1994A&A...292..481A

Time resolved spectroscopy is presented of the SU UMa type dwarf nova VY Aqr in superoutburst and quiescence. From the radial velocity variations found in outburst I derive on the basis of the value for the superhump period an orbital period of 0.06348(12)days (or possibly 0.06787(13)days). The radial-velocity amplitude is 29(5)km/s. In the outburst spectra taken ∼5days after maximum light evidence is found for the presence of a blue shifted narrow emission component superposed on the broad absorption lines, which is not found in spectra taken 2 nights later. Also a change of ∼150km/s in the system velocity is found over these 2 nights. Using various observational constraints I derive q=M_WD/M_RD≃8-10 and i≃30-40deg. The orbital period and mass ratio of VY Aqr are very similar to those of the well known SU UMa type dwarf nova OY Car. However, the amplitudes of the outburst in VY Aqr are ∼3magnitude larger than those of OY Car. I argue that this is due to a lower mass transfer rate during quiescence in VY Aqr compared to OY Car, which results in VY Aqr being relatively fainter in quiescence.