Vol. 584
In section 7. Stellar structure and evolution

Outburst evolution, historic light curve and a flash-ionized nebula around the WZ Sge-type object PNV J03093063+2638031

The paper reports detection of a time-variable circumstellar emission region revealed by an ionizing outburst, which is a lovely new and unexpected phenomenon observed during the outburst of a WZ Sge-type binary. While such ambient, flash-ionized nebulae have already been detected around supernovae, this is the first found around a non-explosive cataclysmic binary. The authors use long-slit spectroscopy to spatially distinguish the nebula from the star. It has an angular extent of 50 arcsec, and they estimate the density from the recombination rate during the post-outburst relaxation. The mass presented for this nebula cannot be produced by any active source, such as a wind from the current system, nor is there any indication of explosive mass ejection. Several hypotheses, including that it is the remnant of the slow pre-cataclysmic AGB wind, are critically examined, but none yields a satisfactory explanation. This is very likely a generic property of many such systems and promises to be a fruitful area for future research.