Spirals, Gas Motions, and their Differences among the Protostellar Binaries in the L1551 Region

We will report our latest ALMA results of the Class I protostellar binaries L1551 IRS 5, L1551 NE, and the Class II binary XZ Tau in the dust-continuum and molecular-line emission. The 0.9-mm continuum image of L1551 NE at an angular resolution of 0.2 arcsec (= 30 au) shows that the r~300 au scale circumbinary disk (CBD) consists of two spiral arms. Furthermore, the western part of the spiral arms are brighter than the eastern part, suggesting the presence of an m = 1 spiral mode. The 0.9-mm continuum image of L1551 IRS 5 also shows a compact (r~60 au), two spiral-arm feature, but the spiral arms are rather point symmetric and no m=1 mode is seen. The C18O (3-2) image cube of the CBD in L1551 NE shows both rotating and infalling gas motions, while in L1551 IRS 5 rotating and expanding gas motions are dominant. In the more evolved, Class II binary XZ Tau the CBD is not seen, but two circumstellar disks in Keplerian rotation are identified. The different observed properties of the three binaries in the same L1551 region likely reflect the differences of the binary properties and the evolutional stages. We will discuss these observed results along with our numerical simulation