263 research outputs found
Exoplanet detection with simultaneous spectral differential imaging: effects of out-of-pupil-plane optical aberrations
Imaging faint companions (exoplanets and brown dwarfs) around nearby stars is
currently limited by speckle noise. To efficiently attenuate this noise, a
technique called simultaneous spectral differential imaging (SSDI) can be used.
This technique consists of acquiring simultaneously images of the field of view
in several adjacent narrow bands and in combining these images to suppress
speckles. Simulations predict that SSDI can achieve, with the acquisition of
three wavelengths, speckle noise attenuation of several thousands. These
simulations are usually performed using the Fraunhofer approximation, i.e.
considering that all aberrations are located in the pupil plane. We have
performed wavefront propagation simulations to evaluate how out-of-pupil-plane
aberrations affect SSDI speckle noise attenuation performance. The Talbot
formalism is used to give a physical insight of the problem; results are
confirmed using a proper wavefront propagation algorithm. We will show that
near-focal-plane aberrations can significantly reduce SSDI speckle noise
attenuation performance at several lambda/D separation. It is also shown that
the Talbot effect correctly predicts the PSF chromaticity. Both differential
atmospheric refraction effects and the use of a coronagraph will be discussed.Comment: 11 pages, 7 figures. To be published in Proc. SPIE Vol. 6269, p.
1147-1157, Ground-based and Airborne Instrumentation for Astronomy; Ian S.
McLean, Masanori Iye; Ed
Fomalhaut b: Independent Analysis of the Hubble Space Telescope Public Archive Data
The nature and even the existence of a putative planet-mass companion
("Fomalhaut b") to Fomalhaut has been debated since 2008. In the present paper
we reanalyze the multi-epoch ACS/STIS/WFC3 Hubble Space Telescope (HST)
optical/near infrared images on which the discovery and some other claims were
based. We confirm that the HST images do reveal an object in orbit around
Fomalhaut but the detailed results from our analysis differ in some ways from
previous discussions. In particular, we do not confirm flux variability over a
two-year interval at 0.6 microns wavelength and we detect Fomalhaut b for the
first time at the short wavelength of 0.43 microns. We find that the HST image
of Fomalhaut b at m may be extended beyond the PSF. We cannot
determine from our astrometry if Fomalhaut b will cross or not the dust ring.
The optical through mid-infrared spectral energy distribution (SED) of
Fomalhaut b cannot be explained as due to direct or scattered radiation from a
massive planet. We consider two models to explain the SED: (1) a large
circumplanetary disk around an unseen planet and (2) the aftermath of a
collision during the past 50-150 years of two Kuiper Belt-like objects of radii
50 km.Comment: 24 pages, 9 figures, 5 tables, accepted on April, 3rd, 201
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,
reference star observations, etc. 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 3 at small
separation over the algorithm used in Marois et al. (2006).Comment: 7 pages, 11 figures, to appear in May 10, 2007 issue of Ap
Pre-Discovery 2007 Image of the HR 8799 Planetary System
We present a pre-discovery H-band image of the HR 8799 planetary system that
reveals all three planets in August 2007. The data were obtained with the Keck
adaptive optics system, using angular differential imaging and a coronagraph.
We confirm the physical association of all three planets, including HR 8799d,
which had only been detected in 2008 images taken two months apart, and whose
association with HR 8799 was least secure until now. We confirm that the
planets are 2-3 mag fainter than field brown dwarfs of comparable near-infrared
colors. We note that similar under-luminosity is characteristic of young
substellar objects at the L/T spectral type transition, and is likely due to
enhanced dust content and non-equilibrium CO/CH_4 chemistry in their
atmospheres. Finally, we place an upper limit of 18 mag per square arc second
on the >120 AU H-band dust-scattered light from the HR 8799 debris disk. The
upper limit on the integrated scattered light flux is 1e-4 times the
photospheric level, 24 times fainter than the debris ring around HR 4796A.Comment: ApJ Letters, in press; 13 pages, 3 figures, 1 tabl
Recherche de planètes extra-solaires : les limites imposées à l'imagerie
Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal
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