4U 1323-62, a low mass X-ray binary with an orbital period of 2.94 hr, exhibits periodic X-ray dips, which are due to absorption by the bulge of the outer accretion disk. The purpose of this study is to search for orbital period changes using archived X-ray data over a time span of 20 years. We present our preliminary results from analyzing light curves observed by RXTE, BeppoSAX, XMM-Newton and Suzaku. We used the method proposed by Hu et al. (2008) to estimate dip center time and adopted the Observed - Calculated method to measure changes in period. We obtained an orbital period of 2.941917(36) hr and a period derivative of _Porb=Porb = (-9.9 ± 3.5) X 10-7yr-1. The F-test result shows that the quadratic ephemeris is describes the evolution of the dip phases better than the linear ephemeris at a greater than 95% confidence level. More X-ray data collected from the early 80s will be included to further rfine the orbital ephemeris.

ABSTRACT
1. INTRODUCTION
2. OBSERVATIONS AND DATA REDUCTION
3. DATA ANALYSIS
4. DISCUSSION
REFERENCES

• Po-Sheng Chuang(Graduate Institute of Astromony, National Central University)
• Yi Chou(Graduate Institute of Astromony, National Central University)
• Chin-Ping Hu(Graduate Institute of Astromony, National Central University)
• Ting-Chang Yang(Graduate Institute of Astromony, National Central University)
• Yi-Hao Su(Graduate Institute of Astromony, National Central University)
• Nai-Hui Liao(Graduate Institute of Astromony, National Central University)
• Hung-En Hsieh(Graduate Institute of Astromony, National Central University)
• Ching-Ping Lin(Graduate Institute of Astromony, National Central University)