The enigmatic central star of the planetary nebula PRTM 1

The central star of the planetary nebula PRTM 1 (PN G243.8-37.1) was previously found to be variable by M. Pena and colleagues. As part of a larger programme aimed towards finding post common-envelope binary central stars we have monitored the central star of PRTM 1 spectroscopically and photometrically for signs of variability. Over a period of ~3 months we find minimal radial velocity (<10 km/s) and photometric (< 0.2 mag) variability. The data suggest a close binary nucleus can be ruled out at all but the lowest orbital inclinations, especially considering the spherical morphology of the nebula which we reveal for the first time. Although the current data strongly support the single star hypothesis, the true nature of the central star of PRTM 1 remains enigmatic and will require further radial velocity monitoring at higher resolution to rule out a close binary. If in the odd case that it is a close binary, it would be the first such case in a spherical planetary nebula, in contradiction to current thinking.Comment: A&A, in pres

Ongoing surveys for close binary central stars and wider implications

Binary central stars have long been invoked to explain the vexing shapes of planetary nebulae (PNe) despite there being scant direct evidence to support this hypothesis. Modern large-scale surveys and improved observing strategies have allowed us to significantly boost the number of known close binary central stars and estimate at least 20% of PNe have close binary nuclei that passed through a common-envelope (CE) phase. The larger sample of post-CE nebulae appears to have a high proportion of bipolar nebulae, low-ionisation structures (especially in SN1987A-like rings) and polar outflows or jets. These trends are guiding our target selection in ongoing multi-epoch spectroscopic and photometric surveys for new binaries. Multiple new discoveries are being uncovered that further strengthen the connection between post-CE trends and close binaries. These ongoing surveys also have wider implications for understanding CE evolution, low-ionisation structure and jet formation, spectral classification of central stars, asymptotic giant branch (AGB) nucleosynthesis and dust obscuration events in PNe.Comment: To appear in IAU Symposium 283: Planetary Nebulae, an Eye to the Future. 4 pages, 1 figur