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We have detected H$_2$O and O$_2$ absorption against the far-UV continuum ofstars located on lines of sight near the nucleus of Comet67P/Churyumov-Gerasimenko using the Alice imaging spectrograph on Rosetta.These stellar appulses occurred at impact parameters of $\rho=4$-20 km, andheliocentric distances ranging from $R_h=-1.8$ to 2.3 AU (negative valuesindicate pre-perihelion observations). The measured H$_2$O column densitiesagree well with nearly contemporaneous values measured by VIRTIS-H. The cleardetection of O$_2$ independently confirms the initial detection by the ROSINAmass spectrometer; however, the relative abundance of O$_2$/H$_2$O derived fromthe stellar spectra (11%-68%, with a median value of 25%) is considerablylarger than published values found by ROSINA. The cause of this difference isunclear, but potentially related to ROSINA measuring number density at thespacecraft position while Alice measures column density along a line of sightthat passes near the nucleus.

H$_2$O and O$_2$ Absorption in the Coma of Comet 67P/Churyumov-Gerasimenko Measured by the Alice Far-Ultraviolet Spectrograph on Rosetta