  We have investigated a wide range of nonclassical behavior exhibited by a
tripartite cavity optomechanical system comprising a two-level atom placed
inside a Fabry-P\'{e}rot type optical cavity with a vibrating mirror attached
to one end. We have shown that the atom's subsystem von Neumann entropy
collapses to its maximum allowed value over a significant time interval during
dynamical evolution. This feature is sensitive to the nature of the initial
state, the specific form of intensity-dependent tripartite coupling, and system
parameters. The extent of nonclassicality of the field is assessed through the
Mandel Q parameter and Wigner function. Both entropic and quadrature squeezing
properties of the field are quantified directly from optical tomograms, thereby
avoiding tedious state reconstruction procedures.
