Multiwavelength Observations of the RV Tauri Variable System U Monocerotis: Long-term Variability Phenomena That Can Be Explained by Binary Interactions with a Circumbinary Disk

We present an X-ray through submillimeter observations of the classical RV Tauri (RVb-type) variable U Mon, a post-asymptotic giant branch (AGB) binary with circumbinary disk (CBD). Our SMA indicate CBD diameter ?550 au. XMM-Newton make Mon first detected in X-rays. The emission is characteristic hot plasma (?10 MK), LX =5 × 1030 erg s?1, and we consider its possible origin from companion, and/or system interactions. Combining DASCH AAVSO data, extend time-series photometric baseline back to late 1880s find evidence that has secular changes appear recur on timescale ?60 yr, possibly caused by feature CBD. From literature radial velocities companion ?2 M? A-type main-sequence star. orientation binary's orbit lies along our line sight (? = 95°), such apastron corresponds RVb minima, consistent post-AGB star becoming obscured near side In addition, size inner-CBD hole (?4.5–9 au) be comparable separation, implying one or both stars may interact at apastron. obscuration implicates as likely source enhanced H? observed minima arise accreted material.