The future influence of six exoplanets on the envelope properties of their parent stars on the giant branches

We study the evolution of six exoplanetary systems with the stellar evolutionary code Modules for Experiments in Stellar Astrophysics (MESA) and conclude that they will likely spin-up the envelope of their parent stars on the red giant branch (RGB) or later on the asymptotic giant branch (AGB) to the degree that the mass-loss process might become non-spherical. We choose six observed exoplanetary systems where the semimajor axis is a_i ≃ 1–2 au, and use the binary mode of MESA to follow the evolution of the systems. In four systems, the star engulfs the planet on the RGB, and in two systems on the AGB, and the systems enter a common envelope evolution (CEE). In two systems where the exoplanet masses are M_p ≃ 10M_J, where M_J is Jupiter mass, the planet spins up the envelope to about 10 per cent of the break-up velocity. Such envelopes are likely to have significant non-spherical mass-loss geometry. In the other four systems where M_p ≃ M_J the planet spins up the envelope to values of 1-2 per cent of break-up velocity. Magnetic activity in the envelope that influences dust formation might lead to a small departure from spherical mass-loss even in these cases. In the two cases of CEE on the AGB, the planet deposits energy to the envelope that amounts to >10 per cent of the envelope binding energy. We expect this to cause a non-spherical mass-loss that will shape an elliptical planetary nebula in each case.