Stellar Occultation by Comet 67P/Churyumov–Gerasimenko Observed with Rosetta 's Alice Far-ultraviolet Spectrograph

Abstract : Following our previous detection of ubiquitous ${{\rm{H}}}_{2}{\rm{O}}$ and ${{\rm{O}}}_{2}$ absorption against the far-ultraviolet continuum of stars located near the nucleus of Comet 67P/Churyumov–Gerasimenko, we present a serendipitously observed stellar occultation that occurred on 2015 September 13, approximately one month after the comet's perihelion passage. The occultation appears in two consecutive 10-minute spectral images obtained by Alice, Rosetta's ultraviolet (700–2100 Å) spectrograph, both of which show H2O absorption with column density >1017.5 cm−2 and significant O2 absorption (O2/H2O ≈ 5%–10%). Because the projected distance from the star to the nucleus changes between exposures, our ability to study the H2O column density profile near the nucleus (impact parameters <1 km) is unmatched by our previous observations. We find that the H20 and O2 column densities decrease with increasing impact parameter, in accordance with expectations, but the O2 column decreases ~3 times more quickly than H2O. When combined with previously published results from stellar appulses, we conclude that the O2 and H2O column densities are highly correlated, and O2/H2O decreases with the increasing H2O column.
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Submitted on : Monday, April 29, 2019 - 5:36:31 PM
Last modification on : Friday, August 2, 2019 - 2:30:11 PM

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Brian Keeney, S. Alan Stern, Paul Feldman, Michael A’hearn, Jean-Loup Bertaux, et al.. Stellar Occultation by Comet 67P/Churyumov–Gerasimenko Observed with Rosetta 's Alice Far-ultraviolet Spectrograph. Astronomical Journal, American Astronomical Society, 2019, 157 (5), pp.art. 173. ⟨10.3847/1538-3881/ab1097⟩. ⟨insu-02114594⟩

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