  We present the first long-term study of the optical counterpart to the X-ray
pulsar LS V +44 17/RX J0440.9+4431. The results of our photometric and
spectroscopic analysis show that LS V +44 17/RX J0440.9+4431 contains a
moderately reddened, E(B-V)=0.65+-0.05, B0.2V star located at about 3.3 kpc.
The Ha line consistently shows a double-peak profile varying from symmetric
shape to completely distorted on one side (V/R phases). A correlation between
the equivalent width of the Ha line and the infrared magnitudes is seen: as the
EW(Ha) decreases the IR magnitudes become fainter. This long-term optical/IR
variability is attributed to structural changes in the Be star's circumstellar
disc. The observations include a recent decline in the circumstellar disc and
subsequent recovery. We have witnessed the cessation of a global oscillation
due to the decline of the circumstellar disc. If the present disc growth rate
continues we predict the onset of another episode of V/R variability by the end
of 2006. We have investigated the typical time scales for disc variability of
various Be/X-ray binaries and found a correlation with the orbital period. This
correlation is hard to establish due to the difficulty in defining the exact
duration of the various activity states, but it is seen both in the duration of
the disc growth/dissipation phase and the value of the Ha equivalent width
prior to the appearance of asymmetric profiles. These relationships provide
further evidence for the interaction of the neutron star with the circumstellar
disc of the Be star's companion and confirms the need of a fully developed disc
for the V/R variability to be observed.
