Nobuhiko Kusakabe

Direct Imaging of a Cold Jovian Exoplanet in Orbit around the Sun-like Star GJ 504

Several exoplanets have recently been imaged at wide separations of >10?AU from their parent stars. These span a limited range of ages ( 0.5?mag), implying thick cloud covers. Furthermore, substantial model uncertainties exist at these young ages due to the unknown initial conditions at formation, which can lead to an order of magnitude of uncertainty in the modeled planet mass. Here, we report the direct-imaging discovery of a Jovian exoplanet around the Sun-like star GJ 504, detected as part of the SEEDS survey. The system is older than all other known directly imaged planets; as a result, its estimated mass remains in the planetary regime independent of uncertainties related to choices of initial conditions in the exoplanet modeling. Using the most common exoplanet cooling model, and given the system age of 160?Myr, GJ 504b has an estimated mass of 4 Jupiter masses, among the lowest of directly imaged planets. Its projected separation of 43.5?AU exceeds the typical outer boundary of ~30?AU predicted for the core accretion mechanism. GJ 504b is also significantly cooler (510 K) and has a bluer color (J ? H = ?0.23?mag) than previously imaged exoplanets, suggesting a largely cloud-free atmosphere accessible to spectroscopic characterization. Thus, it has the potential of providing novel insights into the origins of giant planets as well as their atmospheric properties.

INTERSTELLAR EXTINCTION LAW IN THE J, H, AND Ks BANDS TOWARD THE GALACTIC CENTER

We have determined the ratios of total to selective extinction in the near-infrared bands (J,H,Ks) toward the Galactic center from the observations of the region l 20 and 05 b 10 with the IRSF telescope and the SIRIUS camera. Using the positions of red clump stars in color-magnitude diagrams as a tracer of the extinction and reddening, we determine the average of the ratios of total to selective extinction to be A/E = 1.44 ± 0.01, A/E = 0.494 ± 0.006, and AH/EJ-H = 1.42 ± 0.02, which are significantly smaller than those obtained in previous studies. From these ratios, we estimate that AJ : AH : A = 1 : 0.573 ± 0.009 : 0.331 ± 0.004 and EJ-H/E = 1.72 ± 0.04, and we find that the power law Aλ ∝ λ-1.99±0.02 is a good approximation over these wavelengths. Moreover, we find a small variation in A/E across our survey. This suggests that the infrared extinction law changes from one line of sight to another, and the so-called universality does not necessarily hold in the infrared wavelengths.

Direct Imaging of Fine Structures in Giant Planet Forming Regions of the Protoplanetary Disk around AB Aurigae

We report high-resolution 1.6 μm polarized intensity (PI) images of the circumstellar disk around the Herbig Ae star AB Aur at a radial distance of 22 AU (015) up to 554 AU (385), which have been obtained by the high-contrast instrument HiCIAO with the dual-beam polarimetry. We revealed complicated and asymmetrical structures in the inner part (140 AU) of the disk while confirming the previously reported outer (r 200 AU) spiral structure. We have imaged a double ring structure at ~40 and ~100 AU and a ring-like gap between the two. We found a significant discrepancy of inclination angles between two rings, which may indicate that the disk of AB Aur is warped. Furthermore, we found seven dips (the typical size is ~45 AU or less) within two rings, as well as three prominent PI peaks at ~40 AU. The observed structures, including a bumpy double ring, a ring-like gap, and a warped disk in the innermost regions, provide essential information for understanding the formation mechanism of recently detected wide-orbit (r > 20 AU) planets.

Discovery of the Coldest Imaged Companion of a Sun-like Star

We present the discovery of a brown dwarf or possible planet at a projected separation of 19 = 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 Plutos orbit, possibly as a result of gravitational scattering or outward migration. A candidate second companion is detected at 12 at one epoch.

The Missing Cavities in the SEEDS Polarized Scattered Light Images of Transitional Protoplanetary Disks: A Generic Disk Model

Transitional circumstellar disks around young stellar objects have a distinctive infrared deficit around 10 μm in their spectral energy distributions, 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 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 μm-sized grains, with little discontinuity in the surface density of the μm-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 μm-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.

Subaru imaging of asymmetric features in a transitional disk in upper Scorpius

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

A Distinct Structure inside the Galactic Bar

H

New Techniques for High-contrast Imaging with ADI: The ACORNS-ADI SEEDS Data Reduction Pipeline

-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

The SEEDS Direct Imaging Survey for Planets and Scattered Dust Emission in Debris Disk Systems

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Performance characterization of the HiCIAO instrument for the Subaru Telescope

, respectively. The disk is asymmetric, with one dip located at P.A.s of