5 Summary

Three young open clusters with differential reddenings were selected as targets of a comprehensive spectral classification study. MKK types were obtained for 140, 46 and 77 stars in IC 1805, NGC 654 and NGC 6823 respectively. As these clusters are very young, most of the proper motion members are found to be early-type stars. Seven stars showed at least H$\alpha$ emission in our spectra. Among these, three Be stars in NGC 654 were discovered by us. One Be and one Of star in IC 1805 were confirmed by our spectra. The other two were appropriately classified as early-type supergiants showing H$\alpha$ emission.

The spectral classification work is just the first step to the systematical investigation of stellar contents and cluster properties (e.g., reddening, distance and age) of young open clusters and/or associations. Further study will be followed, based upon homogeneously combined data from spectroscopy, photometry, astrometry and so on.

Acknowledgements

The authors gratefully acknowledge Xinglong Observation-Station of the Joint Laboratories for Optical Astronomy for providing all the needed observing time. They also wish to express their sincere gratitude to Dr. Ram Sagar for his valuable comments on improving the paper. This research has made use of the BDA database, kindly offered by Dr. Jean-Claude Mermilliod, for bibliography information on MKK classification of stars in the clusters studied.