Kelvin-Helmholtz vortices induced by MRI at the inner-edge of protoplanetary disks

Details Kelvin-Helmholtz vortices induced by MRI at the inner-edge of protoplanetary disks Kelvin-Helmholtz vortices induced by MRI at the inner-edge of protoplanetary disks

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...209.7605n&link_type=abstract

2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #76.05; Bulletin of the American Astronomical Society, V

Astronomy and Astrophysics

Astronomy

Scientific paper

When an accretion disk has a weak magnetic field, it is well known that the magneto-rotational instability (MRI) is excited in the disk (Balbus&Hawley 1991).
We study the effect of MRI in protoplanetary disks near the protostar using local three-dimensional resistive MHD simulations. We have done modeling of the near-star part of protoplanetary disks by including the magnetosphere of the protostar and the “dead zone” (low ionized region in protoplanetary disk). Both in the magnetosphere of a protostar and in the dead zone, MRI isn’t excited because of the strong magnetic field and of the low ionization respectively. In this situation, MRI is excited only in the innermost part of the disk and large velocity shear is generated at the inner-edge (the boundary between the magnetosphere of a protostar and the disk). Then Kelvin-Helmholtz instability (KHI) is excited and grows into vortices there. The result suggests that the inner-edge of the disk is perturbed heavily by KH vortices. The chemical analysis results of meteorites suggest “Multiple pulse-like heating events at inner-disk edge” and/or “Oxygen isotopic variation due to fluctuating motion of the disk inner-edge” (Itoh&Yurimoto 2003). Our results suggest that KHI at the inner-edge is a candidate process responsible for this activity.
Furthermore, we have performed several simulations in which a variety of initial field configuration inside the disk is assumed, from a poloidal to a toroidal geometry. The results show that in the case of a nearly toroidal field, azimuthally asymmetric MRI is the dominant mode in the disk and azimuthal velocity changes more slowly than the case where azimuthally symmetric MRI is the dominant. Nevertheless we observe the generation of KH vortices at inner-edge in this case. The important conclusion is that vortices at the inner-edge are born regardless of the geometry of magnetic field in the disks.

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