M1-92: Asymptotic giant branch interruption and isotopic ratio paradox

Chemistry and morpho-kinematics from improved shapemol modelling

¹ Observatorio Astronómico Nacional (OAN-IGN), Alfonso XII 3, 28014 Madrid, Spain
² Facultad de Ciencias Físicas, Pl. de Ciencias 1, Universidad Complutense de Madrid (UCM), 28040 Madrid, Spain
³ Observatorio Astronómico Nacional (OAN-IGN), Apartado 112, 28803 Alcalá de Henares, Spain
⁴ Centro de Astrobiología (CAB), CSIC-INTA, ESAC, Camino Bajo del Castillo s/n, 28691 Villanueva de la Cañada, Spain
⁵ Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 Saint-Martin-d’Hères, France
⁶ Ilumbra, AstroPhysical MediaStudio, Kaiserslautern, Germany
⁷ Department of Physics and Astronomy, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 30 May 2025
Accepted: 19 March 2026

Abstract

Aims. 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.

Methods. 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.

Results. We created a 3D morpho-kinematical model of the nebula in SHAPE that is able to reproduce 23 line profiles from the IRAM 30 m 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.

Conclusions. We obtained a full description of the nebula’s physical and chemical properties, and we provide the total estimates for mass (0.79 M_⊙), linear momentum (4.10×10³⁹ g·cm·s⁻¹), and kinetic energy (6.48×10⁴⁵ 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 ¹²C/¹³C ratio across structures depending on their age.