Planet Hunters TESS IV: a massive, compact hierarchical triple star system TIC 470710327
Aigrain, S.; Lee, S.; Escorza, A.; Sana, H.; Fabry, M.; Abdul-Masih, M.; Frost, A. J.; Arellano-Córdova, K. Z.; Bordier, E.; Howell, S. B.; Beck, P. G.; Toonen, S.; Eisner, N. L.; Miller, G.; Barnet, F.; Bean, S. J.; Bundy, D. M.; Huten, M.; Rogers, D. J.; Tanner, C.; Janssens, S.; Johnston, C.; Lintott, C. J.; Cannon, E.; Hermansson, L.; Sheyte, S.; Alhassan, S.; Baeten, E. M. L.; Bernau, M.; Di Fraia, M. Z.; Emralino, F. M.; Goodwin, B. L.; Hermes, P.; Hoffman, T.; Janíček, R.; Mazzucato, M. T.; Rout, M. P.; Sejpka, J.; Terentev, I. A.; Urvoy, D.
United Kingdom, Belgium, Netherlands, Chile, United States, Spain, Austria, Sweden
Abstract
We report the discovery and analysis of a massive, compact, hierarchical triple system (TIC 470710327) initially identified by citizen scientists in data obtained by NASA's Transiting Exoplanet Survey Satellite (TESS). Spectroscopic follow-up observations obtained with the HERMES spectrograph, combined with eclipse-timing variations (ETVs), confirm that the system is comprised of three OB stars, with a compact 1.10 d eclipsing binary and a non-eclipsing tertiary on a 52.04 d orbit. Dynamical modelling of the system (from radial velocity and ETVs) reveal a rare configuration wherein the tertiary star (O9.5-B0.5V; 14-17 M⊙) is more massive than the combined mass of the inner binary (10.9-13.2 M⊙). Given the high mass of the tertiary, we predict that this system will undergo multiple phases of mass transfer in the future, and likely end up as a double neutron star gravitational wave progenitor or an exotic Thorne-Żytkow object. Further observational characterization of this system promises constraints on both formation scenarios of massive stars as well as their exotic evolutionary end-products.