Keplerian injection velocities reflected in helium pick-up ion spectra

It is usually assumed that pick-up ions at the event of their production, s een in the solar rest frame, have peculiar velocities which are negligible with respect to solar wind velocities. This assumption, however, is no more valid for pick-up ion injections at small solar distances. As we are showi ng here, the He+ - pick-up ion spectra to be expected at distances inside 1 AU clearly reflect the fact that ion injection took place with non-negligi ble velocities due to the Keplerian motion of parent He atoms entering from the interstellar medium, as was already recognized in SOHO CELIAS measurem ents by Mobius ct al. (1999). We demonstrate that these injection signature s are less pronounced under conditions of high-speed compared to those of l ow-speed solar winds and are variable with the off-upwind angle. Careful st udy of these injection features can help to identify the actual He ionizati on rate.