Near-infrared coronagraph imager on the Subaru 8m telescope Koji Murakawa 1 , Hiroshi Suto 1 , Motohide Tamura 2 , Hideki Takami 1 , Naruhisa Takato 1 , Saeko S. Hayashi 1 , Yoshiyuki Doi 1 , Norio Kaifu 2 Yutaka Hayano 2 , Wolfgang Gaessler 3 and Yukiko Kamata 2 1 Subaru Telescope, 650 North A’ohoku Place, Hilo, HI 96720 2 National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan 3 Max-Plank institute f¨ ur Astronomie, K¨onigstuhl 17, 69117 Heidelberg, Germany ABSTRACT We introduce a near-infrared camera named coronagraph imager with adaptive optics (CIAO) mounted on the Subaru 8m telescope. Combined with the Subaru 36 elements adaptive optics (AO), CIAO can produce nearly diffraction limited image with ∼0.07 arcsec FWHM at K band and high dynamic range imaging with ∼10 mag difference at 1 arcsec separation under typical seeing conditions. We have carried out performance tests of imaging without and with coronagraph mask since its first light observation held on 2000 February. Because of limited weather conditions, the performance under best seeing conditions has not been tested yet. At a typical natural seeing condition of 0.4-0.8 arcsec, halo component of PSF using 0.2-0.8 arcsec mask can be reduced up to 70% comparing with that without mask using AO. Even after correction, residual wave front error has typically 1.2 rad 2 which corresponds to the Strehl ratio of ∼0.3 at K band. Such wave front errors degrades the image quality; this is a common problem of coronagraph on the ground-based telescope with non high-order AO. Nevertheless we emphasize that there are various advantages on our coronagraph: the clean PSF of CIAO, reduction of readout noise, and less effect of detector memory problem. Compared with coronagraphs on smaller telescopes, the PSF shape is sharper and it brings higher detectability of sources around bright objects. Keywords: coronagraph, high resolution camera, 8m telescope, near infrared 1. INTRODUCTION Infrared observation techniques on the ground-based telescope have rapidly progressed and been improved since realization of adaptive optics. While previous observations have been limited as the natural seeing (eg. ∼0.6 arcsec at Mauna Kea), currently a FWHM of ∼0.07 arcsec at K band can be achieved with 8m class telescopes. Owing to such big progress of high angular resolution technique, high quality imaging has been requested for dynamic range as well. A technique named solar-coronagraph was originally invented by Lyot (1930) 1 and the solar corona was first detected without the total solar eclipse. In 1984, Smith & Terrile 2 were successful with imaging debris disk around a Vega-like star β-Pic using coronagraph optimized for non-solar objects. Now coronagraph is recognized to be a powerful instrument to detect faint objects around bright sources. We have manufactured a near-infrared stellar coronagraph (Coronagraphic Imager with Adaptive Optics; CIAO) which allows to obtain sub-0.1 arcsec angular resolution and high dynamic range images combined with the Subaru telescope of 8.2m aperture and the 36 element adaptive optics 3,4 . Our scientific goals are (1) detection of companion brown dwarfs and extra-solar planets around nearby stars, (2) detection of proto-planetary disks and jets around young stellar objects (YSOs), (3) imaging of circumstellar envelope around late type stars and (4) detection of circumnuclear regions around AGN and quasar host. Since its first light observation held in 2002 February, we have tested the performance of CIAO and have obtained some scientific results. In this Further author information: (Send correspondence to K. Murakawa) K. Murakawa: E-mail: murakawa@subaru.naoj.org, Telephone: 1 808 934 5924 Subaru Telescope, 650 North A’ohoku Place, Hilo, HI 96720, USA