Orbital periods of cataclysmic variables identified by the SDSS. VI. The 4.5-h period eclipsing system SDSS J100658.40+233724.4

We present time-resolved spectroscopy and photometry of SDSS J100658.40+233724.4, which we have discovered to be an eclipsing cataclysmic variable with an orbital period of 0.18591324 days (267.71507 min). The observed velocity amplitude of the secondary star is 276 ± 7 kms−1, which an irradiation correction reduces to 258 ± 12 km s−1. Doppler tomography of emission lines from the infrared calcium triplet supports this measurement. We have modelled the light curve using the lcurve code and Markov Chain Monte Carlo simulations, finding a mass ratio of 0.51 ± 0.08. From the velocity amplitude and the light curve analysis we find the mass of the white dwarf to be 0.78±0.12 M and the masses and radii of the secondary star to be 0.40±0.10 M and 0.466±0.036 R,respectively. The secondary component is less dense than a normal main sequence star but its properties are in good agreement with the expected values for a CV of this orbital period. By modelling the spectral energy distribution of the system we find a distance of 676 ± 40 pc and estimate a white dwarf effective temperature of 16 500 ± 2000 K.