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Abstract: The heliosphere refers to a region of space formed through interactions between the solar wind and the interstellar plasma. Neutral helium from the local interstellar medium (LISM) travels into the heliosphere and proceeds along Keplerian orbits under the central solar gravitational force. Primary helium neutrals, which originate from outside of the heliosphere, can be used to determine parameters of the LISM. However, the heliosphere also contains so-called “secondary” helium neutrals that originate from within the heliosphere, rather than from outside of it. Secondary neutrals are formed from charge exchange when a primary neutral atom encounters a helium ion. The production of secondary neutrals at each location in the heliosphere is dependent on the velocity distribution functions (VDFs) of the primaries, and can be modeled using numerical codes developed by the Dartmouth heliosphere research group. At certain locations in the heliosphere, the shape of primary VDFs is distorted and not well modeled with a Maxwellian distribution. This project builds on prior work that created more accurate modeling of primary helium in the Dartmouth codes in order to calculate the production of secondaries more accurately. This project will implement the production of secondary neutral helium, for a realistic primary neutral helium that accounts for regions where the latter is Maxwellian, and regions where it is not. NASA spacecraft such as the Interstellar Boundary Explorer (IBEX) are capable of measuring the flux of neutral helium particles in the heliosphere. However, IBEX does not only measure primary neutral helium, but also secondaries that do not serve as messengers from the LISM. Because the IBEX data is used to determine parameters of the interstellar medium, differentiating the primary neutrals from the secondaries observed by spacecraft will lead to increased accuracy in determining conditions of the interstellar medium. This project will be useful for interpreting data from IBEX, and can also be used to prepare for the upcoming Interstellar Mapping Acceleration Probe (IMAP) NASA mission. The VDFs will be converted into fluxes that will be observed by IMAP.

Advisor: Hans Mueller

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Meeting ID: 918 2834 3167
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