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IRD is the near-infrared high-precision radial velocity instrument for the Subaru 8.2-m telescope. It is a relatively compact (~1m size) spectrometer with a new echelle-grating and Volume-Phase Holographic gratings covering 1-2 micron wavelengths combined with an original frequency comb using optical pulse synthesizer. The spectrometer will employ a 4096x4096-pixel HgCdTe array under testing at IfA, University of Hawaii. Both the telescope/Adaptive Optics and comb beams are fed to the spectrometer via optical fibers, while the instrument is placed at the Nasmyth platform of the Subaru telescope. Expected accuracy of the Doppler-shifted velocity measurements is about 1 m s-1. Helped with the large collecting area and high image quality of the Subaru telescope, IRD can conduct systematic radial velocity surveys of nearby middle-to-late M stars aiming for down to one Earth-mass planet. Systematic observational and theoretical studies of M stars and their planets for the IRD science are also ongoing. We will report the design and preliminary development progresses of the whole and each component of IRD.

We report that HAT-P-7 has a common proper motion stellar companion. The companion is located at $\sim3.9$ arcsec to the east and estimated as an M5.5V dwarf based on its colors. We also confirm the presence of the third companion, which was first reported by Winn et al. (2009), based on long-term radial velocity measurements. We revisit the migration mechanism of HAT-P-7b given the presence of those companions, and propose sequential Kozai migration as a likely scenario in this system. This scenario may explain the reason for an outlier in the discussion of the spin-orbit alignment timescale for HAT-P-7b by Albrecht et al. (2012)., 5 pages, 4 figures, 2 tables, PASJ Letters in press

We report high-resolution (0.07 arcsec) near-infrared polarized intensity images of the circumstellar disk around the star 2MASS J16042165-2130284 obtained with HiCIAO mounted on the Subaru 8.2 m telescope. We present our $H$-band data, which clearly exhibits a resolved, face-on disk with a large inner hole for the first time at infrared wavelengths. We detect the centrosymmetric polarization pattern in the circumstellar material as has been observed in other disks. Elliptical fitting gives the semimajor axis, semiminor axis, and position angle (P.A.) of the disk as 63 AU, 62 AU, and -14 $^{\circ}$, respectively. The disk is asymmetric, with one dip located at P.A.s of $\sim85^{\circ}$. Our observed disk size agrees well with a previous study of dust and CO emission at submillimeter wavelength with Submillimeter Array. Hence, the near-infrared light is interpreted as scattered light reflected from the inner edge of the disk. Our observations also detect an elongated arc (50 AU) extending over the disk inner hole. It emanates at the inner edge of the western side of the disk, extending inward first, then curving to the northeast. We discuss the possibility that the inner hole, the dip, and the arc that we have observed may be related to the existence of unseen bodies within the disk., Comment: 21 pages, 3 figures, published 2012 November 7 by ApJL, typo corrected

Transitional circumstellar disks around young stellar objects have a distinctive infrared deficit around 10 microns in their Spectral Energy Distributions (SED), recently measured by the Spitzer Infrared Spectrograph (IRS), suggesting dust depletion in the inner regions. These disks have been confirmed to have giant central cavities by imaging of the submillimeter (sub-mm) continuum emission using the Submillimeter Array (SMA). However, the polarized near-infrared scattered light images for most objects in a systematic IRS/SMA cross sample, obtained by HiCIAO on the Subaru telescope, show no evidence for the cavity, in clear contrast with SMA and Spitzer observations. Radiative transfer modeling indicates that many of these scattered light images are consistent with a smooth spatial distribution for micron-sized grains, with little discontinuity in the surface density of the micron-sized grains at the cavity edge. Here we present a generic disk model that can simultaneously account for the general features in IRS, SMA, and Subaru observations. Particularly, the scattered light images for this model are computed, which agree with the general trend seen in Subaru data. Decoupling between the spatial distributions of the micron-sized dust and mm-sized dust inside the cavity is suggested by the model, which, if confirmed, necessitates a mechanism, such as dust filtration, for differentiating the small and big dust in the cavity clearing process. Our model also suggests an inwardly increasing gas-to-dust-ratio in the inner disk, and different spatial distributions for the small dust inside and outside the cavity, echoing the predictions in grain coagulation and growth models., 41 pages (single column), 1 table, 10 figures, ApJ accepted

GJ 758 B is a cold (~600K) companion to a Sun-like star at 29 AU projected separation, which was recently detected with high-contrast imaging. Here we present photometry of the companion in seven photometric bands from Subaru/HiCIAO, Gemini/NIRI and Keck/NIRC2, providing a rich sampling of the spectral energy distribution in the 1-5 micron wavelength range. A clear detection at 1.58 micron combined with an upper limit at 1.69 micron shows methane absorption in the atmosphere of the companion. The mass of the companion remains uncertain, but an updated age estimate indicates that the most likely mass range is ~30-40 Mjup. In addition, we present an updated astrometric analysis that imposes tighter constraints on GJ 758 B's orbit and identifies the proposed second candidate companion, "GJ 758 C", as a background star., Comment: 10 pages, 4 figures, accepted for publication in ApJ Letters. New version: Corrected a few numbers in the astrometry section (which were already correct in the print version, but were based on an outdated simulation in the astro-ph version)

We present H- and Ks-band imaging data resolving the gap in the transitional disk around LkCa 15, revealing the surrounding nebulosity. We detect sharp elliptical contours delimiting the nebulosity on the inside as well as the outside, consistent with the shape, size, ellipticity, and orientation of starlight reflected from the far-side disk wall, whereas the near-side wall is shielded from view by the disk's optically thick bulk. We note that forward-scattering of starlight on the near-side disk surface could provide an alternate interpretation of the nebulosity. In either case, this discovery provides confirmation of the disk geometry that has been proposed to explain the spectral energy distributions (SED) of such systems, comprising an optically thick outer disk with an inner truncation radius of ~46 AU enclosing a largely evacuated gap. Our data show an offset of the nebulosity contours along the major axis, likely corresponding to a physical pericenter offset of the disk gap. This reinforces the leading theory that dynamical clearing by at least one orbiting body is the cause of the gap. Based on evolutionary models, our high-contrast imagery imposes an upper limit of 21 Jupiter masses on companions at separations outside of 0.1" and of 13 Jupiter masses outside of 0.2". Thus, we find that a planetary system around LkCa 15 is the most likely explanation for the disk architecture., Comment: 5 pages, 4 figures, accepted for publication in ApJ Letters. Minor change to Figure 4

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.

HiCIAO (the High‐Contrast Instrument with Adaptive Optics) is a high‐contrast instrument for the 8.2‐meter Subaru Telescope. The instrument is a near‐infrared camera which benefits from a new adaptive optics (AO) system on the Subaru Telescope (AO188). The instrument realizes the high contrast with a help of AO188, a classical Lyot coronagraph, and three differential imaging techniques (polarimetric, spectral, and angular). Besides the differential imaging modes, HiCIAO also offers a normal imaging mode which covers 20″×20″ FOV with 0.″01 pixel−1 resolution, and a pupil viewing mode for a precise alignment of the Lyot stop on the pupil image. The expected contrasts are 105.5 at 1.″0 separation and 104 at 0.″1 separation from a central star in the spectral differential imaging mode. The instrument is currently in its commissioning phase after the first‐light observation in December 2008. This paper is an introductory review of the instrument.

We present the discovery of a brown dwarf or possible planet at a projected separation of 1.9" = 29 AU around the star GJ 758, placing it between the separations at which substellar companions are expected to form by core accretion (~5 AU) or direct gravitational collapse (typically >100 AU). The object was detected by direct imaging of its thermal glow with Subaru/HiCIAO. At 10-40 times the mass of Jupiter and a temperature of 550-640 K, GJ 758 B constitutes one of the few known T-type companions, and the coldest ever to be imaged in thermal light around a Sun-like star. Its orbit is likely eccentric and of a size comparable to Pluto's orbit, possibly as a result of gravitational scattering or outward migration. A candidate second companion is detected at 1.2" at one epoch., 5 pages, 3 figures, 2 tables. Accepted for publication in ApJ Letters

The High-Contrast Coronographic Imager for Adaptive Optics (HiCIAO), is a coronographic simultaneous differential imager for the new 188-actuator AO system at the Subaru Telescope Nasmyth focus. It is designed primarily to search for faint companions, brown dwarves and young giant planets around nearby stars, but will also allow observations of disks around young stars and of emission line regions near other bright central sources. HiCIAO will work in conjunction with the new Subaru Telescope 188-actuator adaptive optics system. It is designed as a flexible, experimental instrument that will grow from the initial, simple coronographic system into more complex, innovative optics as these technologies become available. The main component of HiCIAO is an infrared camera optimized for spectral simultaneous differential imaging that uses a Teledyne 2.5 μm HAWAII-2RG detector array operated by a Sidecar ASIC. This paper reports on the assembly, testing, and "first light" observations at the Subaru Telescope.

We have upgraded the 60-cm radio survey telescope located in Nobeyama, Japan. We developed a new waveguide-type sideband-separating SIS mixer for the telescope, which enables the simultaneous detection of distinct molecular emission lines both in the upper and lower sidebands. Over the RF frequency range of 205-240 GHz, the single-sideband receiver noise temperatures of the new mixer are 40-100 K for the 4.0-8.0 GHz IF frequency band. The image rejection ratios are greater than 10 dB over the same range. For the dual IF signals obtained by the receiver, we have developed two sets of acousto-optical spectrometers and a telescope control system. Using the new telescope system, we successfully detected the 12CO (J=2-1) and 13CO (J=2-1) emission lines simultaneously toward Orion KL in 2005 March. Using the waveguide-type sideband-separating SIS mixer for the 200 GHz band, we have initiated the first simultaneous 12CO (J=2-1) and 13CO (J=2-1) survey of the galactic plane as well as large-scale mapping observations of nearby molecular clouds., Comment: 15 pages, 15 figures, Accepted for publication in PASJ, version with high resolution figures is available via http://www.nro.nao.ac.jp/~nakajima/vst1_2sb.pdf

Coronagraphic imagery of the circumstellar disk around HD 169142 in H-band polarized intensity (PI) with Subaru/HiCIAO is presented. The emission scattered by dust particles at the disk surface in 0.2", 26 pages, 7 figures, accepted for publication in PASJ

We present a new Subaru/HiCIAO high-contrast H-band polarized intensity (PI) image of a nearby transitional disk associated with TW Hydrae. The scattered light from the disk was detected from 0.2" to 1.5" (11 - 81 AU) and the PI image shows a clear axisymmetric depression in polarized intensity at ~ 0.4" (~ 20 AU) from the central star, similar to the ~ 80 AU gap previously reported from HST images. Azimuthal polarized intensity profile also shows the disk beyond 0.2" is almost axisymmetric. We discuss two possible scenarios explaining the origin of the polarized intensity depression: 1) a gap structure may exist at ~ 20 AU from the central star because of shallow slope seen in the polarized intensity profile, and 2) grain growth may be occurring in the inner region of the disk. Multi-band observations at NIR and millimeter/sub-millimeter wavelengths play a complementary role in investigating dust opacity and may help reveal the origin of the gap more precisely., 8 pages, 2 figures, ApJL accepted for publication

Direct exploration of exoplanets is one of the most exciting topics in astronomy. Our current efforts in this field are concentrated on the Subaru 8.2m telescope at Mauna Kea, Hawaii. Making use of the good observing site and the excellent image quality, the infrared coronagraph CIAO (Coronagraphic Imager with Adaptive Optics) has been used for various kinds of surveys, which is the first dedicated cold coronagraph on the 8-10m class telescopes. However, its contrast is limited by the low-order adaptive optics and a limited suppression of the halo speckle noise. HiCIAO is a new high-contrast instrument for the Subaru telescope. HiCIAO will be used in conjunction with the new adaptive optics system (188 actuators and/or its laser guide star - AO188/LGSAO188) at the Subaru infrared Nasmyth platform. It is designed as a flexible camera comprising several modules that can be configured into different modes of operation. The main modules are the AO module with its future extreme AO capability, the warm coronagraph module, and the cold infrared camera module. HiCIAO can combine coronagraphic techniques with either polarization or spectral simultaneous differential imaging modes. The basic concept of such differential imaging is to split up the image into two or more images, and then use either different planes of polarization or different spectral filter band-passes to produce a signal that distinguishes faint objects near a bright central object from scattered halo or residual speckles. In this contribution, we will outline the HiCIAO instrument, its science, and performance simulations. The optical and mechanical details are described by Hodapp et al. (2006)1. We also present a roadmap of Japanese facilities and future plans, including ASTRO-F (AKARI), SPICA, and JTPF, for extrasolar planet explorations.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The infrared source IRc2 (ref. 1) in the star-forming region Orion-KL is generally believed to contain a massive and very young star2. Its nature and evolutionary status, however, are difficult to determine because it is hidden from direct view by a dense disk-like envelope of gas and dust. Here we report observations of infrared radiation (at a wavelength of about 2 μm) that has escaped the surrounding dust in the polar direction, perpendicular to the plane of the disk, and then been reflected towards us by dust farther away from the star. The reflected spectrum contains absorption lines of neutral metallic atoms and carbon monoxide, which we interpret as indicating a source temperature of about 4,500 K. But, given the luminosity of the source, its radius must be at least 300 solar radii—too large to be attained with the modest gas-accretion rates in existing theories of massive-star formation. Whether the infrared radiation is coming from the protostar itself or the self-luminous accretion disk around it, the accretion rate must be around (5–15) × 10−3 solar masses per year, at least two orders of magnitude greater than is commonly assumed in models of star formation.

著者人数: 58名, Accepted: 2014-01-16, 資料番号: SA1004554000

Debris disks around young main-sequence stars often have gaps and cavities which for a long time have been interpreted as possibly being caused by planets. In recent years, several giant planet discoveries have been made in systems hosting disks of precisely this nature, further implying that interactions with planets could be a common cause of such disk structures. As part of the SEEDS high-contrast imaging survey, we are surveying a population of debris disk-hosting stars with gaps and cavities implied by their spectral energy distributions, in order to attempt to spatially resolve the disk as well as to detect any planets that may be responsible for the disk structure. Here we report on intermediate results from this survey. Five debris disks have been spatially resolved, and a number of faint point sources have been discovered, most of which have been tested for common proper motion, which in each case has excluded physical companionship with the target stars. From the detection limits of the 50 targets that have been observed, we find that beta Pic b-like planets (~10 Mjup planets around G--A-type stars) near the gap edges are less frequent than 15--30%, implying that if giant planets are the dominant cause of these wide (27 AU on average) gaps, they are generally less massive than beta Pic b., 17 pages, 9 figures, accepted for publication in ApJ

We present Subaru/HiCIAO H-band high-contrast images of the debris disk around HIP 79977, whose pres- ence was recently inferred from an infrared excess. Our images resolve the disk for the first time, allowing characterization of its shape, size, and dust grain properties. We use angular differential imaging (ADI) to reveal the disk geometry in unpolarized light out to a radius of ~2", as well as polarized differential imaging (PDI) to measure the degree of scattering polarization out to ~1.5". In order to strike a favorable balance between suppression of the stellar halo and conservation of disk flux, we explore the application of principal component analysis (PCA) to both ADI and reference star subtraction. This allows accurate forward modeling of the effects of data reduction on simulated disk images, and thus direct comparison with the imaged disk. The resulting best-fit values and well-fitting intervals for the model parameters are a surface brightness power-law slope of S_out = -3.2 [-3.6,-2.9], an inclination of i = 84{\deg} [81{\deg},86{\deg}], a high Henyey-Greenstein forward-scattering parameter of g = 0.45 [0.35, 0.60], and a non-significant disk-star offset of u = 3.0 [-1.5, 7.5] AU = 24 [-13, 61] mas along the line of nodes. Furthermore, the tangential linear polarization along the disk rises from ~10% at 0.5" to ~45% at 1.5". These measurements paint a consistent picture of a disk of dust grains produced by collisional cascades and blown out to larger radii by stellar radiation pressure., Comment: 6 pages, 4 figures, 1 table. Accepted for publication in ApJ Letters

We describe Algorithms for Calibration, Optimized Registration, and Nulling the Star in Angular Differential Imaging (ACORNS-ADI), a new, parallelized software package to reduce high-contrast imaging data, and its application to data from the SEEDS survey. We implement several new algorithms, including a method to register saturated images, a trimmed mean for combining an image sequence that reduces noise by up to ~20%, and a robust and computationally fast method to compute the sensitivity of a high-contrast observation everywhere on the field-of-view without introducing artificial sources. We also include a description of image processing steps to remove electronic artifacts specific to Hawaii2-RG detectors like the one used for SEEDS, and a detailed analysis of the Locally Optimized Combination of Images (LOCI) algorithm commonly used to reduce high-contrast imaging data. ACORNS-ADI is written in python. It is efficient and open-source, and includes several optional features which may improve performance on data from other instruments. ACORNS-ADI requires minimal modification to reduce data from instruments other than HiCIAO. It is freely available for download at www.github.com/t-brandt/acorns-adi under a BSD license., Comment: 15 pages, 9 figures, accepted to ApJ. Replaced with accepted version; mostly minor changes. Software updated

We performed 12CO(J = 2 − 1) and 13CO(J = 2 − 1) line surveys of the galactic plane using the AMANOGAWA telescope (Nakajima et al. 2007) which covers 5° ≤ l ≤ 180° on a 7'.5 grid. The telescope beamsize and velocity resolution are 8.7′ ± 0.4′ and 1.3 km s−1. The resultant rms noise level is typically 0.12 K in TA*. We found a linear correlation between 12CO(J = 2 − 1) and 12CO(J = 1 − 0) and a curved correlation between 12CO(J = 2 − 1) and 13CO (J = 2 − 1), although the intensity ratios of these three lines have intrinsic variation. These correlations can be reproduced with simple radiative transfer equations suggesting some restrictions on the physical quantities of molecular gas on a galactic scale.

We present high-resolution, H-band, imaging observations, collected with Subaru/HiCIAO, of the scattered light from the transitional disk around SAO 206462 (HD 135344B). Although previous sub-mm imagery suggested the existence of the dust-depleted cavity at r~46AU, our observations reveal the presence of scattered light components as close as 0.2" (~28AU) from the star. Moreover, we have discovered two small-scale spiral structures lying within 0.5" (~70AU). We present models for the spiral structures using the spiral density wave theory, and derive a disk aspect ratio of h~0.1, which is consistent with previous sub-mm observations. This model can potentially give estimates of the temperature and rotation profiles of the disk based on dynamical processes, independently from sub-mm observations. It also predicts the evolution of the spiral structures, which can be observable on timescales of 10-20 years, providing conclusive tests of the model. While we cannot uniquely identify the origin of these spirals, planets embedded in the disk may be capable of exciting the observed morphology. Assuming that this is the case, we can make predictions on the locations and, possibly, the masses of the unseen planets. Such planets may be detected by future multi-wavelengths observations., Comment: 8 pages, 5 figures, ApJL in press, typo corrected

To address its temperature and density we made observations of the galactic plane in CO (2-1) line with VST1 and VST2. Using a kinetic model we estimate the volume emissivities and the line intensity ratio as a function of galactocentric radius. Using data in the first and 4th quadrants separately we got shallow gradient in the both quadrants; at the smaller radius is the higher in ratio. The gradient is contributed by less bright pixels in the l-v diagram, suggesting molecular gas in interarm is different along the galactocentric radius but in arm is not.

We present high-contrast images of HR 4796 A taken with Subaru/HiCIAO in H-band, resolving the debris disk in scattered light. The application of specialized angular differential imaging methods (ADI) allows us to trace the inner edge of the disk with high precision, and reveals a pair of "streamers" extending radially outwards from the ansae. Using a simple disk model with a power-law surface brightness profile, we demonstrate that the observed streamers can be understood as part of the smoothly tapered outer boundary of the debris disk, which is most visible at the ansae. Our observations are consistent with the expected result of a narrow planetesimal ring being ground up in a collisional cascade, yielding dust with a wide range of grain sizes. Radiation forces leave large grains in the ring and push smaller grains onto elliptical, or even hyperbolic trajectories. We measure and characterize the disk's surface brightness profile, and confirm the previously suspected offset of the disk's center from the star's position along the ring's major axis. Furthermore, we present first evidence for an offset along the minor axis. Such offsets are commonly viewed as signposts for the presence of unseen planets within a disk's cavity. Our images also offer new constraints on the presence of companions down to the planetary mass regime (~9 Jupiter masses at 0.5", ~3 Jupiter masses at 1")., Comment: 6 pages, 4 figures, 1 table; accepted for publication in ApJ Letters

We analyze the kinematic histories of stars within 30 pc of the Sun, for which three-dimensional spatial coordinates and three-dimensional velocity vectors are available. From this sample, we extract members of stellar kinematic groups (SKGs) in the following manner. First, we consider in the three-dimensional velocity space centered on the local standard of rest, a sphere with a radius of 8 km s–1 centered on the mean velocity vector of a particular SKG. Around each SKG velocity center, we have found a significant excess of stars compared to background field stars. For each candidate, in the three-dimensional spatial coordinate space, its trajectory is traced back in time by the age of the relevant SKG to obtain the estimated distance from the SKG center at the time of the SKG's birth by the epicyclic approximation and harmonic vertical motion. It often happens that a star is a candidate member of multiple SKGs. Then we rank the candidacy to multiple SKGs based on the smallness of distance separations. In this manner, we have kinematically selected 238 candidates. We further impose at least one of the following qualitative criteria for being a member: spectral type A or B, variability, or EUV and X-ray emission. We have finally selected 137 candidate members of SKGs out of a sample of 966 stars.

We are conducting a survey of the CO J=2-1 line emission in the southern Milky Way (the Tokyo-Onsala-ESO-Calán Galactic CO survey), using the 60-cm radio telescope (VST2) in La Silla, Chile. It is combined with the northern survey made with the identical telescope (VST1) at Nobeyama (e.g., Sakamoto et al. 1995), and is directly comparable with the Columbia survey of the CO J=1-0 emission (e.g., Dame et al. 1987).

Because of their large numbers, red dwarfs may be the most abundant planet hosts in our Galaxy. In order to detect Earth-like planets around nearby red dwarfs (in particular late-M stars), it is crucial to conduct the precise radial velocity (RV) measurements at near-infrared wavelengths where these stars emit most of light. We report the development of the Infrared Doppler (IRD) spectrometer for the Subaru telescope. IRD is a fiber-fed, high-precision, near infrared spectrometer with a spectral resolution of R∼70,000 covering from 0.97 to 1.75 µm. To achieve 1m/s RV measurement precision, we employ our original laser frequency comb of a wide-wavelength coverage as an extremely stable wavelength standard in the near-infrared. The spectrometer optics is composed of a new wide-pitch Echelle-grating and Volume-Phase Holographic gratings. To achieve ultimate thermal stability, very low thermal expansion ceramic is used for most of the optical components including the optical bench. The spectrometer will utilize a 4096×4096-pixel HgCdTe array.