  The spherically symmetric thin shells of the barotropic fluids with the
linear equation of state are considered within the frameworks of general
relativity. We study several aspects of the shells as completely relativistic
models of stars, first of all the neutron stars and white dwarfs, and
circumstellar shells. The exact equations of motion of the shells are obtained.
Also we calculate the parameters of the equilibrium configurations, including
the radii of static shells. Finally, we study the stability of the equilibrium
shells against radial perturbations.
