Stellar Occultation by Comet 67P/Churyumov-Gerasimenko Observed with Rosetta's Alice Far-ultraviolet Spectrograph
Abstract
Following our previous detection of ubiquitous {{{H}}}2{{O}} and {{{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 {{{H}}}2{{O}} absorption with column density >1017.5 cm-2 and significant {{{O}}}2 absorption ({{{O}}}2/{{{H}}}2{{O}} ≈ 5%-10%). Because the projected distance from the star to the nucleus changes between exposures, our ability to study the {{{H}}}2{{O}} column density profile near the nucleus (impact parameters <1 km) is unmatched by our previous observations. We find that the {{{H}}}2{{O}} and {{{O}}}2 column densities decrease with increasing impact parameter, in accordance with expectations, but the {{{O}}}2 column decreases ∼3 times more quickly than {{{H}}}2{{O}}. When combined with previously published results from stellar appulses, we conclude that the {{{O}}}2 and {{{H}}}2{{O}} column densities are highly correlated, and {{{O}}}2/{{{H}}}2{{O}} decreases with the increasing {{{H}}}2{{O}} column.
- Publication:
-
The Astronomical Journal
- Pub Date:
- May 2019
- DOI:
- 10.3847/1538-3881/ab1097
- arXiv:
- arXiv:1903.06793
- Bibcode:
- 2019AJ....157..173K
- Keywords:
-
- comets: individual: 67P;
- ultraviolet: planetary systems;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- Accepted for publication in the Astronomical Journal