PSJC #179 January 23 2015

Basmah Riaz (U. Maryland)

Cometary dust composition signatures in circum(sub)stellar disks

I will present results from our on-going work on the 20 μm silicate emission features for young brown dwarf disks. These features probe the cold component of the disks, located at radii of ~1-2 AU from the central sub-stellar source, with prevailing temperatures of <100K, much less than the required thermal annealing temperature. Our results indicate significant crystalline mass fractions of ~40-50% in the cold component, with less than 5% of disks being dominated by ISM-like amorphous silicate grains. A few interesting cases also show prominent features indicating high-temperature polymorphs of silica (crystalline silicon dioxide). Similar high-temperature material has been found in comets, the coma molecules of which have temperatures commensurate with ice sublimation temperatures. I will discuss the similarities in the spectral appearance and composition between brown dwarf disks and comets, and the applicability of the various mechanisms that have been proposed for comets on the formation and the transport of high-temperature silicates from the inner regions of the solar nebula to the cold outer regions where comets formed.