Ultracool
subdwarfs are very old, very
cool ("ultra-cool"), low-mass objects that reside primarily in the halo
of our galaxy. Because of their extreme
ages they have much lower metallicities and hence have very different
spectral features than their dwarf counterparts. As with
ultracool dwarfs,
ultracool subdwarfs have spectral energy distributions that peak in the
near-infrared and which are dominated by overlapping
molecular absorption bands. The differences are the interesting
part though; they contain valuable information about how
metallicity affects atmospheric chemistry. The meer existence of
ultracool subdwarfs can tell us something about low-mass star formation
at low metallicities.
For
the next eight months I'll be working with
Mike Liu and
Michael
Cushing on reducing and analyzing spectra of an ultracool subdwarf
companion to a low-metallicity primary star. Because it's safe to
assume these stars formed at the same time, we can tag the companion
with the same metallicity as that of the primary. This object
will serve as the only benchmark source with a known metallicity in
this field and will act as a crucial test for atmospheric models of
ultracool subdwarfs. If time permits we would also like to
search for other, similar, binary systems to test models over a wide
range of metallicities.