講演者: Dr. Oliver Krauss (Institut fuer Planetologie, Muenster University, Germany)
  題名: Radiation Pressure and Photophoresis in Circumstellar Disks
  日時: 2006年05月24日（水）16:00-17:00
  場所: 自然科学3号館6階セミナー室 609号室







The dynamical evolution of the dust in a protoplanetary disk, and as
a consequence also the eventual formation of planets, is governed by
the different forces that act on the dust grains in the disk. As soon
as a circumstellar disk turns optically thin, radiative forces become
important. Radiation pressure is known to substantially reduce the
lifetime of (sub-)micron-sized dust particles by blowing them
radially out of the disk. However, the knowledge of the radiation
pressure effect on fluffy irregularly shaped dust aggregates, as they
commonly occur in protoplanetary disks, is far from being complete.
Especially, experimental data are missing almost entirely. In
Muenster we have developed a method to measure the radiation pressure
on individual micron-sized dust particles by observing their motion
in response to a pulsed laser beam.



Another effect that is important for the dynamics of dust in an
optically thin and gas-rich (part of) a circumstellar disk is
photophoresis. The unilateral illumination by the central star leads
to a temperature gradient over the dust grains' surface resulting in
a momentum transfer from the accommodated gas molecules onto the dust
particles in radial direction. The strength of the resulting force
depends on the gas density and on the thermal conductivity of the
particles. This effect gives rise to radial migration of dust grains
ranging in size from some オm to several cm. For large enough
particles, photophoresis is much stronger than radiation pressure.
The radial transport of dust particles by photophoresis may have a
number of effects on the structure of circumstellar disks like the
clearing of the inner part of the disk, or the formation of dust
rings or belts around the star. It may also be relevant for the
composition of bodies that are formed in the outer regions of a
protoplanetary disk, such as comets or Kuiper belt objects