“Long before NASA’s Kepler space telescope’s discovery of transiting circumbinary planets, astronomers discussed an unusual observational signature such planets would have — the occurrence of multiple transits during one conjunction,” Dr. Veselin Kostov of NASA’s Goddard Space Flight Center and his colleagues wrote in their paper.
“This effect is caused by the planet transiting one or both stars of the host eclipsing binary several times over the course of a fraction of its orbital period.”
“The configuration of such transits depends on the relative sky-projected velocities of circumbinary planets and the stars being transited. Importantly, the orbital period of these planets can be estimated from such transits provided the host system is a double-lined spectroscopic binary.”
“Several groups of astronomers attempted to detect transits of circumbinary planets from the ground before the turn of the century — single-conjunction or otherwise — but were ultimately hampered by the limited time sampling,” they added.
“Fortunately, thanks to its long dwell time and high photometric precision, the Kepler mission enabled the discovery of a dozen transiting circumbinary planets and also demonstrated that the occurrence of pairs of transits during one conjunction is common.”
“Four of the eleven known Kepler circumbinary systems exhibit such transits: Kepler-16, Kepler-34, Kepler-35, and Kepler-1647.”
TIC 172900988b is 1.01 times larger than Jupiter and 11.07 times larger than Earth.
With a mass of 2.9 Jupiter masses, it is the most massive transiting circumbinary planet known, a factor of two times larger than the next most massive planet, Kepler-1647b.
The planet has an orbital period between 189 and 204 days and is too hot to be in the habitable zone.
It was detected in data from NASA’s Transiting Exoplanet Survey Satellite (TESS) using the multiple-transits-in-one-conjunction technique.
The analysis of the TIC 172900988 binary system’s light curve revealed one primary and two secondary eclipses with depths of 40% and 35%, respectively.
“TIC 172900988 was observed in a single sector and the planet produced just two transits — one across each star — during the same conjunction,” the astronomers wrote.
“The planet transited the primary star and then 5 days later it transited the secondary star.”
“The binary star is itself eclipsing, with a period of 19.7 days and an eccentricity of 0.45.”
TIC 172900988 is located approximately 824 light-years away in the constellation of Cancer.
Otherwise known as TYC 2483-160-1 and 2MASS J08343881+3133147, the system is 3.1 billion years old.
“TIC 172900988 demonstrates the discovery potential of TESS for circumbinary planets with orbital periods greatly exceeding the duration of the observing window,” the researchers wrote.
Veselin B. Kostov et al. 2021. TIC 172900988: A Transiting Circumbinary Planet Detected in One Sector of TESS Data. AAS journals, submitted for publication; arXiv: 2105.08614