TIC 278825952: a triply eclipsing hierarchical triple system with the most intrinsically circular outer orbit

TL;DR

This paper reports the discovery and detailed analysis of TIC 278825952, a highly coplanar, circular hierarchical triple star system with a 4.78-day binary and a 235.55-day tertiary, using TESS data and photodynamical modeling.

Contribution

It presents the first detailed characterization of a triply eclipsing system with an intrinsically circular outer orbit, combining photodynamical analysis with stellar isochrones.

Findings

Inner binary consists of near twin stars with ~1.1 M_sun and radii ~1.3 R_sun.

Outer tertiary star has 0.75 M_sun and 0.70 R_sun.

System is highly coplanar and has an exceptionally circular outer orbit.

Abstract

We report the discovery of a compact triply eclipsing triple star system in the southern continuous viewing zone of the TESS space telescope. TIC 278825952 is a previously unstudied, circular eclipsing binary with a period of 4.781 days with a tertiary component in a wider, circular orbit of 235.55 days period that was found from three sets of third-body eclipses and from light travel-time effect dominated eclipse timing variations. We performed a joint photodynamical analysis of the eclipse timing variation curves, photometric data, and the spectral energy distribution, coupled with the use of PARSEC stellar isochrones. We find that the inner binary consists of slightly evolved, near twin stars of masses of 1.12 and 1.09 $M_\odot$ and radii of 1.40 and 1.31 $R_\odot$. The third, less massive star has a mass of 0.75 $M_\odot$ and radius of 0.70 $R_\odot$. The low mutual inclination and eccentricities of the orbits show that the system is highly coplanar and surprisingly circular.