A tidal encounter caught in the act: modelling a star-disc fly-by in the young RW Aurigae system

RW Aurigae (RW Aur) is a binary star system with a long molecular arm trailing the primary star. Cabrit et al. (2006) noted the resemblance between this extended structure and the tidal arm stripped from the primary star in the simulations of star-disc encounters by Clarke & Pringle (1993). In this paper we use new hydrodynamical models and synthetic observations to fit many of the parameters of RW Aur. Using hydrodynamic models we find that the morphological appearance of RW Aur can be indeed explained by a tidal encounter with the secondary star. We reproduce all the major morphological and kinematic features of the system. Using radiative transfer calculations, we find that synthetic CO and dust continuum observations of our hydrodynamic models agree well with observations. We reproduce all the main features of the line profiles, from emission fluxes to the optical depth of the different components of the system. The agreement between observations and simulations thus lends strong support to the hypothesis of a tidal encounter scenario. Finally, we propose a possible solution for the origin of the dimming of the primary star observed in 2010/2011 by Rodriguez et al. (2013).