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

TL;DR

This study investigates the detection and characterization of self-lensing and eclipsing signals in edge-on double white dwarf systems, assessing their observability with current and upcoming astronomical surveys.

Contribution

It provides a detailed analysis of the conditions for lensing and eclipsing signals in DWDs and evaluates their detectability with TESS, LSST, and Roman telescopes.

Findings

Detection efficiency peaks for low-mass WDs in close orbits.

Number of detectable DWDs within 100 pc is about 1 for TESS.

LSST's long cadence limits its ability to detect these signals.

Abstract

Stellar lightcurves from edge-on double white dwarf systems(DWDs) have periodic lensing/eclipsing signals at times of alignment between 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 with WDs' radii, and the projected source and lens radii normalized to the Einstein radius ($\rho_{\star}$, and $\rho_{\rm l}$) are $\sim 1$. Both of them are reduced with the orbital period and the lens mass. If $\rho_{\rm l}\simeq 1$ the lensing-induced minor image is always blocked by the lens which results lower magnification factors. If $\rho_{\rm l}\lesssim 1$ and in transit events the finite-lens effects decrease the lightcurves' width. When $\rho_{\rm l}\gtrsim1$ (happens for close DWDs including one low-mass and one massive WD) deep or complete eclipses dominate to lensing effects. The self-lensing signals maximize for massive DWDs in wide orbits. We study the detect-ability of lensing/eclipsing signals in edge-on DWDs in observations by The NASA's Transiting Exoplanet Survey Satellite(TESS), The Vera Rubin Observatory(LSST) and The Nancy Grace Roman Space Telescope. We simulate stellar lightcurves due to edge-on DWDs and generate synthetic data points based on their observing strategies. Detection efficiency maximizes 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 $27.4$-day TESS and $62$-day Roman observing window are $\sim1$ and $<1$, respectively. Detecting these signals by LSST is barely possible because of its long cadence.