Local RR Lyrae Stars: native and alien
  Measurements of [Fe/H] and radial velocity are presented for 89 RR Lyrae
(RRL) candidates within 6 kpc of the Sun. After removal of two suspected
non-RRL, these stars were added to an existing database, which yielded 464 RRL
with [Fe/H] on a homogeneous scale. Using data from the Gaia satellite (Data
Release 2), we calculated the positions and space velocities for this sample.
These data confirm the existence of a thin-disc of RRL with [alpha/Fe] ~ solar.
The majority of the halo RRL with large total energies have near zero angular
momenta about the Z axis. Kinematically these stars closely resemble the
Gaia-Sausage/Gaia-Enceladus stars that others have proposed are debris from the
merger of a large galaxy with the Milky Way. The metallicity and period
distributions of the RRL and their positions in the period-amplitude diagram
suggest that this disrupted galaxy was as massive as the Large Magellanic Cloud
and possibly greater.
