M1-92: AGB interruption and isotopic ratio paradox. Chemistry and morpho-kinematics from improved shapemol modelling

TL;DR

This paper updates the SHAPE and SHAPEMOL modelling tools to include more molecular species, applying them to study the pre-planetary nebula M1-92's physical, chemical, and isotopic properties using extensive observational data.

Contribution

The authors enhanced the modelling tools with new molecular species and demonstrated their application to M1-92, revealing detailed nebular properties and isotopic ratio variations.

Findings

Successfully reproduced 23 spectral line profiles and 5 maps of M1-92.

Derived nebula mass, momentum, and energy distributions.

Identified significant isotopic ratio discrepancies across nebular structures.

Abstract

The shaping of planetary nebulae on their evolution from asymptotic giant branch circumstellar envelopes to their final, most often axisymmetrical, form is still a process with many unknown details. The key to understanding the whole shaping process is the study of the transition objects called pre-planetary nebulae (pPNe). In this context, modelling tools must be kept to the standard of radio telescope capabilities, so we can make the most of the data they collect. In this work we first present the newest update of the SHAPE and SHAPEMOL modelling tools, adding ten new molecular species to be reproduced together with other general improvements. Later, we put this new update into practice to study M1-92, a pPN with a rich chemistry that can provide valuable information on its origin and shaping. We created a 3D morpho-kinematical model of the nebula in SHAPE that is able to reproduce 23 line profiles from the IRAM 30m telescope and HIFI/HSO and five maps from IRAM NOEMA. The observational dataset is reproduced simultaneously under the same physical conditions, adjusting only the relative abundance of the different species. We obtained a full description of the nebula's physical and chemical properties, and we provide the total estimates for mass (0.79 $M_\odot$), linear momentum (4.10$\times10^{39}$ g cm s$^{-1}$), and kinetic energy (6.48$\times10^{45}$ erg) as well as their detailed distribution across the nebula. We also analysed the isotopic ratios, finding robust discrepancies (values of 10 versus 30) in the $^{12}$C/$^{13}$C ratio across structures depending on their age.