Emission-line mapping of the dwarf nova IP Pegasi in outburst and quiescence

Time-resolved spectroscopy covering half an orbit and one eclipse during an outburst of the dwarf nova IP Peg are presented and compared with quiescent data. The outburst spectra show strong Balmer and He II 4686 A emission lines that are atypical of outbursting dwarf novae. Double-peaked velocity profiles and rotational distortions during eclipse show that the lines arise primarily in a Keplerian accretional disk. The He II line profile is filled in between the two disk peaks by non-Keplerian emission from close to the white dwarf, possibly indicative of a compact outflowing wind or inflowing magnetic accretion column. During outburst, an accretion rate of roughly 10 to the 17th g/s is needed to acccount for the continuum emission of the disk. The associated boundary layer generates soft X-ray and Lyman continuum fluxes sufficient to photoionize the disk's He II and Balmer emission-line regions. The disk appears to shield the red star totally from the soft X-rays, and in the equatorial region, from the Lyman continuum. 46 refs