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
Journal article, 2021

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 a circumbinary disk (CBD). Our SMA observations indicate a CBD diameter of less than or similar to 550 au. Our XMM-Newton observations make U Mon the first RV Tauri variable detected in X-rays. The X-ray emission is characteristic of a hot plasma (similar to 10 MK), with L-X =5 x 10(30) erg s(-1), and we consider its possible origin from U Mon, its companion, and/or binary system interactions. Combining DASCH and AAVSO data, we extend the time-series photometric baseline back to the late 1880s and find evidence that U Mon has secular changes that appear to recur on a timescale of similar to 60 yr, possibly caused by a feature in the CBD. From literature radial velocities we find that the binary companion is a similar to 2 M A-type main-sequence star. The orientation of the binary's orbit lies along our line of sight (omega = 95 degrees), such that apastron corresponds to photometric RVb minima, consistent with the post-AGB star becoming obscured by the near side of the CBD. In addition, we find the size of the inner-CBD hole (similar to 4.5-9 au) to be comparable to the binary separation, implying that one or both stars may interact with the CBD at apastron. The obscuration of the post-AGB star implicates the companion as the likely source of the enhanced H alpha observed at RVb minima and of the X-ray emission that may arise from accreted material.

Submillimeter astronomy

Spectral energy distribution

Binary stars

Post-asymptotic giant branch stars

Circumstellar matter

RV Tauri variable stars

X-ray astronomy


Laura D. Vega

NASA Goddard Space Flight Center

Vanderbilt University

Keivan G. Stassun

Vanderbilt University


Harvard-Smithsonian Center for Astrophysics

Tomasz Kaminski

Polish Academy of Sciences

Laurence Sabin

Universidad Nacional Autonoma de Mexico

Eric M. Schlegel

University of Texas at San Antonio

Wouter Vlemmings

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics

Joel H. Kastner

Rochester Institute of Technology

Sofia Ramstedt

Uppsala University

Patricia T. Boyd

NASA Goddard Space Flight Center

Astrophysical Journal

0004-637X (ISSN) 1538-4357 (eISSN)

Vol. 909 2 138

Subject Categories

Astronomy, Astrophysics and Cosmology





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