RU Cen and SX Cen: Two strongly depleted RV Tauri stars in binary systems - The RV Tauri photometric b phenomenon and binarity

We present a chemical abundance analysis on the basis of high signal-to-noise and high-resolution (lambda/Deltalambda similar to 48 000) optical spectra of two RV Tauri stars RU Cen and SX Cen. With an [Fe=H] = -1.9 and a [Zn=Fe] = +0.9 for RU Cen and a [Fe/H] = -1.1 and a [Zn=Fe] = +0.6 for SX Cen, both stars of spectroscopic class B display strong depletion of refractory elements in their photospheres. Our CORALIE radial velocity measurements prove the stars to be members of binary systems and a detailed construction of the spectral energy distribution indicate the presence of a large amount of hot circumstellar dust. Moreover, the orbital period of SX Cen of around 600 days is similar to the published period of mean magnitude variation in the light curve (RV Tauri phomometric class b phenomenon). All these observations indicate the presence of a stable circumbinary disk in the objects and strengthen the model that this is a necessary condition for the depletion process to take place.