The crowded magnetosphere of the post-common-envelope binary QS Virginis

We present high-speed photometry and high-resolution spectroscopy of the short-period (P_rot = 3.6 h) eclipsing post-common-envelope binary QS Virginis (QS Vir). Our UVES spectra span in excess of 6 orbits, over more than a year, and reveal the presence of several large prominences passing in front of both the M star and its white dwarf (WD) companion. Despite showing small variations on a time-scale of days, they persist for more than a year and may last decades. Roche tomography reveals a heavily spotted M star, with long-lived spots remaining in fixed locations, preferentially found on the hemisphere facing the WD. We find the 14,220 ± 350 K WD is relatively massive at 0.782 ± 0.013 M\(_{\odot}\), with a radius of 0.01068 ± 0.00007 R\(_{\odot}\), consistent with evolutionary models. The tidally distorted M star has a mass of 0.382 ± 0.006 M\(_{\odot}\) and a radius of 0.381 ± 0.003 R\(_{\odot}\), also consistent with evolutionary models. Since the M star’s radius is still within its Roche lobe and there is no evidence that it is overinflated, we conclude that QS Vir is most likely a pre-cataclysmic binary just about to become semidetached.