Title:

Ultracool Subdwarfs: Probing the Galactic Halo Below the Hydrogen Burning
Limit




Adam Burgasser
Ammerican Museum of Natural History
Visiting Scientist, MIT




Abstract:

The past three years has witnessed a dramatic surge in the number of
"ultracool" subdwarf discoveries - metal-poor stars with spectral types
sdM7 and later.  These discoveries have been spurred on by both new red
optical proper motion surveys and serendipitous finds in the 2MASS and
SDSS catalogs.  The newly discovered collection of metal-poor members of
the Galactic halo include a few objects with similarities (and
differences!) to nearby field L dwarfs, including one source that is
likely to be the first Population II brown dwarf identified.  In this
talk, I will review the optical, near-infrared and infrared properties of
these objects.  I will discuss their importance in understanding how
metallicity affects the evolution of cool dwarf atmospheres, including the
formation of dust condensates; and how future subtellar subdwarf
discoveries might be used to probe the mass function and star formation
history of the early Galaxy.