We apply a simple axisymmetric disc model to 218 Galactic Cepheids whose accurate measurements of the distance and velocities are obtained by cross-matching an existing Cepheids catalogue with the Gaia DR2 data .
Our model fit determines the ‘ ‘ local centrifugal speed ’ ’ , V _ { \mathrm { c } } —defined as the rotation speed required to balance the local radial gravitational force—at the Sun ’ s location to be V _ { c } ( R _ { 0 } ) = 236 \pm 3 km s ^ { -1 } and the Sun ’ s azimuthal and radial peculiar motions to be V _ { \sun } = 12.4 \pm 0.7 km s ^ { -1 } and U _ { \sun } = 7.7 \pm 0.9 km s ^ { -1 } , respectively .
These results are obtained with strong priors on the solar radius , R _ { 0 } = 8.2 \pm 0.1 kpc , and Sun ’ s angular rotation velocity , \Omega _ { \sun } = 30.24 \pm 0.12 km s ^ { -1 } kpc ^ { -1 } .
We also applied the axisymmetric model to mock data from an N -body/hydrodynamic simulation of a Milky Way-like galaxy with a bar and spiral arms .
We find that our axisymmetric model fit to the young stars recovers the local centrifugal speed reasonably well , even in the face of significant non-axisymmetry .
However , the local centrifugal speed determined from our Cepheid sample could suffer from systematic uncertainty as large as 6 km s ^ { -1 } .