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Cryogenic infrared optics for the SPICA coronagraph

Published online by Cambridge University Press:  02 May 2006

Keigo Enya ,
Takao Nakagawa ,
Hirokazu Kataza ,
Hidehiro Kaneda ,
Yukari Yamashita Yui ,
Motohide Tamura ,
Lyu Abe ,
Yoshiyuki Obuchi ,
Takashi Miyata  and
Shigeyuki Sako
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Keigo Enya
Affiliation:
Department of Infrared Astrophysics, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa, 229-8510
Takao Nakagawa
Affiliation:
Department of Infrared Astrophysics, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa, 229-8510
Hirokazu Kataza
Affiliation:
Department of Infrared Astrophysics, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa, 229-8510
Hidehiro Kaneda
Affiliation:
Department of Infrared Astrophysics, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa, 229-8510
Yukari Yamashita Yui
Affiliation:
Department of Infrared Astrophysics, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa, 229-8510
Motohide Tamura
Affiliation:
Optical and Infrared Astronomy Division, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588 Japan
Lyu Abe
Affiliation:
Optical and Infrared Astronomy Division, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588 Japan
Yoshiyuki Obuchi
Affiliation:
Optical and Infrared Astronomy Division, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588 Japan
Takashi Miyata
Affiliation:
Institute of Astronomy, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588 Japan
Shigeyuki Sako
Affiliation:
Institute of Astronomy, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588 Japan
Takashi Onaka
Affiliation:
Department of Astronomy, University of Tokyo, 7-3-1 Hongo, bunkyo, Tokyo, 113-0033 Japan email: enya@ir.isas.jaxa.jp
Hidenori Takahashi
Affiliation:
Department of Astronomy, University of Tokyo, 7-3-1 Hongo, bunkyo, Tokyo, 113-0033 Japan email: enya@ir.isas.jaxa.jp
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Abstract

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SPICA is a cooled, single large-mirror space-telescope, which is under discussion as an succsesor of the ASTRO-F mission. One of the most ambitious challenges of the SPICA mission is the direct observations of exoplanets with a coronagraph instrument. We report cryogenic infrared optics to realize high quality wavefronts for the SPICA coronagraph.

The SPICA satellite will be launched by an H-IIA rocket to Sun-Earth L2 Halo orbit early in the 2010s. The SPICA telescope is a Ritchey-Chretien optics with 3.5m diameter primary mirror, and cooled down to 4.5 K in orbit by radiation cooling and mechanical cryo-coolers. Main working wavelengths are 5–200 micron. Advantages of the SPICA coronagraph are the infrared wavelenths where the contrast between planets and central stars are smaller than the optical wavelengths, and that the cooled space telescope consists of monolithic mirrors.

Development of light-weight cooled telescope is one of the most important tasks to realize SPICA. At the present, sintered SiC and carbon fiber reinforced SiC (C/SiC) composite are candidate materials for the mirrors, truss, and optical bench. For these materials, estimations and improvements of basic property and surface roughness in cryogenic temperatures have been carried out. Deformation of trial product mirrors by cooling is also examined.

We are developing cryogenic deformable mirrors (DMs) because wave front accuracy of the SPICA telescope is 0.35 micron RMS, which is not enough for our coronagraphic instrument. For MEMS (Micro Electro Mechanical System) DM and some others, measurements of thermal deformation by cooling, electrical response, and heat generation are undergoing. Developments of a tip-tilt system for cryogenic usage started to cancel vibration caused by the cryo-coolers and other components and to realize a diffraction limit resolution. The first result of our binary mask coronagraph experiment is also shown.

Keywords

SPICAinfraredtelescopecryogenictip-tiltdeformable mirror
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 1 , Colloquium C200: Direct Imaging of Exoplanets: Science & Techniques , October 2005 , pp. 467 - 472
Copyright
© 2006 International Astronomical Union