ALMA Observations of Spiral Accretion Flows Towards An Extremely Young Protostellar system—VLA1623

• Main Authors: Cheong, Pou-Ieng, 張寶瑩
• Other Authors: Lai, Shih-Ping
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/7th582

碩士 === 國立清華大學 === 天文研究所 === 106 === Studying the accretion flows surrounding extremely young protostars is an im- portant step toward understanding how protostellar disks are assembled in the early stage of star formation. The accretion flows are commonly seen in magnetohydro- dynamics (MHD) simulations; however, they are rarely observed due to their low intensity. Here we report our discovery of thousand-AU scale accretion flows around an extremely young protostar VLA1623A with a protostellar disk likely just formed, using Atacama Large Millimeter/submillimeter Array (ALMA) observations of C18O (2–1) emission. We identify three groups of stream-like structures at different velocity ranges from the three-dimensional Position-Position-Velocity (PPV) data cube using the “Dendrogram” algorithm. Some of these stream-like structures are likely to be outflows or the envelope material shocks by outflows, but we find that the kinematics of two identified streams are well matched with the CMU model (Ulrich, 1976; Cassen and Moosman, 1981) which describes the velocity structure of the accreting gas with constant angular momentum. Our results give a centrifugal radius of 150 AU, same as the Keplerian disk size estimated by Murillo et al. (2013). With the CMU model, we are able to produce a three dimensional (Position-Position-Position) view of the accretion flows which shows that the thickness of the Keplerian disk at r = 150 AU is < 30 AU.