Spatially resolved spectra of the accretion disc of the nova-like variable UU Aquarii

Time-resolved spectroscopy of the nova-like variable UU Aquarii is analysed with eclipse mapping techniques to produce spatially resolved spectra of its accretion disc and gas stream as a function of distance from disc centre in the range 3600–6900 Å. The spatially resolved spectra show that the continuum emission becomes progressively fainter and redder for increasing disc radius – reflecting the radial temperature gradient – and reveal that the H i and He i lines appear as deep, narrow absorption features in the inner disc regions, transitioning to emission with P Cyg profiles for intermediate and large disc radii. The spectrum of the uneclipsed component has strong H i and He i emission lines plus a Balmer jump in emission, and is explained as optically thin emission from a vertically extended disc chromosphere+wind. Most of the line emission probably arises from the wind. The spatially resolved spectra also suggest the existence of gas stream ‘disc-skimming’ overflow in UU Aqr, which can be seen down to R≃0.2R_L1. The comparison of our eclipse maps with those of Baptista, Steiner & Horne suggests that the asymmetric structure in the outer disc previously identified as the bright-spot may be the signature of an elliptical disc similar to those possibly present in SU UMa stars during superoutbursts.