Minkowski's Footprint revisited. Planetary Nebula formation from a single sudden event?

TL;DR

This study uses high-resolution interferometry to analyze the molecular gas in the bipolar pre-planetary nebula M1-92, suggesting it was formed by a brief, magneto-rotational explosion event that shaped its axial symmetry.

Contribution

It provides detailed morphological and kinematic analysis of M1-92, proposing a single sudden event as the formation mechanism for the nebula's structure.

Findings

Equatorial component is a thin, expanding disk.

Nebula's shape formed within 100-120 years.

Single brief acceleration event explains current kinematics.

Abstract

M1-92 can be considered an archetype of bipolar pre-planetary nebulae. It shows a clear axial symmetry, along with the kinematics and momentum excess characteristic of this class of envelopes around post-AGB stars. By taking advantage of the new extended configuration of the IRAM Plateau de Bure interferometer, we wanted to study the morphology and velocity field of the molecular gas better in this nebula, particularly in its central part. We performed sub-arcsecond resolution interferometric observations of the J=2-1 rotational line 13CO M1-92. We found that the equatorial component is a thin flat disk, which expands radially with a velocity proportional to the distance to the center. The kinetic age of this equatorial flow is very similar to that of the two lobes. The small widths and velocity dispersion in the gas forming the lobe walls confirm that the acceleration responsible for the nebular shape could not last more than 100-120 yr. The present kinematics of the molecular gas can be explained as the result of a single brief acceleration event, after which the nebula reached an expansion velocity field with axial symmetry. In view of the similarity to other objects, we speculate on the possibility that the whole nebula was formed as a result of a magneto-rotational explosion in a common-envelope system.