On the post-common-envelope central star of the planetary nebula NGC 2346

Abstract

The common-envelope phase is one of the most poorly understood phases of (binary) stellar evolution, in spite of its importance in the formation of a wide-range of astrophysical phenomena ranging from cataclysmic variables to cosmologically important supernova type Ia, and even recently discovered gravitational wave producing black hole mergers. The central star of the planetary nebula NGC~2346 has long been held as one of the longest period post-common-envelope systems known with a published period of approximately 16 days, however the data presented were also consistent with much shorter periods of around 1 day (a more typical period among the known sample of post-common-envelope binary central stars). Here, using the modern high-stability, high-resolution spectrograph HERMES, we conclusively show the period to, indeed, be 16 days while also revising the surface gravity to a value typical of a sub-giant (rather than main-sequence) resulting in an intrinsic luminosity consistent with the recently published GAIA parallax distance. Intriguingly, the implied mass for the secondary ($\gtrsim$3.5 M${}_{\odot }$) makes it, to our knowledge, the most massive post-common-envelope secondary known, whilst also indicating that the primary may be a post-RGB star.

6 pages, 6 figures

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• Catalogue of central stars of planetary nebulae: Expanded edition
• Binary Central Stars of Planetary Nebulae Identified With Kepler/K2
• Observational Constraints on the Common Envelope Phase
• Mysterious, Variable, and Extremely Hot: White Dwarfs Showing Ultra-High Excitation Lines I. Photometric Variability
• The ionised and molecular mass of post-common-envelope planetary nebulae. The missing mass problem
• The post-common-envelope binary nucleus of the planetary nebula IC~4776: Neither an anomalously long orbital period nor a Wolf-Rayet binary
• Morphokinematic modelling of the point-symmetric Cat's Eye, NGC 6543: Ring-like remnants of a precessing jet
• The future influence of six exoplanets on the envelope properties of their parent stars on the giant branches
• The Central Star of NGC 2346 as a Clue to Binary Evolution through the Common Envelope Phase