Cool Subdwarf Investigations II: Multiplicity
  Cool subdwarfs of types K and M are the fainter counterparts of cool main
sequence dwarfs that dominate the Galactic population. In this paper we present
the results of an optical speckle survey of 62 confirmed cool subdwarf systems
within 60 pc. We have resolved two new companions and confirmed two previously
known companions with separations 0\farcs13 to 3\farcs29. After including
previously known wide companions and all known spectroscopic binaries, we
determine the multiplicity rate of cool subdwarfs to be 26$\pm$6%, which is
somewhat lower than comparable main sequence stars, which have a multiplicity
rate of 37$\pm$5%. We find that only 3% of the cool subdwarfs surveyed have
companions within 10 AU, 3% have companions between 10 and 100 AU, and 14% have
companions beyond 100 AU. The other 6% of cool subdwarfs are spectroscopic
binaries. This is very different from K/M dwarfs that have most companions
(13%) at separations closer than 10 AU. However, because a search for close
binaries among a large sample of nearby cool subdwarfs remains elusive, it is
not yet settled whether or not the multiplicity rates are significantly
different. Nonetheless, several different observational results and theories
pointing to a possible dearth of subdwarf multiples are discussed.
