Milky Way rotation and the distance to the Galactic center from Cepheid variables

Abstract

The existing data on Milky Way Cepheids are fitted with an axisymmetric Galactic rotation model. A new “standard candle” m_o is determined: the unreddened apparent magnitude of a hypothetical Cepheid with standard period, color, and metallicity at a distance of 1 R_o. It then follows that Ro = 7.8 ± 0.7 kpc from the cluster Cepheid zero point. Further important results are that 2AR₀ = 228 ± 19 km s⁻¹, and that the observed Cepheid mean velocities average 3.1 ± 0.9 km s⁻¹ too negative compared with the center-of-mass velocities.