| 基金项目： | Supported by the National Natural Science Foundation of China.Acknowledgements The authors would like to thank Fang X. S. and the observing assistants at the 85 cm telescope of Xinglong station for their help during our observations. We also thank Profs. Zhou X., Jiang X. J., and Zhao Y. H., for allocation of observing time and their kind help during a visit to NAOC. This work is partly supported by Guizhou University （Grant No. 2008036）, the Guizhou Natural Science Foundation （Grant Nos. 20092263 and 20104014） and partly supported by the Joint Fund of Astronomy of the National Natural Science Foundation of China （Grant Nos. 10978010 and 10963001）. |
