IP Pegasi in outburst: Echelle spectroscopy & Modulation Doppler Tomography∗

We analyse a unique set of time-resolved echelle spectra of the dwarf nova IP Peg, obtained at the ESO NTT with EMMI on the 4th of August 1999, just one day after the peak of an outburst. The dataset covers the wavelength range of 4000–7500 Å and shows Balmer, HeI, HeII and heavier elements in emission. IP Peg was observed one day after the peak of an outburst. The trailed spectra, spectrograms and Doppler maps show characteristics typical of IP Pegasi during the early stages of its outburst, such as prograde rotation from the accretion disc flow, chromospheric emission from the secondary and spiral arms. The high-ionisation line of HeII λ4686 is the most centrally located line and its formation region has the greatest radial extension compared to the HeI lines. The Balmer lines extend from close to the white dwarf up to ≈ 0.45RL, with the outer radius gradually increasing when moving from Hδ to Hα. The application, for the first time, of the modulation Doppler tomography technique, maps any harmoni-cally varying components present in the system configuration, and this variabilit