Origin of the concentric rings around GR Cygni

Determine whether the concentric ionized rings around the carbon-rich symbiotic binary GR Cygni were produced by recurring nova outbursts rather than by enhanced mass loss during helium-shell thermal pulses.

Background

The paper proposes that the two rings around GR Cygni may record separate episodes of enhanced mass loss. Their spacing is broadly consistent with the interval between helium-shell thermal pulses in an asymptotic-giant-branch star, but the authors also identify recurring nova outbursts from the accreting white-dwarf companion as an alternative explanation. The available historical photometry does not rule out a short, unobserved nova eruption, so the origin of the rings remains unresolved.