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Register a new userThe masses of the cataclysmic variables AC Cancri and V363 Aurigae
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T. D. Thoroughgood
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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 and its rotational velocity to be v sin i = 135 pm 3 km/s. From these parameters we obtain masses of M_1 = 0.76 pm 0.03 M_sun for the white dwarf primary and M_2 = 0.77 pm 0.05 M_sun 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 and v sin i = 143 pm 5 km/s respectively. The component masses of V363 Aur are M_1 = 0.90 pm 0.06 M_sun and M_2 = 1.06 pm 0.11 M_sun, 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.
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