Daniel Nadeau

A New Algorithm for Point-Spread Function Subtraction in High-Contrast Imaging: A Demonstration with Angular Differential Imaging

Direct imaging of exoplanets is limited by bright quasi-static speckles in the point-spread function (PSF) of the central star. This limitation can be reduced by subtraction of reference PSF images. We have developed an algorithm to construct an optimized reference PSF image from a set of reference images. This image is built as a linear combination of the reference images available, and the coefficients of the combination are optimized inside multiple subsections of the image independently to minimize the residual noise within each subsection. The algorithm developed can be used with many high-contrast imaging observing strategies relying on PSF subtraction, such as angular differential imaging (ADI), roll subtraction, spectral differential imaging, and reference star observations. The performance of the algorithm is demonstrated for ADI data. It is shown that for this type of data the new algorithm provides a gain in sensitivity by up to a factor of 3 at small separation over the algorithm previously used by Marois and colleagues.

Speckle Noise and the Detection of Faint Companions

ABSTRACT Speckles dominate shot noise within the halo of adaptively corrected bright star images and, consequently, impose severe limits on ground‐based attempts to directly detect planets around nearby stars. The effect is orders of magnitude greater than conventional photon noise. It depends on the dwell time of the speckle pattern, the brightness of the star, and the fraction \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Efficient Speckle Noise Attenuation in Faint Companion Imaging

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TRIDENT: An Infrared Differential Imaging Camera Optimized for the Detection of Methanated Substellar Companions

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Discovery of the Brightest T Dwarf in the Northern Hemisphere

ABSTRACT Numerical simulations are used to evaluate a technique to attenuate speckle noise and enhance faint companion images buried in a bright‐star point‐spread function (PSF). It is shown that when frames taken simultaneously at two different wavelengths are subtracted from one another, the general evolution of the PSF profile with wavelength limits the attenuation to \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Infrared and visible photometry of the gravitational lens systems 2237 + 030

A_{2}\sim 2\sigma ^{2}_{\phi }\Delta \lambda / \lambda

A Subarcsecond Resolution Near infrared Study of Seyfert and “Normal” Galaxies. I. Imaging Data

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THE MONTREAL NEAR-INFRARED CAMERA

ABSTRACT We describe a near‐infrared camera in use at the Canada‐France‐Hawaii Telescope (CFHT) and at the 1.6 m telescope of the Observatoire du mont Megantic (OMM). The camera is based on a Hawaii‐1 1024 × 1024 HgCdTe array detector. Its main feature is the acquisition of three simultaneous images at three wavelengths across the methane absorption bandhead at 1.6 μm, enabling, in theory, an accurate subtraction of the stellar point‐spread function (PSF) and the detection of faint close, methanated companions. The instrument has no coronagraph and features fast data acquisition, yielding high observing efficiency on bright stars. The performance of the instrument is described, and it is illustrated by laboratory tests and CFHT observations of the nearby stars GL 526, υ And, and χ And. TRIDENT can detect (6 σ) a methanated companion with \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \use...

CLOUDS search for variability in brown dwarf atmospheres. Infrared spectroscopic time series of L/T transition brown dwarfs ⋆

We report the discovery of a bright (H = 12.77) brown dwarf designated SIMP J013656.5+093347. The discovery was made as part of a near-infrared proper-motion survey, SIMP (Sondage Infrarouge de Mouvement Propre), which uses proper motion and near-infrared/optical photometry to identify brown dwarf candidates. A low-resolution (λ/Δλ ~ 40) spectrum of this brown dwarf covering the 0.88-2.35 μm wavelength interval is presented. Analysis of the spectrum indicates a spectral type of T2.5 ± 0.5. A photometric distance of 6.4 ± 0.3 pc is estimated, assuming it is a single object. Current observations rule out a binary of mass ratio ~1 and separation 5 AU. SIMP J013656.5+093347 is the brightest T dwarf in the northern hemisphere and is surpassed only by e Indi Bab over the whole sky. It is thus an excellent candidate for detailed studies and should become a benchmark object for the early T spectral class.

Discovery of the Widest Very Low Mass Binary

As part of a program of high spatial resolution imaging of gravitationally lensed sources in the visible and IR, images of 2237 + 030 were obtained in the Gunn r and infrared J, H, K, and 3.3 micron filters. The results of the photometry of the four bright quasar components provide evidence of extinction through the lens and a determination of the extinction law in the galaxy is made. The energy distribution shows evidence of a sharp decrease of the spectral index at wavelengths longer than a rest wavelength of 1 micron. Assuming that microlensing amplification in the IR is of similar strength as in the visible, the data constrain the suggested microlensing event of August-September 1988 to a time scale of 100 days.