Activity cycle and surface differential rotation of the single Pleiades star HD 82443 (DX Leo)

The results of a long-term photometric monitoring of the young Pleiades mov ing group member HD 82443 are presented. A sequence of fifteen optical ligh t curves obtained from 1989 to 1998 confirms the presence of a rotational m odulation with a mean period of 5.377 days attributable to cool photospheri c spots. The Maximum Entropy and the Tilchonov regularization criteria have been applied to compute maps of the photospheric spot pattern. They show t hat the total spotted area is subject to cyclic changes as large as similar to 10% of the star's surface with a mean period of 3.89 yr. The seasonal photometric period shows variations correlated with the phase of the activity cycle, which can be interpreted as the result of a migratio n of the starspots in latitude over a differentially rotating star. The dep endence of the photometric period on the cycle phase is opposite that of th e Sun and similar to those observed in HD 114710 and HD 10476. A lower limi t for the amplitude of the differential rotation in latitude can be estimat ed to be Delta Omega/Omega similar or equal to 0.04. Nearly simultaneous UV observations obtained in 1991 show the presence of c hromospheric and transition region plages which do not seem to be in close spatial association with the photospheric spots.