Photometric study of the young open cluster NGC 3293

Deep and extensive CCD photometric observations at UBV(RI)_CH_alpha were carried out in the area of the open cluster NGC 3293. The new data set allows to see the entire cluster sequence down to M_V ~ +4.5, revealing that stars with M_V < -2 are evolving off the main sequence; stars with -2 < M_V < +2 are located on the main sequence and stars with M_V > +2 are placed above it. According to our analysis, the cluster distance is d = 2750 +/- 250 pc (V₀-M_V = 12.2 +/- 0.2) and its nuclear age is 8 +/- 1 Myr. NGC 3293 contains an important fraction of pre-main sequence (PMS) stars distributed along a parallel band to the ZAMS with masses from 1 to 2.5 cal M_sun and a mean contraction age of 10 Myr. This last value does not differ too much from the nuclear age estimate. If we take into account the many factors that may affect the PMS star positions on the colour-magnitude diagram, both ages can be perfectly reconciled. The star formation rate, on the other hand, suggests that NGC 3293 stars formed surely in one single event, therefore favouring a coeval process of star formation. Using the H_alpha data, we detected nineteen stars with signs of H_alpha emission in the region of NGC 3293, another indication that the star formation process is still active in the region. The computed initial mass function for the cluster has a slope of x = 1.2 +/- 0.2, a bit flatter than the typical slope for field stars and similar to the values found for other young open clusters.

Based on observations collected at UTSO, ESO (Dutch 0.9 m telescope) and CASLEO. The CCD and data acquisition system at CASLEO has been partly financed by R.M. Rich through U.S. NSF Grant AST-90-15827.

Full Table 1 is only available in electronic form at the CDS via an anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/402/549