The evolution of complex organic molecules during star formation

¹ Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS, CNES, 9 av. du Colonel Roche, 31028 Toulouse Cedex 4, France
² Institut des Sciences Moléculaires (ISM), CNRS, Univ. Bordeaux, 351 cours de la Libération, 33400 Talence, France
³ Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France

^★ Corresponding author: pierre.marchand.astr@gmail.com

Received: 19 May 2025
Accepted: 15 August 2025

Abstract

Complex organic molecules (COMs) are thought to be the precursors of pre-biotic molecules and are observed in many protostellar sources. For this paper we studied the formation of COMs during star formation and their evolution in the midplane of the circumstellar disk up to the end of the Class I stage. We used the Analytical Protostellar Environment (APE) code to perform analytical simulations of star formation and the Nautilus code to model the chemical evolution. Most COMs mainly form during the collapse or in the disk, except the lightest (CH₃CCH, C₃H₆, CH₃OH, CH₃CHO, CH₃OCH₃, C₂H₅OH, CH₃CN, CH₃NC, C₂H₃CN, and CH₃SH), which are significantly inherited by the disk from the prestellar phase. Over the first 150 kyr of the disk, the abundances of several COMs in the midplane vary negligibly (e.g., CH₃CCH, CH₃OH, and CH₃CN), while others experience a variation of one order of magnitude (e.g., C₂H₃CHO HOCH₂CHO, and CH₃COCH₂OH). Changing physical conditions also have an impact on the abundance profiles of COMs in the disk, and their inheritance. For example, increasing the temperature of the molecular cloud from 10 K to 15 K significantly promotes the formation of COMs in the prestellar phase, notably c-C₂H₄O and N-bearing species. Conversely, increasing the cloud mass from 2 M_⊙ to 5 M_⊙ only has a minor effect on the disk abundances in the early stages.