Authors: E. Möbius, Y. Litvinenko, H. Grünwaldt, M.R. Aellig, A. Bogdanov,
F.M. Ipavich, P. Bochsler, M. Hilchenbach, D. Judge, B. Klecker,
M.A. Lee, H. Ogawa
Reference: Geophysical Research Letters 1999
Vol. 26 , No. 20 , p. 3181-3184
Abstract:
He+ pickup ions as observed with SOHO CELIAS CTOF have
been analyzed for the time period DOY 160 - 190, 1996. During this time of
the year the Earth is 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/Vsw = 2, predicted for pickup ions. The difference
increases with lower solar wind speeds. This behavior is interpreted as an
effect of the local interstellar gas flow velocity (inflow at large
distances including gravitational acceleration by the sun) on the pickup ion
distribution. The neutral velocity 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 the interstellar gas flow and will
thus complement direct neutral gas measurements.