Spitzer Space Telescope - Directors Discretionary Time Proposal #243


Remnant Gas in Debris Disk Systems:  Confirmation of the Remarkable
[FeI] Line Emission in HD 216803

Principal Investigator: Ilaria Pascucci
           Institution: University of Arizona

Co-Investigators: 
Dave Hollenbach, NASA Ames Research Center                            
U. Gorti, NASA Ames Research Center                                   
Serena Kim, Univ. of Arizona                                          
Murray Silverstone, Univ. of Arizona                                  
Pat Morris, NASA Herschel Science Center                              
J. Najita, National Optical Astronomy Observatory                     
Debbie Padgett, SSC                                                   
Dan Watson, University of Rochester                                   

Science Category: circumstellar/debris disks 
 Observing Modes: IrsStare 
  Hours Approved: 1.0 

Abstract:
We propose to use 1 hour of Spitzer Director's Discretionary Time to
perform follow-up high-resolution spectroscopy of the nearby
main-sequence star HD 216803 and its disk.  HD 216803 was observed as
part of our 10  FEPS first-look sources to characterize the
dissipation timescale in disks around solar-type stars.  From a
detailed analysis of its high-resolution Spitzer spectrum, we
tentatively discovered [FeI] emission at 24 micron.  Here, we propose
to obtain more sensitive exposures with the LH module of the IRS to
confirm this probable detection.  The detection, if confirmed by the
proposed DDT observations, will provide the first strong evidence for
the existence of gas in the disk surrounding a main-sequence star at
an age of about 100  Myr.  This finding will have strong implications
on planet formation models, favoring the core accretion over the
gravitational instability scenario, and provides us with a powerful
new tool for detecting gas in circumstellar disks.  Thus, confirmation
of this result is urgently needed.  Because of the interest in these
observations from the broader scientific community and of the
implications that such a finding will have on the analysis of current
data and planning of future GO proposals, we believe that the
observations cannot be deferred until the next GO cycle.  Therefore we
ask for Director's Discretionary Time to re-observe our target in May.
If these observations were delayed to Cycle 3, general observers would
not have access to the results before Cycle 4, about two years from
now.