We present a kinematical study of 314 RR Lyrae stars in the solar neighbourhood using the publicly available photometric , spectroscopic , and 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 Gaia Sausage ( 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 Gaia -Enceladus based on their kinematics and chemical composition show a considerable metallicity spread in the old population ( \sim 1 dex ) .