Common-path achromatic rotational-shearing coronagraph

Abstract

To suppress starlight for direct exoplanet observation, we propose a common-path achromatic rotational-shearing coronagraph (CP-ARC), which is an interferocoronagraph with an angular-adjustable field rotator. The CP-ARC aims to maintain unwanted detection of stellar light, which can be suppressed incompletely by interference because of the finite diameter of the star. Compared to the previous interferocoronagraph, which had a nonadjustable 180° field rotation, the proposed CP-ARC can improve the coronagraphic contrast by several orders if the CP-ARC is combined with medium or large telescopes where the companion-star separation is optically resolved by more than a few Airy radii. The CP-ARC is made robust against mechanical disturbances due to the common-path interferometer principle.

Stellar imaging coronagraph and exoplanet coronal spectrometer: two additional instruments for exoplanet exploration onboard the WSO-UV 1.7-m orbital telescope

“…In Fig We have estimated the effect of an extended source considering a 0.1 λ/D stellar size, aberrations, and micro-roughness. Without the two latter factors, theoretically [12,39], the coronagraphic contrast is predicted to be better than 7 orders at a stellocentric distance 10 λ/D.…”

“…A CP-ARCcommon-path achromatic rotational shear coronagraph [11,12], is planned (for the first time) as a coronagraphic device for real onboard observations, and it has a science-related advantage. CP-ARC introduces a centrostellar occultation effect under a variable angle of rotational shear.…”

“…As a minimum success scenario, the goal is to test the coronagraph as an in-flight demonstrator, and to photometrically characterize ~10 giant planets, which have been previously detected by the radial velocity technique. A CP-ARCcommon-path achromatic rotational shear coronagraph [11,12], is planned (for the first time) as a coronagraphic device for real onboard observations, and it has a science-related advantage. CP-ARC introduces a centrostellar occultation effect under a variable angle of rotational shear.…”

“…by the WSO-UV), the Solar-type star at 10 parsec has an apparent size of ~0.02•λ/D, limiting the destructive interference to 4-5 orders of magnitude for starlight suppression. To overcome this effect, an interfero-coronagraph with variable rotational shear, abbreviated as ARC [39] (later re-designed in a mechanically robust common-path (or cyclic path) CP-ARC [11,12]), offers the possibility to adjust the arbitrary pupil rotation angle to an optimal angle for the observing configuration. With a 1.7 m WSO-UV telescope, the 10 degree image rotating CP-ARC suppresses stellar leakage caused by a finite stellar disk for a Sun-like star at 10 pc, almost eight orders of magnitude below the raw coronagraphic contrast.…”

“…SCEDI's goal is to test the coronagraph as an in-flight demonstrator, to photometrically characterize several known giant planets detected by the radial velocity technique, and in the best case, to image exoplanets and circumstellar discs by searching several tens of nearby stars. Coronagraph design is proposed based on the common-path achromatic rotational shear interfero-coronagraph [11,12] which introduces a centrostellar occultation effect under a variable angle for two-image superposition (rotational shear). Rotational shear is planned to be fixed between 5 and 10 degrees; therefore, the interfero-coronagraph will have low sensitivity to static low-order aberrations from a telescope's images.…”