Evidence for Galactic disc RR~Lyrae stars in the Solar neighbourhood
  We present a kinematical study of 314 RR~Lyrae stars in the solar
neighbourhood using the publicly available photometric, spectroscopic, and {\it
Gaia} DR2 astrometric data to explore their distribution in the Milky Way. We
report an overdensity of 22 RR~Lyrae stars in the solar neighbourhood at a
pericenter distance of between 5--9\,kpc from the Galactic center. Their
orbital parameters and their chemistry indicate that these 22 variables share
the kinematics and the [Fe/H] values of the Galactic disc, with an average
metallicity and tangential velocity of [Fe/H]=$-0.60$\,dex and $v_{\theta} =
241$\,km\,s$^{-1}$, respectively. From the distribution of the Galactocentric
spherical velocity components, we find that these 22 disc-like RR~Lyrae
variables are not consistent with the {\it Gaia} Sausage ({\it
Gaia}-Enceladus), unlike almost half of the local RR~Lyrae stars. Chemical
information from the literature shows that the majority of the selected
pericenter peak RR~Lyrae variables are $\alpha$-poor, a property shared by
typically much younger stars in the thin disc. Using the available photometry
we rule out a possible misclassification with the known classical and anomalous
Cepheids. The similar kinematic, chemical, and pulsation properties of these
disc RR~Lyrae stars suggest they share a common origin. In contrast, we find
the RR~Lyrae stars associated with the {\it Gaia}-Enceladus based on their
kinematics and chemical composition show a considerable metallicity spread in
the old population ($\sim$~1\,dex).
