Detection of 55-80 keV hydrogen atoms of heliospheric origin by CELIAS/HSTOF on Soho

The High-Energy Suprathermal Time-of-Flight sensor (HSTOF) of the Charge, E lement, and Isotope Analysis System (CELIAS) on the Solar and Heliospheric Observatory (SOHO) near the Lagrangian point L1 is capable of identifying e nergetic hydrogen atoms (EHAs) between 55 and 80 keV. Between 1996 February 13 and 1997 August 31, near solar minimum, there were 285 "quiet" days whe n the interplanetary charged-particle flux was low. During these quiet time s, HSTOF scanned the apex of the heliosphere once and the antiapex twice. T he flux level and time profile, and hence the arrival direction, of the EHA s accumulated during these quiet times are best interpreted as fluxes of EH As coming from the heliosheath.