A spectroscopic study of V603 Aquilae: stellar parameters and continuum-line variations

A time-resolved spectroscopic study of V603 Aql (Nova Aquilae 1918) is pres ented. An orbital period of P-orb = 0.(d)1385 +/- 0.(d)0002, consistent wit h previous results, and a radial velocity semi-amplitude of K = 20 +/- 3 km s(-1) are obtained from the radial velocity variations of the H beta emiss ion line. Similar K values are also found in H gamma, H delta, and He I emi ssion lines. Using the measured FWHM of the H beta line and assuming that t he derived semi-amplitude is that of the white dwarf, we deduce a most like ly mass ratio of q = 0.24 +/- 0.05 and stellar masses of M-2 = 0.29 +/- 0.0 4 M-circle dot and M-1 = 1.2 +/- 0.2 M-circle dot for the secondary and pri mary (the white dwarf) star, respectively. The dynamical solution also indi cates a very low orbital inclination, i = 13 degrees +/- 2 degrees. We find that the continuum and line variations are modulated with both the positiv e and the negative superhump periods, indicating that they arise from simil ar regions of the accretion disc. Moreover, we find, for the first time fro m 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 ob served positive superhumps. A nodal precession in the accretion disc is cur rently believed to be the cause of the observed negative superhumps. The lo w value of q is consistent with the expected value for systems that show su perhumps, in accordance with the eccentric disc model. We find no evidence of periodicity associated with the spin period.