Constraints on Common Envelope Magnetic Fields from Observations of Jets in Planetary Nebulae

TL;DR

This study uses observations of jets in planetary nebulae to infer magnetic field strengths during common envelope interactions, revealing different jet timings and magnetic field magnitudes that inform models of stellar evolution.

Contribution

It provides new estimates of magnetic field strengths associated with jets in post-common envelope planetary nebulae, highlighting differences between pre- and post-CE jet formation scenarios.

Findings

Pre-CE jets likely launched before Roche lobe overflow with magnetic fields of a few Gauss.

Post-CE jets show magnetic fields of hundreds to thousands of Gauss.

Inconsistent jet formation scenarios for NGC 6778 due to orbital constraints.

Abstract

The common envelope (CE) interaction describes the swallowing of a nearby companion by a growing, evolving star. CEs that take place during the asymptotic giant branch phase of the primary and may lead to the formation of a planetary nebula (PN) with a post-CE close binary in the middle. We have used published observations of masses and kinematics of jets in four post-CE PN to infer physical characteristics of the CE interaction. In three of the four systems studied, Abell 63, ETHOS 1 and the Necklace PN, the kinematics indicate that the jets were launched a few thousand years before the CE and we favour a scenario where this happened before Roche lobe overflow, although better models of wind accretion and wind Roche lobe overflow are needed. The magnetic fields inferred to launch pre-CE jets are of the order of a few Gauss. In the fourth case, NGC 6778, the kinematics indicate that the jets were launched about 3000 years after the CE interaction. Magnetic fields of the order of a few hundreds to a few thousands Gauss are inferred in this case, approximately in line with predictions of post-CE magnetic fields. However, we remark that in the case of this system, it is impossible to find a reasonable scenario for the formation of the two jet pairs observed: the small orbital separation would preclude the formation of even one accretion disk able to supply the necessary accretion rate to cause the observed jets.