  We study the order-disorder transition in a collection of polar
self-propelled particles, interacting through a distance dependent short range
alignment interaction. A distance dependent interaction parameter $a_0$ is
introduced such that on decreasing $a_0$ interaction decay faster with distance
$d$ and for $a_0=1.0$ model reduces to Vicsek's type. For all $a_0>0.0$, system
shows a transition from disorder to long ranged ordered state. We find another
phase transition from phase separated to nonphase separated state with
decreasing $a_0$: at the same time order-disorder transition changes from
discontinuous to continuous type. Hence density phase separation plays an
important role in predicting the nature of order-disorder transition. We also
calculate the two-point density structure factor using coarse-grained
hydrodynamic equations of motion with an introduction of a density dependent
alignment term in the equation introduced by Toner and Tu \cite{tonertu}.
Density structure factor shows a divergence at a critical wave-vector $q_c$,
which decreases with decreasing density dependent alignment term. Alignment
term in the coarse-grained equation plays the same role as the distance
dependent parameter $a_0$ in the microscopic simulation. Our results can be
tested in many biological systems: where particle have tendency to interact
strongly with their closest neighbours.
