Speckle suppression and companion detection using coherent differential imaging

TL;DR

This paper introduces a novel method combining a coronagraph and phase-shifting interferometry to suppress speckles and detect faint companions in direct imaging of exoplanets, demonstrated on real observations.

Contribution

The paper presents a new technique that measures and corrects speckles in the focal plane using coherence, enabling detection of substellar companions without calibration.

Findings

Successful demonstration on the Stellar Double Coronagraph at Palomar.

First detection of a substellar companion using coherence properties of light.

Ability to detect companions buried in speckle noise without calibration.

Abstract

Residual speckles due to aberrations arising from optical errors after the split between the wavefront sensor and the science camera path are the most significant barriers to imaging extrasolar planets. While speckles can be suppressed using the science camera in conjunction with the deformable mirror, this requires knowledge of the phase of the electric field in the focal plane. We describe a method which combines a coronagraph with a simple phase-shifting interferometer to measure and correct speckles in the full focal plane. We demonstrate its initial use on the Stellar Double Coronagraph at the Palomar Observatory. We also describe how the same hardware can be used to distinguish speckles from true companions by measuring the coherence of the optical field in the focal plane. We present results observing the brown dwarf HD 49197b with this technique, demonstrating the ability to detect the presence of a companion even when it is buried in the speckle noise, without the use of any standard "calibration" techniques. We believe this is the first detection of a substellar companion using the coherence properties of light.