Warm Gas Giant Found Circling Young Active Star TOI-201
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Using data from NASA’s Transiting Exoplanet Survey Satellite (TESS) and several ground-based telescopes, astronomers have discovered and confirmed a massive exoplanet transiting the young F-type star TOI-201.

An artist’s impression of the warm giant exoplanet TOI-201b and its parent star. Image credit: Sci-News.com.

“Transiting warm giants are planets with radii over 0.8 times that of Jupiter and orbital periods between 10 and 100 days,” Dr. Melissa Hobson, an astronomer at the Millennium Institute for Astrophysics and the Pontificia Universidad Catolica de Chile, and her colleagues wrote in their paper.

“They are particularly important for understanding the formation and evolution of giant planets.”

“Unlike hot Jupiters — i.e., planets with radii over 0.8 times that of Jupiter and orbital periods less than 10 days — which are inflated by mechanisms that are still unclear but likely connected to irradiation, these more distant planets are less strongly irradiated by their host star, meaning their size and mass can be effectively modeled by their metallicity.”

“Both hot and warm Jupiters are unlikely to form in situ, but rather are expected to have formed in the outer regions of the disk and migrated to their current locations; the main mechanisms proposed are gas disk migration and high eccentricity migration,” they wrote.

“However, hot Jupiters’ orbital histories are affected by tidal evolution, which can erase traces of past interactions between planets; this is not the case for warm Jupiters. Therefore, this population of planets preserves valuable information for the study of giant planet formation in their physical and orbital parameters.”

The newfound warm giant has a mass of 0.42 times that of Jupiter and a radius about the same as Jupiter.

Named TOI-201b, the planet orbits the bright F-type star TOI-201 once every 53 days.

“TOI-201b appears to still be undergoing fairly rapid cooling, as expected given the youth of the host star,” the astronomers wrote.

TOI-201 is located approximately 372 light-years away in the constellation of Pictor.

Also known as HD 39474 and TIC 350618622, the star is 32% bigger and more massive than the Sun and is around 870 million years old.

TOI-201b was first identified as a candidate in TESS data and then confirmed using ground-based data from the Next Generation Transit Survey (NGTS).

The researchers also used radial velocity data from three spectrographs (FEROS, HARPS, CORALIE) at La Silla Observatory and an array of four telescopes called the Minerva-Australis.

“TOI-201b falls within the youngest 5% of exoplanet host stars with measured ages, making this system a valuable addition to the known planets around young stars, which are important for testing and constraining planet formation and evolution theories,” they wrote.

“It also joins the small but growing population of longer-period giant planets, helping to populate a still relatively sparse region of the radius-period diagram.”

The team’s paper will be published in the Astronomical Journal.

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Melissa J. Hobson et al. 2021. A transiting warm giant planet around the young active star TOI-201. AJ, in press; arXiv: 2103.02685

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