The stellar mass function, binary content and radial structure of the open cluster Praesepe derived from PPMXL and SDSS data

We have determined possible cluster members of the nearby open cluster Praesepe (M44) based on J and K photometry and proper motions from the PPMXL catalogue and z photometry from the Sloan Digital Sky Survey (SDSS). In total we identied 893 possible cluster members down to a magnitude of J = 15:5 mag, corresponding to a mass of about 0.15 M for an assumed cluster distance modulus of (m M)0 = 6:30 mag (d 182 pc), within a radius of 3.5 around the cluster centre. We derive a new cluster centre for Praesepe ( centre = 8 h 39 m 37 s ; centre = 19 35 0 02 00 ). We also derive a total cluster mass of about 630 M and a 2D half-number and half-mass radius of 4:25 pc and 3:90 pc respectively. The global mass function (MF) of the cluster members shows evidence for a turnover around m = 0:65 M . While more massive stars can be t by a power-law (m) m with slope = 2:88 0:22, stars less