Cool Stars 14 - Submitted Abstract # 335
This version created on 05 October 2006

An immediate precursor to Debris Disks?  Coronagraphic Observations of
HD


David Ardila, Spitzer Science Center
David Golimowski, Johns Hopkins University
John Krist, NASA Jet Propulsion Laboratory
Mark Clampin, NASA Goddard Space Flight Center
Holland Ford, Johns Hopkins University
Garth Illingworth, University of California at Santa Cruz

We present multicolor, optical coronagraphic observations of HD
100546, obtained with the Advanced Camera for Surveys.  These data
demonstrate the analytical power of coronagraphic observations.  The
HD 100546 system is a massive, old protoplanetary disk, and can be
thought of as an immediate precursor to some of the debris disks that
have been imaged with HST, like Beta Pictoris and HD 141569.  The
previously known spiral structures are revealed to have complex
substructure within them, perhaps the result of an interior planet.
Other explanations, like those seeking to explain the spiral arms as
the result of disk inclination, are rejected.  The multicolor
observations show that the dust scatters more light at longer
wavelengths:  i.e.  it is red with respect to the star.  While this
behavior is not uncommon in debris disks, its presence in this
protoplanetary disk suggests that that the star is surrounded by a
flattened optically thin structure.  The optically thick disk is not
seen in these images, indicating that its profile is fairly constant
with distance.  The envelope is redder (B-I is 0.6 mags larger than
the star) than the reddest colors ever measured in debris disks (B-I
is 0.2 mags larger than the star).  We show that the disk color is
similar to that of Kuiper Belt objects.  In the later case, the color
is due to the effect of cosmic rays on the icy surfaces of
planetesimals.  That effect may be at work here, although its time
scale (~100  Myrs) is too large to work in HD 100546.  

----------------------------------