On-sky observations with an achromatic hybrid phase knife coronagraph in the visible

TL;DR

This paper reports on the development and on-sky testing of an achromatic hybrid phase knife coronagraph in the visible spectrum, demonstrating its potential for high-contrast imaging and exoplanet detection despite challenging conditions.

Contribution

It introduces a novel achromatic hybrid phase knife coronagraph derived from the four-quadrant phase mask, with a real-time image selection algorithm tested on on-sky data.

Findings

Proven efficiency of the coronagraph under poor observing conditions

Development of procedures for future adaptive optics and coronagraphic instruments

Successful on-sky demonstration with binary star HD80081

Abstract

CONTEXT: The four-quadrant phase mask stellar coronagraph, introduced by D. Rouan et al., is capable of achieving very high dynamical range imaging and was studied in the context of the direct detection of extra-solar planets. Achromatic four-quadrant phase mask is currently being developed for broadband IR applications. AIMS: We report on laboratory and on-sky tests of a prototype coronagraph in the visible. This prototype, the achromatic hybrid phase knife coronagraph, was derived from the four-quadrant phase mask principle. METHODS: The instrumental setup implementing the coronagraph itself was designed to record the pre- and post-coronagraphic images simultaneously so that an efficient real-time image selection procedure can be performed. We describe the coronagraph and the associated tools that enable robust and repeatable observations. We present an algorithm of image selection that has been tested against the real on-sky data of the binary star HD80081 (* 38 Lyn). RESULTS Although the observing conditions were poor, the efficiency of the proposed method is proven. From this experiment, we derive procedures that can apply to future focal instruments associating adaptive optics and coronagraphy, targeting high dynamic range imaging in astronomy, such as detecting extra-solar planets.