An XMM-Newton observation of the nearby “ pre-cataclysmic ” short-period ( P _ { orb } = 3.62 hr ) binary QS Vir ( EC 13471-1258 ) revealed regular narrow X-ray eclipses when the white dwarf passed behind its M2–4 dwarf companion .
The X-ray emission provides a clear signature of mass transfer and accretion onto the white dwarf .
The low-resolution XMM-Newton EPIC spectra are consistent with a cooling flow model and indicate an accretion rate of \dot { M } = 1.7 \times 10 ^ { -13 } M _ { \odot } /yr .
At 48 pc distant , QS Vir is then the second nearest accreting cataclysmic variable known , with one of the lowest accretion rates found to date for a non-magnetic system .
To feed this accretion through a wind would require a wind mass loss rate of \dot { M } \sim 2 \times 10 ^ { -12 } M _ { \odot } yr ^ { -1 } if the accretion efficiency is of the order of 10 % .
Consideration of likely mass loss rates for M dwarfs suggests this is improbably high and pure wind accretion unlikely .
A lack of accretion disk signatures also presents some difficulties for direct Roche lobe overflow .
We speculate that QS Vir is on the verge of Roche lobe overflow , and that the observed mass transfer could be supplemented by upward chromospheric flows on the M dwarf , analogous to spicules and mottles on the Sun , that escape the Roche surface to be subsequently swept up into the white dwarf Roche lobe .
If so , QS Vir would be in a rare evolutionary phase lasting only a million years .
The X-ray luminosity of the M dwarf estimated during primary eclipse is L _ { X } = 3 \times 10 ^ { 28 } erg s ^ { -1 } , which is consistent with that of rapidly rotating “ saturated ” K and M dwarfs .