We have obtained Spitzer Space Telescope IRS 5.5 - 35 \mu m spectra of 59 main sequence stars that possess IRAS 60 \mu m excess .
The spectra of five objects possess spectral features that are well-modeled using micron-sized grains and silicates with crystalline mass fractions 0 % - 80 % , consistent with T-Tauri and Herbig AeBe stars .
With the exception of \eta Crv , these objects are young with ages \leq 50 Myr .
Our fits require the presence of a cool black body continuum , T _ { gr } = 80 - 200 K , in addition to hot , amorphous and crystalline silicates , T _ { gr } = 290 - 600 K , suggesting that multiple parent body belts are present in some debris disks , analogous to the asteroid and Kuiper belts in our solar system .
The spectra for the majority of objects are featureless , suggesting that the emitting grains probably have radii a > 10 \mu m. We have modeled the excess continua using a continuous disk with a uniform surface density distribution , expected if Poynting-Robertson and stellar wind drag are the dominant grain removal processes , and using a single temperature black body , expected if the dust is located in a narrow ring around the star .
The IRS spectra of many objects are better modeled with a single temperature black body , suggesting that the disks possess inner holes .
The distribution of grain temperatures , based on our black body fits , peaks at T _ { gr } = 110 - 120 K. Since the timescale for ice sublimation of micron-sized grains with T _ { gr } > 110 K is a fraction of a Myr , the lack of warmer material may be explained if the grains are icy .
If planets dynamically clear the central portions of debris disks , then the frequency of planets around other stars is probably high .
We estimate that the majority of debris disk systems possess parent body masses , M _ { PB } < 1 M _ { \earth } .
The low inferred parent body masses suggest that planet formation is an efficient process .