Photodynamical analysis of the triply eclipsing hierarchical triple system EPIC 249432662

Abstract

Using Campaign 15 data from the K2 mission, we have discovered a triply-eclipsing triple star system: EPIC 249432662. The inner eclipsing binary system has a period of 8.23 days, with shallow ∼3% eclipses. During the entire 80-day campaign, there is also a single eclipse event of a third-body in the system that reaches a depth of nearly 50% and has a total duration of 1.7 days, longer than for any previously known thirdbody eclipse involving unevolved stars. The binary eclipses exhibit clear eclipse timing variations. A combination of photodynamical modeling of the lightcurve, as well as seven follow-up radial velocity measurements, has led to a prediction of the subsequent eclipses of the third star with a period of 188 days. A campaign of follow-up groundbased photometry was able to capture the subsequent pair of third-body events as well as two further 8-day eclipses. A combined photo-spectro-dynamical analysis then leads to the determination of many of the system parameters. The 8-day binary consists of a pair of M stars, while most of the system light is from a K star around which the pair of M stars orbits.1 In this paper, we use the following notations. The orbital elements of the inner and outer orbits are subscripted by numbers '1' and '2', respectively. Regarding the three stars, we label them as A, Ba, and Bb, where A denotes the brightest and most massive component, i.e., the distant, third star, while Ba and Bb refer to the primary and the secondary components of the close, inner 8-day binary. When we refer to physical quantities of individual stars, we use these subscripts. In such a way, for example, m A or m Ba stands for the masses of components A or Ba, respectively, but m B denotes the total mass of the inner binary, (m Ba + m Bb ), while m AB refers to the total mass of the entire triple system.

TICs 167692429 and 220397947: the first compact hierarchical triple stars discovered with TESS

“…This led us to collect all the observations and then carry out a complex photodynamical light curve and ETV analysis (see e.g. Borkovits et al 2019a). For this purpose, we used the simple aperture photometry (SAP) data.…”

“…(4) Finally, four (five) other parameters that are related (almost) exclusively to the light-curve solutions, as follows: the duration of the primary eclipse ( t) pri closest to epoch t 0 (which 5 Two other inner-orbit related parameters, namely the instantaneous orbital periods (P 1 ) and inferior conjunction time (T 0 ) 1 of the secondary components of the inner binaries, i.e. the mid-primary-eclipse-times, were constrained with the use of the ETV curves in the manner explained in appendix A of Borkovits et al (2019a), whilst the sixth orbital element, 1 , as irrelevant, was kept fixed at zero. 6 As 1 = 0 • was assumed at epoch t 0 for all runs, 2 set the initial trial value of the differences of the nodes (i.e.…”

“…Moreover, Borkovits et al (2016) have shown that the absence of further very short outer period triples amongst Kepler's EBs cannot be an observational selection effect. At least three additional very short outer period triple stars were detected in the fields of the K2 mission; two of them, HD 144548 (Alonso et al 2015) and EPIC 249432662 (Borkovits et al 2019a), exhibit outer eclipses, whilst the third, HIP 41431, was discovered independently as a spectroscopic triple is indeed at least a 2+1+1 quadruple system (Borkovits et al 2019b). Moreover, Hajdu et al (2017) identified four triple-star candidates with outer periods probably less than 1 yr amongst EBs observed by the CoRoT spacecraft (Auvergne et al 2009).…”

TIC 278956474: Two Close Binaries in One Young Quadruple System Identified by TESS

“…The two periods (P A,B ) and reference primary eclipse times ((T 0 ) A,B ) of both binaries were not adjusted, but constrained through the ETV curves, as was explained in the Appendix A of Borkovits et al (2019b). Furthermore, the systemic radial velocity of the center of mass of the whole quadruple system (γ) which in the current model occurs only as an additive parameter independent of any other parameters, was calculated in each trial step by simply minimizing a posteriori the goodness of fit of the RV curve (i.e.…”

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

“…Other multiply-eclipsing systems include KIC 4247791 (Lehmann et al [207]) which shows two sets of eclipses plus spectral lines from four stars; KIC 6543674, which shows eclipses on a 2.39 d period with extra eclipses from a third body on a 1090-d orbit (Masuda et al [208]); KIC 7177553 which shows four sets of spectral lines and one set of eclipses (Lehmann et al [209]); and the doubly-eclipsing systems EPIC 219217635 and EPIC 249432662 (Borkovits et al [210,211]) observed during the K2 mission and showing eclipse timing variations due to being hierarchical multiple systems. KIC 2856960 shows eclipses on a 0.258 d period and forests of eclipses every 204 d (Figure 6; Armstrong et al [212]), similar to KIC 4150611, but its configuration remains unclear as no model has been found that satisfies the observations (Marsh et al [213]).…”