Spiral Structure in Ip Pegasi; How Persistent Is It?

Figure 4. Trailed spectrograms (top panels), Doppler maps (middle panels) and computed data (bottom panels) are plotted for Hβ, He ii λ4686Å, and He i λ4472Å for both nights. The computed data were reconstructed from the Doppler maps. The letters A, B and C mark flares visible in both Hβ and He ii λ4686Å; these lead to some artifacts (diagonal stripes) in the maps. ABSTRACT We present spectroscopy of the dwarf nova IP Pegasi taken during two consecutive nights, 5 and 6 days after the start of an outburst. Even this late in the outburst, Doppler maps show marked spiral structure in the accretion disc, at least as strongly as seen earlier in other outbursts of IP Peg. The spiral shocks are present on both nights with no diminution in strength from one night to the next. The light curves of the lines show an offset to earlier phases, with the mid-eclipse of the emission lines displaced to phases between −0.015 ± 0.001 and −0.045 ± 0.009. This cannot be explained by the presence of the accretion shocks. As well as the fixed spiral pattern, the disc shows strong flaring in the Balmer and He ii λ4686Å lines. Irradiation-induced emission is seen from the companion star in the Balmer, He i, He ii, Mg ii, C ii, and other lines. The emission is located near the poles of the companion star, suggesting that the accretion disc shields the companion star substantially and thus has an effective H/R of order 0.2 at EUV wavelengths. The Balmer emission is distinctly broader than the other lines consistent with non-Doppler broadening.