Behavior of Remnant Speckles in an Adaptively Corrected Imaging System

Bloemhof, E. E.; Dekany, Richard; Troy, Mitchell; Oppenheimer, Ben R.

doi:10.1086/323494

Cited by 78 publications

(75 citation statements)

References 13 publications

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“…Linearization of the complex quantity in the pupil plane is put forward to account for the speckle symmetry. A similar reasoning is presented by Bloemhof et al (2001) to explain the "speckle pinning effect." The FQPM can take advantage of this welcoming effect with a centrosymmetrical subtraction and yield a higher S/N than others coronagraphs.…”

Section: Resultssupporting

confidence: 61%

Speckle Symmetry with High‐Contrast Coronagraphs

Boccaletti

Riaud

Rouan

2002

PUBL ASTRON SOC PAC

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ABSTRACT. We investigate the pattern of residual speckles obtained with high-contrast coronagraphs and extreme adaptive optics systems. In particular, we provide evidence of symmetry occurring for very small phase defects depending only on the ability of the coronagraph to attenuate the pupil diffraction pattern. In such a case, a centrosymmetrical subtraction of the image significantly increases the signal-to-noise ratio. Detection of very faint companions around bright stars may benefit from this characteristic in some particular conditions. Numerical simulations show that speckle symmetry takes place when using a four-quadrant phase mask coronagraph, for very high Strehl ratio ( ) and with a filled circular aperture. SR 1 0.96

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Section: Resultssupporting

confidence: 61%

Speckle Symmetry with High‐Contrast Coronagraphs

Boccaletti

Riaud

Rouan

2002

PUBL ASTRON SOC PAC

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“…Aime & Soummer (2004) and Soummer et al (2007a) have shown that the speckle noise from "pinned" speckles (Bloemhof et al 2001;Sivaramakrishnan et al 2002;Bloemhof 2003;Perrin et al 2003) can be reduced with a coronagraph. The variance of the speckles and photon noise in a coronagraphic image is given by…”

Section: Impact Of Chromaticity On Contrast Performancementioning

confidence: 99%

Apodized Pupil Lyot Coronagraphs for Arbitrary Apertures. Iii. Quasi-Achromatic Solutions

Soummer

Sivaramakrishnan

Pueyo

et al. 2011

ApJ

107

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Direct imaging and spectroscopy of young giant planets from the ground requires broadband starlight suppression with coronagraphy. It is important to minimize the coronagraph chromatic sensitivity to help remove residual speckles through post-processing of images at multiple wavelengths. The coronagraph must also be able to mitigate the effects of ground-based telescopes with central obstruction. We present new properties of the Apodized Pupil Lyot Coronagraph (APLC) that enable quasi-achromatic starlight suppression over a broad bandpass (20%) and with central obstructions. We discuss the existence of these quasi-achromatic solutions using the properties of the generalized prolate spheroidal functions, which are used to define the apodizer profile. We discuss a broadband optimization method and illustrate its parameter space in terms of inner working angle and contrast. These new APLC solutions are implemented in the Gemini Planet Imager (GPI), a new facility instrument to detect and characterize young giant planets and disks, which will be commissioned in 2011. The coronagraph design delivers a contrast better than 10 −7 beyond a separation of 0.2 arcsec in the presence of Gemini's central obstruction over a 20% bandpass. The science camera is an integral field spectrograph observing in one of the Y, J, or H, or in about two-thirds of the K bandpass, at a single time. Similar solutions have also been used for the Palomar 1640 coronagraphic integral field spectrograph.

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“…Residual mirror polishing errors (which tend to be rotationally symmetric anyway) and aberrations downstream the optical system are modulated by the symmetry of the Airy pattern in the small-aberration regime. "Pinned speckles" [6,16] form an additional rotationally symmetrical component in the focal plane because they are modulated by the Airy pattern. All of these effects contribute to confusion when trying to identify planets among many objectlike features, having the same spatial scale ( / D λ -the wavelength divided by the aperture width) and shape.…”

Section: Symmetry and The Imagementioning

confidence: 99%

Fainter and closer: finding planets by symmetry breaking

Ribak¹,

Gładysz²

2008

Opt. Express

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Imaging of planets is very difficult, due to the glare from their nearby, much brighter suns. Static and slowly-evolving aberrations are the limiting factors, even after application of adaptive optics. The residual speckle pattern is highly symmetrical due to diffraction from the telescope's aperture. We suggest to break this symmetry and thus to locate planets hidden beneath it. An eccentric pupil mask is rotated to modulate the residual light pattern not removed by other means. This modulation is then exploited to reveal the planet's constant signal. In well-corrected ground-based observations we can reach planets six stellar magnitudes fainter than their sun, and only 2-3 times the diffraction limit from it. At ten times the diffraction limit, we detect planets 16 magnitudes fainter. The stellar background drops by five magnitudes. The trouble with planetsPlanets in other stellar systems (exoplanets) are difficult to discover, and even more difficult to image. This is because there is a very large intensity difference between them and their parent stars, which can be anything from 10 -4 in the infrared down to 10 -10 and fainter in the visible regime, depending on the physical properties of the system [1,2]. Light from the star is scattered off-axis by the atmosphere, the aperture of the telescope, the secondary mirror holders (spiders) and other optical elements in the path to the imaging camera. Techniques such as adaptive optics (AO) and coronagraphy aim to remove this effect by concentrating light back on the optical axis and removing it [3]. All future ground-based high-contrast imaging systems will employ coronagraphs and AO [4,5].It has been shown through simulations and experiments that the limiting factors in highcontrast imaging from ground and space are static and quasi-static speckles [6][7][8]. While residual atmospheric aberrations after AO correction are random and will average out over time, these persistent speckles will stand out against the AO-corrected stellar halo and masquerade as faint sources even after long integrations. This is why future efforts to directly image planets will also entail post-processing schemes based on the concept of point spread function (PSF) subtraction. Proposed approaches utilize PSF estimates provided by on-sky rotation [9], as well as spectral [10,11] and polarization-based [12] discrimination between the light coming from the parent star and the companion. The problem with some of these techniques is that the PSF-subtracted images still contain static speckles (at a lower brightness level than in the direct images) due to errors in PSF estimation. These errors arise due to the inherent sensitivity of PSF subtraction to changes in "seeing", mechanical flexure or the introduction of extra imaging channels. Recently a detection algorithm has been proposed which relies only on multiple exposures and statistical properties of AO-corrected intensity [13].

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Behavior of Remnant Speckles in an Adaptively Corrected Imaging System

Cited by 78 publications

References 13 publications

Speckle Symmetry with High‐Contrast Coronagraphs

Speckle Symmetry with High‐Contrast Coronagraphs

Apodized Pupil Lyot Coronagraphs for Arbitrary Apertures. Iii. Quasi-Achromatic Solutions

Fainter and closer: finding planets by symmetry breaking

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