Galactoseismology: Discovery of a cluster of receding, variable halo
  stars
  A dynamical characterization of dark matter dominated dwarf galaxies from
their observed effects on galactic disks (i.e. Galactoseismology) has remained
an elusive goal. Here, we present preliminary results from spectroscopic
observations of three clustered Cepheid candidates identified from $K$-band
light curves towards Norma. The average heliocentric radial velocity of these
stars is $\sim$ 156 km/s, which is large and distinct from that of the Galaxy's
stellar disk. These objects at $l \sim 333 ^\circ$ and $b \sim -1 ^\circ$ are
therefore halo stars; using the $3.6~\micron$ period-luminosity relation of
Type I Cepheids, they are at $\sim$ 73 kpc. Our ongoing $I$-band photometry
indicates variability on the same time scale as the period determined from the
$K_{s}$-band light curve. Distances determined from the $K$-band
period-luminosity relation and the 3.6 $\micron$ period-luminosity relation are
comparable. The observed radial velocity of these stars agrees roughly with
predictions from dynamical models. If these stars are indeed members of the
predicted dwarf galaxy that perturbed the outer HI disk of the Milky Way, this
would mark the first application of Galactoseismology.
