Astronomers using NASA’s Transiting Exoplanet Survey Satellite (TESS) have discovered a transiting hot-Jupiter exoplanet around a slightly evolved star called TOI-1789.
An artist’s rendition of the hot-Jupiter exoplanet TOI-1789b. Image credit: Sci-News.com.
“Hot Jupiters have set several firsts, from being the first kind of exoplanets discovered with the radial velocity method (51 Peg), to being also the first kind of transiting systems studied for precise radii and orbits (HD 209458b),” said Akanksha Khandelwal, an astronomer at the Indian Institute of Techonology and the Physical Research Laboratory, and colleagues.
“These systems have intrigued the theorists triggering a critical revision of planet formation theories.”
“Two theories have been used the most to explain close-in giant planets: the in-situ formation by gravitational instability or core accretion followed by inward migration,” they added.
“Gravitational instability envisions the formation of giant planets via the fragmentation of proto-planetary disk into bound clumps.”
“In the case of core accretion, the giant planet is formed at several astronomical units (AU) beyond the so-called ice-line where sufficient solid material is present to form the core, and then it migrates inward.”
“The migration is caused by either torques from the proto-planetary disk or by gravitational scattering due to a third body. This can shrink the orbital separation of the planet from their formation location of several AU to hundredths of AU.”
TOI-1789 is a slightly evolved, metal-rich, and late F-type star located 729 light-years away in the constellation of Leo.
Also known as HD 82139, TIC 172518755, TYC 1962-00303-1 and 2MASS J09305841+2632246, the star is 2.8 billion years old, about 2.2 times larger than the Sun and 1.5 times as massive.
“TYC 1962-00303-1 is a relatively bright star in the northern celestial hemisphere, first listed as TOI-1789 on March 12, 2020,” the astronomers said.
“This source was observed by TESS between January 21 and February 18, 2020 with a gap of 2 days due to the data transferring from the spacecraft.”
“The high-precision radial velocity observations were obtained from the high-resolution spectrographs, PARAS at the Physical Research Laboratory in India and TCES at Thüringer Landessternwarte Tautenburg in Germany.”
The newfound planet orbits TOI-1789 once every 3.2 days at a distance of 0.05 AU.
Named TOI-1789b, the planet has a mass and a radius of 0.7 and 1.4 times that of Jupiter, and a bulk density of 0.31 g/cm3. This puts TOI-1789b in the category of inflated hot Jupiters.
“There are only 8 exoplanets — including TOI-1789b — discovered as of now, which are hosted by either similar or more evolved stars than TOI-1789 and orbiting in very close-proximity to their host star (less than 0.05 AU),” the researchers said.
“Despite the rarity of hot Jupiters across slightly evolved stars in close-in orbits, TOI-1789b is completely ‘non-anomalous,’ satisfying most of the evolutionary models at place.”
“The detection of similar types of exoplanets will help us to improve our understanding of the distribution, formation, and migration of hot Jupiters around evolving stars.”
The team’s paper has been submitted for publication in the Monthly Notices of the Royal Astronomical Society.
_____
Akanksha Khandelwal et al. 2021. Discovery of an inflated hot Jupiter around a slightly evolved star TOI-1789. MNRAS, submitted for publication; arXiv: 2106.08660
