Cometary dust in the debris disks of HD 31648 and HD 163296: Two "baby" beta Pictoris stars

The debris disks surrounding the pre-main-sequence stars HD 31648 and HD 16 3296 were observed spectroscopically between 3 and 14 mu m. Both stars poss ess a silicate emission Feature at 10 mu m that resembles that of the star beta Pictoris and those observed in solar system comets. The structure of t he band is consistent with a mixture of olivine and pyroxene material, plus an underlying continuum of unspecified origin. The similarity in both size and structure of the silicate band suggests that the material in these sys tems had a processing history similar to that in our own solar system prior to the time that the grains were incorporated into comets.