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  • Star Formation across the Mass Spectrum


    Seminar Title  

    Star Formation across the Mass Spectrum

    Speaker:   Dr. ZHANG Yichen


    (Institute of Physical and Chemical Research (RIKEN), Japan)  

    When Thursday morning, May 18, 10:30 a.m


    Room 302, Astronomy Building

                             Welcome to Attend   

      ( PMO Academic Committee & Academic Circulating committee)

       Abstract: Whether stars of different masses form in a similar way is still highly debated. In one of the scenarios, both low and high-mass stars form by accreting from pre-existing cores (core accretion), and their final masses are determined by the initial core masses and the strength of the feedback. I will explore two aspects of this scenario. First, we will talk about the outflow entrainment and feedback. In particular, we observed the HH 46/47 molecular outflow with ALMA. With the total power observation, and with 13CO and C18O emission to trace optically-denser and slower outflowing material than 12CO only, we are now able to estimate the mass, momentum and other properties of this outflow much more accurately than ever. The estimated outflow properties indicate that the outflow is capable to disperse the parent core within the typical lifetime of the embedded phase of a low-mass protostar, and is regulating the core-to-star efficiency to about 1/4 to 1/3. These results are consistent with the prediction of the core accretion theory. Multiple outflowing shells with wide opening angles are detected in this outflow. With simple model fitting, we can explain these wide outflowing shells as results of entrainment of ambient gas by the wide-angle wind in multiple outburst events, which suggests that the wide-angle wind, same as the collimated jet, experiences episodicity, as expected by theories of episodic accretion and wind launching. Secondly, we have constructed a self-consistent evolutionary models of massive star formation, and by combining with continuum radiative transfer models, chemical models, and photoionization models we are able to predict the evolution of the IR continuum emission, the chemical abundances or development of ionized region in the massive protostellar cores. The goal is to understand the effect of the initial conditions (such as initial core mass and surface densities of the star forming environment) on the evolution of the massive protostellar cores. In particular our model provides a SED fitting tool which can generate more reliable estimates on the properties of the massive young stellar objects.

    A Brief CV of the speaker:
    2013: University of Florida (PhD)
    2013-2014: Yale University (Yale-UChile Postdoc)
    2014-2016: Universidad de Chile (Yale-UChile Postdoc)
    2016-: The Institute of Physical and Chemical Research (RIKEN), Japan (Postdoc)
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