YY Hya and its interstellar environment

During a search for previously unknown Galactic emission nebulae, we discovered faint 36' diameter Halpha nebula centered around the periodic variable YY Hya. Although this star has been classified as RR-Lyr variable, such classification is inconsistent Gaia distance of ~450 pc. GALEX image data also shows Hya to have strong UV excess, suggesting existence hot, compact binary companion. In addition our discovery data, obtained region with CHILESCOPE time-series spectroscopy at MDM observatory. Also, used from various space missions derive an exact orbital period and SED. We find that system containing K dwarf which strongly irradiated by hot WD The spectral characteristics lines, visible only during maximum light perfectly sinusoidal optical}light curve signatures much like members BE UMa family. These are post common envelope pre-cataclysmic variables. However companion here more massive than found in other group progenitor white must 3 4 Mo star. seems be ejected shell mass order one age 500000 years. This makes it biggest hitherto known shell. Alignment neighboring nebulosities some 45' northeast southwest suggests had bipolar outflows. briefly speculate might related 1065 BP "guest-star" reported ancient Chinese records well.