Speckle suppression and companion detection using coherent differential imaging

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.

arXiv comment32 pages, 11 figures. Accepted for publication in MNRAS

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• Design and performance of the PALM-3000 3.5 kHz upgrade
• High-contrast imaging of tight resolved binaries with two vector vortex coronagraphs in cascade with the Palomar SDC instrument
• Improving VLT/SPHERE without additional hardware: Comparing quasi-static correction strategies
• The coherent differential imaging on speckle area nulling (CDI-SAN) method for high-contrast imaging under speckle variation