UBV(RI)_C CCD photometry of a 2.1x3.3 arcmin^2 field centred on the young open cluster Haffner 18 is presented and discussed. Spectroscopic classification of seven stars is also provided. 44 cluster members are identified, the earliest type being O6. The distance to the cluster 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 excellent fit to the observed main sequence is achieved by a solar composition isochrone of 2x10^6 yr reddened by E(B-V)=0.62 mag. Differential reddening of intracluster origin is present. Pre-main-sequence members are likely to be present over the 6 mag range explored by our observations (reaching down to earliest A spectral types). The presence of differential reddening and pre-main-sequence members agrees with the evidence for a bright parent nebulosity embedding the whole cluster. The radial velocity of the cluster is consistent with the Hron model of Galactic rotation.
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- July 1998
- HERTZSPRUNG-RUSSELL (HR) DIAGRAM;
- OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: HAFFNER 18;
- 6 pages, 5 figures, to be pubblished in MNRAS