We have obtained membership probabilities of stars within a field of radius \sim 3 \degr around the centre of the open cluster Alpha Persei using proper motions and photometry from the PPMXL and WISE catalogues .
We have identified 810 possible stellar members of Alpha Persei .
We derived the global and radial present-day mass function ( MF ) of the cluster and found that they are well matched by two-stage power-law relations with different slopes at different radii .
The global MF of Alpha Persei shows a turnover at m = 0.62 \mathrm { M } _ { \sun } with low and high-mass slopes of \alpha _ { \mathrm { low } } = 0.50 \pm 0.09 ( 0.1 < m / \mathrm { M } _ { \sun } < 0.62 ) and \alpha _ { \mathrm { high } } = 2.32 \pm 0.14 ( 0.62 \leq m / \mathrm { M } _ { \sun } < 4.68 ) respectively .
The high-mass slope of the cluster increases from 2.01 inside 1 \fdg 10 to 2.63 outside 2 \fdg 2 , whereas the mean stellar mass decreases from 0.95 to 0.57 \mathrm { M } _ { \sun } in the same regions , signifying clear evidence of mass segregation in the cluster .
From an examination of the high-quality colour-magnitude data of the cluster and performing a series of Monte Carlo simulations we obtained a binary fraction of f _ { bin } = 34 \pm 12 per cent for stars with 0.70 < m / \mathrm { M } _ { \sun } < 4.68 .
This is significantly larger than the observed binary fraction , indicating that this open cluster contains a large population of unresolved binaries .
Finally , we corrected the mass-function slopes for the effect of unresolved binaries and found low- and high-mass slopes of \alpha _ { \mathrm { low } } = 0.89 \pm 0.11 and \alpha _ { \mathrm { high } } = 2.37 \pm 0.09 and a total cluster mass of 352 \mathrm { M } _ { \sun } .