A Spectrophotometric Study of the L-T Dwarf Transition

Details A Spectrophotometric Study of the L-T Dwarf Transition A Spectrophotometric Study of the L-T Dwarf Transition

Jun 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005sptz.prop20514g&link_type=abstract

Spitzer Proposal ID #20514

Computer Science

Scientific paper

Recent 1-5 micron studies of L and T dwarfs indicate that changes in the near-infrared spectra across the L-T transition are governed by complex cloud dynamics rather than by large changes in effective temperature. These studies also suggest that nonequilibrium chemistry significantly affects the photospheric abundances of CO, CH4, and NH3, all of which influence the spectral energy distributions from 1 to 15 micron. A focused study of L-T transition dwarfs longward of 5 micron is crucial to understanding the agents that govern the dynamic and chemical processes in the atmospheres of these brown dwarfs. We request 39.7 hours of IRS time in Cycle 2 to study 7 late-L and early-T dwarfs. This proposal is an extension of our similarly aimed Cycle 1 proposal. Our combined Cycle 1 and Cycle 2 samples will be 40% larger than the number of L-T transition dwarfs observed with IRS by the GTO team, and will include dwarfs with extremely blue and extremely red near-infrared colors. We also request 2.6 hours of IRAC time in Cycle 2 to obtain four-band photometry of 9 L-T transition dwarfs from our Cycle 1 and 2 programs. By combining the IRS and IRAC data with our existing 0.8-2.5 micron spectra and 0.9-2.2 micron photometry, we will (1) investigate the effects of grain condensation, metallicity, and nonequilibrium chemistry on the atmospheres of these brown dwarfs and (2) accurately determine the bolometric fluxes of the dwarfs in our Cycle 1 and 2 programs. Our comprehensive data set will allow us to constrain models of the transition from dusty red L dwarfs to clear blue T dwarfs and to determine the importance of nonequilibrium chemistry in defining the L-T transition.

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