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tokens: Whilst a reasonable harmonic fit to the ESPaDOnS data can be achieved using this period, it does not produce an acceptable phasing of all available 〈 B z 〉 measurements. Figure 1. Photometric ( top ) and magnetic 〈 B z 〉 ( bottom ) measurements, phased with periods determined from (left to right) K2 photometry, all 〈 B z 〉 measurements, and all photometric measurements. 〈 B z 〉 measurements were obtained from ESPaDOnS by Shultz et al. ( 2018 ) and photopolarimetric data by Borra et al. ( 1983 , BLT83) and Bohlender et al. ( 1993 , BLT93). The solid and dashed curves show, respectively, the best second-order harmonic fit to the ESPaDOnS 〈 B z 〉 data and the 1σ fit uncertainty. Photometric data are from K2, SMEI, Hipparcos ( H p ), and Strömgren y photometry published by Sterken et al. ( 1995 , S95), Manfroid et al. ( 1995 , M95), and Pedersen Thomsen ( 1977 , P77). For clarity the K2 and SMEI data have been binned by phase, using bin sizes of 0.01 cycles. The mean magnitude of each data set was subtracted for display purposes. All of the periods obtained since the year 2000 are approximately consistent with one another; the two periods determined using photometric data obtained prior to the year 2000 are also consistent with one another. At the same time, the difference between the Bowman et al. ( 2018 ) and Catalano Leone ( 1996 ) periods, 0.00015 d, is almost eight times larger than the formal uncertainty in the Bowman et al. period (the less precise of the two). This suggests that the period may have changed. 3.2 Period analysis We now turn to a re-examination of the period analysis of the individual data sets; the results are summarized in Table 2 . Period analysis was performed using standard Lomb–Scargle statistics (Lomb 1976 ; Scargle 1982 ), utilizing both the idl program periodogram 4 and the period04 package (Lenz Breger 2005 ). The uncertainties were determined in the same manner as by Shultz et al. ( 2018 ), i.e. according to the analytic method described by Bloomfield ( 1976 ). Examining the ESPaDOnS data in isolation yields P rot = 0.97887(6) d, consistent within uncertainty with the K2 period (Bowman et al. 2018 ). The period determined from all available magnetic data (i.e. including the previously overlooked 〈 B z 〉 measurements of Borra et al. 1983 ) is 0.979855(5) d. The photometric and magnetic data are shown phased with this period in the middle panel of Fig. 1 . Phasing 〈 B z 〉 with this period and fitting the ESPaDOnS data with a second-order sinusoid yields a reduced χ 2 = 5, i.e. a poor fit. This period also does not provide a coherent phasing of the majority of the photometric data set. Notably, the variation in the phase-binned SMEI data almost completely disappears, likely because observations are being binned as though they were at the same phase when, in fact, they are not. We can also combine all available photometric data (shifted to the mean magnitude of each data set, as in Fig. 1 ), which yields P rot =