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Published online by Cambridge University Press: 12 April 2016
The ionization of the the Local Interstellar Cloud (LIC) is quite unusual compared with most warm (T ~ 104 K) interstellar gas. Hydrogen and helium are both partially ionized with helium surprisingly more ionized than hydrogen. Directly observed ionization sources including nearby stellar EUV sources and the diffuse emission of the Soft X-ray Background (SXRB), do not provide enough ionization and heating to account for both the ionization state and temperature of the LIC. We propose that an evaporative boundary between the LIC and the hot gas of the Local Bubble can provide the necessary ionizing radiation. Results of detailed models of the emission from the interface are presented and shown to be adequate to explain the observations.