ALMA Observation of a Prototypical Protostellar Binary System L1551 NE - Keplerian Cirsumbinary Disk and Accretion Streams
Formation of binary star is one of the fundamental mechanisms which determine IMF etc. However, this formation mechanism is poorly understood, because there is no observation of binary accretion with sufficiently high resolution and sensitivity in the main accretion phase. In this talk, we show ALMA Band 7 results of L1551NE, a Class I protostellar binary in Taurus with a projection separation of 73AU, in the 0.9mm continuum and C18O(3-2) line emission. Our previous SMA C18O(3-2) observation of L1551NE showed presence of Keplerian circumbinary disk of r $\sim$ 300AU with the central dynamical mass of 0.8 Msun and showed presence of an infalling envelope around the disk (r > 300AU). On the other hand, the kinematic structure between the cirumbinary disk and binary stars was still unclear. However, fortunately, our ALMA Cycle0 “filler” observation of L1551NE has been executed in November 2012. The ALMA image clearly resolves the structure of a circumbinary disk and a gap between cirumbinary disk and stellar disks. These kinematical structures well match with the results of numerical simulations quantitatively. Our ALMA result also shows the presence of accretion streams in the binary gap. This is the first observation of the accretion streams of proto-binary in the main accretion phase. We plan to determine the accretion rate onto each star and observe the mass flow between stars in ALMA Cycle2. Our ALMA observations will give valuable observational information about theoretical dispute of mass accretion rate between primary star and secondary star.