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We present observations proving the close binary nature of the central starsbelonging to the planetary nebulae (PNe) NGC 6326 and NGC 6778. Photometricmonitoring reveals irradiated lightcurves with orbital periods of 0.372 and0.1534 days, respectively, constituting firm evidence that they passed througha common-envelope (CE) phase. Unlike most surveys for close binary centralstars (CSPN) however, the binary nature of NGC 6326 was first revealedspectroscopically and only later did photometry obtain an orbital period.Gemini South observations revealed a large 160 km/s shift between the nebulaand emission lines of C III and N III well known to originate from irradiatedatmospheres of main-sequence companions. These so-called weak emission linesare fairly common in PNe and measurement of their radial velocity shifts inspectroscopic surveys could facilitate the construction of a statisticallysignificant sample of post-CE nebulae. There is growing evidence that thisprocess can be further accelerated by pre-selecting nebulae with traits ofknown post-CE nebulae. Both NGC 6326 and NGC 6778 were selected for their richattribution of low-ionisation filaments and collimated outflows, therebystrengthening the connection between these traits and post-CE CSPN.

Discovery of close binary central stars in the planetary nebulae NGC 6326 and NGC 6778