Non-redundant Masking Research Articles

High-angular-resolution Imaging of the V892 Tau Binary System: A New Circumprimary Disk Detection and Updated Orbital Constraints

We present a direct imaging study of V892 Tau, a young Herbig Ae/Be star with a close-in stellar companion and circumbinary disk. Our observations consist of images acquired via Keck II/NIRC2 with nonredundant masking and the pyramid wavefront sensor at band (2.12 μm) and band (3.78 μm). Sensitivity to low-mass accreting companions and cool disk material is high at band, while complimentary observations at band probe hotter material with higher angular resolution. These multiwavelength, multiepoch data allow us to differentiate the secondary stellar emission from disk emission and deeply probe the structure of the circumbinary disk at small angular separations. We constrain architectural properties of the system by fitting geometric disk and companion models to the - and -band data. From these models, we constrain the astrometric and photometric properties of the stellar binary and update the orbit, placing the tightest estimates to date on the V892 Tau orbital parameters. We also constrain the geometric structure of the circumbinary disk, and resolve a circumprimary disk for the first time.

Detecting Exoplanets Closer to Stars with Moderate Spectral Resolution Integral-field Spectroscopy

While radial velocity surveys have demonstrated that the population of gas giants peaks around 3 au, the most recent high-contrast imaging surveys have only been sensitive to planets beyond ∼10 au. Sensitivity at small angular separations from stars is currently limited by the variability of the point-spread function. We demonstrate how moderate-resolution integral-field spectrographs can detect planets at smaller separations (≲ 0.3“) by detecting the distinct spectral signature of planets compared to the host star. Using OSIRIS (R ≈ 4000) at the W.M. Keck Observatory, we present the results of a planet search via this methodology around 20 young targets in the Ophiuchus and Taurus star-forming regions. We show that OSIRIS can outperform high-contrast coronagraphic instruments equipped with extreme adaptive optics and non-redundant masking in the 0.05“–0.3“ regime. As a proof of concept, we present the 34σ detection of a high-contrast M dwarf companion at ≈0.1“ with flux ratio of ≈ 0.92% around the field F2 star HD 148352. We developed an open-source Python package, breads, for the analysis of moderate-resolution integral-field spectroscopy data in which the planet and the host star signal are jointly modeled. The diffracted starlight continuum is forward-modeled using a spline model, which removes the need for prior high-pass filtering or continuum normalization. The code allows for analytic marginalization of linear hyperparameters, which simplifies the posterior sampling of other parameters (e.g., radial velocity, effective temperature). This technique could prove very powerful when applied to integral-field spectrographs such as NIRSpec on the JWST and other upcoming first-light instruments on the future Extremely Large Telescopes.

The Near Infrared Imager and Slitless Spectrograph for the James Webb Space Telescope. IV. Aperture Masking Interferometry

The James Webb Space Telescope’s Near Infrared Imager and Slitless Spectrograph (JWST-NIRISS) flies a 7-hole non-redundant mask (NRM), the first such interferometer in space, operating at 3–5 μm wavelengths, and a bright limit of ≃4 mag in W2. We describe the NIRISS Aperture Masking Interferometry (AMI) mode to help potential observers understand its underlying principles, present some sample science cases, explain its operational observing strategies, indicate how AMI proposals can be developed with data simulations, and how AMI data can be analyzed. We also present key results from commissioning AMI. Since the allied Kernel Phase Imaging (KPI) technique benefits from AMI operational strategies, we also cover NIRISS KPI methods and analysis techniques, including a new user-friendly KPI pipeline. The NIRISS KPI bright limit is ≃8 W2 (4.6 μm) magnitudes. AMI NRM and KPI achieve an inner working angle of ∼70 mas, which is well inside the ∼400 mas NIRCam inner working angle for its circular occulter coronagraphs at comparable wavelengths.

ELT Imaging of MWC 297 from the 23 m LBTI: Complex Disk Structure and a Companion Candidate

Abstract Herbig Ae/Be stars represent the early outcomes of star formation and the initial stages of planet formation at intermediate stellar masses. Understanding both of these processes requires detailed characterization of their disk structures and companion frequencies. We present new 3.7 μm imaging of the Herbig Be star MWC 297 from nonredundant masking observations on the phase-controlled, 23 m Large Binocular Telescope Interferometer. The images reveal complex disk structure on the scales of several au, as well as a companion candidate. We discuss physical interpretations for these features and demonstrate that the imaging results are independent of choices such as priors, regularization hyperparameters, and error-bar estimates. With an angular resolution of ∼17 mas, these data provide the first robust Extremely Large Telescope–resolution view of a distant young star.

Performance of the Gemini Planet Imager Non-redundant Mask and Spectroscopy of Two Close-separation Binaries: HR 2690 and HD 142527

Abstract The Gemini Planet Imager (GPI) contains a 10-hole non-redundant mask (NRM), enabling interferometric resolution in complement to its coronagraphic capabilities. The NRM operates both in spectroscopic (integral field spectrograph, henceforth IFS) and polarimetric configurations. NRM observations were taken between 2013 and 2016 to characterize its performance. Most observations were taken in spectroscopic mode, with the goal of obtaining precise astrometry and spectroscopy of faint companions to bright stars. We find a clear correlation between residual wavefront error measured by the adaptive optic system and the contrast sensitivity by comparing phase errors in observations of the same source, taken on different dates. We find a typical 5σ contrast sensitivity of (2–3) × 10−3 at ∼λ/D. We explore the accuracy of spectral extraction of secondary components of binary systems by recovering the signal from a simulated source injected into several data sets. We outline data reduction procedures unique to GPI’s IFS and describe a newly public data pipeline used for the presented analyses. We demonstrate recovery of astrometry and spectroscopy of two known companions to HR 2690 and HD 142527. NRM+polarimetry observations achieve differential visibility precision of σ ∼ 0.4% in the best case. We discuss its limitations on Gemini-S/GPI for resolving inner regions of protoplanetary disks and prospects for future upgrades. We summarize lessons learned in observing with NRM in spectroscopic and polarimetric modes.

Comparing nonredundant masking and filled-aperture kernel phase for exoplanet detection and characterization

The limitations of adaptive optics and coronagraph performance make exoplanet detection close to {\lambda}/D extremely difficult with conventional imaging methods. The technique of non-redundant masking (NRM), which turns a filled aperture into an interferometric array, has pushed the planet detection parameter space to within {\lambda}/D. For high Strehl, the related filled-aperture kernel phase technique can achieve resolution comparable to NRM, without the associated dramatic decrease in throughput. We present non-redundant masking and kernel phase contrast curves generated for ground- and space-based instruments. We use both real and simulated observations to assess the performance of each technique, and discuss their capabilities for different exoplanet science goals such as broadband detection and spectral characterization.

非冗余孔径掩模技术在双星探测中的实验研究

非冗余孔径掩模技术在双星探测中的实验研究

Data Reduction and Image Reconstruction Techniques for Non-redundant Masking

Abstract The technique of non-redundant masking (NRM) transforms a conventional telescope into an interferometric array. In practice, this provides a much better constrained point-spread function than a filled aperture and thus higher resolution than traditional imaging methods. Here, we describe an NRM data reduction pipeline. We discuss strategies for NRM observations regarding dithering patterns and calibrator selection. We describe relevant image calibrations and use example Large Binocular Telescope data sets to show their effects on the scatter in the Fourier measurements. We also describe the various ways to calculate Fourier quantities, and discuss different calibration strategies. We present the results of image reconstructions from simulated observations where we adjust prior images, weighting schemes, and error bar estimation. We compare two imaging algorithms and discuss implications for reconstructing images from real observations. Finally, we explore how the current state of the art compares to next-generation Extremely Large Telescopes.

The frequency of binary star interlopers amongst transitional discs

Using Non-Redundant Mask interferometry (NRM), we searched for binary companions to objects previously classified as Transitional Disks (TD). These objects are thought to be an evolutionary stage between an optically thick disk and optically thin disk. We investigate the presence of a stellar companion as a possible mechanism of material depletion in the inner region of these disks, which would rule out an ongoing planetary formation process in distances comparable to the binary separation. For our detection limits, we implement a new method of completeness correction using a combination of randomly sampled binary orbits and Bayesian inference. The selected sample of 24 TDs belong to the nearby and young star forming regions: Ophiuchus ($\sim$ 130 pc), Taurus-Auriga ($\sim$ 140 pc) and IC348 ( $\sim$ 220 pc). These regions are suitable to resolve faint stellar companions with moderate to high confidence levels at distances as low as 2 au from the central star. With a total of 31 objects, including 11 known TDs and circumbinary disks from the literature, we have found that a fraction of 0.38 $\pm$ 0.09 of the SEDs of these objects are likely due to the tidal interaction between a close binary and its disk, while the remaining SEDs are likely the result of other internal processes such as photoevaporation, grain growth, planet disk interactions. In addition, we detected four companions orbiting outside the area of the truncation radii and we propose that the IR excesses of these systems are due to a disk orbiting a secondary companion

The Palomar kernel-phase experiment: testing kernel phase interferometry for ground-based astronomical observations

At present, the principal limitation on the resolution and contrast of astronomical imaging instruments comes from aberrations in the optical path, which may be imposed by the Earth's turbulent atmosphere or by variations in the alignment and shape of the telescope optics. These errors can be corrected physically, with active and adaptive optics, and in post-processing of the resulting image. A recently-developed adaptive optics post-processing technique, called kernel phase interferometry, uses linear combinations of phases that are self-calibrating with respect to small errors, with the goal of constructing observables that are robust against the residual optical aberrations in otherwise well-corrected imaging systems. Here we present a direct comparison between kernel phase and the more established competing techniques, aperture masking interferometry, point spread function (PSF) fitting and bispectral analysis. We resolve the alpha Ophiuchi binary system near periastron, using the Palomar 200-Inch Telescope. This is the first case in which kernel phase has been used with a full aperture to resolve a system close to the diffraction limit with ground-based extreme adaptive optics observations. Excellent agreement in astrometric quantities is found between kernel phase and masking, and kernel phase significantly outperforms PSF fitting and bispectral analysis, demonstrating its viability as an alternative to conventional non-redundant masking under appropriate conditions.

NEW SPATIALLY RESOLVED OBSERVATIONS OF THE T Cha TRANSITION DISK AND CONSTRAINTS ON THE PREVIOUSLY CLAIMED SUBSTELLAR COMPANION

We present multi-epoch non-redundant masking observations of the T Cha transition disk, taken at the VLT and Magellan in H, Ks, and L' bands. T Cha is one of a small number of transition disks that host companion candidates discovered by high-resolution imaging techniques, with a putative companion at a position angle of 78 degrees, separation of 62 mas, and contrast at L' of 5.1 mag. We find comparable binary parameters in our re-reduction of the initial detection images, and similar parameters in the 2011 L', 2013 NaCo L', and 2013 NaCo Ks data sets. We find a close-in companion signal in the 2012 NaCo L' dataset that cannot be explained by orbital motion, and a non-detection in the 2013 MagAO/Clio2 L' data. However, Monte-carlo simulations show that the best fits to the 2012 NaCo and 2013 MagAO/Clio2 followup data may be consistent with noise. There is also a significant probability of false non-detections in both of these data sets. We discuss physical scenarios that could cause the best fits, and argue that previous companion and scattering explanations are inconsistent with the results of the much larger dataset presented here.

AN IMAGE-PLANE ALGORITHM FORJWST'S NON-REDUNDANT APERTURE MASK DATA

The high angular resolution technique of non-redundant masking (NRM) or aperture masking interferometry (AMI) has yielded images of faint protoplanetary companions of nearby stars from the ground. AMI on James Webb Space Telescope (JWST)'s Near Infrared Imager and Slitless Spectrograph (NIRISS) has a lower thermal background than ground-based facilites and does not suffer from atmospheric instability. NIRISS AMI images are likely to have 90 - 95% Strehl ratio between 2.77 and 4.8 micron. In this paper we quantify factors that limit the raw point source contrast of JWST NRM. We develop an analytic model of the NRM point spread function which includes different optical path delays (pistons) between mask holes and fit the model parameters with image plane data. It enables a straightforward way to exclude bad pixels, is suited to limited fields of view, and can incorporate effects such as intra-pixel sensitivity variations. We simulate various sources of noise to estimate their effect on the standard deviation of closure phase, sigma_CP (a proxy for binary point source contrast). If sigma_CP < 10^-4 radians --- a contrast ratio of 10 magnitudes --- young accreting gas giant planets (e.g. in the nearby Taurus star-forming region) could be imaged with JWST NIRISS. We show the feasibility of using NIRISS' NRM with the sub-Nyquist sampled F277W, which would enable some exoplanet chemistry characterization. In the presence of small piston errors, the dominant sources of closure phase error (depending on pixel sampling, and filter bandwidth) are flat field errors and unmodeled variations in intra-pixel sensitivity. The in-flight stability of NIRISS will determine how well these errors can be calibrated by observing a point source. Our results help develop efficient observing strategies for space-based NRM.

ACTIVE GALACTIC NUCLEUS AND QUASAR SCIENCE WITH APERTURE MASKING INTERFEROMETRY ON THEJAMES WEBB SPACE TELESCOPE

Due to feedback from accretion onto supermassive black holes (SMBHs), Active Galactic Nuclei (AGNs) are believed to play a key role in LambdaCDM cosmology and galaxy formation. However, AGNs' extreme luminosities and the small angular size of their accretion flows create a challenging imaging problem. We show James Webb Space Telescope's Near Infrared Imager and Slitless Spectrograph (JWST-NIRISS) Aperture Masking Interferometry (AMI) mode will enable true imaging (i.e. without any requirement of prior assumptions on source geometry) at ~65 mas angular resolution at the centers of AGNs. This is advantageous for studying complex extended accretion flows around SMBHs, and in other areas of angular-resolution-limited astrophysics. By simulating data sequences incorporating expected sources of noise, we demonstrate that JWST-NIRISS AMI mode can map extended structure at a pixel-to-pixel contrast of ~10^{-2} around an L=7.5 point source, using short exposure times (minutes). Such images will test models of AGN feedback, fuelling and structure (complementary with ALMA observations), and are not currently supported by any ground-based IR interferometer or telescope. Binary point source contrast with NIRISS is ~10^{-4} (for observing binary nuclei in merging galaxies), significantly better than current ground-based optical or IR interferometry. JWST-NIRISS' seven-hole non-redundant mask has a throughput of 15%, and utilizes NIRISS' F277W (2.77\micron), F380M (3.8\micron), F430M (4.3\micron), and F480M (4.8\micron) filters. NIRISS' square pixels are 65mas per side, with a field of view ~2\arcmin x 2\arcmin. We also extrapolate our results to AGN science enabled by non-redundant masking on future 2.4m and 16m space telescopes working at long-UV to near-IR wavelengths.

New Methods for Masked‐Aperture and Speckle Interferometry

ABSTRACTDiffraction‐limited images can be obtained with a large optical telescope using interferometry. One such method for objects of sufficient brightness is nonredundant masking (NRM), in which observations are made through a pupil mask that contains an array of small holes. However, NRM uses only a small fraction of the available light. Here I describe a method for extended NRM in which a cylindrical lens allows interferograms from many one‐dimensional arrays to be recorded side by side on a two‐dimensional detector. For fainter objects, the holes in the aperture mask should be replaced by slits. In this case, the mask can be removed entirely, with the cylindrical lens effectively creating a continuous series of one‐dimensional interferograms. This modified form of speckle interferometry, which I call MODS (multiplexed one‐dimensional speckle), is intermediate between NRM and conventional full‐aperture speckle. An existing speckle camera can easily be converted to MODS observations by inserting a cylindrical lens. The feasibility of both MODS and extended NRM are demonstrated using observations with MAPPIT at the Anglo‐Australian Telescope.

MAPPIT 2: Second Generation High-resolution Imaging at the AAT

AbstractInterferometric methods have been used at a number of observatories to improve the spatial resolution of large optical telescopes, approaching and in some cases reaching the diffraction limit. The principal methods used have been speckle interferometry and non-redundant masking (NRM). The MAPPIT (Masked APerture Plane Interference Telescope) instrument has been used for NRM observations at the 3·9 m Anglo-Australian Telescope. This paper describes a proposed instrument, MAPPIT 2, which would use a Shack-Hartmann wavefront sensor in parallel with an interferometer performing NRM or one-dimensional speckle interferometry. The inclusion of the data from the wavefront sensor will enhance the sensitivity of the instrument, especially for the imaging of relatively complex objects (those giving more than a few resolution elements with non-zero intensities). Limiting the instantaneous spatial resolution to one dimension allows available CCD detectors to operate with 100% duty cycle. Observations at a number of position angles allow two-dimensional images to be obtained.

Speckle v Non-Redundant Masking

Unlike their radio counterparts, optical astronomers have paid relatively little attention to the role of the aperture function when designing their high resolution imaging experiments. This is despite the fact that it can be easily modified with the use of a suitable pupil plane mask. While the defining characteristics of the two most favoured pupil configurations have never been in doubt – negligible atmospheric noise in the case of a non-redundant configuration of small holes and high photon rates for a filled pupil – the relative merits of these two choices in terms of imaging performance in the presence of turbulence appear not to have been carefully investigated until very recently.Most existing comparisons of fully-filled aperture (FFA) and non-redundant mask (NRM) based imaging strategies appear to have ignored a number of fundamental and practical difficulties that are often encountered in practice. In the intermediate regime, between very high and very low light levels, that characterizes most astrophysical applications hybrid imaging schemes seem most profitable. These utilize partially-redundant pupil geometries that combine the advantages of redundancy at low light levels without incurring the penalties associated with fully redundant beam recombination. Such pupil geometries are also useful in reducing the level of systematic effects that often plague speckle imaging experiments.

Minimum Redundant Aperture Masking Interferometry With Tip-Tilt Wavefront Correction

We made aperture masking optical interferometry experiments using up to 30 apertures and with a tip-tilt correction of wavefront error. We examined the performance of minimum redundant configurations of 11–30 sub-apertures on the pupil plane mask. These configurations have two advantages; the redundancy noise is as small as realized in non-redundant masking method, and the uv-coverage is as high as in speckle interferometry enabling to get reconstructed images without mask exchange. We also examined the effect of tip-tilt wavefront correction within a telescope pupil in front of the aperture masking optics. The light coherency between sub-apertures was shown to increase by the correction.

MAPPIT: OPTICAL INTERFEROMETRY WITH THE ANGLO-AUSTRALIAN TELESCOPE

ABSTRACT Turbulence in the Earth's atmosphere usually prevents large optical telescopes from achieving their full resolving power. Instead, the image of a star is blurred to a seeing disk about one arcsecond in diameter. Several techniques are available which use interferometry to overcome atmospheric seeing and restore diffraction-limited performance. This thesis describes the design, construction and use of an optical interferometer located at the coude focus of the 3.9m Anglo-Australian Telescope. The instrument, known as MAPPIT (Masked APerture-Plane Interference Telescope), uses the technique of non-redundant masking. This involves placing a mask with several small holes over the aperture of the telescope and recording a succession of short-exposure interferograms. These interferograms are analysed to determine the power spectrum and closure phases of the object, which are used to reconstruct a diffraction-limited image. One advantage of using a non-redundant aperture mask is that, at least for bright objects, it increases the signal-to-noise ratios of the power spectrum and closure phase measurements relative to observations with an unobstructed aperture. This is despite the fact that much of the light is blocked by the mask. Another advantage is that it improves the accuracy with which one can correct for variations in atmospheric seeing, something which is often the limiting factor in high-resolution imaging. The main drawback of non-redundant masking is a less efficient coverage of spatial frequencies. However, for simple objects such as multiple and barely resolved stars, adequate spatial frequency coverage can be obtained by combining observations made with different masks and with the masks rotated to several different position angles on the sky. An important feature of MAPPIT is the use of a prism to disperse the interference pattern in wavelength. This overcomes a restriction common to all forms of interferometry, namely the requirement that one observe over a narrow band of wavelengths. By using an aperture mask with a linear array of holes, one obtains a one-dimensional fringe pattern which can then be dispersed in the direction parallel to the fringes. In MAPPIT, a prism and a cylindrical lens produce wavelength-dispersed fringes using a novel combination of image-plane and pupil-plane imaging. Results presented in this thesis include observations of several close double stars. One of these is delta Sco, and I provide the first image of this star and the first determination of its orbit. Another bright star, sigma Sgr, is found to a barely-resolved double with a separation of just 12 milliarcsec. Observations of two resolved single stars, alpha Sco and beta Gru, are also reported. The measured angular diameter of aSco agrees well with published values. For the M5 III giant beta Gru, which has not previously been resolved, I find a uniform-disk diameter of (27±3) milliarcsec.

Mappit: Optical Interferometry with the Anglo-Australian Telescope

Turbulence in the Earth's atmosphere usually prevents large optical telescopes from achieving their full resolving power. Instead, the image of a star is blurred to a seeing disk about one arcsecond in diameter. Several techniques are available which use interferometry to overcome atmospheric seeing and restore diffraction-limited performance. This thesis describes the design, construction and use of an optical interferometer located at the coude focus of the 3.9m Anglo-Australian Telescope. The instrument, known as MAPPIT (Masked APerture-Plane Interference Telescope), uses the technique of non-redundant masking. This involves placing a mask with several small holes over the aperture of the telescope and recording a succession of short-exposure interferograms. These interferograms are analysed to determine the power spectrum and closure phases of the object, which are used to reconstruct a diffraction-limited image. One advantage of using a non-redundant aperture mask is that, at least for bright objects, it increases the signal-to-noise ratios of the power spectrum and closure phase measurements relative to observations with an unobstructed aperture. This is despite the fact that much of the light is blocked by the mask. Another advantage is that it improves the accuracy with which one can correct for variations in atmospheric seeing, something which is often the limiting factor in high-resolution imaging. The main drawback of non-redundant masking is a less efficient coverage of spatial frequencies. However, for simple objects such as multiple and barely resolved stars, adequate spatial frequency coverage can be obtained by combining observations made with different masks and with the masks rotated to several different position angles on the sky. An important feature of MAPPIT is the use of a prism to disperse the interference pattern in wavelength. This overcomes a restriction common to all forms of interferometry, namely the requirement that one observe over a narrow band of wavelengths. By using an aperture mask with a linear array of holes, one obtains a one-dimensional fringe pattern which can then be dispersed in the direction parallel to the fringes. In MAPPIT, a prism and a cylindrical lens produce wavelength-dispersed fringes using a novel combination of image-plane and pupil-plane imaging. Results presented in this thesis include observations of several close double stars. One of these is delta Sco, and I provide the first image of this star and the first determination of its orbit. Another bright star, sigma Sgr, is found to a barely-resolved double with a separation of just 12 milliarcsec. Observations of two resolved single stars, alpha Sco and beta Gru, are also reported. The measured angular diameter of aSco agrees well with published values. For the M5 III giant beta Gru, which has not previously been resolved, I find a uniform-disk diameter of (27±3) milliarcsec.

High-resolution imaging of Betelgeuse and Mira

Diffraction-limited images have been made of the M giant stars α Orionis (Betelgeuse) and ο Ceti (Mira), using the non-redundant masking method at the 4.2-m William Herschel Telescope, for wavelengths between 546 and 710 nm. The brightness distribution for the surface of Betelgeuse is non-uniform, and has shown large changes over a period of 22 months. The disc of Mira is significantly elongated along position angle 120°, and there is evidence that the radial intensity profile is approximately Gaussian.