Summary of Interiors Subgroup 
Group Leader: Don Hunten, University of Arizona 
 
  Although only 8 people were present, the group was able to have a good,
productive discussion.
  In the following, we use the terms "p-modes" and "seismic waves", which
may need explanation for some.  A p-mode is a standing acoustic (or pressure,
hence the "p") wave in a kind of cavity formed at the top by a propagation
barrier at a level of a few bars, and at the bottom by the rapid increase
of sound speed with depth.  A seismic wave (as used here) is a wave front
of the same physical nature, but propagating downward from an impact site,
then refracted back to the visible part of the atmosphere.  Natural p-modes
may or may not have been detected, but there is hope that they will be
more strongly excited by the impacts.  Acoustic and gravity wave fronts
should also propagate (at different speeds) horizontally in a duct centered
on the tropopause.  The surface trace of a seismic wave spreads at several
km/s or greater; acoustic and gravity waves travel at about 1 and 0.15
km/s.  Although some of these fronts might be observable as patterns in
the clouds, all those present favored use of mid-IR imaging to reveal
the temperature perturbations accompanying the pressure fronts.
 
  Marley made a short presentation on behalf of Hugh Hudson, who had had
to leave the meeting early.  He and Fisher have been seeking p-modes with
a 64 by 64 array, observing at 10 and 20 microns.  They confirm the slow-
moving wave discovered by Deming et al., Ap. J. 343, 456 (1989).  There
is a weak indication of p-modes in the 20-30 millihertz region.  They plan
to continue this work with the 60-inch Minnesota-UCSD telescope on Mount
Lemmon near Tucson.
  Barbara Jones (UCSD) hopes to have a 96 by 96 array working by July,
and may use it on either the Keck telescope or the 60-inch.
 
  Deming commented that, in any search for p-modes, wavenumber resolution
is not improved by observations over several days.
  He presented results of a computation of the spreading rate of seismic
waves that agrees very well with those of Marley (Ap. J. Lett. in press).
He used an older profile of sound speed by Zharkov and Trubitsyn.  He also
explored the effect of differential rotation in concentric cylinders
(like the Busse model) and found it too small to be observable unless he
artificially multiplied the differential speeds by 10.  Hunten mentioned
that he too had duplicated Marley's results (but in a simplified model);
both used sound speeds from Saumon and Chabrier.
 
  Pierre-Olivier Lagage reported observing plans on behalf of the Mosser
group. They have obtained 4 nights and have applied for 6 more on the Nordic
telescope in the Canary Islands.  They will use a 64 by 64 camera (CAMIRAS).
At ESO they have shared used of the 3.6 m with the TIMMI camera.  They
have proposed to use the CFHT with a 10 micron camera.
 
  Although the schedule for the IRTF will not be defined for some time,
it is expected to make use of the MIRAC camera of W.F. Hoffmann (University
of Arizona).  This camera is being modified to use a 128 by 128 array.
Pre-impact observations will be made at the U of A 90-inch in April
and the IRTF in June.  On both telescopes the field is slightly bigger
than Jupiter.  A team including MIRAC and HIFOGS (F. Witteborn) is led
by Hunten, and hopes to coordinate imaging and spectroscopic observations
on the IRTF and KAO.
 
  Deming led a discussion of the best choice of wavelength.  The main
candidates are the methane emission at 7.8 microns and almost any wavelength
in the 10 to 20 micron range.  Methane is expected to be more sensitive
for two reasons: it is further out on the "blue" side of the Planck
function, and its source is the 20 mbar level where the fractional
pressure perturbations are amplified.  The longer wavelengths generally
arise from the 500 mbar level; their major advantage is a much larger flux.
However, according to Deming the snr is not really limited by the flux,
but rather by flatfielding.  He volunteered to look at some of his existing
data to see if this statement can be made quantitative.
 
  There was some discussion of communications.  It was agreed that they will
be important, but no specific plans were put forward.  It was pointed out
that communication is one of the tasks laid on the newly-appointed IRTF
team, and a possibility is that this team might take on a broader
responsibility in this area.
 
  Anne Raugh (UMD) led a brief discussion of archiving.  It will be
important to use standard key words; if any observing teams already have
a standard, UMD would like to know the details.  One good way would be
simply to send a sample data set.