RX J0558.0+5353

N. M. Shakhovskoj, Crimean Astrophysical Observatory, Nauchnij; and S. V. Kolesnikov, Odessa Astronomical Observatory, write: "Periodic variations in the circular polarization, with period P = 0.006301 +/- 0.000055 day (544.4 +/- 4.8 s) and semiamplitude of 1.80 +/- 0.16 percent, were detected in this object on Oct. 4 at the Shajn 2.6-m telescope (+ one-channel polarimeter + fast-rotating achromatic quarter-wave plate and a broad red filter spanning 0.500-0.750 nm). Variations of the circular polarization are sinusoidal with the changing of the polarity. The photometric variations of the same observing run show P = 0.003592 +/- 0.000012 day; however, the peaks of the periodogram are accompanied by aliases, one of which corresponds to the double frequency (P = 0.003120 +/- 0.000012 day = 269.5 +/- 1.0 s) and amplitude 0.035 +/- 0.003 mag. This period is very near the period of 272.785 s detected by Ashoka et al. (1995, A.Ap. 297, L83) in white light, and the period of 272.74 s found by Haberl et al. (1994, A.Ap. 291, 171) in x-rays. Light maxima coincide with the extreme positive and negative circular polarization. Johnson magnitudes from Oct. 4 (1.25-m telescope): U = 13.29, B = 13.98, V = 13.91, R = 13.49, I = 13.31."