The Orbit and Mass of the Cepheid AW Per

The Cepheid AW Per is a component in a multiple system with a long period orbit. The radial velocities of Griffin (2016) cover the 38 year orbit well. An extensive program of interferometry with the CHARA array is reported here, from which the long period orbit is determined. In addition, a Hubble Space Telescope high resolution spectrum in the ultraviolet demonstrates that the companion is itself a binary with nearly equal mass components. These data combined with a distance from Gaia provide a mass of the Cepheid (primary) of M_1 = 6.79 ± 0.85 M_⊙. The combined mass of the secondary is M_S = 8.79 ± 0.50 M_⊙. The accuracy of the mass will be improved after the fourth Gaia data release expected in approximately two years.