TIC 295741342: A Triply-Eclipsing Triple Star System with a Giant Tertiary

TL;DR

This paper reports the discovery and detailed analysis of TIC 295741342, a triply-eclipsing triple star system with a giant tertiary, using TESS data and spectro-photodynamical modeling to understand its structure and evolution.

Contribution

The study provides the first comprehensive characterization of a triply-eclipsing triple system with a giant tertiary, including detailed modeling and evolutionary predictions.

Findings

System is near-coplanar with two degenerate solutions for the giant's evolutionary stage.

The system's next outer eclipse is predicted for September 1, 2026.

The tertiary will overflow its Roche lobe, leading to mass transfer or merger events.

Abstract

We present the discovery and characterization of TIC 295741342, a triply-eclipsing triple star system with a giant tertiary. The eclipsing binary consists of two similar main-sequence stars in a 4.75-day orbit. The binary is in a 412.8-day orbit with the giant tertiary. We found two degenerate solutions for the system: one where the tertiary is ascending the Red Giant Branch (RGB), and the other where the tertiary is on the Horizontal Branch (HB) and will eventually ascend the Asymptotic Giant Branch (AGB). In both solutions, the system is near-perfectly coplanar. In TESS Sector 33, the binary passes behind the giant tertiary, producing a distinctive "head-and-shoulders" eclipse that directly constrains the relative flux contributions and radii of all three stars. We modeled the system using a comprehensive spectro-photodynamical model that simultaneously fits the TESS lightcurve, eclipse times, spectral energy distribution, and radial velocities from 48 TRES spectra obtained over four years of observation resolving all three components. Evolutionary analysis using MIST tracks indicates that, in both solutions, the tertiary will overflow its Roche lobe, one in the RGB and the other in the AGB. The Roche lobe overflow will initiate either a stable mass transfer to the binary or a common envelope evolution that will likely result in ejections and/or mergers. Our models predict the midpoint of the next outer eclipse will occur on September 1, 2026 and we encourage follow-up observations with a $\pm$3 day window to observe the full event and further constrain the system parameters.