Abstract. We present CCD photometry and proper motion studies of the three open star clusters NGC 4103, NGC 5281, and NGC 4755 (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 = 45 Myr. They are located at distances from approx. 1600 pc to 2200 pc, derived from distance moduli (m−M )0 ranging from 11 mag to 12 mag. We combined membership determinations based on proper motions and statistical field star subtraction to derive the initial mass function (

Abstract. CCD UBV I imaging photometry was carried out in the field of the open cluster NGC 2571. From the analysis of our data we state the cluster is at a distance of 1380 ± 130 pc and its age is 50±10×10 6 yr. The cluster mass function has a slope larger than a typical Salpeter's law. There are two notorious features in NGC 2571: the cluster contains a high proportion of stars located below the reference line that are serious candidates to be metallic line stars (probably Am-Fm), and shows also a sharp gap along its main sequence that cannot be explained by a random process nor by a biased rejection of cluster members. A striking blue object was detected in the cluster field that could be a white dwarf candidate.

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Abstract. The OB association LH 47 inside the superbubble N 44 in the Large Magellanic Cloud (LMC) is analyzed with CCD photometry. For the bright blue stars spectra in the optical and UV have been taken. The observed U , B, and V magnitudes and colours are converted to T eff and L. From isochrone fits to the colour magnitude diagram (CMD), we find an age of the association of about 5 to 6 Myr. The stellar population outside the shell is of similar age, so there is no direct evidence for sequential star formation.The slope of the luminosity function (γ = 0.24) agrees with what has been found for other young associations. We compare two methods to derive the slope of the initial mass function (IMF). First we count all stars along the main sequence in the BV CMD. Second we count the stars between stellar evolutionary tracks in the HertzsprungRussell diagram (HRD). Both methods give mainly the same result, i.e. x = 1.37 and x = 1.22, respectively. The IMF of the stars outside the shell shows a slightly steeper slope than inside the shell. The slope of the IMF is very similar to values found for other associations and open clusters as well as in the solar neighborhood, thus supporting the idea of an universal shape of the IMF. LH 47 turns out to be a well behaved young association embedded in a molecular cloud.

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