• accretion
• astrophysics
• interacting binary stars
• spectroscopy

AU Mon (HD 50846) is an eclipsing, double-lined spectroscopic binary caught in a stage of rapid mass transfer. It has many feature in common with β Lyr, the prototype of such systems, such as an accretion disk around an intermediate mass main sequence star, but is less extreme and more tractable. The orbital inclination of about 80 degrees opens a direct line of sight toward the gainer and permits a study of its interaction with the accretion environment. Besides eclipses and other optical photometric modulation on the orbital period, 11.11 days, the AU Mon system shows photometric variability of around 0.25 mag on a timescale of about 37.5 times the orbital period (so is included among the Double Periodic Variables).
This work presents a multi-wavelength spectroscopic study using the available archival data of the system: IUE high resolution (1200-3200 Å) spectra in the UV range and optical spectra (from about 3700 to 9000 Å) from FEROS, HARPS and SOPHIE.
New parameters were obtained for the temperature and gravity of the gainer. There is evidence for non-axisymmetric structures in the accretion disk, possibly connected with the impacting stream, and indications of mass loss from the system. The long term variability appears to be due to changes in the accretion disk structure and circumstellar environment.