TIC 168789840 is the first known sextuple (six-star) system consisting of three eclipsing binaries.
Structure of TIC 168789840, a sextuple system of three eclipsing binaries arranged as inner quadruple AC and outer binary B. Image credit: Sci-News.com.
“Prior to the discovery of TIC 168789840, there were 17 known sextuple star systems according to the June 2020 update of the Multiple Star Catalog,” lead author Dr. Brian Powell of NASA’s Goddard Space Flight Center and colleagues wrote in their paper.
TIC 168789840 resides approximately 1,428 light-years from Earth in the constellation of Eridanus.
Also known as TYC 7037-89-1, the system consists of three gravitationally-bound binary stars in a hierarchical structure of an inner quadruple system with an outer binary subsystem.
The inner system is comprised of two eclipsing binaries, designated A and C, and is orbited by another eclipsing binary, designated B.
“Our analysis shows that the orbital periods of the three constituent eclipsing binaries are 1.57 days (binary A), 1.3 days (binary C) and 8.2 days (binary B), such that binaries A and C form an inner quadruple system with a period of about 4 years, and the latter forms the outer subsystem with a period of about 2,000 years,” the astronomers wrote.
They observed all six eclipses — three primary and three secondary — in the TIC 168789840 system using NASA’s Transiting Exoplanet Survey Satellite (TESS).
“Interestingly, of the known sextuple systems, TIC 168789840 is most similar to the famous Castor system, which also contains three close binaries,” they wrote.
The TIC 168789840 sextuple system (center). Image credit: Centre de Données astronomiques de Strasbourg / SIMBAD / DSS2.
The three binary stars in the system are ‘triplets,’ as each binary is similar to the others in terms of mass, radius, and temperature.
The primary stars in the binaries have masses between 1.23 and 1.3 times that of the Sun and radii between 1.46 and 1.69 solar radii, while the secondary stars have masses and radii of 0.56-0.66 solar masses and 0.52-0.62 solar radii.
“TIC 168789840 is a fascinating system that naturally merits additional observation and analysis,” the authors wrote.
“Though quite similar to the Castor system, the triplet nature of TIC 168789840 combined with the presence of three primary and three secondary eclipses enable further investigations into its stellar formation and evolution.”
“Remarkable objects like TIC 168789840 or Castor give us insights on the formation of multiple systems — a matter of active research and debate.”
The team’s paper will be published in one of the AAS journals.
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Brian P. Powell et al. 2021. TIC 168789840: A Sextuply-Eclipsing Sextuple Star System. AAS journals; arXiv: 2101.03433
