Quantifying the C/O ratio in the planet-forming environments around very low-mass stars

The material in planet-forming disks will determine the composition of planets; hence, it is crucial to understand the physical and chemical processes that set the abundance and distribution of key volatiles. Recent James Webb Space Telescope (JWST) observations of disks around three very low-mass (~0.1Msun) stars have revealed their hydrocarbon-rich inner regions (e.g., C2H2, C4H2, and C6H6), with column densities significantly higher than predicted. To understand and interpret these observations, we employ chemical kinetics models using the physical structure of the inner disk around an M-Dwarf star and compute the abundances of key volatiles. We adopt different initial elemental abundances to mimic the effects of carbon enhancement and oxygen depletion (C/O from 0.44 to 88) and quantify how the abundances and distributions of key volatiles respond to C/O variations. We attempt to constrain the elemental ratios that best explain the trends in the observations. In this talk, we present the model results and discuss how the magnitude of the mechanisms that set the inner-disk composition is not necessarily equal for the three sources even if they all show a hydrocarbon-rich inner disk. We also talk about the implications for planet formation and some caveats to take into consideration at the moment to interpret the results from chemical models.