A red giant branch common envelope evolution scenario for the exoplanet WD 1856 b

Abstract

We propose a common envelope evolution (CEE) scenario where a red giant branch (RGB) star engulfs a planet during its core helium flash to explain the puzzling system WD 1856+534 where a planet orbits a white dwarf (WD) of mass 0.52Mo with an orbital period of 1.4 day. At the heart of the scenario is the recently proposed assumption that the vigorous convection that core helium flash of RGB stars drive in the core excite waves that propagate and deposit their energy in the envelope. Using the binary-MESA stellar evolution code we show that this energy deposition substantially reduces the binding energy of the envelope and causes its expansion. We propose that in some cases RGB stars might engulf massive planets of ~0.01Mo during their core helium flash phase, and that the planet can unbind most of the mass of the bloated envelope. We show that there is a large range of initial orbital radii for which this scenario might take place under our assumptions. This scenario is relevant to other systems of close sub-stellar objects orbiting white dwarfs, like the brown dwarf-WD system ZTFJ003855.0+203025.5.

Accept for publication in The Astrophysical Journal Letters

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• Potential for life to exist and be detected on Earth-like planets orbiting white dwarfs
• Small and Close-In Planets are Uncommon Around A-type Stars
• Rapid expansion of red giant stars during core helium flash by waves propagation to the envelope and implications to exoplanets
• Common envelope evolution and triple dynamics as potential pathways to form the inner white dwarf + brown dwarf binary of the triple star system Gaia 0007-1605
• Residual eccentricity of an Earth-like planet orbiting a red giant Sun
• Aerosols and hydrocarbons in the atmosphere of a white dwarf planet
• Second-generation planet formation after tidal disruption from common envelope evolution
• Atmospheric Signatures of Common Envelope Evolution in White Dwarf Planets