TIC 366240660 - A Dynamically Active Triple With a Very Short Outer Period of 30.5 Days
Abstract
Methods: We analyze TESS photometric data, radial velocity measurements, and eclipse timing variation curves for the triple star system, TIC 366240660, with a photodynamical code to infer the properties of all three stars and orbital motions. Results: With an outer orbital period of only 30.5 d, this is the second most compact triple reported in the literature. We have determined the masses and Teff values of the three stars with an accuracy of about 1% and the radii to about 2%. The inclination angles of the two planes, and the mutual inclination angle are found with an accuracy of better than 1/3∘. The system is determined to be quite flat (to within 1/2∘), but with an outer eccentricity of eout ≃ 0.33. We find that the properties of the secondary star of the inner binary are completely inconsistent with the evolution of a single star in isolation, and it must have transferred most of its envelope to the current primary star in the inner binary during a prior episode of mass transfer. The eclipse timing variation (ETV) curve derived from the TESS photometric data shows that, in addition to a typical dynamical delay curve at the period of the outer orbit, there is also a much larger amplitude anomalous sinusoidal-like delay with a period of 840 d. This latter feature in the ETV curve is not yet describable in simple analytic terms, but it appears certain that it can be explained by the near integer (≃13:1) ratio of the outer to the inner orbital periods. Conclusions: We have extensively explored the exotic and anomalous ETVs of this highly compact triple system and found that they can exceed hours for the inner binary eclipses, and several days for the outer orbital eclipses. We provide a preliminary explanation for how these are related to the 13:1 mean motion resonance of the outer to inner orbits.
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BibTeX
@misc{rappaport2026366240660,
title = {{TIC 366240660 - A Dynamically Active Triple With a Very Short Outer Period of 30.5 Days}},
author = {S. A. Rappaport and T. Borkovits and G. Torres and H. -L. Chen and P. Zasche and D. Vokrouhlický and B. Deme and M. Mašek and H. Kučáková and R. Uhlař and M. Wolf and Z. Garai and T. Pribulla and I. B. Bíró and I. Csányi and Z. Dencs and D. Latham and T. Mitnyan and V. B. Kostov and B. P. Powell},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.25332},
eprint = {2609.25332},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.25332},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - TIC 366240660 - A Dynamically Active Triple With a Very Short Outer Period of 30.5 Days
AU - S. A. Rappaport
AU - T. Borkovits
AU - G. Torres
AU - H. -L. Chen
AU - P. Zasche
AU - D. Vokrouhlický
AU - B. Deme
AU - M. Mašek
AU - H. Kučáková
AU - R. Uhlař
AU - M. Wolf
AU - Z. Garai
AU - T. Pribulla
AU - I. B. Bíró
AU - I. Csányi
AU - Z. Dencs
AU - D. Latham
AU - T. Mitnyan
AU - V. B. Kostov
AU - B. P. Powell
PY - 2026
DA - 2026/09/21
PB - arXiv
DO - 10.48550/arxiv.2609.25332
UR - https://arxiv.org/abs/2609.25332
AB - Methods: We analyze TESS photometric data, radial velocity measurements, and eclipse timing variation curves for the triple star system, TIC 366240660, with a photodynamical code to infer the properties of all three stars and orbital motions. Results: With an outer orbital period of only 30.5 d, this is the second most compact triple reported in the literature. We have determined the masses and T_eff values of the three stars with an accuracy of about 1% and the radii to about 2%. The inclination angles of the two planes, and the mutual inclination angle are found with an accuracy of better than 1/3^∘. The system is determined to be quite flat (to within 1/2^∘), but with an outer eccentricity of e_out ≃ 0.33. We find that the properties of the secondary star of the inner binary are completely inconsistent with the evolution of a single star in isolation, and it must have transferred most of its envelope to the current primary star in the inner binary during a prior episode of mass transfer. The eclipse timing variation (ETV) curve derived from the TESS photometric data shows that, in addition to a typical dynamical delay curve at the period of the outer orbit, there is also a much larger amplitude anomalous sinusoidal-like delay with a period of 840 d. This latter feature in the ETV curve is not yet describable in simple analytic terms, but it appears certain that it can be explained by the near integer (≃13:1) ratio of the outer to the inner orbital periods. Conclusions: We have extensively explored the exotic and anomalous ETVs of this highly compact triple system and found that they can exceed hours for the inner binary eclipses, and several days for the outer orbital eclipses. We provide a preliminary explanation for how these are related to the 13:1 mean motion resonance of the outer to inner orbits.
ER -