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We present the results of a study of differential rotation on the K2 IVprimary of the RS CVn binary II Pegasi (HD 224085) performed by inverting lightcurves to produce images of the dark starspots on its surface. The data wereobtained in the standard Johnson B and V filter passbands via the TennesseeState University T3 0.4-m Automated Photometric Telescope from JD 2447115.8086to 2454136.6221 (1987 November 16 to 2007 February 5). The observations weresubdivided into 68 data sets consisting of pairs of B and V light curves, whichwere then inverted using a constrained non-linear inversion algorithm thatmakes no a priori assumptions regarding the number of spots or their shapes.The resulting surface images were then assigned to 21 groups corresponding totime intervals over which we could observe the evolution of a given group ofspots (except for three groups consisting of single data sets). Of these 21groups, six showed convincing evidence of differential rotation over timeintervals of several months. For the others, the spot configuration was suchthat differential rotation was neither exhibited nor contraindicated. Thedifferential rotation we infer is in the same sense as that on the Sun: lowerlatitudes have shorter rotation periods. From plots of the range in longitudespanned by the spotted regions vs. time, we obtain estimates of thedifferential rotation coefficient k defined in earlier work by Henry et al.,and show that our results for its value are consistent with the value obtainedtherein.

A Study of Differential Rotation on II Pegasi via Photometric Starspot Imaging