BG Ind: the nearest doubly eclipsing, compact hierarchical quadruple system

TL;DR

This study reveals BG Ind as a unique compact quadruple system with two eclipsing binaries gravitationally bound in a 721-day orbit, providing detailed stellar parameters and orbital alignment insights through combined photometric and spectroscopic analysis.

Contribution

First detailed joint analysis confirming the quadruple nature of BG Ind and refining stellar and orbital parameters using multi-source data.

Findings

BG Ind contains two eclipsing binaries in a 721-day orbit.

The primary binary has slightly evolved F-type stars with known masses and radii.

The secondary binary consists of less massive stars with well-constrained parameters.

Abstract

BG Ind is a well studied, bright, nearby binary consisting of a pair of F stars in a 1.46-day orbit. We have discovered in the TESS lightcurve for TIC 229804573 (aka BG Ind) a second eclipsing binary in the system with a 0.53-day. Our subsequent analyses of the recent TESS and archival ground-based photometric and radial velocity data, reveal that the two binaries are gravitationally bound in a 721-day period, moderately eccentric orbit. We present the results of a joint spectro-photodynamical analysis of the eclipse timing variation curves of both binaries based on TESS and ground-based archival data, the TESS lightcurve, archival radial velocity data and the spectral energy distribution, coupled with the use of PARSEC stellar isochrones. We confirm prior studies of BG Ind which found that the brighter binary A consists of slightly evolved F-type stars with refined masses of 1.32 and 1.43 $M_\odot$, and radii of 1.59 and 2.34 $R_\odot$. The previously unknown binary B has two less massive stars of 0.69 and 0.64 $M_\odot$ and radii of 0.64 and 0.61 $R_\odot$. Based on a number of different arguments which we discuss, we conclude that the three orbital planes are likely aligned to within 17$^\circ$.