Detection of the white dwarf and the secondary star in the newSU UMa dwarf nova HS 2219+1824

We report the discovery of a new, non-eclipsing SU UMa-type dwarf nova, HS 2219+1824. Photometry obtained in quiescence ($V\approx17.5$) reveals a double-humped light curve from which we derive an orbital period of $\simeq$86.2 min. Additional photometry obtained during a superoutburst reaching $V\simeq12.0$ clearly shows superhumps with a period of $\simeq$89.05 min. The optical spectrum contains double-peaked Balmer and He I emission lines from the accretion disc as well as broad absorption troughs of ${\mathrm H\beta}$, ${\mathrm H\gamma}$, and ${\mathrm H\delta}$ from the white dwarf primary star. Modelling of the optical spectrum implies a white dwarf temperature of $13\,000\,\mathrm{K}\la\mbox{$T_{\mathrm{eff}}$}\la17\,000\,\mathrm{K}$, a distance of $180\,\mathrm{pc}\la d\la230\,\mathrm{pc}$, and suggests that the spectral type of the donor star is later than M 5. Phase-resolved spectroscopy obtained during quiescence reveals a narrow ${\mathrm H\alpha}$ emission line component which has a radial velocity amplitude and phase consistent with an origin on the secondary star, possibly on the irradiated hemisphere facing the white dwarf. This constitutes the first detection of line emission from the secondary star in a quiescent SU UMa star.