Shin Oya

Spiral Structure in the Circumstellar Disk around AB Aurigae

We present a near-infrared image of the Herbig Ae star AB Aur obtained with the Coronagraphic Imager with Adaptive Optics mounted on the Subaru Telescope. The image shows a circumstellar emission extending out to a radius of r = 580 AU, with a double spiral structure detected at r = 200-450 AU. The surface brightness decreases as r-3.0±0.1, steeper than the radial profile of the optical emission possibly affected by the scattered light from the envelope surrounding AB Aur. This result, together with the size of the infrared emission similar to that of the 13CO (J = 1-0) disk, suggests that the spiral structure is indeed associated with the circumstellar disk but is not part of the extended envelope. We identified four major spiral arms, which are trailing if the brighter southeastern part of the disk is the near side. The weak gravitational instability, maintained for millions of years by continuous mass supply from the envelope, might explain the presence of the spiral structure at the relatively late phase of the pre-main-sequence period.

Current performance and on-going improvements of the 8.2 m Subaru Telescope

An overview of the current status of the 8.2m Subaru Telescope constructed and operated at Mauna Kea, Hawaii, by the National Astronomical Observatory of Japan is presented. The basic design concept and the verified performance of the telescope system are described. Also given are the status of the instrument package offered to the astronomical community, the status of operation, and some of the future plans. The status of the telescope reported in a number of SPIE papers as of the summer of 2002 are incorporated with some updates included as of 2004 February. However, readers are encouraged to check the most updated status of the telescope through the home page, http://subarutelescope.org/index.html, and/or the direct contact with the observatory staff.

A Young Brown Dwarf Companion to DH Tauri

We present the detection of a young brown dwarf companion, DH Tau B, associated with the classical T Tauri star DH Tau. Near-infrared coronagraphic observations with CIAO on the Subaru Telescope have revealed DH Tau B with H = 15 mag located 23 (330 AU) away from the primary, DH Tau A. Comparing its position with a Hubble Space Telescope archive image, we confirmed that DH Tau A and B share a common proper motion, suggesting that they are physically associated with each other. The near-infrared color of DH Tau B is consistent with those of young stellar objects. The near-infrared spectra of DH Tau B show deep water absorption bands, a strong K I absorption line, and a moderate Na I absorption line. We derived its effective temperature and surface gravity of Teff = 2700-2800 K and log g = 4.0-4.5, respectively, by comparing the observed spectra with synthesized spectra of low-mass objects. The location of DH Tau B on the H-R diagram gives its mass of 30MJ-50MJ.

Commissioning status of Subaru laser guide star adaptive optics system

The current status of commissioning and recent results in performance of Subaru laser guide star adaptive optics system is presented. After the first light using natural guide stars with limited configuration of the system in October 2006, we concentrated to complete a final configuration for a natural guide star to serve AO188 to an open use observation. On sky test with full configurations using natural guide star started in August 2008, and opened to a public one month later. We continuously achieved around 0.6 to 0.7 of Strehl ratio at K band using a bright guide star around 9th to 10th magnitude in R band. We found an unexpectedly large wavefront error in our laser launching telescope. The modification to fix this large wavefront error was made and we resumed the characterization of a laser guide star in February 2009. Finally we obtained a round-shaped laser guide star, whose image size is about 1.2 to 1.6 arcsec under the typical seeing condition. We are in the final phase of commissioning. A diffraction limited image by our AO system using a laser guide star will be obtained in the end of 2010. An open use observation with laser guide star system will start in the middle of 2011.

Subaru Deep Survey I. Near-Infrared Observations

Deep near-infraredimages of a blank 2 � ×2 � section of skynear the galactic north pole taken by Subaru Telescope are presented. The total integration times of the J and Kbands were 12.1 hr and 9.7 hr, resulting in 5 σ limiting magnitudes of 25.1 and 23.5 mag, respectively. The numbers of sources within these limiting magnitudes found with an automated detection procedure are 385 in the J band and 350 in K � . Based on photometric measurements of these sources, we present number count vs. magnitude relations, color vs. magnitude diagrams, size vs. color relationships, etc. The slope of the galaxy number count plotted against the AB magnitude scale is about 0.23 in the 22 to 26 AB magnitude range of both bands. The spatial number density of galaxies as well as the slopes in the faint-end region given by the Subaru Deep Field (SDF) survey are consistent with those given by HST-NICMOS surveys, as expressed on the AB magnitude diagram. Several sources having very large J − Kcolor have been found, including a few Kobjects without detection at J. In addition, a number of faint galactic stars were also

Performance of Subaru adaptive optics system AO188

Subaru adaptive optics system (AO188) is an 188-elements curvature sensor adaptive optics system that is operated in both natural and laser guide star modes. AO188 was installed at Nasmyth platform of the Subaru telescope and it has been successfully operating in the natural guide star mode since October 2008. The performance of AO188 in the natural guide star mode has been well verified from on-sky data obtained with the infrared camera and spectrograph (IRCS). Under normal seeing condition, AO188 achieves K-band Strehl ratio between 60% and 70% using R = 9.0 magnitude natural guide stars and it works well with faint guide stars down to R = 16.5 magnitude. We measured the FWHM and Strehl ratio of stellar images in globular clusters and found that the isoplanatic angle is approximately 30 arcsec. In this paper, we describe an overview of the operation procedure for AO188, as well as its performance such as angular resolution, Strehl ration, and sensitivity gain for detecting faint objects.

Hawaii 167 and Q0059-2735: Heavily Dust-Enshrouded Young QSOs

Using the OH-airglow suppressor spectrograph at the University of Hawaii 2.2m telescope and the CGS4 spectrometer at the United Kingdom Infrared Telescope, we have found exceptionally large Balmer decrements in two unusual high-z QSOs, Hawaii 167 (z=2.36, Ha/Hb = 13) and Q0059-2735 (z=1.59, Ha/Hb = 7.6), the latter being a so-called low-ionization broad absorption line QSO (BALQSO). We argue that these objects are young QSOs heavily enshrouded by dust. In fact, the internal reddening might be so large as to completely extinguish the QSO light in the restframe UV, allowing us to see the underlying stellar population. Our possible detection of the 4000 A break in Hawaii 167 supports this idea. Its small amplitude indicates a very young age for the population, ~15 Myrs. To explain the properties of these QSOs, we propose a model in which a young QSO is surrounded by a shell of young massive stars mixed with significant amounts of dust. We predict that as the QSO emerges from this dust cocoon, it will eventually take on the appearance of a normal BALQSO.

Current status of the laser guide star adaptive optics system for Subaru Telescope

The current status and recent results, since last SPIE conference at Orlando in 2006, for the laser guide star adaptive optics system for Subaru Telescope is presented. We had a first light using natural guide star and succeed to launch the sodium laser beam in October 2006. The achieved Strehl ratio on the 10th magnitude star was around 0.5 at K band. We confirmed that the full-width-half-maximum of the stellar point spread function is smaller than 0.1 arcsec even at the 0.9 micrometer wavelehgth. The size of the artificial guide star by the laser beam tuned at the wavelength of 589 nm was estimated to be 10 arcsec. The obtained blurred artificial guide star is caused by the wavefront error on the laser launching telescope. After the first light and first launch, we found that we need to modify and to fix the components, which are temporarily finished. Also components, which were postponed to fabricate after the first light, are required to build newly. All components used by the natural guide star adaptive optics system are finalized recently and we are ready to go on the sky. Next engineering observation is scheduled in August, 2008.

Performance characterization of the HiCIAO instrument for the Subaru Telescope

HiCIAO is a near-infrared, high contrast instrument which is specifically designed for searches and studies for extrasolar planets and proto-planetary/debris disks on the Subaru 8.2 m telescope. A coronagraph technique and three differential observing modes, i.e., a dual-beam simultaneous polarimetric differential imaging mode, quad-beam simultaneous spectral differential imaging mode, and angular differential imaging mode, are used to extract faint objects from the sea of speckle around bright stars. We describe the instrument performances verified in the laboratory and during the commissioning period. Readout noise with a correlated double sampling method is 15 e- using the Sidecar ASIC controller with the HAWAII-2RG detector array, and it is as low as 5 e- with a multiple sampling method. Strehl ratio obtained by HiCIAO on the sky combined with the 188-actuator adaptive optics system (AO188) is 0.4 and 0.7 in the H and K-band, respectively, with natural guide stars that have R ~ 5 and under median seeing conditions. Image distortion is correctable to 7 milli-arcsec level using the ACS data as a reference image. Examples of contrast performances in the observing modes are presented from data obtained during the commissioning period. An observation for HR 8799 in the angular differential imaging mode shows a clear detection of three known planets, demonstrating the high contrast capability of AO188+HiCIAO.

SPATIALLY RESOLVED 3 μm SPECTROSCOPY OF ELIAS 1: ORIGIN OF DIAMONDS IN PROTOPLANETARY DISKS*

We present spatially resolved 3 μm spectra of Elias 1 obtained with an adaptive optics system. The central part of the disk is almost devoid of polycyclic aromatic hydrocarbon (PAH) emission at 3.3 μm; it shows up only at 30 AU and beyond. The PAH emission extends up to 100 AU, at least to the outer boundary of our observation. The diamond emission, in contrast, is more centrally concentrated, with the column density peaked around 30 AU from the star. There are only three Herbig Ae/Be stars known to date that show diamond emission at 3.53 μm. Two of them have low-mass companions likely responsible for the large X-ray flares observed toward the Herbig Ae/Be stars. We speculate on the origin of diamonds in circumstellar disks in terms of the graphitic material being transformed into diamond under the irradiation of highly energetic particles.