Left panel: χ² of a Fourier polynomial fit varying the period between 1.75 and 2.05 d. The solid curve represents results from fitting data from 1, 2, 5, and 6 Dec 2016, while the dashed curve uses data from 29 Dec 2016 and 01 Jan 2017. The red solid and dotted vertical straight lines indicate best-fitted periods of 1.936 ± 0.002 and 1.848 ± 0.028 d, respectively. The black solid and dotted lines represent 1, 2, and 3σ uncertainties for each fit as follows: ± 7.5, , and ± 12 × 10⁻³ d. Right panel: χ² distribution for a two-period Fourier polynomial fit. The single-period solution of 1.936 d is indicated by the vertical red line.