High Tide: A Systematic Search for Ellipsoidal Variables in ASAS-SN

TL;DR

This study systematically searches for ellipsoidal variables in the ASAS-SN data to identify non-interacting black holes and neutron stars by analyzing stellar variability.

Contribution

It introduces a method combining statistical tests and visual inspection to find ellipsoidal variables and estimates companion masses to identify promising black hole and neutron star candidates.

Findings

Identified 369 ellipsoidal variability candidates.

Developed a technique to estimate minimum companion mass.

Highlighted promising candidates for non-interacting compact objects.

Abstract

The majority of non-merging stellar mass black holes are discovered by observing high energy emission from accretion processes. Here we pursue the large, but still mostly unstudied population of non-interacting black holes and neutron stars by searching for the tidally-induced ellipsoidal variability of their stellar companions. We start from a sample of about 200,000 rotational variables, semi-regular variables, and eclipsing binary stars from the All-Sky Automated Survey for Supernovae (ASAS-SN). We use a $\chi^2$ ratio test followed by visual inspection to identify 369 candidates for ellipsoidal variability. We also discuss how to combine the amplitude of the variability with mass and radius estimates for observed stars to calculate a minimum companion mass, identifying the most promising candidates for high mass companions.