Kernel-Phase in Fizeau Inteferometry

TL;DR

This paper introduces kernel-phase, a new phase-noise immune observable derived from pupil geometry, enabling high-contrast companion detection at small angular separations in direct images, demonstrated with Hubble data.

Contribution

It presents the kernel-phase technique, extending closure-phase concepts to redundant apertures, applicable in high-Strehl regimes for improved astronomical imaging.

Findings

Successfully detected a known star companion with milli-arcsecond precision

Demonstrated kernel-phase's effectiveness on Hubble NICMOS data

Enabled detection below the diffraction limit

Abstract

The detection of high contrast companions at small angular separation appears feasible in conventional direct images using the self-calibration properties of interferometric observable quantities. The friendly notion of closure-phase, which is key to the recent observational successes of non-redundant aperture masking interferometry used with Adaptive Optics, appears to be one example of a wide family of observable quantities that are not contaminated by phase-noise. In the high-Strehl regime, soon to be available thanks to the coming generation of extreme Adaptive Optics systems on ground based telescopes, and already available from space, closure-phase like information can be extracted from any direct image, even taken with a redundant aperture. These new phase-noise immune observable quantities, called kernel-phases, are determined a-priori from the knowledge of the geometry of the pupil only. Re-analysis of archive data acquired with the Hubble Space Telescope NICMOS instrument, using this new kernel-phase algorithm demonstrates the power of the method as it clearly detects and locates with milli-arcsecond precision a known companion to a star at angular separation less than the diffraction limit.