Cepheid radial velocities

Radial velocities are measured for eight distant Cepheids toward l=300{deg}; these new Cepheids provide a particularly good constraint on the distance to the Galactic center, R_0_. We model the disk with both an axisymmetric rotation curve and one with a weak elliptical component, and find evidence for an ellipticity of 0.043+/-0.016 near the Sun.

Using these models, we derive R_0_=7.66+/-0.32kpc and v_circ_=237+/-12km/s. The distance to the Galactic center agrees well with recent determinations from the distribution of RR Lyrae variables and disfavors most models with large ellipticities at the solar orbit.