Global 3-D Radiation Magnetohydrodynamic Simulations for FU Ori’s Accretion Disk and Observational Signatures of Magnetic Fields. (arXiv:1912.01632v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Zhu_Z/0/1/0/all/0/1">Zhaohuan Zhu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jiang_Y/0/1/0/all/0/1">Yan-Fei Jiang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stone_J/0/1/0/all/0/1">James M. Stone</a>
FU Orionis systems are outbursting protoplanetary disks where the accretion
disks outshine the central stars and strong disk winds are launched. Magnetic
fields in these accretion disks have previously been detected through their
Zeeman effects in spectropolarimetry observations. We carry out global
radiation ideal MHD simulations to study FU Ori’s inner accretion disk. We find
that (1) when the disk is threaded by vertical magnetic fields, most accretion
occurs in the magnetically dominated atmosphere at z$sim$R, similar to the
“surface accretion” mechanism in previous locally-isothermal MHD simulations.
(2) A moderate disk wind is launched in these vertical field simulations with
terminal speeds of $sim$300-500 km/s and a mass loss rate of 1-10% disk
accretion rate. Both the speed and loss rate are consistent with observations.
Disk wind fails to be launched in net toroidal field simulations. (3) The disk
photosphere at the unit optical depth can be either in the wind launching
region or the accreting surface region, depending on the accretion rates and
the disk radii. Magnetic fields have drastically different directions and
magnitudes between these two regions. Our fiducial model agrees with previous
optical Zeeman observations regarding both the field directions and magnitudes.
On the other hand, simulations indicate that future Zeeman observations at
near-IR wavelengths or towards other FU Orionis systems may reveal very
different magnetic field structures. (4) Due to energy loss by the disk wind,
the disk photosphere temperature is lower than that predicted by the thin disk
theory, and the previously inferred disk accretion rate may be lower than the
real accretion rate by a factor of $sim$2-3.
FU Orionis systems are outbursting protoplanetary disks where the accretion
disks outshine the central stars and strong disk winds are launched. Magnetic
fields in these accretion disks have previously been detected through their
Zeeman effects in spectropolarimetry observations. We carry out global
radiation ideal MHD simulations to study FU Ori’s inner accretion disk. We find
that (1) when the disk is threaded by vertical magnetic fields, most accretion
occurs in the magnetically dominated atmosphere at z$sim$R, similar to the
“surface accretion” mechanism in previous locally-isothermal MHD simulations.
(2) A moderate disk wind is launched in these vertical field simulations with
terminal speeds of $sim$300-500 km/s and a mass loss rate of 1-10% disk
accretion rate. Both the speed and loss rate are consistent with observations.
Disk wind fails to be launched in net toroidal field simulations. (3) The disk
photosphere at the unit optical depth can be either in the wind launching
region or the accreting surface region, depending on the accretion rates and
the disk radii. Magnetic fields have drastically different directions and
magnitudes between these two regions. Our fiducial model agrees with previous
optical Zeeman observations regarding both the field directions and magnitudes.
On the other hand, simulations indicate that future Zeeman observations at
near-IR wavelengths or towards other FU Orionis systems may reveal very
different magnetic field structures. (4) Due to energy loss by the disk wind,
the disk photosphere temperature is lower than that predicted by the thin disk
theory, and the previously inferred disk accretion rate may be lower than the
real accretion rate by a factor of $sim$2-3.
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