Runaway Dwarf Carbon Stars as Candidate Supernova Ejecta
  The dwarf carbon (dC) star SDSS J112801.67+004034.6 has an unusually high
radial velocity, 531$\pm 4$ km s$^{-1}$. We present proper motion and new
spectroscopic observations which imply a large Galactic rest frame velocity,
425$\pm 9$ km s$^{-1}$. Several other SDSS dC stars are also inferred to have
very high galactocentric velocities, again each based on both high heliocentric
radial velocity and also confidently detected proper motions. Extreme
velocities and the presence of $C_2$ bands in the spectra of dwarf stars are
both rare. Passage near the Galactic center can accelerate stars to such
extreme velocities, but the large orbital angular momentum of SDSS J1128
precludes this explanation. Ejection from a supernova in a binary system or
disruption of a binary by other stars are possibilities, particularly as dC
stars are thought to obtain their photospheric $C_2$ via mass transfer from an
evolved companion.
