Cool Stars 14 - Submitted Abstract # 271
This version created on 05 October 2006

Binaries and the L/T Transition


Adam J. Burgasser, Massachusetts Institute of Technology
Dagny Looper, University of Hawaii
Michael Liu, University of Hawaii
J. Davy Kirkpatrick, Caltech/IPAC
Kelle Cruz, American Museum of Natural History
I. Neill Reid, Space Telescope Science Insitute

The transition between the L dwarf and T dwarf spectral classes has
been shown to be rather peculiar.  The dramatic shift in spectral
morphology across this transition occurs over a narrow range of
temperature and luminosity, and is accompanied by an apparent
brightening at 1 micron (the J-band bump) that has cannot be explained
by current brown dwarf atmospheric and evolutionary models.  On the
basis of these empirical trends, several groups have suggested that
the L/T transition is driven by a dynamic (i.e., nonequilibrium)
evolution of photospheric condensate clouds.  Recently,
high-resolution imaging has clarified our picture of the L/T
transition through the identification of late-type L/early-type T
dwarf pairs, but have added the new wrinkle of a surprisingly high
binary fraction at the transition.  In this poster, we summarize the
results of resolved imaging studies of L/T transition objects and
their implications on the absolute magnitude and luminosity scale
across the transition.  We also present the results of simulations
demonstrating that the L/T transition binary excess can be properly
explained by a rapid evolution of brown dwarfs across this transition.
This more detailed picture of the L/T transition appears to support a
dynamic evolution of condensate clouds, but perhaps not as dramatic as
previously surmised.

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