Multiwavelength observations of RV Tauri stars II. U Monocerotis

We present ultraviolet spectroscopy, and optical and infrared photometry, of the RV variable U Mon. The MgII emission in this object seems to be chromospheric, with small variations in profile accompanying pulsational variations. The wavelengths of narrow absorption features associated with the MgII emission are essentially constant in time, and seem to be associated with cool circumstellar shell and a steady wind. We conclude that there is no evidence of binarity in U Mon, and that the long-term behaviour of the light curve is associated with R CrB-like ejection of clouds of absorbing material.