EDP Sciences
Free access
Issue A&A
Volume 480, Number 3, March IV 2008
Page(s) 899 - 903
Section Astronomical instrumentation
DOI http://dx.doi.org/10.1051/0004-6361:20078627
Published online 25 January 2008



A&A 480, 899-903 (2008)
DOI: 10.1051/0004-6361:20078627

High contrast experiment of an AO-free coronagraph with a checkerboard pupil mask

K. Enya1, L. Abe2, S. Tanaka1, 3, T. Nakagawa1, K. Haze1, 4, T. Sato5, and T. Wakayama5

1  Department of Infrared Astrophysics, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Yoshinodai 3-1-1, Sagamihara, Kanagawa 229-8510, Japan
    e-mail: enya@ir.isas.jaxa.jp
2  Optical and Infrared Astronomy Division & Extra-solar Planet Project Office, National Astronomical Observatory, Osawa 2-21-2, Mitaka, Tokyo 181-8588, Japan
3  Department of Physics, Graduate School of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan
4  Department of Space and Astronautical Science, The Graduate University for Advanced Study, Yoshinodai 3-1-1, Sagamihara, Kanagawa 229-8510, Japan
5  Nanotechnology Research Institute, Advanced Industrial Science and Technology, Umezono 1-1-1, Tsukuba, Ibaraki 305-8568, Japan

(Received 6 September 2007 / Accepted 28 December 2007)

Abstract
Context.A high contrast coronagraph is expected to provide one of the promising ways to directly observe extra-solar planets. We present the newest results of our laboratory experiment investigating "rigid" coronagraph with a binary shaped checkerboard pupil mask, which should offer a highly stable solution for telescopes without adaptive optics (AO) for wavefront correction in space missions.
Aims. The primary aim of this work was to study the stability of the coronagraph, and to demonstrate its performance without adaptive wavefront correction. Estimation of both the raw contrast and the gain of the point spread function (PSF) subtraction were needed. The limiting factor of the contrast was also important.
Methods. A binary shaped pupil mask of a checkerboard type has been designed. The mask, consisting of an aluminum film on a glass substrate, was manufactured using nano-fabrication techniques with electron beam lithography. Careful evaluation of coronagraphic performance, including PSF subtraction, was carried out in air using the developed mask.
Results. A contrast of $6.7 \times 10^{-8}$ was achieved for the raw coronagraphic image by areal averaging of all of the observed dark regions. Following PSF subtraction, the contrast reached $6.8 \times 10^{-9}$. Speckles were a major limiting factor throughout the dark regions of both the raw image and the PSF subtracted image.
Conclusions. A rigid coronagraph with PSF subtraction without AO is a useful method to achieve high contrast observations. Applications of a rigid coronagraph to a Space Infrared telescope for Cosmology and Astrophysics (SPICA) and other platforms are discussed.


Key words: instrumentation: high angular resolution -- methods: laboratory -- techniques: miscellaneous



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