2004MNRAS.351.1401J

We present a catalogue of R_cI_cZ photometry over an area of 0.855 square degrees, centred on the young open cluster NGC 2547. The survey is substantially complete to limits of R_c= 21.5, I_c= 19.5, Z= 19.5. We use the catalogue to define a sample of NGC 2547 candidates with model-dependent masses of about 0.05 -1.0 M_☉. After correcting for incompleteness and estimating contamination by foreground field dwarfs, we investigate the mass function of the cluster, its binary content, and search for evidence of mass segregation among the lower mass stars. There is ample evidence for mass segregation between high (>3 M_☉) and lower mass stars, but over the range 0.1 < M < 0.7 M_☉, the data are consistent with no further mass segregation. By fitting King profiles we conclude that at least 60 per cent of the low-mass stellar population are contained within our survey. The cluster mass function is remarkably similar to the Pleiades for 0.075 < M < 0.7 M_☉. Because of its age (≃ 30 Myr), we demonstrate that this mass function is robust to a number of systematic uncertainties likely to affect older and younger clusters and is therefore one of the best available estimates for the initial mass function in young disc populations. For 0.05 < M < 0.075 M_☉there is some evidence for a deficit of brown dwarfs in NGC 2547 compared with other clusters. This deficit may extend to lower masses or may only be a dip, perhaps caused by an imperfect understanding of the mass-magnitude relationship at temperatures of around 2800 K. Incompleteness in both our survey and the luminosity functions from which we estimate contamination by foreground objects leave this question open. The binary fraction for systems with mass ratios greater than about 0.5 is 20-35 per cent for M dwarfs in NGC 2547, quite consistent with that found in the field and other young clusters. The full photometric catalogue and our lists of candidate cluster members are made available in electronic format.