Multi-epoch Optical Images of IRC+10216 Tell About the Central Star And
  the Adjacent Environment
  Six images of IRC+10216 taken by the Hubble Space Telescope at three epochs
in 2001, 2011, and 2016 are compared in the rest frame of the central carbon
star. An accurate astrometry has been achieved with the help of Gaia Data
Release 2. The positions of the carbon star in the individual epochs are
determined using its known proper motion, defining the rest frame of the star.
In 2016, a local brightness peak with compact and red nature is detected at the
stellar position. A comparison of the color maps between 2016 and 2011 epochs
reveals that the reddest spot moved along with the star, suggesting a
possibility of its being the dusty material surrounding the carbon star.
Relatively red, ambient region is distributed in an $\Omega$ shape and well
corresponds to the dusty disk previously suggested based on near-infrared
polarization observations. In a larger scale, differential proper motion of
multiple ring-like pattern in the rest frame of the star is used to derive the
average expansion velocity of transverse wind components, resulting in $\sim$
12.5 km s$^{-1}$ ($d$/123 pc), where $d$ is the distance to IRC+10216. Three
dimensional geometry is implied from its comparison with the line-of-sight wind
velocity determined from half-widths of submillimeter emission line profiles of
abundant molecules. Uneven temporal variations in brightness for different
searchlight beams and anisotropic distribution of extended halo are revisited
in the context of the stellar light illumination through a porous envelope with
postulated longer-term variations for a period of $\lesssim10$ years.
