Institut national de recherche scientifique français Univerité Pierre et Marie Curie Université Paris Diderot - Paris 7

Changing disc compositions via internal photoevaporation

mardi 25 juin 2024, par Julia Lienert (MPIA, Allemagne)

Lundi 1er juillet 2024 à 16h00 , Lieu : Salle de confĂ©rence du bâtiment 17

The chemical evolution of protoplanetary discs is not fully understood. One factor influencing the distribution of disc material is the inward-drift and evaporation of pebbles that enriches the inner disc with vapour. In particular, it is first enriched with water vapour, resulting in a low C/O ratio, before carbon-rich gas from the outer disc elevates the C/O ratio again. However, it is unclear how internal photoevaporation, which carries away gas and opens gaps that block inward-drifting pebbles, affects the chemical composition of the disc.

To study these effects, we use a semi-analytical 1D disc model. The code chemcomp includes viscous evolution and heating, pebble growth, drift, evaporation and condensation, and a simple chemical partitioning model.

We show that internal photoevaporation plays a major role for the (chemical) evolution of protoplanetary discs : As it opens a gap, inward-drifting pebbles are stopped and cannot contribute to the volatile content any more. Additionally, gas from the outer disc is carried away by photoevaporative winds. Consequently, the C/O ratio is low. In contrast, gaps opened by giant planets allow the gas to pass, resulting in an elevated C/O ratio, similar to viscous discs without internal photoevaporation. This allows observational differentiation between these two scenarios when measuring the C/O ratio, implying that the cause of gap structures can be inferred. In the case of a photoevaporative disc, we additionally find an elevated water content in the inner disc as the water vapour and ice undergo a cycle of evaporation/re-condensation, preventing its inward accretion onto the star.