An exoplanet's response to anisotropic stellar mass loss during birth and death

Abstract

The birth and death of planets may be affected by mass outflows from their parent stars during the T-Tauri or post-main-sequence phases of stellar evolution. These outflows are often modelled to be isotropic, but this assumption is not realistic for fast rotators, bipolar jets and supernovae. Here we derive the general equations of motion for the time evolution of a single planet, brown dwarf, comet or asteroid perturbed by anisotropic mass loss in terms of a complete set of planetary orbital elements, the ejecta velocity, and the parent star's co-latitude and longitude. We restrict our application of these equations to 1) rapidly rotating giant stars, and 2) arbitrarily-directed jet outflows. We conclude that the isotropic mass-loss assumption can safely be used to model planetary motion during giant branch phases of stellar evolution within distances of hundreds of au. In fact, latitudinal mass loss variations anisotropically affect planetary motion only if the mass loss is asymmetric about the stellar equator. Also, we demonstrate how constant-velocity, asymmetric bipolar outflows in young systems incite orbital inclination changes. Consequently, this phenomenon readily tilts exoplanetary orbits external to a nascent disc on the order of degrees.

ALMA observations of the nearby AGB star L2 Puppis

“…Lower mass planets are more likely to survive as their orbital radius will expand as the star loses mass. Accretion onto the companion or evaporation (Villaver & Livio 2009), anisotropic mass loss or jets (Veras et al 2013) and viscous interaction with the disk (Lin et al 1996) will also influence the companion's orbital evolution. While tidal factors should circularize the orbit relatively quickly, eccentricity pumping of the companion's orbit through interactions with the disk are likely to have a destabilizing influence.…”

The dust disk and companion of the nearby AGB star L2 Puppis

“…The similarity in position between the tip of spiral 1 and the start of plume 1 indicates that the plume may be ejected from this impact point, due to the local increased heating around the location of the shock. Finally, another speculative explanation is that a low mass companion (possibly recently formed in the disk) is accreting material expelled from the AGB star, and ejects material through polar jets (Veras et al 2013;Kim & Taam 2012).…”

Polluting white dwarfs with perturbed exo-comets

“…(5) and Eq. (9) are equivalent to those derived by Veras et al (2013) (their equations 24 and 25), but in our calculations we keep the true anomaly fixed as we change the star's mass. We do not consider the effects of white dwarf kicks, so we do not have to keep track of the orientation of the orbit.…”

“…In the commonly accepted scenario, small rocky bodies, like asteroids, are accreted onto the white dwarf thanks to their interaction with planets that have survived the post-main-sequence evolution of the star. This scenario, however, is hard to implement in reality because, during the last stages of stellar evolution, the inner solar system will evolve adiabatically (Veras et al 2013;Parriott & Alcock 1998;Farihi et al 2010), which means that the orbits of all the planets and asteroids will only scale up and this makes it difficult for them to be tidally disrupted. Models have also been developed in which the metals are accreted from bodies coming from beyond the ice line (Alcock et al 1986;Stone et al 2015).…”