TIC 278825952: a triply eclipsing hierarchical triple system with the most intrinsically 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⊙ and radii of 1.40 and 1.31 R⊙. The third, less massive star has a mass of 0.75 M⊙ and radius of 0.70 R⊙. The low mutual inclination and eccentricities of the orbits show that the system is highly coplanar and surprisingly circular.

Eclipsing Binaries in Dynamically Interacting Close, Multiple Systems

“…In addition to the dynamical determination of the relative orbital inclinations, the discovery of triply eclipsing systems offers another opportunity since the shape and timing of the extra eclipses are extremely sensitive to the relative configuration and movement of the three stars (or, two stars and a circumbinary planet). Via careful modeling of the extra eclipses, the mutual inclination can be accurately determined even in the absence of detectable third-body perturbations (Borkovits et al [23]; Masuda et al [165]; Mitnyan et al [154]; Borkovits et al [155]).…”

“…However, these higher order, non-vanishing DE contributions in the flat, doubly circular case will remain small, and turn out to be negligible in practice. This scenario is realized in at least three known triply eclipsing ECHTs (HD 181068, Borkovits et al [23]; TIC 278825952, Mitnyan et al [154]; TIC 193993801, Borkovits et al [155]), where numerical integrations have justified that, despite the tightness of these systems, their observed ETVs are dominated exclusively by LTTE.…”

“…As of 2021 November, the photodynamical analyses of five TESS-discovered triply eclipsing tiples have been published (see Table 1). Apart from TIC 278825952, which is located in the SCVZ of TESS and, hence, was almost continuously observed during Cycles 1 and 3 (Mitnyan et al [154]), the other four were seen by TESS only during a few 25-27 daylong sectors. Therefore, inclusion of data sets of former, archival, or ongoing surveys such as SuperWASP (Pollaco et al [174]), ASAS-SN (Kochanek et al [175]), ATLAS (Heinze et al [176]), and KELT (Pepper et al [177]), as well as additional ground-based follow-up observations were crucial to their investigations (Borkovits et al [24,155]).…”

Triply eclipsing triple stars in the northern TESS fields: TICs 193993801, 388459317, and 52041148

“…(ii) multi-band light curve, ETV and RV curve emulators, and (iii) for the inverse problem, an MCMC-based parameter search routine, which employs an implementation of the generic Metropolis-Hastings algorithm (see e. g. Ford 2005). The usage of this software package and the philosophy and consecutive steps of the whole process were previously explained in detail for a variety of systems (Borkovits et al 2018(Borkovits et al , 2019a(Borkovits et al ,b, 2020a(Borkovits et al ,b, 2021Mitnyan et al 2020). These included tight and less tight triple systems (either exhibiting extra eclipses or not) as well as quadruple systems (having hierarchies of either the 2+2 or 2+1+1 types) and, therefore, here we discuss only the points specific to the current studies.…”

Space-Based Photometry of Binary Stars: From Voyager to TESS

“…The former system also displays changes in eclipse depth due to precession of the orbital plane caused by a misalignment between the inner and outer orbits. In contrast, TIC 278825952 (Mitnyan et al [303]) is a triple system where both orbits are circular and coplanar. Borkovits et al [304] analysed TIC 209409435, which shows additional eclipses as well as eclipse timing variations due to a third body.…”