We present time–resolved spectroscopy and photometry of the double–lined eclipsing cataclysmic variables AC Cnc and V363 Aur ( = Lanning 10 ) .
There is evidence of irradiation on the inner hemisphere of the secondary star in both systems , which we correct for using a model that reproduces the observations remarkably well .
We find the radial velocity of the secondary star in AC Cnc to be K _ { R } = 176 \pm 3 km s ^ { -1 } and its rotational velocity to be v \sin i = 135 \pm 3 km s ^ { -1 } .
From these parameters we obtain masses of M _ { 1 } = 0.76 \pm 0.03 M _ { \odot } for the white dwarf primary and M _ { 2 } = 0.77 \pm 0.05 M _ { \odot } for the K2 \pm 1V secondary star , giving a mass ratio of q = 1.02 \pm 0.04 .
We measure the radial and rotational velocites of the G7 \pm 2V secondary star in V363 Aur to be K _ { R } = 168 \pm 5 km s ^ { -1 } and v \sin i = 143 \pm 5 km s ^ { -1 } respectively .
The component masses of V363 Aur are M _ { 1 } = 0.90 \pm 0.06 M _ { \odot } and M _ { 2 } = 1.06 \pm 0.11 M _ { \odot } , giving a mass ratio of q = 1.17 \pm 0.07 .
The mass ratios for AC Cnc and V363 Aur fall within the theoretical limits for dynamically and thermally stable mass transfer .
Both systems are similar to the SW Sex stars , exhibiting single–peaked emission lines with transient absorption features , high–velocity S–wave components and phase–offsets in their radial velocity curves .
The Balmer lines in V363 Aur show a rapid increase in flux around phase 0 followed by a rapid decrease , which we attribute to the eclipse of an optically thick region at the centre of the disc .
This model could also account for the behaviour of other SW Sex stars where the Balmer lines show only a shallow eclipse compared to the continuum .