Eppur si muove... On the Origin of Long Secondary Periods in Red Giant Stars

TL;DR

This paper proposes that long secondary periods in red giant stars are caused by a dusty cloud orbiting with a brown-dwarf companion, which was originally a planet that gained mass from its host star.

Contribution

It demonstrates that binarity, involving a dusty cloud and a brown-dwarf companion, explains the long secondary periods in red giant stars, providing a new physical mechanism.

Findings

LSPs are caused by a dusty cloud orbiting with a brown dwarf.

The low-mass companion was originally a planet that accreted mass.

The proposed model explains the observed properties of LSPs.

Abstract

Long secondary periods (LSPs), observed in a third of pulsating red giant and supergiant stars, are the only unexplained type of large-amplitude stellar variability known at this time. Numerous authors have explored various scenarios for the origin of LSPs, but were unable to give a final solution to this problem. We present known properties of LSP variables and show new results proving that the physical mechanism responsible for LSPs is binarity. Namely, the LSP light changes are due to the presence of a dusty cloud orbiting the red giant together with a brown-dwarf companion and obscuring the star once per orbit. In this scenario, the low-mass companion is a former planet that accreted a significant amount of mass from the envelope of its host star and grew into a brown dwarf.