Physics
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007sptz.prop40140m&link_type=abstract
Spitzer Proposal ID #40140
Physics
Scientific paper
We propose two investigations that are directly relevant to understanding Spitzer observations of L- and T-type brown dwarfs. First, we will provide important new constraintson the currently unknown mechanism responsible for the rapid L to T dwarf transition. To do so we will study L/T binary pairs, for which there are abundant Spitzer and groundbased datasets. Each member of a pair has the same age and metallicity, but very different spectral properties owing to their vastly different iron and silicate cloud decks. We will find self-consistent pairs of models that fit the unresolved Spitzer IRAC and IRS data and the available resolved near-infrared photometry. These pairs of models, each with the same age and metallicity, but differing mass, effective temperature, and cloud properties, will provide new constraints on the nature of the L to T transition, which is the major outstanding issue in studies of brown dwarf atmospheres. Secondly, we will produce new models of very cool (Teff < 600 K) brown dwarfs to better understand the spectral signatures associated with the yet to be discovered Y dwarfs. Existing models in the literature have used outdated ammonia opacity datasets and do not account for the role of non-equilibrium chemistry, which we have demonstrated is crucial for understanding the slightly warmer T dwarfs. Our work will provide new predictions for the expected IRAC photometric signatures of Y dwarfs (which critically are fainter in Band 2 than generally expected) and will aid in the characterization of these objects when they are eventually discovered by various ongoing Spitzer (as foreground objects) or ground based surveys.
Marley Mark
Saumon Didier
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