16752

As we move into an epoch of rocky planet detection comma white dwarfs that have accreted exoplanetary bodies are unique laboratories to directly study the bulk composition of exoplanetary material and deduce the geological processes in exoplanets. Gas and dust observed close to the white dwarfs trace the accretion of this planetary material into the atmosphere of the white dwarf. The recent three-fold increase in the number of known white dwarfs with gaseous emission (including emission features from O comma Na comma Mg comma Si comma Ca comma Fe) provides a unique opportunity to study the composition of planetary material in two ways. Abundances can be derived from the gas exterior to the white dwarf comma and they can then be compared to the abundances determined from the accreted material in the photosphere of the white dwarf. We propose to obtain abundances of the accreted exoplanetary material from FUV spectra of four recently discovered comma heavily polluted white dwarfs with at least O comma Ca comma and Fe in circumstellar gaseous emission. By comparing the composition of the circumstellar gas with the composition of the material that has accreted onto the atmosphere of the white dwarf comma we can probe whether volatiles are accreted simultaneously with refractories. This is crucial to using the observed abundances in the white dwarf photosphere to probe the volatile content of exoplanetary bodies comma and to understand how planetary bodies lose (gain) volatiles.