In the present paper, the post-1971 infrared and optical data have been compiled and dealt with by means of the DCF method, the result indicates a strong correlation between these two bands, which suggests that the emission mechanisms in the optical and infrared bands are the same. The color index and brightness association is found from our new optical data. The time-dependent decreasing color indices post large outburst are also presented in the paper.
Acknowledgements
The authors thank the referee Dr. L. Takalo's comments. This work is supported by the National Scientific Foundation of China (the ninth-year important project) and the National Pandeng Project of China.
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