Anomalous helium ions as the source of energetic helium atoms in the outer heliosphere Original Research Article

The helium component of the anomalous cosmic rays (ACR) is a potential source of neutral energetic helium due to charge-exchange of the He+ ions with the hydrogen or helium atoms from the background. The most effective source of the energetic helium atoms should correspond to the relatively low-energy (up to 100 keV/n) ions present in the regions near and beyond the solar wind termination shock. The energetic neutral atoms (ENA) of ACR origin are therefore generated in the distant heliosphere and can provide a means of remote observation of this region. We present the results of numerical calculations of the anomalous helium spectrum and spatial density in a model heliosphere and of the corresponding energetic helium flux. The results are compared with the data obtained by SOHO. We point out that the helium data, covering different region of energy-per-nucleon values, are an important supplement to the hydrogen SOHO data and can be used to test the hypotheses about the origin of the signal.