Title: Understanding Accretion Status of High-mass Protostars 

Speaker: Yichen Zhang 

 
Abstract: It has been debated for a long time whether high-mass forming stars can continue to accrete despite the strong stellar feedback such as photoionization. Photoionized dense HII regions (HCHII or UCHII regions) were considered as the signposts of the end of accretion, while more and more theoretical studies have shown that disk-mediated accretion may continue even in this stage. Observationally, recent ALMA high-resolution observations have started to reveal the accretion and feedback processes of forming massive stars with great detail. 

I will present some of our high-resolution observations toward massive protostellar objects. Our main findings are 1) rotational structures can be consistently found down to tens of au scale around forming massive stars, consistent with relatively order disk accretion scenario; 2) Disks around massive protostars can have both neutral and ionized components, and very compact ionized components are found common even in early stage sources; 3) misalignments of rotation (angular momentum) directions or even counter rotations can be found on different scales, or between two close binary members embedded in a same disk; 4) Some massive disks show a characteristic chemical pattern including salt (NaCl, KCl), silicon compounds (SiO, SiS), and hot water lines at a scale <100 au, indicating dust destruction in very inner region, complementary to volatile hot-core molecules tracing the material on 1000-au scale.  

I will summarize some of my on-going observation programs, including ALMA surveys toward high-mass photoionizing protostars, multi-frequency campaign toward selected targets, and IR observations of the massive star-forming environments. 

 
Bio: Yichen Zhang is a Tenure-track Associate Professor at the Department of Astronomy in Shanghai Jiao Tong University. He received his Ph.D. from University of Florida in 2013. Since then, he has conducted postdoctoral research at Yale University, Universidad de Chile, RIKEN (Japan), and University of Virginia. He joined Shanghai Jiao Tong University in last September. His research focuses on star formation, especially massive star formation, using mostly IR/sub-mm/mm/radio observations. 

Time: 14:00-15:00PM, 10/Jan, Wednesday 

Venue: Room 508 (large seminar room), Department of Astronomy 

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https://m.koushare.com/topic-sc/i/physics_sjtu