The ephemeris of X 1822 - 371

From the analysis of eclipses observed with the HEAO-1, Einstein, Exosat and Ginga satellites, it is shown that the orbital period of X1822 - 371 is increasing on a time-scale of 2.9 million yr. The period change, one of only three determined amongst the LMXBs, is in the opposite sense to the expected evolutionary trend, but in the same sense as the period change of Cyg X-3. The observation of an eclipse simultaneously in the X-ray and optical bands shows that the optical eclipse is asymmetric and has a minimum 3 min later than that of the X-ray eclipse, reflecting a pronounced asymmetry in the optically emitting disk structure.