Detection of Ubiquitous Circumbinary Matter in Hot Subdwarfs Formed from Common-Envelope Ejections

TL;DR

This study provides observational evidence of long-lived circumstellar material around hot subdwarf stars, originating from common-envelope ejections, thereby offering new insights into post-CE binary evolution.

Contribution

It presents the first large-scale spectroscopic detection of circumbinary matter around sdB stars, confirming its persistence long after the CE phase.

Findings

Ca II K absorption lines indicate presence of CSM in 145 sdB stars.

Velocities of CSM match systemic velocities, confirming origin from CE ejections.

Circumstellar material persists long after the CE event.

Abstract

The formation of compact binary systems is largely driven by their evolution through a common envelope (CE) phase, crucial for understanding phenomena such as type Ia supernovae and black hole mergers. Despite their importance, direct observational evidence for CE material has been elusive due to the transient nature of these envelopes. Numerical simulations suggest that some envelope material may persist post-ejection. In this study, we investigate circumstellar material (CSM) surrounding hot subdwarf (sdB) stars, focusing on material ejected during the CE phase of binary evolution. We analyze Ca II K absorption lines in 727 sdB candidates from the LAMOST-LRS survey, selecting 145 stars with strong absorption features, indicating the presence of CSM. We compare the velocities of the Ca II K lines with the systemic velocities of sdB binaries, confirming that the material originates from ejected common-envelope material. The results show that the CSM persists long after the CE event, suggesting the formation of a stable, long-lived circumstellar environment around sdB stars. This study enhances our understanding of the role of CSM in post-CE evolution and provides new insights into the physical processes shaping the evolution of sdB binaries.