Filming the evolution of symbiotic novae with VLBI

In symbiotic novae, the material ejected from the surface of the white dwarf (WD) after the thermonuclear runaway drives a strong shock through the dense circumstellar gas produced by the red giant (RG) wind. Recurring symbiotic novae such as V407 Cyg and RS Oph are perfect real-time laboratories for studying physical processes as diverse as accretion, thermonuclear explosions, shock dynamics and particle acceleration; in many ways they are like supernova remnants on fast forward. In this talk, I will present the results of two intensive VLBI campaigns carried out for the two high energy symbiotic novae V407 Cyg and RS Oph, after their explosions in 2010 and 2021, respectively. These campaigns provided a resolved view of the structure of the ejected material and of its evolution, setting unique and independent constraints on the emission mechanisms, the physical processes at work, the presence and location of shock acceleration, the geometry of the system, and the density profile of the RG wind.