Modeling and Observations of the Ionization of the Local InterstellarCloud

Abstract:

Understanding the ionization of the interstellar cloud that surrounds the Solar System (the Local Interstellar Cloud) is crucial for modeling for the heliosphere. The ionization of the cloud has been inferred from both in situ observations and absorption line data toward nearby stars. New HST data for the line of sight toward the nearby (2.64 pc) star Sirius confirms earlier results for the line of sight toward epsilon Canis Majoris, indicating a partially ionized warm cloud. We discuss the way that the ionization of the cloud is inferred from the observations and how we model the ionization, including the different parts of the ionizing radiation field and the assumptions in the modeling. The results of ionization modeling have implications for both the heliosphere and the nature and history of the local interstellar medium.