[Paper Review] The post-common-envelope binary central star of the planetary nebula PN G283.7-05.1: A possible post-red-giant-branch planetary nebula central star

David Jones, H. M. J. Boffin+9 more|arXiv (Cornell University)|Jul 17, 2020

Stellar, planetary, and galactic studies45 references15 citations

TL;DR

This study identifies and characterizes the post-common-envelope binary central star of planetary nebula PN G283.7−05.1, revealing a 5.9-hour orbit with an irradiated M-type main-sequence star and a hot pre-white dwarf. The system's low central star mass (~0.3–0.4 M⊙) and evolutionary parameters suggest it formed via a common-envelope ejection while still on the red giant branch, making it a rare candidate for a post-red-giant-branch planetary nebula central star.

ABSTRACT

We present the discovery and characterisation of the post-common-envelope central star system in the planetary nebula PN G283.7$-$05.1. Deep images taken as part of the POPIPlaN survey indicate that the nebula may possess a bipolar morphology similar to other post-common-envelope planetary nebulae. Simultaneous light and radial velocity curve modelling reveals the newly discovered binary system to comprise a highly-irradiated, M-type main-sequence star in a 5.9 hour orbit with a hot pre-white-dwarf. The nebular progenitor is found to have a particularly low mass of around 0.4 M$_\odot$, making PN G283.7$-$05.1 one of only a handful of candidate planetary nebulae to be the product of a common-envelope event while still on the red giant branch. Beyond its low mass, the model temperature, surface gravity and luminosity are all found to be consistent with the observed stellar and nebular spectra through comparison with model atmospheres and photoionisation modelling. However, the high temperature (T$_\mathrm{eff}\sim$95kK) and high luminosity of the central star of the nebula are not consistent with post-RGB evolutionary tracks.

Motivation & Objective

• To identify and characterize the central star system of the planetary nebula PN G283.7−05.1, which exhibits signs of a complex, possibly bipolar morphology.
• To determine the orbital and stellar parameters of the binary system through simultaneous light and radial velocity curve modeling.
• To assess whether the nebula's progenitor evolved via a common-envelope phase while still on the red giant branch (post-RGB), based on the derived low central star mass.
• To test the consistency of the observed stellar and nebular spectra with theoretical model atmospheres and photoionization models.
• To evaluate the evolutionary implications of a central star with a mass of ~0.3–0.4 M⊙, which is inconsistent with standard post-AGB evolutionary tracks.

Proposed method

• Acquired deep imaging of PN G283.7−05.1 using the ESO-NTT with EFOSC2, revealing a bipolar-like nebular structure with extended emission arcs.
• Performed simultaneous multi-band photometry (B, V, R, i) and radial velocity monitoring using FORS2 on the ESO-VLT to obtain light and radial velocity curves.
• Applied the phoebe2 code to model the light and radial velocity curves, accounting for irradiated secondary star emission and eclipse depths.
• Used synthetic spectra and model atmospheres to match observed stellar and nebular emission-line fluxes, including [O iii] and Hα lines.
• Constrained the nebular physical parameters via photoionization modeling, comparing predicted to observed line fluxes.
• Evaluated the system's distance and consistency with Gaia parallax and Galactic structure using synthetic reddened magnitudes.

Experimental results

Research questions

• RQ1 Is the central star of PN G283.7−05.1 consistent with a post-common-envelope binary system formed during the red giant branch phase?
• RQ2 What are the orbital and stellar parameters (mass, temperature, radius) of the binary system, and how do they compare to evolutionary models?
• RQ3 Why does the observed high effective temperature (~95 kK) and luminosity of the central star not align with standard post-AGB evolutionary tracks?
• RQ4 Can the observed nebular emission-line fluxes be reproduced by a photoionization model consistent with the derived stellar parameters?
• RQ5 What does the low central star mass (~0.3–0.4 M⊙) imply for the common-envelope ejection mechanism and the evolutionary pathway of the progenitor?

Key findings

• The central star system in PN G283.7−05.1 is a post-common-envelope binary with a 5.9-hour orbital period, consisting of a hot pre-white dwarf and an irradiated M-type main-sequence star.
• The derived primary star mass is 0.34±0.05 M⊙ if irradiated emission lines originate from the stellar photocenter, or 0.42±0.05 M⊙ if they originate from the innermost point of the irradiated hemisphere.
• The system's effective temperature (~95 kK) and luminosity are inconsistent with standard post-AGB evolutionary tracks, suggesting a post-red-giant-branch origin.
• The nebular morphology, with extended emission arcs in Hα and [O iii], supports a bipolar structure, consistent with common-envelope shaping.
• Photoionization modeling of nebular emission lines yields physical parameters consistent with the stellar model, supporting the derived system parameters.
• The distance estimate of ~9 kpc is borderline consistent with Gaia parallax, and the nebula spans ~1 pc, placing it between the Sagittarius and Perseus arms of the Milky Way.