On the Decades-Long Stability of the Interstellar Wind through the Solar
  System
  We have revisited the series of observations recently used to infer a
temporal variation of the interstellar helium flow over the last forty years.
Concerning the recent IBEX-Lo direct detection of Helium neutrals, there are
two types of precise and unambiguous measurements which do not rely on the
exact response of the instrument: the count rate maxima as a function of the
spin angle, which determines the ecliptic latitude of the flow, and the count
rate maxima as a function of IBEX longitude, which determines a tight
relationship between the ecliptic longitude of the flow and its velocity far
from the Sun. These measurements provide parameters (and couples of parameters
in the second case) remarkably similar to the canonical, old values. In
contrast, the preferential choice of a lower velocity and higher longitude
reported before from IBEX data is based only on the count rate variation (at
each spin phase maximum) as a function of the satellite longitude, when
drifting across the region of high fluxes. We have examined the consequences of
dead time counting effects, and conclude that their inclusion at a realistic
level is sufficient to reconcile the data with the old parameters, calling for
further investigations. We discuss the analyses of the STEREO pickup ion (PUI)
data and argue that the statistical method that has been preferred to infer the
neutral flow longitude (instead of the more direct method based on the PUI
maximum flux directions), is not appropriate. Moreover, transport effects may
have been significant at the very weak solar activity level of 2007-2009, in
which case the longitudes of the PUI maxima are only upper limits on the flow
longitude. Finally, we found that the use of some flow longitude determinations
based on UV glow data are not adequate. At variance with recent conclusions we
find no evidence for a temporal variability of the interstellar helium flow.
