VARIATION OF GRAVITATIONAL DELAY IN PULSAR TIMING OBSERVATION DUE TO PROPER MOTION OF FOREGROUND STARS AND MEASUREMENT OF STELLAR MASS

We propose the inclusion of a new correction term, the gravitational t ime delay effect caused by a star between the observer and the pulsar, in the analysis of pulsar timing observation. This effect appears in the form of In(1 + t(2)), where the amplitude connects directly to the mass of the star. When the residuals of the time of arrival have a po sitive hump, it is worthwhile to reanalyze the data by including this correction term in the existing models. The analysis of this effect wi ll not only help to stabilize the pulsar time but also provide a new w ay to determine the mass of a star directly. When the mass of a star i s 0.2 M., the observation accuracy is 200 ns, and the observation peri od is 10 yr, the possibility of detecting this effect is of the order of one-hundredth.