Astron. Astrophys. 363, 555-567 (2000)

Acknowledgements

We thank Dr. Oscar Straniero for very useful suggestions on the original manuscript, and on the finally improved presentation. We thank Dr. Maurizio Busso for fruitful discussion and sending important material to us. We thank Dr. Peng Qiuhe and Dr. Ma Jun for the interesting discussions. Thank Dr. Jiang Biwei, Liu Junhong, Li Ji, Zhang Yanxia, Shi Jianrong and Luo Ali for their friendly help. This research work is supported by the National Natural Science Foundation of China under grant No. 19725312, No. 19973002, and the Major State Basic Research Development Program.

© European Southern Observatory (ESO) 2000

Online publication: December 11, 2000
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