TIC 433545934: The first 2+2-type doubly eclipsing binary with extra, mutual eclipses

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Abstract
Aims. Several hundred previously unknown 2+2 hierarchical doubly eclipsing quadruple stars have been identified in observations made with the space telescope TESS over the past eight years. Moreover, more than one hundred close hierarchical triple star systems have been identified in the same TESS datasets, each consisting of an inner eclipsing binary and a tertiary star that either eclipses the inner binary or is eclipsed by it. In this work we identify and photodynamically analyse the very first 2+2-type quadruple stellar system that is a member of both groups. TIC 433545934 consists of two eclipsing binaries that revolve around each other, forming a 2+2-type quadruple system in which, additionally, one binary eclipses the stars of the other binary. The TESS mission detected one such outer eclipse, which prompted particular interest in this system. Methods. Most of the data used in this study come from TESS observations, but we also obtained supplementary ground-based photometric measurements for this quadruple system. We combined the eclipse timing variation curves extracted from the TESS and ground-based follow-up data, the photometric light curves, and the spectral energy distribution in a complex photodynamical analysis to derive the stellar and orbital parameters of this dynamically interesting system. Results. The periods of the two inner eclipsing binaries are P A = 2 d . 07 and P B = 1 d . 41, while the mutual or outer period is P AB = 224 d . 5. The outer period alone makes this system the fifth most compact known 2+2-type quadruple. Moreover, what makes TIC 433545934 unique is that TESS observed a triple-dipped extra eclipsing event when the stars of binary B eclipsed the two components of binary A. We also identify similar extra eclipsing events in the archival, ground-based data of ASAS-SN and ATLAS. However, we find that these extra events occur only once during an outer revolution; that is, binary A does not eclipse the stars of binary B. This is consistent with our finding that the outer eccentricity is quite high, e AB = 0.62. Our analysis reveals that binary A consists of two quite similar but slightly evolved late A-type stars ( q A = 0.92), while in binary B, the primary star, whose mass lies between the masses of the two stars of binary A, is quite dominant, with q B = 0.60. We find that the system is substantially flat, with mutual inclination angles below ≈2°.
Funding Information
  • Nemzeti Kutatási Fejlesztési és Innovációs Hivatal (K-147131)
  • NASA (80NSSC23K0270)
  • Ministry of Education of the Czech Republic (LM2018102)
  • Ministry of Education of the Czech Republic (MSMT-CR LTT18004)

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