Poster Presentation

The orbital ephemeris of the partial eclipsing X-ray binary X1822-371

Hung-En Hsieh, Yi Chou, Chin-Ping Hu, Ting-Chang Yang, Yi-Hao Su (Institute of Astronomy, National Central University, Taiwan)

X 1822-371 is a low mass X-ray binary with accretion disk corona exhibiting partial eclipses and pulsations in the X-ray band. We update its orbital ephemeris by combining the new RXTE observations and historical records, with total time span of 34 years. There were 11 RXTE observations in 2011 but the eclipsing profile 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 (2012), the O-C analysis was processed. A quadratic model was applied to fit the O-C results and obtained the mean orbital period derivative of P ̇_orb=(1.339±0.025)×〖10〗^(-10) s/s, which is slightly smaller than previous records. However, we found that the cubic model is better to describe the orbital phase change with about 98% confidence level from F-test. The updated orbital parameters from eclipsing profile will be further compared with the ones from pulsar timing.