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Proceedings Paper • Open Access

The evanescent wave coronagraph project: development status and potential for space based observations
Author(s): Mary Angelie Alagao; Christophe Buisset; Thierry Lépine; Eric Thiébaut; Maud Langlois; Michel Tallon; Isabelle Tallon-Bosc; Yves Rabbia; Saran Poshyachinda; Boonrucksar Soonthornthum

Paper Abstract

The Evanescent Wave Coronagraph (EvWaCo) is a coronagraph with an occulting mask based on the frustration of total internal reflection to i) produce an achromatic extinction of the central star and ii) reveal the faint companion surrounding the star. Results obtained in laboratory conditions show contrast performance of a few 10-6 between 10 λC/D and 20 λC/D over the full I-band centered at the wavelength λC = 800 nm with a spectral ratio of Δλ/ λC ≈ 20% in unpolarized light.

In this paper, we discuss the advantages of using EvWaCo to observe and characterize exoplanets with a space-based telescope. In the first section, we describe the system and present the current results obtained with the EvWaCo testbed. We also illustrate the capability of this coronagraph to detect the companion 30,000 times (respectively, 100,000 times) fainter than the central star at distances equal to 15 Airy radii (respectively, 30 Airy radii) from the PSF center in polychromatic and unpolarized light.

In the second section, we describe the design of the prototype dedicated to the on-sky tests of the instrument with the 2.4 m Thai National Telescope at horizon 2020. This prototype has been designed with the objective to reach a contrast equal to a few 10-4 at the inner working angle (IWA) equal to 3 λ/D from the star PSF center while observing through the atmosphere over the full photometric I-band. This prototype will include an adaptive optics specified to reach at λ ≈ 800 nm a Strehl ratio > 0.8 for magnitude m < 7.

In the third section, we show the theoretical performance of EvWaCo: a contrast comprised between a few 10-6 and 10-7 in the I-Band between 3 λ/D and 10 λ/D in the I-Band for an IWA equal to 3 λ/D with a Gaussian apodization in unpolarized light. We also show that similar contrasts performance are obtained in the V-, R-, bands, thus illustrating the EvWaCo quasi-achromaticity. Finally, we discuss the advantages and the limitation using the proposed concept for space-based observations and spectral characterization of exoplanets.

Paper Details

Date Published: 12 July 2019
PDF: 10 pages
Proc. SPIE 11180, International Conference on Space Optics — ICSO 2018, 111806Q (12 July 2019); doi: 10.1117/12.2536161
Show Author Affiliations
Mary Angelie Alagao, National Astronomical Research Institute of Thailand (Thailand)
Christophe Buisset, National Astronomical Research Institute of Thailand (Thailand)
Thierry Lépine, Institut d'Optique Graduate School (France)
Lab. Hubert Curien, Univ. de Lyon, CNRS (France)
Eric Thiébaut, Ctr. de Recherche Astrophysique de Lyon (France)
Maud Langlois, Ctr. de Recherche Astrophysique de Lyon (France)
Michel Tallon, Ctr. de Recherche Astrophysique de Lyon (France)
Isabelle Tallon-Bosc, Ctr. de Recherche Astrophysique de Lyon (France)
Yves Rabbia, Univ. Côte d’Azur (France)
Saran Poshyachinda, National Astronomical Research Institute of Thailand (Thailand)
Boonrucksar Soonthornthum , National Astronomical Research Institute of Thailand (Thailand)

Published in SPIE Proceedings Vol. 11180:
International Conference on Space Optics — ICSO 2018
Zoran Sodnik; Nikos Karafolas; Bruno Cugny, Editor(s)

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