Thinkshop 2020

Elemental abundance ratios in the inner regions of protoplanetary discs are important for setting the composition of exoplanets, but are likely not to represent the bulk composition of the star's parental cloud. Abundance differences are expected to be driven by the differential transport of chemical species in solid and gaseous form: elements which are mainly concentrated in species with high melting points may be either over-represented in the inner disc (due to efficient inward radial drift of icy grains) or else under-represented (if such grains become trapped in the outer disc).

Here I explore a new observational window for determining the relative abundances of C, N and Si in the inner disc through examination of ultraviolet emission lines generated by material accreting onto the central star via an accretion column and shock. I use CLOUDY to calculate the resulting ratios of CIV, NV and SiIV lines and how these vary with input elemental abundance ratios. I conclude that such line ratios provide a sensitive probe of abundances in the inner disc and describe the constraints provided by existing HST spectroscopic observations of T Tauri stars.