Spitzer Space Telescope - General Observer Proposal #3499 Mineralogy, Grain Growth and Dust Settling in Brown Dwarf Disks: Exploring the Conditions for Planet Formation Principal Investigator: Daniel Apai Institution: Steward Observatory/NASA Astrobiology Institute Co-Investigators: Antonella Natta, Arcetri Observatory, Italy Jeroen Bouwman, Max Planck Institute for Astronomy, Heidelberg Cornelius P. Dullemond, Max Planck Institute for Astrophysics, Garching Nicole S. van der Bliek, AURA/CTIO Ilaria Pascucci, Max Planck Institute for Astronomy, Heidelberg Thomas Henning, Max Planck Institute for Astronomy, Heidelberg Science Category: brown dwarfs/very low mass stars Observing Modes: IrsStare Hours Approved: 11.0 Abstract: We propose to use 14.5 hours of SPITZER time to obtain the first low-resolution spectra of 19 selected brown dwarf (BD) disks. Building on the unique wavelength coverage and sensitivity of IRS we aim to study the conditions of planet formation in BD disks. The selected targets are of substellar nature, have known mid-infrared excess emission, and their brightness allows us to obtain high quality spectra. Recent spectroscopic studies demonstrated the remarkable similarity of the dust composition between primitive bodies of our Solar System, and many disks around low- and intermediate-mass stars at the planet-forming age. The major markers of the first steps of planet formation are the coagulation and growth of dust grains, the settling of large grains to the disk midplane influencing the disk structure, and the presence of processed dust, such as crystalline silicates. To identify these signatures in BD disks we adopt the following strategy: we will (1) use two-dimensional radiative transfer codes and model the spectral continuum aiming to determine the disk structure; (2) derive the dust composition and identify crystalline silicates and minor species by comparing synthetic dust spectra to the observations; (3) determine the grain size distribution by modeling the shape and the width of the dust features; (4) probe whether dust settling has occurred, via a self-consistent radiative transfer code incorporating dust settling, grain coagulation, and transfer processes. To reach these ambitious goals we have assembled a team with strong experience in all aspects of the topic. With team members participating in the FEPS and c2d Legacy programs we already have experience with IRS data reduction. Our proposed observations and the subsequent analysis will paint the first global picture of substellar disks and answer the questions whether BD disks are similar to those of low-mass stars, to what extent dust processing occurred and whether they are capable of forming planetary systems - or they already have.