Kallenbach, Reinald Department Planets and Comets, Max Planck Institute for Solar System Research, Max Planck Society;
Saul, L., Wurz, P., & Kallenbach, R. (2009). A Measurement of the Adiabatic Cooling Index for Interstellar Helium Pickup Ions in the Inner Heliosphere. Astrophysical Journal, 703, 325-329. doi:10.1088/0004-637X/703/1/325.