BIB-VERSION:: AST-PP-v1.0
ID:: epreps.stsci//prep1209
ENTRY:: March 9, 1998
TITLE::  On the Difficulty of Launching an Outflow from an Accretion Disk 
SUBTITLE:: 
AUTHOR:: Ogilvie, Gordon I. (1) (2)
AUTHOR:: Livio, Mario (1)
AFFIL:: (1) Space Telescope Science Institute    3700 San Martin Drive    Baltimore, MD 21218    USA
AFFIL:: (2) Permanent address: Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, United Kingdom
DATE:: January 1998
JOURNAL:: To appear in: 
SUBMITTED::
ACCEPTED::
OTHER_ACCESS:: 
COPYRIGHT:: Copyright 1998 The Association of Universities for Research in Astronomy, Inc.  All Rights Reserved.
LANGUAGE:: English
ABSTRACT::

We solve for the local vertical structure of a thin accretion disk
threaded by a poloidal magnetic field. The angular velocity deviates
from the Keplerian value as a result of the radial Lorentz force,
but is constant on magnetic surfaces. Angular momentum transport
and energy dissipation in the disk are parametrized by an
<IMG SRC="/science/preprints/Icons/alpha.gif" WIDTH=10 HEIGHT=8 ALT="alpha">-prescription, and a Kramers opacity law is assumed to
hold. We also determine the stability of the equilibria with respect
to the magnetorotational (or Balbus-Hawley) instability. If the
magnetic field is sufficiently strong, stable equilibria can be 
found in which the angle of inclination, <I>i</I>, of the magnetic
field to the vertical at the surface of the disk has any value in the
range 0&nbsp;<IMG SRC="/science/preprints/Icons/leq.gif" WIDTH=13 HEIGHT=18 ALIGN=absbottom ALT="&lt;=">&nbsp;<I>i</I>&nbsp;&lt;&nbsp;90<SUP>o</SUP>. By analyzing the dynamics
of a transonic outflow in the corona of the disk, we show that a
certain potential difference must be overcome even when 
<I>i</I>&nbsp;&gt;&nbsp;30<SUP>o</SUP>. We determine this potential
difference as a function of <I>i</I> for increasing values of the
vertical magnetic field strength. For magnetorotationally stable
equilibria, the potential difference increases faster than the 
fourth power of the magnetic field strength, quickly exceeding a
value corresponding to the central temperature of the disk, and is
minimized with respect to <I>i</I> at 
<I>i</I>&nbsp;<IMG SRC="/science/preprints/Icons/approx.gif" WIDTH=12 HEIGHT=9 ALT="~">&nbsp;38<SUP>o</SUP>. We show that this property is relatively
insensitive to the form of the opacity law. Our results suggest that
an additional source of energy, such as coronal heating. may be
required for the launching of an outflow from a magnetized disk.

END:: epreps.stsci//prep1209