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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 moving group member HD 82443 are presented. A sequence of fifteen optical light curves obtained from 1989 to 1998 confirms the presence of a rotational mod- ulation with a mean period of 5.377 days attributable to cool photospheric spots. The Maximum Entropy and the Tikhonov regularization criteria have been applied to compute maps of the photospheric spot pattern. They show that the total spotted area is subject to cyclic changes as large as 10% of the star's surface with a mean period of 3.89 yr. The seasonal photometric period shows variations corre- lated with the phase of the activity cycle, which can be inter- preted as the result of a migration of the starspots in latitude over a differentially rotating star. The dependence of the photometric period on the cycle phase is opposite that of the Sun and similar to those observed in HD 114710 and HD 10476. A lower limit for the amplitude of the differential rotation in latitude can be estimated to be ' 0:04. Nearly simultaneous UV observations obtained in 1991 show the presence of chromospheric and transition region plages which do not seem to be in close spatial association with the photospheric spots.