Simulating Self-Lensing and Eclipsing Signals due to Detached Compact Objects in the TESS Light Curves

TL;DR

This paper simulates self-lensing and eclipsing signals in binary systems with compact objects observed by TESS, assessing detection efficiencies and predicting discovery numbers of white dwarfs, neutron stars, and black holes.

Contribution

It introduces a detailed simulation framework for self-lensing signals in detached binaries and evaluates TESS's capability to detect these signals, providing estimates of expected discoveries.

Findings

Detection efficiency for WDMS, NSMS, and BHMS systems is 4-7% for low inclination angles.

Only a small fraction of events show detectable lensing features, less than 33%.

Predicted discoveries include 15-18 white dwarfs, 6-7 neutron stars, and fewer than 1 black hole.

Abstract

A fraction of Galactic stars have compact companions which could be white dwarfs (WDs), neutron stars (NSs) or stellar-mass black holes (SBHs). In a detached and edge-on binary system including a main-sequence star and a compact object (denoted by WDMS, NSMS, and BHMS systems), the stellar brightness can change periodically due to self-lensing or eclipsing features. The shape of a self-lensing signals is a degenerate function of stellar radius and compact object's mass because the self-lensing peak strongly depends on the projected source radius normalized to Einstein radius. Increasing the inclination angle $i$ changes the self-lensing shape from a strict top-hat model to one with slow-increasing edges. We simulate stellar light curves due to these binary systems which are observed by NASA's Transiting Exoplanet Survey Satellite (TESS) telescope and evaluate the efficiencies to detect their periodic signatures using two sets of criteria (i)SNR$>3$ and $N_{\rm{tran}}>1$ (Low-Confidence, LC), and (ii) SNR$>5$ and $N_{\rm{tran}}>2$ (High-Confidence, HC). The HC efficiencies for detecting WDMS, NSMS, and BHMS systems with the inclination angle $i<20^{\circ}$ during different time spans are $5$-$7\%$, $4.5$-$6\%$, and $4$-$5\%$, respectively. Detecting lensing-induced features is possible in only $\lesssim3\%$ and $\lesssim33\%$ of detectable WDMS and NSMS events. The detection efficiencies for closer source stars with higher priorities are higher and drop to zero for $b\gtrsim R_{\star}$, where $b\simeq \tan(i) a$ is the impact parameter($a$ is the semi-major axis). We predict the numbers of WDs, NSs, and SBHs that are discovered from the TESS Candidate Target List stars are $15$-$18$, $6$-$7$, and $<1$.