Spitzer Space Telescope - General Observer Proposal #30551


Quantitative Mineralogy of Brown Dwarf Disks:  Measuring the Effect of
Luminosity on Dust Evolution

Principal Investigator: Daniel Apai
           Institution: Steward Observatory/NASA Astrobiology Institute

Co-Investigators: 
Ilaria Pascucci, Steward Observatory, University of Arizona           
Kevin Luhman, The Pennsylvania State University                       
Michael R. Meyer, Steward Observatory                                 
Thomas Henning, Max Planck Institute for Astronomy, Heidelberg        
Antonella Natta, Arcetri Observatory                                  
Jeroen Bouwman, Max Planck Institute for Astronomy, Heidelberg        

Science Category: circumstellar/debris disks 
 Observing Modes: IrsStare 
  Hours Approved: 25.2 

Abstract:
The first step toward planetesimal formation is the processing of dust
grains via grain growth and crystallization accompanied by dust
settling toward the disk mid-plane.  Our Cycle-1 IRS survey answered
four questions concerning potential planet formation in brown dwarf
disks:  1.  Most brown dwarf disks are flat or only moderately flared;
2.  We identified very high crystalline mass fractions (40-50%) in all
but one brown dwarf disk.  3.  Substantial grain growth occurs in
brown dwarf disks already at very young ages (1-3 Myr).  4.  The dust
processing and the disk geometries are consistent with the picture of
larger dust grains settling toward the disk mid-plane.  The two most
surprising findings were the highly crystalline disks and a dust
compositional difference between sources in two different star-forming
regions.  We propose here to utilize 25.2 hours of Spitzer/IRS time to
obtain very high signal-to-noise spectra to conduct a quantitative
dust composition study on 22 disks around brown dwarfs and very
low-mass stars.  We aim to:  1, determine whether crystalline mass
fractions decrease with age or with increasing luminosity;  2, confirm
the dust compositional difference.  Both questions are fundamental to
understanding the processing and evolution of dust in protoplanetary
disks - the raw material of terrestrial planets.  Our team consists of
some of the leading experts in the field of astromineralogy,
protoplanetary disks, brown dwarf disks, and brown dwarf
characterization.  We have a strong record of successful Spitzer/IRS
disk studies and all the reduction and analysis tools required to
reach all proposed goals.