2008MNRAS.383..139M

The 6.4d classical Cepheid AW Per is a spectroscopic binary with a period of 40yr. Analysing the centroids of Hubble Space Telescope/Space Telescope Imaging Spectrograph (HST/STIS) spectra obtained in 2001 November, we have determined the angular separation of the binary system. Although we currently have spatially resolved data for a single epoch in the orbit, the success of our approach opens the possibility of determining the inclination, sini, for the system if the measurements are repeated at additional epochs. Since the system is potentially a double lined spectroscopic binary, the combination of spectroscopic orbits for both components and the visual orbit would give the distance to the system and the masses of its components, thereby providing a direct measurement of a Cepheid mass.