Planets around Extreme Horizontal Branch Stars

TL;DR

This paper reviews recent findings on how tidal interactions affect planetary survival during stellar evolution, the potential multiplicity of planets around sdB/sdO stars, and the evaporation of close-in substellar objects due to stellar radiation.

Contribution

It introduces a refined model of tidal interactions influencing planetary survival, suggests multiple planets can exist around certain evolved stars, and discusses observational signatures of evaporating substellar objects.

Findings

Proper tidal treatment increases planetary survivability during common envelope phases.

Multiple planets likely exist around sdB/sdO stars, with diverse orbital periods.

Evaporated gas from close-in substellar objects produces detectable Doppler-shifted emission lines.

Abstract

We review three main results of our recent study: We show that a proper treatment of the tidal interaction prior to the onset of the common envelope (CE) leads to an enhance mass loss. This might increase the survivability of planets and brown dwarfs that enter a CE phase. From the distribution of planets around main sequence stars, we conclude that around many sdB/sdO stars more than one planet might be present. One of these might have a close orbit and the others at about orbital periods of years or more. We show that the intense ionizing flux of the extreme horizontal branch star might evaporate large quantities of a very close surviving substellar object. Balmer emission lines from the evaporated gas can be detected via their Doppler shifts.