2000MNRAS.311..135A

A time-resolved spectroscopic study of V603 Aql (Nova Aquilae 1918) is presented. An orbital period of P_orb=0{fday}1385±0{fday}0002, consistent with previous results, and a radial velocity semi-amplitude of K=20±3km.s^–1 are obtained from the radial velocity variations of the Hβ emission line. Similar K values are also found in Hγ, Hδ, and Hei emission lines. Using the measured FWHM of the Hβ line and assuming that the derived semi-amplitude is that of the white dwarf, we deduce a most likely mass ratio of q=0.24±0.05 and stellar masses of M₂=0.29±0.04M_☉ and M₁=1.2±0.2M_☉ for the secondary and primary (the white dwarf) star, respectively. The dynamical solution also indicates a very low orbital inclination, i=13°±2°. We find that the continuum and line variations are modulated with both the positive and the negative superhump periods, indicating that they arise from similar regions of the accretion disc. Moreover, we find, for the first time from spectroscopy, evidence of negative superhumps in addition to the positive superhumps. Positive superhumps are explained within the disc instability model as caused by an eccentric disc surrounding the white dwarf, which is precessing (apsidal advance) because of tidal instabilities, causing the observed positive superhumps. A nodal precession in the accretion disc is currently believed to be the cause of the observed negative superhumps. The low value of q is consistent with the expected value for systems that show superhumps, in accordance with the eccentric disc model. We find no evidence of periodicity associated with the spin period.