Kernel phase imaging with VLT/NACO: high-contrast detection of new candidate low-mass stellar companions at the diffraction limit
Date
2019
Authors
Kammerer, Jens
Ireland, Michael
Martinache, Frantz
Girard, Julien H.
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Publisher
Oxford University Press
Abstract
Directly imaging exoplanets is challenging because quasi-static phase aberrations in the pupil
plane (speckles) can mimic the signal of a companion at small angular separations. Kernel
phase, which is a generalization of closure phase (known from sparse aperture masking), is
independent of pupil plane phase noise to second order and allows for a robust calibration
of full pupil, extreme adaptive optics observations. We applied kernel phase combined with
a principal component based calibration process to a suitable but not optimal, high cadence,
pupil stabilized L’-band (3.8 μm) data set from the ESO archive. We detect eight low-mass
companions, five of which were previously unknown, and two have angular separations of
∼0.8–1.2 λ/D (i.e. ∼80–110 mas), demonstrating that kernel phase achieves a resolution below
the classical diffraction limit of a telescope. While we reach a 5σ contrast limit of ∼1/100
at such angular separations, we demonstrate that an optimized observing strategy with more
diversity of PSF references (e.g. star-hopping sequences) would have led to a better calibration
and even better performance. As such, kernel phase is a promising technique for achieving the
best possible resolution with future space-based telescopes (e.g. James Webb Space Telescope),
which are limited by the mirror size rather than atmospheric turbulence, and with a dedicated
calibration process also for extreme adaptive optics facilities from the ground.
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Keywords
planets and satellites: detection, planets and satellites: formation, techniques: high angular resolution, techniques: image processing, techniques: interferometric, binaries: close
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Monthly Notices of the Royal Astronomical Society
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Journal article
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Open Access
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