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

Abstract

We present high speed photometry and high resolution spectroscopy of the eclipsing post common envelope binary QS Virginis (QS Vir). Our UVES spectra span multiple 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 companion, allowing us to triangulate their positions. Despite showing small variations on a timescale of days, they persist for more than a year and may last decades. One large prominence extends almost three stellar radii from the M star. Roche tomography reveals that the M star is heavily spotted and that these spots are longlived and in relatively fixed locations, preferentially found on the hemisphere facing the white dwarf. We also determine precise binary and physical parameters for the system. We find that the 14, 220 ± 350 K white dwarf is relatively massive, 0.782 ± 0.013M ⊙ , and has a radius of 0.01068 ± 0.00007R ⊙ , consistent with evolutionary models. The tidally distorted M star has a mass of 0.382 ± 0.006M ⊙ and a radius of 0.381 ± 0.003R ⊙ , also consistent with evolutionary models. We find that the magnesium absorption line from the white dwarf is broader than expected. This could be due to rotation (implying a spin period of only ∼700 seconds), or due to a weak (∼100kG) magnetic field, we favour the latter interpretation. Since the M star's radius is still within its Roche lobe and there is no evidence that its over-inflated we conclude that QS Vir is most likely a pre-cataclysmic binary just about to become semi-detached.

Exploring the M-dwarf Luminosity–Temperature–Radius relationships using Gaia DR2

“…To produce the simulated input catalogue we iterated through immaculate photosphere temperature, adopting the effective temperature of the combined photosphere as given in Equation 13. Parsons et al (2018Parsons et al ( , 2016Parsons et al ( , 2012aParsons et al ( ,c,b, 2010.…”

Discovery of a pre-cataclysmic binary with unusual chromaticity of the eclipsed white dwarf by the GPX survey

“…Note that g, V model light curves are still not in perfect agreement with the observed one with either one or two spots. The small remaining differences are possibly related to the complex spot activity of the red dwarf (for an example, see Parsons et al 2016). We did not try to further improve the fit as it would require many more free parameters and make their values rather ambiguous.…”

The scatter of the M dwarf mass–radius relationship

“…Spectral types indicated with a * symbol were determined from the ineclipse r − i colour instead of template fitting. References for the other measurements are given in the final column: (1) This paper, (2) Parsons et al (2016), (3) Object Table 2 for those M dwarfs with spectral types between M1 and M5. In several cases the quality of the near-infrared spectrum was insufficient to give reliable equivalent width measurements for the sodium doublet.…”