Study of Self-lensing/Eclipsing Signals in Edge-on Double White-dwarf Systems

Abstract Stellar light curves from edge-on double white dwarf (DWD) systems have periodic lensing/eclipsing signals at times of alignment between the two components as seen by the observer. Here, we study the characterization and detection of these signals. In common DWDs, the Einstein radii have similar orders of magnitude to the radii of the white dwarfs (WDs), and the projected source and lens radii normalized to the Einstein radius ( ρ ⋆ and ρ l ) are ∼1. Both of them are reduced with the orbital period and the lens mass. If ρ l ≃ 1 the lensing-induced minor image is always blocked by the lens, which results in lower magnification factors. If ρ l ≲ 1, and in transit events, the finite-lens effects decrease the light curves’ width. When ρ l ≳ 1 (which happens for close DWDs consisting of a low-mass WD and a massive one) deep or complete eclipses dominate over lensing effects. The self-lensing signals are maximal for massive DWDs in wide orbits. We study the detectability of lensing/eclipsing signals in edge-on DWDs in observations by NASA’s Transiting Exoplanet Survey Satellite (TESS), the Vera Rubin Observatory Large Synoptic Survey Telescope (LSST), and the Nancy Grace Roman Space Telescope. We simulate stellar light curves due to edge-on DWDs and generate synthetic data points based on their observing strategies. Detection efficiency is maximal for extremely low-mass WDs in close orbits, and the numbers of DWDs within 100 pc and an observing cone with detectable lensing/eclipsing signals in one observing window of 27.4 days for TESS and 62 days for Roman are ∼1 and <1, respectively. Detecting these signals by LSST is barely possible because of its long cadence.