Program: GS-2019A-Q-231

White dwarf stars have recently emerged as valuable exoplanetary laboratories, displaying evidence of dynamic post-main sequence planetary environments and enabling precise measurements of abundace ratios of rocky exoplanetary bodies. In a handful of these systems, a circumstellar gas disc is also detected via Ca II 8600 angstrom emission lines and these emission lines have been shown to be variable on timescales ranging from years to decades. We recently detected a low-amplitude ~2 hr modulation of the line flux in the emission lines in one such system, which we interpret as the signature of a planetesimal orbiting within the disc. We suggest that similar bodies are present in all white dwarf systems with circumstellar gas discs in emission, and the embedded planetesimals are responsible for both the origin and long term evolution of the emission lines. We propose to obtain high-quality GMOS observations of two other white dwarf systems with gaseous emission lines at high (~4 min) cadence to probe for hourly variability signaling the presence of a embedded planetesimal, in an attempt unambiguously link the presence of a gas disc to a close-in planetary body.