Multiwavelength observations of RV Tauri stars. 4: SX Centauri

We present ultraviolet, optical and infrared observations of the RV Tauri star SX Cen. From a fit of model atmospheres to the data we conclude that Z/Z solar = 0.033, that SX Cen has an extended atmosphere, and that the spectral types implied by the ultraviolet data close to deep minimum are consistent with those implied from optical spectra. Unlike AC Her, there seems to be no silicate component in the circumstellar dust shell, and the star pulsates in purely radial modes. The implication is that, despite their many similarities, SX Cen seems to be at a significantly earlier phase of post-AGB evolution than AC Her. Additional data, particularly in the infrared, are necessary to confirm this conclusion.