Relation between rotational phase and polarization degree of 1999 JD₆. The open squares, open circles, and crosses indicate individual data obtained on July 16, 19, and 20, 2016, respectively (see Table B.1). The plotted data are the deviations after subtracting the increasing portion of the polarization degree from the phase angle. Both bands (V band in green and R_C band in red) show small but similar fluctuations in the rotation phase (light curve from Vaduvescu et al. 2017). Our data provide insufficient coverage of the rotational phase to confirm its repeatability.