NGC 4103 220 , the SIMBAD biblio

We present CCD photometry and proper motion studies of the three open star clusters NGC4103, NGC5281, and NGC4755 (κ Cru). By fitting isochrones to the colour magnitude diagrams, we found that all three objects are young open star clusters with ages of at most t=45Myr. They are located at distances from approx. 1600pc to 2200pc, derived from distance moduli (m-M)₀ ranging from 11mag to 12mag. We combined membership determinations based on proper motions and statistical field star subtraction to derive the initial mass function (IMF) of the clusters. The shape of the IMFs could be represented by power laws with exponents of Γ=-1.46±0.22 for NGC 4103, Γ=-1.60±0.50 for NGC 5281, and Γ=-1.68±0.14 for NGC 4755, when - as a reference - Salpeter's (1955ApJ...121..161S) value would be Γ=-1.35. These results agree well with other IMF studies of open star clusters.