  I suggest that the behavior of the photospheric opacity in oxygen-rich
(similar to solar abundance) upper asymptotic giant branch stars may cause
these stars to substantially expand for a few thousand years. I term this
process over-expansion. This may occur when the photospheric (effective)
temperature drops to Tp~3000K, and because the opacity sharply increases as
temperature further decreases down to Tp~2000K$. The much higher opacity
implies a much lower photospheric density, which stabilizes the envelope
structure. As mass loss proceeds, the star eventually contracts to become a
post-asymptotic giant branch star. Some possible outcomes of the over-expanded
phase are discussed: (1) The over-expanded phase may be connected to the
formation of semi-periodic concentric arcs (rings; shells); (2) The
over-expanded phase may be related to the positive correlation between the mass
loss rate and the transition to axisymmetric mass loss geometry; and (3) An
over-expanded asymptotic giant branch star, which doubles its radius, is
somewhat more likely to swallow a low mass companion.
