http://arxiv.org/abs/1703.10891
Whether planetary nebulae (PNe) are predominantly the product of binary stellar evolution as some population synthesis models (PSM) suggest remains an open question. Around 50 short period binary central stars ($P\sim1$ d) are known, but with only four known with $P>10$ d our knowledge is severely incomplete. Here we report on the first discovery from a systematic SALT HRS survey for long period binary central stars. We find a 142 d orbital period from radial velocities of the central star of NGC 1360, HIP 16566, infamous for its now disproven kilogauss magnetic field. NGC 1360 appears to be the product of common-envelope (CE) evolution with an orbital period at the upper range predicted for post-CE PSM and nebula features similar to post-CE PNe. The most striking feature is a newly-identified ring of low-ionisation structures (LIS) whose inclination matches $i=30\pm10$ deg from spatio-kinematic modelling of the nebula. Assuming a binary coplanar with the nebula, multi-wavelength observations best fit an evolved WD companion with $M=0.7$ $M_\odot$, $L\sim50$ $L_\odot$ and $T_\mathrm{eff}=115$ kK. Nebular kinematics also indicate fallback of CE ejecta occurred in NGC 1360 and simulations show that $\sim$0.2 $M_\odot$ could have formed into a circumbinary disk. Photoionisation and fragmentation of such a disk, or a post-AGB binary disk that survived into the PN phase, may be central to forming the ring of LIS. Large radial velocity variability detected by lower resolution surveys suggests long period binaries may be much more common than PSM models predict, supporting a 40–50 per cent total binary fraction for PNe.
B. Miszalski, R. Manick, J. Mikolajewska, et. al.
Mon, 3 Apr 17
6/38
Comments: 13 pages, 8 figures, 4 tables. Submitted to MNRAS
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