Miki Ishii

National Astronomical Observatory of Japan

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Motohide Tamura

The University of Tokyo

179

Tomonori Usuda

National Astronomical Observatory of Japan

168

Tomoyuki Kudo

National Astronomical Observatory of Japan

Hiroshi Suto

Japan Aerospace Exploration Agency

Tae‐Soo Pyo

National Astronomical Observatory of Japan

Masahiko Hayashi

National Astronomical Observatory of Japan

Saeko S. Hayashi

National Astronomical Observatory of Japan

Jun Hashimoto

The Graduate University for Advanced Studies, SOKENDAI

Masayuki Kuzuhara

National Astronomical Observatory of Japan

Ryo Kandori

Astrobiology Center

Cooperative Institutions

National Astronomical Observatory of Japan

200

The University of Tokyo

124

National Institutes of Natural Sciences

100

Nagoya University

Max Planck Institute for Astronomy

Japan Aerospace Exploration Agency

Max Planck Society

Institute of Space and Astronautical Science

The Graduate University for Advanced Studies, SOKENDAI

Osaka University

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Selection of Nearby Star Targets for the Subaru Strategic Exploration of Exoplanets and Disks

AIP conference proceedings (2009)

Ryo Kandori Motohide Tamura Jun‐Ichi Morino Miki Ishii Ryuji Suzuki

SEEDS (the Subaru Strategic Exploration of Exoplanets and Disks with Hi‐CIAO/AO188) is a strategic five‐year campaign of direct imaging surveys of exoplanets/disks using the Subaru telescope equipped with the new adaptive optics system AO188 and our new high‐contrast instrument, HiCIAO. The goals of the survey are to address the following key issues in exoplanet/disk sciences: (1) the detection and census of exoplanets; (2) the evolution of protoplanetary and debris disks; and (3) the link between exoplanets and disks. Targets prepared for the SEEDS exoplanet searches are in four categories, including nearby stars. We present our scientific motivations and current status of the SEEDS target selection in the nearby stars category.

Subaru Telescope

Direct imaging

Optical telescope

10.1063/1.3215857

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Subaru Near-Infrared Multicolor Images of Class II Young Stellar Object, RNO 91

Publications of the Astronomical Society of Japan (2007)

Satoshi Mayama Motohide Tamura Masahiko Hayashi Yoichi Itoh Miki Ishii

We conducted sub-arcsecond near-infrared imaging observations of RNO91 with CIAO mounted on the SUBARU 8.2 m telescope. We present our JHK band data along with optical images, which when considered together reveal a complex circumstellar structure. We examined the colors of associated nebula and compared the geometry of the outflow/disk system suggested by our data with that already proposed on the basis of previous studies. Our K-band image shows bright circumstellar nebulosity detected within 2"(300AU) around the central source while it is less conspicuous at shorter wavelengths such as J and optical. P.A. and size of this red color nebulosity in our H-K color image agree with those of the previously detected polarization disk. These data agreement indicate that this bright circumstellar nebulosity region which follows the reddening law might be attributed to a disk-like structure. At J and optical wavelengths, several blue knot-like structures are detected around and beyond the bright circumstellar nebulosity. We suggest that these knotty reflection nebulae may represent disintegrating fragments of an infalling envelope. The three-color composite image has an appearance of arc-shaped nebulosity extending to the north and to the east through the central source. On the other end of this arc-shaped structure, the nebula appears to become more extended (2."3 long) to the southwest. We interpret these structures as roots of bipolar cavities opening to the northeast and southwest. The complex distribution of reflection nebulosity seen around RNO91 appears to confirm the interpretation of this source as an object dispersing its molecular envelope while transitioning from protostar to T Tauri star.

Subaru Telescope

Young stellar object

10.1093/pasj/59.6.1153

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Exoplanet Search Via Gravitational Microlensing

AIP conference proceedings (2009)

T. Sumi Tomonori Usuda Motohide Tamura Miki Ishii

We review the recent results of the exoplanet search via gravitational microlensing. The microlensing technique is unique and complementary to other methods because it does not rely on the light from the primary. Microlensing is sensitive to small‐size planets down to those of Earth mass around dim M‐dwarfs. Planets with large semi‐major axes more distant than the snow line can also be detected instantaneously without waiting for one orbital period to elapse. Most significantly, distant planetary systems as far as out as the galactic bulge can be probed, which helps us understand the galactic distribution of the planetary systems. We present the current status of the observations focusing on the survey by Microlensing Observation in Astrophysics (MOA) collaboration and summarize the features of the detected planetary systems.

Gravitational microlensing

Snow line

10.1063/1.3215851

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The Detection of a Large-mass Planet Around a K0 IV Subgiant With an Almost-circular Orbit

AIP conference proceedings (2009)

Hiroki Harakawa Bun’ei Sato Debra A. Fischer Shigeru Ida Masashi Omiya

We report the detection of a new large‐mass planet orbiting around a K0 IV(V = 8.26) star which has a minimum mass Mpsin i = 10.70±0.50 MJup in a 696.0±2.6‐day orbit. It was detected in precise radial velocity (RV) measurements from Subaru and Keck. The derived orbital parameters, based on a ϰ2 which minimized by Downhill Simplex algorithm, suggests that these radial velocity variations are consistent with an almost circular planetary orbit and a Mars‐like semimajor axis(e∼0.0, a = 1.70±0.03 AU). Extra‐solar planets that have several times the mass of Jupiter orbiting in periods of hundreds or thousands of days, with very low eccentricities(e<0.1), are rare discoveries. Our detection presents a new sample of these circular orbit massive planets.

Subgiant

Circular orbit

Radial velocity

Orbit (dynamics)

Minimum mass

Jupiter mass

10.1063/1.3215854

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A Short Guide to Debris Disk Spectroscopy

AIP conference proceedings (2009)

Christine Chen Tomonori Usuda Motohide Tamura Miki Ishii

Multi-wavelength spectroscopy can be used to constrain the dust and gas properties in debris disks. Circumstellar dust absorbs and scatters incident stellar light. The scattered light is sometimes resolved spatially at visual and near-infrared wavelengths using high contrast imaging techniques that suppress light from the central star. The thermal emission is inferred from infrared through submillimeter excess emission that may be 1-2 orders of magnitude brighter than the stellar photosphere alone. If the disk is not spatially resolved, then the radial distribution of the dust can be inferred from Spectral Energy Distribution (SED) modeling. If the grains are sufficiently small and warm, then their composition can be determined from mid-infrared spectroscopy. Otherwise, their composition may be determined from reflectance and/or far-infrared spectroscopy. Atomic and molecular gas absorb and resonantly scatter stellar light. Since the gas is believed to be secondary, detailed analysis analysis of the gas distribution, kinematics, and composition may also shed light on the dust composition and processing history.

Spectral energy distribution

Photosphere

10.1063/1.3215921

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A Search for T Tauri Stars toward Dense Cores

AIP conference proceedings (2009)

Koji Sugitani Makoto Watanabe Tomonori Usuda Motohide Tamura Miki Ishii

We have been conducting a systematic search for T Tauri stars toward optically selected dense cores with the Wide Field Grism Spectrograph 2 (WFGS2) on the University of Hawaii 2.2‐m telescope. These T Tauri stars would be unbiased samples for future studies of the protoplanetary disk and exoplanets. Here we present the preliminary results of our search.

Grism

10.1063/1.3215864

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Near-infrared imaging polarimetry of LkCa 15: A possible warped inner disk

Publications of the Astronomical Society of Japan (2016)

Daehyeon Oh Jun Hashimoto Motohide Tamura John P. Wisniewski Eiji Akiyama

Abstract We present high-contrast H-band polarized intensity images of the transitional disk around the young solar-like star LkCa 15. By utilizing Subaru/HiCIAO for polarimetric differential imaging, the angular resolution and the inner working angle reach 0${^{\prime\prime}_{.}}$07 and r = 0${^{\prime\prime}_{.}}$1, respectively. We obtained a clearly resolved gap (width ≲ 27 au) at ∼48 au from the central star. This gap is consistent with images reported in previous studies. We also confirmed the existence of a bright inner disk with a misaligned position angle of 13° ± 4° with respect to that of the outer disk, i.e., the inner disk is possibly warped. The large gap and the warped inner disk both point to the existence of a multiple planetary system with a mass of ≲ 1 MJup.

Debris disk

Position angle

10.1093/pasj/psv133

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Citations (19)

High-resolution Near-infrared Polarimetry and Submillimeter Imaging of FS Tau A: Possible Streamers in Misaligned Circumbinary Disk System

The Astrophysical Journal (2020)

Yi Yang Eiji Akiyama Thayne Currie Ruobing Dong Jun Hashimoto

We analyzed the young (2.8-Myr-old) binary system FS Tau A using near-infrared (H-band) high-contrast polarimetry data from Subaru/HiCIAO and sub-millimeter CO (J=2-1) line emission data from ALMA. Both the near-infrared and sub-millimeter observations reveal several clear structures extending to $\sim$240 AU from the stars. Based on these observations at different wavelengths, we report the following discoveries. One arm-like structure detected in the near-infrared band initially extends from the south of the binary with a subsequent turn to the northeast, corresponding to two bar-like structures detected in ALMA observations with an LSRK velocity of 1.19-5.64 km/s. Another feature detected in the near-infrared band extends initially from the north of the binary, relating to an arm-like structure detected in ALMA observations with an LSRK velocity of 8.17-16.43 km/s. From their shapes and velocities, we suggest that these structures can mostly be explained by two streamers that connect the outer circumbinary disk and the central binary components. These discoveries will be helpful for understanding the evolution of streamers and circumstellar disks in young binary systems.

Circumbinary planet

Circumstellar disk

10.3847/1538-4357/ab64f9

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Subarcsecond Near-Infrared Images of Massive Star Formation Region NGC 6334 V

Publications of the Astronomical Society of Japan (2007)

Jun Hashimoto Motohide Tamura Hiroshi Suto L. Abe Miki Ishii

Abstract We present high spatial resolution (0$\rlap{.}^{\prime\prime}3$) polarimetric images in the $H$ and $K$ bands and direct images in the $L'$ and $M'$ bands of the NGC 6334 V infrared nebulae. The images show complex structures including the multishells and various knots in the nebulae. The appearances and colors of the eastern and western nebulae differ considerably. Our polarization images also show differences between the illuminating sources of the nebulae: the eastern nebula is illuminated by a deeply embedded mid-infrared source, KDJ 4, and the western nebula by our newly detected near-infrared source, WN-A1. The degree of polarization of the nebulae is very large, up to 70% at $K$ and 60% at $H$, which is consistent with a single scattering of near-infrared radiation from each source at the walls of the mass outflows.

10.1093/pasj/59.1.221

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Citations (14)

Gas Accretion Rate onto a Protoplanet during the Stage of Runaway Gas Accretion

AIP conference proceedings (2009)

Yasunori Hori Masahiro Ikoma Shigeru Ida Tomonori Usuda Motohide Tamura

Interior models suggest that transiting giant extrasolar planets have a significant difference in the amount of heavy elements, including their solid cores. This divergence may have originated from planetesimals accreted onto a protoplanet during the stage of runaway gas accretion. Recent work suggests the rate of planetesimals accreted onto a protoplanet depends strongly on the rate of gas accretion. We have calculated the evolution of a protoplanet by using a one‐dimensional quasi‐static model and investigated gas accretion rates onto a protoplanet during runaway gas accretion. We have also examined the effects of changing the equation of state for gas, grain opacity, and an initial core mass on the results. After the onset of runaway gas accretion, the magnitude of gas accretion rates was strongly dependent on the three factors, but the dependence of gas accretion rates on planetary mass was not affected by them.

Protoplanet

Gas giant

Opacity

Giant planet

10.1063/1.3215856

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