Secular acceleration of Phobos confirmed from positions obtained on La Palma

We have measured 332 positions of the satellites of Mars with CCD detectors on the Jacobus Kapteyn Telescope on La Palma between 1988 September 21 and 30. Comparison of the observations with an accurate orbital model shows that the average accuracy of one observation is 0.15 arcsec. The observations have been used, together with all available previous Earth-based and spacecraft observations, to improve the determination of the parameters of the orbital model, and in particular the secular acceleration of Phobos.