  We conducted a survey for infrared excess emission from 16 nearby main
sequence shell stars using the Multiband Imaging Photometer for Spitzer (MIPS)
on the Spitzer Space Telescope. Shell stars are early-type stars with narrow
absorption lines in their spectra that appear to arise from circumstellar (CS)
gas. Four of the 16 stars in our survey showed excess emission at 24 microns
and 70 microns characteristic of cool CS dust and are likely to be edge-on
debris disks. Including previously known disks, it appears that the fraction of
protoplanetary and debris disks among the main sequence shell stars is at least
48% +/- 14%. While dust in debris disks has been extensively studied,
relatively little is known about their gas content. In the case of Beta
Pictoris, extensive observations of gaseous species have provided insights into
the dynamics of the CS material and surprises about the composition of the CS
gas coming from young planetesimals (e.g. Roberge et al. 2006). To understand
the co-evolution of gas and dust through the terrestrial planet formation
phase, we need to study the gas in additional debris disks. The new debris disk
candidates from this Spitzer survey double the number of systems in which the
gas can be observed right now with sensitive line of sight absorption
spectroscopy.
