Diagnostics of the Interstellar Gas with IBEX Neutral Atom Observations in the Inner Heliosphere
Abstract
The Interstellar Boundary Explorer (IBEX) observes the interstellar gas flow, which penetrates the heliosphere, every spring when the Earth moves antiparallel to the flow direction. During the previous deep solar minimum, four interstellar species, H, He, O, and Ne have been observed. Based on the flux ratios obtained with the IBEX-Lo sensor at the location of the spacecraft at 1 AU, the abundance ratios in the gas phase of the local interstellar cloud can be inferred within measurement and modeling uncertainties. Using independently obtained ionization rates for the prevailing solar minimum conditions during the observations, the ratios at the termination shock are obtained. To infer the abundance ratios in the interstellar medium, the filtration of the gas in the heliospheric interface and the degree of ionization of the species also are taken into account. Here, we concentrate on the first direct measurement of the neutral Ne/O abundance ratio at 1 AU with IBEX. Including all uncertainties, our preliminary estimate of the Ne/O ratio in the surrounding interstellar gas is 0.27±0.10, which is—within uncertainties—consistent with previous results from pickup ions. Strategies to reduce the observational and modeling uncertainties involving extended observations under varying solar activity conditions will be discussed. Even with the large uncertainties, the current abundance value is significantly different from the solar and the average galactic abundance ratio; it is larger than both values. This result may indicate that a significant fraction of oxygen in the local interstellar medium is hidden in grains and/or ices. The result may also tell us something about variations in the composition of different interstellar gas environments.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMSH22A..01M
- Keywords:
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- 2126 INTERPLANETARY PHYSICS / Heliosphere/interstellar medium interactions;
- 2144 INTERPLANETARY PHYSICS / Interstellar gas;
- 7837 SPACE PLASMA PHYSICS / Neutral particles