The first-discovered triple-binary sextuple star system and a Sun-like star with five exoplanets orbiting within the distance of Mercury are just two recent examples of the extraordinary systems being investigated and discovered by scientist using data from the Transiting Exoplanet Survey Satellite, or TESS.
The joint NASA-Massachusetts Institute of Technology (MIT) mission is the cornerstone of two recently presented discoveries that characterize two tantalizing systems and their benefit to understanding stellar system formation.
A sextuplly-eclipsing sextuple system
Finding a system with six stars is rare to begin with. Finding such a system with three sets of binaries, all of which are eclipsing binaries when viewed from Earth is even more rare.
In fact, TYC 7037-89-1 is the first star system ever discovered to fall into such a category — though 17 other sextuple star systems have already been observed.
The discovery from a team led by NASA’s Brian Powell (Powell et al.) stems from the primary nature of the TESS mission, which is to continuously observe a large portion of the sky for month-long intervals at most searching for the telltale change in brightness coming from stars.
This design is meant to find exoplanets transiting their host stars in relation to TESS’s field of view; the telescope is therefore perfectly primed to detect the changes in brightness that occur when two stars of the same system eclipse one another.
The TYC 7037-89-1 system had been observed previously, but its true nature had evaded detection until Sector 4 and 5 observations during Cycle 1 of TESS investigations which placed the system in the telescope’s field of view.
Based on information extracted from the test light curves and follow-up observations not just from TESS but other telescopes as well, scientists were able to show that the six stars are arranged in three binary groups, with an inner grouping of two binaries and an additional outer binary.
The outer binary is known as binary B, while the inner binary pair are known separately as A and C.
The inner binaries A and C orbit each other every 3.7 years while the outer binary, B, orbits the inner binaries every 2,000 years.
Within each binary, the orbital periods of the stars were calculated as:
- Binary A: 1.570 days
- Binary C: 1.306 days
- Binary B: 8.217 days
When investigating other systems, the letter/number convention can often appear confusing, as it does here where the inner binaries are A and C while the outer binary is B. This arises from the fact that alphanumeric designations are given in order of discovery and are not based on intra-system relationship or distance from the center of a system.
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Additional observations of the system will have to be made to either confirm the exoplanet candidate or dismiss it.
Nevertheless, a completely different observation of the system from a different team using the European Space Agency’s CHEOPS planet hunting satellite did find a fifth planet in the system, though not the potential one identified by TESS.
This confirmed exoplanet, HD 108236 f, orbits every 29.5 days and is still well within the orbit of Mercury when compared to our solar system. The paper for this discovery can be found here.
Luckily, the system’s proximity to Earth and the parent star’s brightness makes this a highly accessible target for such observations, as well as those for mass measurement, photometric assessment, atmospheric characterization, and search for additional planets.
The paper from Daylan et al. on this discovery is published in
The Astronomical Journal and is available
here.
