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(TOP) Near-Infrared composite color image of L1551 NE observed with SUBARU (Hayashi & Pyo 2009). The blue, green, and red colors are assigned to the H, [Fe II], and H2 filter frames, respectively. (Bottom) Moment 0 (white contours) and Moment 1 maps (color scale) of the 13CO (J=3-2) (Left) and C18O (J=3-2) lines (Right) in L1551 NE observed with the SMA. Contour levels are from 2σ in steps of 4σ (1σ = 0.189 Jy beam-1 km s-1) in the 13CO moment 0 map and 2σ in steps of 2σ (1σ = 0.173 Jy beam-1 km s-1) in the C18O moment 0 map. Crosses indicate the positions of the protobinary, and filled ellipses at the bottom-right corners the synthesized beam. Blue and red arrows show the direction of the blueshifted and redshifted [Fe II] jets driven by Source A. The submillimeter circumbinary features show clear velocity gradients along the major axis, and furthermore, the observed velocity gradients can be well-reproduced by a geometrically-thin Keplerian Disk with the central mass of 0.8 Msolar.

High angular-resolution SMA observations can unveil kinematics of disks around protostellar sources. Here we present results of SMA observations of L1551 NE, a prototypical Class I binary protostellar system, in the submillimeter 13CO and C18O (J=3-2) lines at a sub-arcsecond resolution (~0.95×0.66 arcsec; P.A. =-88 deg). The south-eastern binary companion (Source A) drives spectacular collimated near-infrared jets. The submillimeter 13CO and C18O emission show ~600 AU, Keplerian-rotating circumbinary features elongated approximately perpendicular to the jets. These results present firm evidence that Keplerian disks around binary protostellar systems, "Keplerian circumbinary disks", can exist. (Takakuwa et al. 2012, ApJ, in press.)