PhD candidate: Antoine Espagnet
PhD supervisor: Audrey Coutens (IRAP)
Start of the thesis: 2023
Thematic group: MICMAC
Date of the defense: Thursday, November 12th, 2026, 2PM
Location of the defense: Salle de conférence, IRAP-Roche, Toulouse
Abstract
Star formation is a central topic in astrophysics. Seeking to understand it allows us to put the formation of our own solar system into context. Radio/millimeter/submillimeter observations are a key tool to characterize the chemical composition of protostars, but it is necessary to understand which physical phenomena may be responsible for the observed differences. Modeling thus plays an essential role in predicting the impact that a parameter or physical phenomenon may have on the chemical composition of protostars. In this thesis, I studied the impact of luminosity outbursts on the chemistry of the envelopes of solar-type protostars. These luminosity outbursts are associated with the process of episodic accretion, involving periods of intense accretion of the surrounding material by the young forming star. To this end, I conducted a modeling study using the semi-analytical APE code, which describes the physical dynamics of the system, and the Nautilus gas-grain chemistry model.
For most of the species studied, the main observed impact of an outburst is the temporary displacement of the snowlines toward the outer regions of the envelope. The gradual return to their initial positions occurs over timescales ranging from a few hundred years within the 100 astronomical units closest to the protostar to several tens of thousands of years beyond 1,000 astronomical units. In the hot inner regions of the envelope, the abundances of most complex organic molecules remain similar in scenarios with and without an outburst. However, I found that eight molecules (HOCH2CHO, CH3COCH2OH, C2H5CHO, OCS, SO2, C2S, C3S, and HC3N) exhibit changes in their abundances in the hot inner regions several tens of thousands of years after the outburst. These modifications originate from changes in the abundance of precursors induced by the outburst within the cold, outer regions of the envelope. These precursors then form the molecules mentioned, which are transported to the hot, inner regions via the collapse.
With these results, this thesis provides new insights for the interpretation and comparison of observations of protostellar sources. In particular, they show that the abundances of most complex organic molecules can be compared between sources that have and have not undergone a luminosity outburst associated with the phenomenon of episodic accretion.