Non-steady state line locking in broad absorption line quasi-stellar objects

A nonsteady state model for absorption-absorption line locking in broad absorption line quasars is discussed in which an approximate balance between the forces is not required. It is assumed that locking is on velocity differences, not on absolute velocities relative to the central source. The locking occurs between two gas elements neither of which is at a constant velocity, and it is only the relative velocity between the two that remains constant and equal to the doublet velocity. This picture can work equally well for decelerating gas and can also work for objects which exhibit large luminosity fluctuations. 15 refs