Probing periodic trends in the TESS light curves of the seventeen known Double White Dwarf systems

Abstract: There is a relatively large population of known double white dwarfs (DWDs) that were mostly discovered through spectroscopic observations and by measuring their radial velocity variations. Photometric observations from these systems give us additional information about their faint components by manifesting eclipsing or lensing signals or periodic trends such as ellipsoidal variations or Doppler boosting. To find these signals and trends we probe the public photometric data collected by the Transiting Exoplanet Survey Satellite (TESS) telescope from 17 known DWD systems. We use the Singular Spectrum Analysis (SSA) technique to de-noise their light curves. For DWD systems J1717$+$6757, J1557$+$2823, LP400$-$22, J1449$+$1717, J2132$+$0754, and J2151$+$1614 we find regular and periodic trends in their TESS light curves. The periodic trend in light curve J1449$+$1717 is caused by the blending effect due to a variable and bright star close to it which are unresolvable in the TESS observations. The discovered periodic trend for J1717$+$6757 was recovered by the TESS data. The periodic trends in light curves of J1557$+$2823 and J2151$+$1614 have the False Alarm Probability (FAP) values $\simeq 14.8,~36.5\%$. So their detected trends are likely noises with non-orbital origins. Periods of trends in light curves of LP400$-$22 and J2132$+$0754 are the same as and half of orbital periods, respectively. We evaluate possible ranges for Doppler boosting and ellipsoidal variations's amplitudes for these targets. This study highlights the importance of TESS data for identifying periodic trends such as ellipsoidal or intrinsic variations rather than short eclipsing/lensing signals in DWD light curves specially bright targets with ignorable blending.