Real time CCD differential photometry was performed for BT Cnc in Praesepe cluster from February to March, 1994. New 885 differential V magnitudes were obtained for thirteen nights. From the frequency analysis, we have detected two distinct pulsational frequencies of f1=9.7783c/d and f2=7.0153c/d. The first frequency is nearly equal to the previous result(Breger 1980), but the second one is much different. Our reanalysis of the previous data obtained by Guerrero el al.(1979) indicates that the previous result of f3=5.95c/d might be uncertain; it was not detected in the power spectrum. Also it turns out that our second frequency could not be fitted to the previous data and the reanalyzed frequency(f2=7.8813c/d) of the previous data was poor-fitted to our data. Therefore we suggest that the second frequency which might be newly excited in the nonradial mode, has been changed over the last eighteen years.

• Kim Seung-Lee(Bohyunsan Optical Astronomy Observatory, Korea Astronomy Observatory/Department of Astronomy, Seoul National University)
• Lee See-Woo(Department of Astronomy, Seoul National University)