Two short mass-loss events that unveil the binary heart of Minkowski's Butterfly Nebula

TL;DR

This study uses high-resolution interferometric observations to reveal two short mass-loss events and binary system evidence at the center of Minkowski's Butterfly Nebula, shedding light on bipolar planetary nebula formation.

Contribution

It provides the first detailed observational evidence of binary-induced equatorial structures in Minkowski's Butterfly Nebula through millimeter interferometry.

Findings

Two eccentric rings formed during short mass-loss episodes.

Evidence of a binary system with a secondary mass < 0.2 solar masses.

Supports binary models for bipolar planetary nebulae formation.

Abstract

Studying the appearance and properties of bipolar winds is critical to understand the stellar evolution from the AGB to the planetary nebula (PN) phase. Many uncertainties exist regarding the presence and role of binary stellar systems, mainly due to the deficit of conclusive observational evidences. We investigate the extended equatorial distribution around the early bipolar planetary nebula M 2-9 ("Minkowski's Butterfly Nebula") to gather new information on the mechanism of the axial ejections. Interferometric millimeter observations of molecular emission provide the most comprehensive view of the equatorial mass distribution and kinematics in early PNe. Here we present subarcsecond angular-resolution observations of the 12CO J=2-1 line and continuum emission with the Plateau de Bure interferometer. The data reveal two ring-shaped and eccentric structures at the equatorial basis of the two coaxial optical lobes. The two rings were formed during short mass-loss episodes (~ 40 yr), separated by ~ 500 yr. Their positional and dynamical imprints provide evidence of the presence of a binary stellar system at the center, which yields critical information on its orbital characteristics, including a mass estimate for the secondary of ~< 0.2 \ms. The presence of a stellar system with a modest-mass companion at the center of such an elongated bipolar PN strongly supports the binary-based models, because these are more easily able to explain the frequent axisymmetric ejections in PNe.