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Context. We present time-resolved spectroscopy and photometry of HS0218+3229, a new long-period cataclysmic variable discovered within the HamburgQuasar Survey. It is one of the few systems that allow a dynamical measurementof the masses of the stellar components. Aims. We combine the analysis oftime-resolved optical spectroscopy and R-band photometry with the aim ofmeasuring the mass of the white dwarf and the donor star and the orbitalinclination. Methods. Cross-correlation of the spectra with K-type dwarftemplates is used to derive the radial velocity curve of the donor star. Anoptimal subtraction of the broadened templates is performed to measure therotational broadening and constrain the spectral type of the donor. Finally, anellipsoidal model is fitted to the R-band light curve to obtain constraintsupon the orbital inclination of the binary system. Results. The orbital periodof HS 0218+3229 is found to be 0.297229661 +- 0.1 d (7.13351186 +-0.2 h), and the amplitude of the donor's radial velocity curve is K2 =162.4 +- 1.4 km/s. Modelling the ellipsoidal light curves gives an orbitalinclination in the range i = 59 +- 3 deg. A rotational broadening between 82.4+- 1.2 km/s and 89.4 +- 1.3 km/s is found when assuming zero and continuum limbdarkening, respectively. The secondary star has most likely a spectral type K5and contributes ~ 80-85% to the R-band light. Our analysis yields a mass ratioof 0.52 < q < 0.65, a white dwarf mass of 0.44 < M1(Msol) < 0.65, and a donorstar mass of 0.23 < M2(Msol) < 0.44. Conclusions. We find that the donor starin HS 0218+3229 is significantly undermassive for its spectral type. It istherefore very likely that it has undergone nuclear evolution prior to theonset of mass transfer.

An evolved donor star in the long-period cataclysmic variable HS 0218+3229