The binary fraction and mass segregation in alpha persei open cluster

Abstract

We have obtained membership probabilities of stars within a field of ∼3° from the centre of the open cluster Alpha Persei using proper motions and photometry from the PPMXL and Wide-Field Infrared Survey Explorer 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=0.62M⊙ with Low- and High-Mass slopes of alow=0.50 ± 0.09 (0.1 < 0.62) and αhigh=2.32 ± 0.14 (0.62 ≤ m/M⊙ < 4.68), respectively. The High-Mass slope of the cluster increases from 2.01 inside 1.°10 to 2.63 outside 2.°2, whereas the mean stellar mass decreases from 0.95 to 0.57M⊙ 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 fbin=34 ± 12 per cent for stars with 0.70 < 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 MF slopes for the effect of unresolved binaries and found Low- and High-Mass slopes of αlow=0.89 ± 0.11 and αα=2.37 ± 0.09 and a total cluster mass of 352M⊙ for Alpha Persei.