ASTROMETRIC ANALYSIS OF TIMING OBSERVATIONS OF THE FAST PULSAR PSR-1937 + 214

A new analysis of the first two years of timing data acquired on the fast pulsar PSR 1937 + 214 at Arecibo is presented. Parameters are evaluated with various models based on two ephemerides, two atomic time scales and two TT-TB time transformations and comparison is carried out with previously published results. We provide evidence that systematic errors induced by the model adopted are 5 to 10 times larger than the formal uncertainties calculated by the fitting procedure. One must therefore exercise great care in the reduction method when comparing results from different timing programs for precise astrometric applications.