X1822-371 is a low mass X-ray binary with an accretion disk corona exhibiting partial eclipses and pulsations in the X-ray band. We update its orbital ephemeris by combining new RXTE observations and historical records, with a total time span of 34 years. There were 11 RXTE observations in 2011 but the eclipsing prole can be seen in only 4 of them. The eclipsing center times were obtained by fitting the profile with the same model as previous studies. Combined with the eclipsing center times reported by Iaria et al. (2011), the O-C analysis was processed. A quadratic model was applied to fit the O-C results and produced a mean orbital period derivative of _Porb = 1.339(25) X 10-10s=s, which is slightly smaller than previous records. In addition to the orbital modulation from the orbital profile, we also present our preliminary results for measuring the orbital parameters using the orbital Doppler effect from the pulsation of the neutron star in X1822-371. The updated orbital parameters from eclipsing profiles will be further compared with the ones from pulsar timing.

ABSTRACT
1. INTRODUCTION
2. OBSERVATIONS AND DATA ANALYSIS
3. SUMMARY
REFERENCES

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