MOVIES OF PHOTOEVAPORATING DISKS
Harold W. Yorke (Jet Propulsion Laboratory / California Institute of Technology)
At a distance of 0.1 pc from a 1 solar mass star + disk embeded inside a
molecular cloud clump an O5 star suddenly turns on and begins to ionize
and heat its surroundings. The configuration quickly evolves into a "proplyd"
which survives a few 100,000 years, until the disk material is
either photoevaporated or accretes onto the 1 solar mass star.
Click on image to see each portion of the movie:
0 ... 400 years:
The molecular cloud contains a star+disk system which still accretes material.
The left half frame depicts the temperature, the right half depicts the
density and velocity distributions. Initially, the left half is black,
because the temperature everywhere is below a few hundred degrees. After
the O star turns on at t=0, an ionization front enters into the frame from
the top. At the same time the O star's FUV radiation begins to heat the
material at the surface of the disk. The I-front encounters the expanding
disk material and is stopped here. It begins to wrap itself around the
star+disk configuration. We "zoom" into the central portions at t=100 years
for a better view and increase the speed of the film. The white lines depict
contours of constant temperature and density, separated by one (left half of
frame) and two (right half) orders of magnitude, respectively.
400 ... 40,000 years:
The outer layers of the disk are only weakly bound
to its central star and this material is eventually photo- evaporated away.
A quasi-steady-state configuration develops. Molecular material at the
surface of the disk is dissociated and heated up to several 1000 K. It
expands away from the disk and - within this flow - both density and temperature
decrease. Moving at approximately 10 km/s the warm atomic gas is stopped
by a denser shell of material (there is a shock front at the interface).
There is some flow of gas within this shell towards the "tail side", in
a direction away from the O star. The shell is enveloped by the ionization
front, where the neutral flow is ionized and heated to ~ 10,000 K. The
ionized gas expands at velocities of several 10's km/s. Note that the speed
of the movie has again been increased.
40,000 ... 100,000 years: This is a continuation of the quasi-steady-state
flow. As the mass within the disk decreases, it becomes more compact and
more tightly bound to its central star. The proplyd decreases in size but
all of the basic elements are present: the neutral warm flow from the disk's
outer surface, the shock front, and the somewhat denser neutral "shell",
which has a "tail" in the opposite direction of the hot O star, the ionization
front, and the expanding ionized flow.
100,000 ... 217,000 years: We begin this portion of the movie with another
zoom and continue the gradual photo-evaporation of the disk. After about
200,000 years the numerical resolution of the disk is insufficient to model
the flow accurately and we stop the simulation. Less than 1% of the original
disk's mass is still present.
115,000 ... 116,000 years: For this movie we assume that at an
evolutionary age of 100,000 years an isotropic stellar
wind from the disk's central star is suddenly turned on (mass loss rate:
0.2 millionths solar masses per year; velocity: 50 km/s). This movie covers
the evolution for 1000 years, 15,000 years after the wind has been turned on.
Note that the wind does not greatly influence the disk.
Reference:
Richling S., Yorke H.W., 2000, ApJ, 539, 258
Harold W. Yorke, Lead Scientist for Astrophysics
Jet Propulsion Laboratory,
California Institute of Technology
MS 169-506; 4800 Oak Grove Drive; Pasadena, CA 91109
e-mail:
Harold.Yorke@jpl.nasa.gov
(JPL clearance: CL002652)
0 ... 400 years:
The molecular cloud contains a star+disk system which still accretes material.
The left half frame depicts the temperature, the right half depicts the
density and velocity distributions. Initially, the left half is black,
because the temperature everywhere is below a few hundred degrees. After
the O star turns on at t=0, an ionization front enters into the frame from
the top. At the same time the O star's FUV radiation begins to heat the
material at the surface of the disk. The I-front encounters the expanding
disk material and is stopped here. It begins to wrap itself around the
star+disk configuration. We "zoom" into the central portions at t=100 years
for a better view and increase the speed of the film. The white lines depict
contours of constant temperature and density, separated by one (left half of
frame) and two (right half) orders of magnitude, respectively.
