Kinematics of Type II Cepheids of the Galactic Halo
  In a step toward understanding the origin of the Galactic Halo, we have
reexamined Type II Cepheids (T2C) in the field with new input from the second
data release (DR2) of Gaia. For 45 T2C with periods from 1 to 20 days,
parallaxes, proper motions, and [Fe/H] values are available for 25 stars. Only
5 show [Fe/H] < -1.5, while the remaining stars show thick disk kinematics and
[Fe/H] > -0.90. We have compared the T2C stars of the field with their cousins
in the globular clusters of the Halo and found that the globular clusters with
T2C stars show metallicities and kinematics of a pure Halo population. The
globulars may have formed during the overall collapse of the Galaxy while the
individual thick disk T2C stars may have been captured from small systems that
self-enriched prior to capture. The relationship of these two populations to
the micro-galaxies currently recognized as surrounding the Galaxy is unclear.
