) from the central star. We also recover the two spiral arms (southeast and northwest), already imaged by previous studies in polarized light, and discover a third arm to the southwest of the star. No additional companions were detected in the system down to 5 Jupiter masses beyond 0.′′6 from the star. Results. We propose that the bright L′-band emission could be caused by the presence of an embedded and accreting protoplanet, although the possibility of it being an asymmetric disk feature cannot be excluded. The spiral structure is probably not related to the protoplanet candidate, unless on an inclined and eccentric orbit, and it could be due to one (or more) yet undetected planetary companions at the edge of or outside the spiral pattern. Future observations and additional simulations will be needed to shed light on the true nature of the point-like source and its link with the spiral arms.
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ABSTRACT An optical vortex coronagraph has been implemented within the NIRC2 camera on the Keck II telescope and used to carry out on-sky tests and observations. The development of this new L′-band ...observational mode is described, and an initial demonstration of the new capability is presented: a resolved image of the low-mass companion to HIP 79124, which had previously been detected by means of interferometry. With HIP 79124 B at a projected separation of 186.5 mas, both the small inner working angle of the vortex coronagraph and the related imaging improvements were crucial in imaging this close companion directly. Due to higher Strehl ratios and more relaxed contrasts in L′ band versus H band, this new coronagraphic capability will enable high-contrast, small-angle observations of nearby young exoplanets and disks on a par with those of shorter-wavelength extreme adaptive optics coronagraphs.
Forty-seven nearby main-sequence stars were surveyed with the Keck Interferometer mid-infrared Nulling instrument (KIN) between 2008 and 2011, searching for faint resolved emission from exozodiacal ...dust. Observations of a subset of the sample have already been reported, focusing essentially on stars with no previously known dust. Here we extend this previous analysis to the whole KIN sample, including 22 more stars with known near- and/or far-infrared excesses. In addition to an analysis similar to that of the first paper of this series, which was restricted to the 8-9 mu m spectral region, we present measurements obtained in all 10 spectral channels covering the 8-13 mu m instrumental bandwidth. For solar-type stars with no known infrared excess, likely to be the most relevant targets for a future exo-Earth direct imaging mission, we find that their median zodi level is 12+ or -24 zodis and lower than 60 zodis with 95% confidence, if a lognormal zodi luminosity distribution is assumed.
ABSTRACT
The Palomar Fiber Nuller (PFN) is a rotating-baseline nulling interferometer that enables high-accuracy near-infrared (NIR) nulling observations with full azimuth coverage. To achieve NIR ...null-depth accuracies of several x 10−4, the PFN uses a common-mode optical system to provide a high degree of symmetry, single-mode-fibre beam combination to reduce sensitivity to pointing and wavefront errors, extreme adaptive optics to stabilize the fibre coupling and the cross-aperture fringe phase, rapid signal calibration and camera readout to minimize temporal effects, and a statistical null-depth fluctuation analysis to relax the phase stabilization requirement. Here, we describe the PFN’s final design and performance and provide a demonstration of faint-companion detection by means of nulling-baseline rotation, as originally envisioned for space-based nulling interferometry. Specifically, the Ks-band null-depth rotation curve measured on the spectroscopic binary η Peg reflects both a secondary star 1.08 ± 0.06 × 10−2 as bright as the primary, and a null-depth contribution of 4.8 ± 1.6 × 10−4 due to the size of the primary star. With a 30 mas separation at the time, η Peg B was well inside both the telescope’s diffraction-limited beam diameter (88 mas) and typical coronagraphic inner working angles. Finally, we discuss potential improvements that can enable a number of small-angle nulling observations on larger telescopes.
Residual speckles due to aberrations arising from optical errors after the split between the wavefront sensor and the science camera path are the most significant barriers to imaging extrasolar ...planets. While speckles can be suppressed using the science camera in conjunction with the deformable mirror, this requires knowledge of the phase of the electric field in the focal plane. We describe a method which combines a coronagraph with a simple phase-shifting interferometer to measure and correct speckles in the full focal plane. We demonstrate its initial use on the Stellar Double Coronagraph at the Palomar Observatory. We also describe how the same hardware can be used to distinguish speckles from true companions by measuring the coherence of the optical field in the focal plane. We present results observing the brown dwarf HD49197b with this technique, demonstrating the ability to detect the presence of a companion even when it is buried in the speckle noise, without the use of any standard 'calibration' techniques. We believe this is the first detection of a substellar companion using the coherence properties of light.
High-dispersion coronagraphy (HDC) optimally combines high-contrast imaging techniques such as adaptive optics/wavefront control plus coronagraphy to high spectral resolution spectroscopy. HDC is a ...critical pathway toward fully characterizing exoplanet atmospheres across a broad range of masses from giant gaseous planets down to Earth-like planets. In addition to determining the molecular composition of exoplanet atmospheres, HDC also enables Doppler mapping of atmosphere inhomogeneities (temperature, clouds, wind), as well as precise measurements of exoplanet rotational velocities. Here, we demonstrate an innovative concept for injecting the directly imaged planet light into a single-mode fiber, linking a high-contrast adaptively corrected coronagraph to a high-resolution spectrograph (diffraction-limited or not). Our laboratory demonstration includes three key milestones: close-to-theoretical injection efficiency, accurate pointing and tracking, and on-fiber coherent modulation and speckle nulling of spurious starlight signal coupling into the fiber. Using the extreme modal selectivity of single-mode fibers, we also demonstrated speckle suppression gains that outperform conventional image-based speckle nulling by at least two orders of magnitude.
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is a multipurpose high-contrast imaging platform designed for the discovery and detailed characterization of exoplanetary systems ...and serves as a testbed for high-contrast imaging technologies for ELTs. It is a multiband instrument which makes use of light from 600 to 2500 nm, allowing for coronagraphic direct exoplanet imaging of the inner 3λ/D from the stellar host. Wavefront sensing and control are key to the operation of SCExAO. A partial correction of low-order modes is provided by Subaru's facility adaptive optics system with the final correction, including high-order modes, implemented downstream by a combination of a visible pyramid wavefront sensor and a 2000-element deformable mirror. The well-corrected NIR (y-K bands) wavefronts can then be injected into any of the available coronagraphs, including but not limited to the phase-induced amplitude apodization and the vector vortex coronagraphs, both of which offer an inner working angle as low as 1λ/D. Noncommon path, low-order aberrations are sensed with a coronagraphic low-order wavefront sensor in the infrared (IR). Low noise, high frame rate NIR detectors allow for active speckle nulling and coherent differential imaging, while the HAWAII 2RG detector in the HiCIAO imager and/or the CHARIS integral field spectrograph (from mid-2016) can take deeper exposures and/or perform angular, spectral, and polarimetric differential imaging. Science in the visible is provided by two interferometric modules: VAMPIRES and FIRST, which enable subdiffraction limited imaging in the visible region with polarimetric and spectroscopic capabilities respectively. We describe the instrument in detail and present preliminary results both on-sky and in the laboratory.
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