Discovery of a close substellar companion to the hot subdwarf star HD 149382 - The decisive influence of substellar objects on late stellar evolution

TL;DR

This paper reports the discovery of a close substellar companion to the hot subdwarf star HD 149382, demonstrating how such objects can influence stellar evolution and the formation of hot subdwarfs.

Contribution

It provides the first direct evidence that substellar objects can survive engulfment and trigger envelope ejection, affecting the evolution of hot subdwarf stars.

Findings

Discovered a 8-23 Jupiter-mass companion orbiting HD 149382.

The companion likely survived red-giant envelope engulfment.

Substellar objects may influence UV emission in elliptical galaxies.

Abstract

Substellar objects, like planets and brown dwarfs orbiting stars, are by-products of the star formation process. The evolution of their host stars may have an enourmous impact on these small companions. Vice versa a planet might also influence stellar evolution as has recently been argued. Here we report the discovery of a 8-23 Jupiter-mass substellar object orbiting the hot subdwarf HD 149382 in 2.391 days at a distance of only about five solar radii. Obviously the companion must have survived engulfment in the red-giant envelope. Moreover, the substellar companion has triggered envelope ejection and enabled the sdB star to form. Hot subdwarf stars have been identified as the sources of the unexpected ultravoilet emission in elliptical galaxies, but the formation of these stars is not fully understood. Being the brightest star of its class, HD 149382 offers the best conditions to detect the substellar companion. Hence, undisclosed substellar companions offer a natural solution for the long-standing formation problem of apparently single hot subdwarf stars. Planets and brown dwarfs may therefore alter the evolution of old stellar populations and may also significantly affect the UV-emission of elliptical galaxies.