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Scientific Highlights with the SMA

Transition from the Infalling Envelope to the Keplerian Disk around L1551 IRS 5

A Class I protostellar binary L1551 IRS 5 was observed with the SMA in the 343 GHz dust continuum and the CS (J = 7-6) line at a sub-arcsecond (~0.7 arcsec) resolution. The continuum image (gray scale in the figure below) shows an elongated feature along northwest-southeast direction (160 x 80 AU), perpendicular to the associated radio jets. The combined SMA+ASTE images show that the high-velocity CS emission (≳1.5 km/s; left panel of the figure) traces the continuum feature, and exhibits a velocity gradient along the major axis, which is reproduced by a Keplerian-disk model with a central stellar mass of ~0.5 M☉. On the other hand, the low-velocity CS emission (right panel) shows an extended feature that exhibits south (blueshifted) to north (redshifted) emission offsets, which is modeled with a rotating and infalling envelope with a conserved angular momentum. The inferred infalling velocity is ~three times lower than the free-fall velocity toward the central stellar mass of 0.5 M , while the rotational motion of the envelope connects smoothly to the inner Keplerian rotation at a radius of ~64 AU. These results demonstrate a transition from the infalling envelope to the Keplerian disk around the protostellar binary system. (Chou et al. 2014, ApJ, 796, 70 ADS )


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