A Coronagraph with a Sub-$\lambda/D$ IWA and a Moderate Spectral Bandwidth

TL;DR

This paper introduces a novel coronagraph capable of achieving a sub-$7/D$ inner working angle with moderate spectral bandwidth, enhancing the detection of Earth-like exoplanets by providing high contrast and low sensitivity to certain aberrations.

Contribution

The paper presents a new coronagraph design that achieves an IWA less than 1$7/D$ over a moderate wavelength range, with high contrast and improved aberration sensitivity.

Findings

Achieves contrast below 10^{-10} at 1$7/D$ over 650--750nm

Core throughput of ≥10% at 0.7--1.4$7/D$

Reduced sensitivity to tilt aberration compared to existing coronagraphs

Abstract

Future high-contrast imaging spectroscopy with a large segmented telescope will be able to detect atmospheric molecules of Earth-like planets around G- or K-type main-sequence stars. Increasing the number of target planets will require a coronagraph with a small inner working angle (IWA), and wide spectral bandwidth is required if we enhance a variety of detectable atmospheric molecules. To satisfy these requirements, in this paper, we present a coronagraphic system that provides an IWA less than 1$\lambda_0 / D$ over a moderate wavelength band, where $\lambda_0$ is the design-center wavelength and $D$ denotes the full width of the rectangular aperture included in the telescope aperture. A performance simulation shows that the proposed system approximately achieves a contrast below $10^{-10}$ at 1$\lambda_0 / D$ over the wavelengths of 650--750nm. In addition, this system has a core throughput $\geq$ 10\% at input separation angles of $\sim$ 0.7--1.4$\lambda_0 / D$; to reduce telescope time, we need prior information on the target's orbit by other observational methods to a precision higher than the width of the field of view. For some types of aberration including tilt aberration, the proposed system has a sensitivity less than ever-proposed coronagraphs that have IWAs of approximately $1\lambda_0/D$. In future observations of Earth-like planets, the proposed coronagraphic system may serve as a supplementary coronagraphic system dedicated to achieving an extremely small IWA.