2011A&A...531A..34S

Medium-resolution spectroscopic observations with full phase coverage of the eclipsing polar HU Aqr are presented. NaI absorption and CaII emission lines are used to trace the secondary star. While the NaI lines seem to have contributions from both hemispheres of the donor star, the CaII lines were found to originate from the irradiated part of its surface alone. An irradiation model was applied and the irradiation-weighted radial velocity amplitude was used to determine the mass ratio Q=M_WD/M₂=4.58±0.20. When combined with high-speed photometric low-state eclipse light curves, the white dwarf mass is constrained to 0.75<M_WD/M_☉<0.84 with a best-fit value of M_WD=(0.80±0.04)M_☉, and M₂=(0.18±0.06)M_☉ at an orbital inclination of i=87°^+0.8_–0.5.