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We present analysis of time-variable, shifted absorption features in far-UVspectra of the unusual 49 Ceti debris disk. This nearly edge-on disk is one ofthe brightest known, and is one of the very few containing detectable amountsof circumstellar gas as well as dust. In our two visits of Hubble SpaceTelescope STIS spectra, variable absorption features are seen on the wings oflines arising from C II and C IV, but not for any of the other circumstellarabsorption lines. Similar variable features have long been seen in spectra ofthe well-studied $\beta$ Pictoris debris disk and attributed to the transits ofstar-grazing comets. We calculate the velocity ranges and apparent columndensities of the 49 Cet variable gas, which appears to be moving at velocitiesof tens to hundreds of km s$^{-1}$ relative to the central star. The velocitiesof the gas in the redshifted variable event in Visit 2 show that the maximumdistances of the infalling gas at the time of transit are about 0.05 to 0.2 AUfrom the central star. A preliminary attempt at a composition analysis of theredshifted event suggests that the C/O ratio in the infalling gas may besuper-solar, as it is in the bulk of the stable disk gas.

UV Spectroscopy of Star-Grazing Comets within the 49 Ceti Debris Disk