Direct evidence of the interstellar gas flow velocity in the pickup ion cut-off as observed with SOHOCELIAS CTOF

He+ pickup ions as observed with SOHO CELIAS CTOF have been analyzed for th e time period DOY 160 - 190, 1996. During this time of the year the Earth i s on the upwind side of the interstellar gas flow with respect to the sun. The high-speed cut-off in the frame of the sun is significantly higher v/V- sw = 2, predicted for pickup ions. The difference increases with lower sola r wind speeds. This behavior is interpreted as an effect of the local inter stellar gas flow velocity (inflow at large distances including gravitationa l acceleration by the sun) on the pickup ion distribution. The neutral velo city is added to the solar wind velocity in the determination of the pickup ion cut-off on the upwind side and subtracted on the downwind side of the gas flow. This new observation will provide a valuable tool to determine th e interstellar gas flow and will thus complement direct neutral gas measure ments.