SDSO1 is a Ghost Planetary Nebula Bow Shock in Front of M31

TL;DR

This paper identifies SDSO1 as a ghost planetary nebula bow shock driven by a binary star, revealing a new phase of planetary nebula evolution characterized by shock interactions with the interstellar medium.

Contribution

It introduces the shock-powered GPN phase as a novel stage in planetary nebula evolution and presents evidence linking SDSO1 to a specific binary star, EG Andromedae.

Findings

SDSO1 is a bow shock caused by a ghost planetary nebula.

The shock-powered GPN phase is a newly identified evolutionary stage.

Seven additional candidate GPNs with shock-tail morphology were found.

Abstract

We present new, deep narrow band imagery and discuss the nature of SDSO1, the large [O III]-emitting nebula centered 1.5 degrees SE of M31. We find strong evidence to support the hypothesis that SDSO1 is unrelated to M31 and is instead a bow shock driven by a faded, giant (D = 20 pc), 400 kyr-old, ghost planetary nebula (GPN) expelled by the symbiotic WD binary star EG Andromedae. Because EG And lags the rotation of the Milky Way, its hypersonic velocity of 107 km/s drives a shock into the local interstellar medium. SDSO1 also sports a 45-pc long turbulent tail that crosses M31. We establish the shock-powered GPN phase as a new phase of PN evolution, and identify seven more candidate GPNe by their large size and shock-tail morphology. This includes several giant halos of younger planetary nebulae, possibly expelled by now degenerate binary companions. The interaction of an old, fast-moving GPN with the ISM generates a shock that remains visible long after the photoionized PN shell has faded below the limit of detectability. The SDSO1 GPN has reached a phase in its evolution where its outward expansion has been slowed considerably by the work it has done on the interstellar medium. Once the GPN outflow expends the rest of its kinetic energy, it will be stripped from EG And and mix into the surrounding ISM.