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PSR Team -CPS Seminar on Sep 19

category : Seminar 2014年8月17日 

AICS Makino Team -CPS Seminar on Sep 19

  • date: Sep 19, 2014 13:30-15:30
  • Place: Seminar Room, CPS, Kobe University
  • Everyone is welcome!
  • Speaker: Kengo Tomida(Princeton U.)
  • Title: Non-Ideal RMHD Simulations of Protostellar Collapse: Early Formation of Circumstellar Disks
  • Abstract: Angular momentum transport by magnetic fields is a dominant physical process in star and disk formation processes. Dissipation of magnetic fields such as ambipolar diffusion and Ohmic dissipation during protostellar collapse is of critical importance because the ionization degree in star forming clouds is extremely low. These non-ideal magnetohydrodynamic effects extract magnetic flux and suppress angular momentum transport. In particular, the so-called magnetic braking catastrophe can be resolved with these effects. In this work, we perform three-dimensional radiation magnetohydrodynamic simulations including Ohmic dissipation and ambipolar diffusion. Without these effects, magnetic fields redistribute angular momentum so efficiently that no rotationally-supported circumstellar disk is formed even after formation of a second core. Ohmic dissipation works in a relatively high density region within a first core and suppresses angular momentum transport, and it enables formaiton of a small circumstellar disk around a second core. With both Ohmic dissipation and ambipolar diffusion, almost the entire first core becomes resistive and significant magnetic flux loss occurs. As a result, a circumstellar disk supported by rotation is formed even before the second collapse begins. Although the size of the disk remains still small, about 5 AU at the end of the first core phase, this disk will grow as gas accretion continues.

Speaker Profile
http://v1.jmlab.jp/~makino/wordpress-3.5.1/wp-content/uploads/2014/09/photo1.php_.jpg Kengo Tomida: Kengo Tomida obtained his PhD in Department of Astronomical Science, The Graduate University for Advanced Studies (SOKENDAI) / Division of Theoretical Astrophysics, National Astronomical Observatory of Japan. He worked on numerical simulations of star formation processes with his supervisor Prof. Kohji Tomisaka. He successfully achieved the first radiation magnetohydrodynamic simulations of formation of protostellar cores in the world, and was awarded SOKENDAI President’s award. Now he is working at Princeton University as a JSPS fellow and is contributing to development of the new version of the Athena MHD code. His recent interests include MHD simulations of interaction between turbulent circumstellar disks and strongly-magnetized protostars. He also collaborates with observers especially for ALMA using the results of his star formation simulations.


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