Direct Imaging Confirmation and Characterization of a Dust-Enshrouded Candidate Exoplanet Orbiting Fomalhaut

We present Subaru/IRCS J band data for Fomalhaut and a (re)reduction of archival 2004--2006 HST/ACS data first presented by Kalas et al. (2008). We confirm the existence of a candidate exoplanet, Fomalhaut b, in both the 2004 and 2006 F606W data sets at a high signal-to-noise. Additionally, we confirm the detection at F814W and present a new detection in F435W. Fomalhaut b's space motion may be consistent with it being in an apsidally-aligned, non debris ring-crossing orbit, although new astrometry is required for firmer conclusions. We cannot confirm that Fomalhaut b exhibits 0.7-0.8 mag variability cited as evidence for planet accretion or a semi-transient dust cloud. The new, combined optical SED and IR upper limits confirm that emission identifying Fomalhaut b originates from starlight scattered by small dust, but this dust is most likely associated with a massive body. The Subaru and IRAC/4.5 micron upper limits imply M < 2 Mj, still consistent with the range of Fomalhaut b masses needed to sculpt the disk. Fomalhaut b is very plausibly "a planet identified from direct imaging" even if current images of it do not, strictly speaking, show thermal emission from a directly imaged planet.Comment: 13 pages, 3 figures; ApJ Letters in press. Fixed one outdated reference and a few typo

First Two-Micron Imaging Polarimetry of Beta Pictoris

High-resolution K band imaging polarimetry of the beta Pic dust disk has been conducted with adaptive optics and a coronagraph using the Subaru 8.2-m telescope. Polarization of ~10 % is detected out to r ~ 120 AU with a centro-symmetric vector pattern around the central star, confirming that the disk is seen as an infrared reflection nebula. We have modeled our near-infrared and previous optical polarization results in terms of dust scattering in the disk and have found that both the degrees of polarization and the radial intensity profiles are well reproduced. We argue that the observed characteristics of the disk dust are consistent with the presence of ice-filled fluffy aggregates consisting of submicron grains in the beta Pic system. There is a gap around 100 AU in both the intensity and polarization profiles, which suggests a paucity of planetesimals in this region. The radial intensity profile also shows ripple-like structures, which are indicative of the presence of multiple planetesimal belts, as in the case of the M-type Vega-like star AU Mic.Comment: 18 pages, 6 figures, accepted for Jp

SUBARU Near-Infrared Multi-Color Images of Class II Young Stellar Object, RNO91

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.Comment: 18 pages, 6 figures, Accepted by Publications of the Astronomical Society of Japa

Possible Molecular Spiral Arms in the Protoplanetary Disk of AB Aur

The circumstellar dust disk of the Herbig Ae star AB Aur has been found to exhibit complex spiral-like structures in the near-IR image obtained with the Subaru Telescope. We present maps of the disk in both 12CO (3-2) and dust continuum at 345 GHz with the SMA at an angular resolution of 1.0"x0.7" (144AU x 100AU). The continuum emission traces a dust disk with a central depression and a maximum overall dimension of 450AU (FWHM). This dust disk exhibits several distinct peaks that appear to coincide with bright features in the near-IR image, in particular the brightest inner spiral arm. The CO emission traces a rotating gas disk of size 530AU x 330AU with a deprojected maximum velocity of 2.8km/s at 450AU. In contrast to the dust disk, the gas disk exhibits an intensity peak at the stellar position. Furthermore, the CO emission in several velocity channels traces the innermost spiral arm seen in the near-IR. We compare the observed spatial-kinematic structure of the CO emission to a simple model of a disk in Keplerian rotation, and find that only the emission tracing the main spiral arm clearly lies outside the confines of our model. This emission has a net outward radial motion compared with the radial velocity predicted by the model at the location of the main spiral arms. The disk of AB Aur is therefore quite different from the Keplerian disks seen around many Herbig Ae stars. The spiral-like structures of the disk with non-Keplerian motions we revealed in 12CO (3-2), together with the central depression of the dust disk, may be explained to be driven by the possible existence of a giant planet forming in the disk.Comment: 21 pages, 6 figures. Accepted by ApJ on Mar 14, 200