Fig. 4: Optical light variation.
From: A helium-burning white dwarf binary as a supersoft X-ray source
a, b, Lomb–Scargle periodograms derived from the OGLE I-band data (a) and the TESS data (b). For the interpretation of the OGLE peaks, see Extended Data Table 1. c, d, The TESS data are folded with a period of P = 1.1635 days (c) and P = 2.327 days (d), corresponding to an ephemeris of 2,459,036.2885297858(14) + 1.1635*N or 2,459,036.288557(8) + 2.327*N (Barycentric Julian Date), respectively. The error bars for a given point represent the root mean square error of the individual 10-min data points that went into that one bin. Although the Lomb–Scargle periodograms show the highest power at P = 1.1635 days, the folded light curve for the longer period (d) has a lower variance and a clear odd–even asymmetry. Lacking phase-resolved spectroscopy for a definite proof, we tentatively identify P = 2.327 days as the orbital period of [HP99] 159.
