  We apply a PCA-based pre-whitening method to the entire collection of main
Kepler mission long-cadence data for KIC 8462852 spanning four years. This
technique removes the correlated variations of instrumental origin in both the
detected light curves and astrometry, resolving intrinsic changes in flux and
image position of less than 100 ppm and 1 mas, respectively. Beside the major
dips in the light curve during mission quarters 8 and 16, when the flux dropped
by up to 20%, we confirm multiple smaller dips across the time span of
observation with amplitudes ranging from 0.1% to 7%. A variation of flux with a
period of 0.88 d and a half-amplitude of approximately 90 ppm is confirmed in
the PCA-cleaned data. We find that the phase of the wave is steady over the
entire 15-month interval. We confidently detect a weak variability-induced
motion (VIM) effect in the cleaned astrometric trajectories, when the
moment-based centroids shift synchronously with the flux dips by up to 0.0008
pixels on the detector. The inconsistent magnitude and direction of VIM effects
within the same quarter point at more than one source of photometric
variability in the blended image. The 0.88 d periodicity comes from a different
source, not from the target star KIC 8462852. We discuss a possible
interpretation of the bizarre properties of the source as a swarm of
interstellar junk (comets and planetoids) crossing the line of sight to the
star and its optical companions at approximately 7 mas per year.
