Stellar Occultation by Comet 67P/Churyumov–Gerasimenko Observed with Rosetta 's Alice Far-ultraviolet Spectrograph
Résumé
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.
Domaines
Astrophysique [astro-ph]| Origine | Fichiers produits par l'(les) auteur(s) |
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