UBV(RI)(C) PHOTOMETRY AND SPECTROSCOPY OF THE YOUNG OPEN CLUSTER HAFFNER-18

UBV(RI)(C) CCD photometry of a 2.1 x 3.3 arcmin(2) field centred on th e young open cluster Haffner 18 is presented and discussed. Spectrosco pic classification of seven stars is also provided. 44 cluster members are identified, the earliest type being O6. The distance to the clust er is found to be 6.3 kpc, corresponding to a galactocentric distance of 12.7 kpc (for a Sun galactocentric distance of 8,5 kpc). An excelle nt fit to the observed main sequence is achieved by a solar compositio n isochrone of 2x10(6) yr reddened by E(B - V) = 0.62 mag. Differentia l reddening of intracluster origin is present. Pre-main-sequence membe rs are likely to be present over the 6 mag range explored by our obser vations (reaching down to earliest A spectral types). The presence of differential reddening and pre-main-sequence members agrees with the e vidence for a bright parent nebulosity embedding the whole cluster. Th e radial velocity of the cluster is consistent with the Hron model of Galactic rotation.