Exploring the Structure of the Local Interstellar Medium with the Interstellar Boundary Explorer (IBEX)

• Applicant: Privatdozent Dr. Horst Fichtner
• Subject Area: Astrophysics and Astronomy
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 319217929

The goal of this project is a comprehensive quantitative assessment of a recently proposed model explaining the so-called ribbon of enhanced differential fluxes of energetic neutral atoms (ENAs). According to this model the ribbon, that was detected in the all-sky ENA flux maps with the Interstellar Boundary Explorer (IBEX) spacecraft, is a consequence of a so-called H-wave, i.e. a localized enhancement of the neutral hydrogen number density that is propagating from the ISM into the heliosphere. The corresponding study will contribute in a threefold way to the contemporary research regarding the outer heliosphere and the local interstellar medium (ISM) that -- with the recent entry of the Voyager~1 spacecraft into interstellar space -- received renewed attention due to the opportunity to make in situ measurements of the ISM: First, the study will contribute to clarify the nature of the IBEX ribbon. Second, it will constrain physical properties of the local ISM (such as the orientation of the interstellar magnetic field and neutral density variations). And, third, it will significantly improve our understanding of the interaction of the solar wind with its interstellar environment.The main objectives of the project is the answering of the following three scientific key questions: (Q1) What is the influence of the inner-heliosheath proton velocity distribution on the ENA spectra?, (Q2) How does the ribbon of enhanced differential ENA fluxes form in a self-consistently simulated 'realistic' heliosphere?, and (Q3) What are the properties of disturbances of the neutral gas in the local interstellar medium? These objectives imply corresponding tasks, namely (T1) the computation of the velocity distribution of the ENA seed population, i.e. protons, (T2) the computation of the differential ENA fluxes from the ribbon using a simulated heliosphere, and (T3) the determination the properties of disturbances in the interstellar neutral gas. With achieving the goal of the project by the completion of these tasks, we will not only make the mentioned threefold contribution to the contemporary research regarding the most distant frontier of in situ exploration, but help to transform the always existing conceptual link between heliospheric physics and astrophysics into an actual physical link by constraining the state and structure of the local ISM, which can be considered as representative for the general ISM.

• DFG Programme: Research Grants