The discovery was made using PRL’s advanced radial-velocity abu-sky search (PARAS) optical fiber-fed spectrograph, the first of its kind in India, on the 1.2-metre telescope situated at Mount Abu observatory. The discovery team includes Prof Abhijit Chakraborty, students and his team members, and international collaborators from Europe and the US, an Isro statement stated.
This is the second exoplanet discovered by PRL scientists using PARAS. The first exoplanet K2-236b, a sub-Saturn size at 600 light-years away, was discovered in 2018.
The measurements related to the exoplanet find were carried out between December 2020 and March 2021. Further follow-up measurements were also obtained from TCES spectrograph from Germany in April 2021. The discovered star is known as HD 82139 as per the Henry Draper catalogue (which has spectroscopic classifications for 225,300 stars) and TOI 1789 as per TESS catalogue. Hence, the planet is known as TOI 1789b or HD 82139b as per the International Astronomical Union nomenclature, it said.
The newly discovered star-planet system is very unique — the planet orbits the host star in just 3.2 days, thus placing it very close to the star at a distance of 0.05 AU (roughly one tenth the distance between Sun and Mercury). There are less than 10 such close-in systems known among the zoo of exoplanets.
Because of the close proximity of the planet to its host star, it is extremely heated with a surface temperature reaching up to 2000K, and hence an inflated radius, making it one of the lowest density planets known (0.31 gm per cc). Such close-in exoplanets around stars with masses between 0.25 to a few Jupiter masses are called ‘Hot-Jupiters’.
“The detection of such systems will contribute to our understanding of mechanisms responsible for inflation in hot Jupiters and also provide an opportunity to understand the evolution of planets around stars leaving the main sequence branch,” Chakraborty said in his citation. His team includes Akanksha Khandelwal and Rishikesh Sharma from PRL and Priyanka Chaturvedi from Thüringer Landessternwarte Tautenburg (Institute of Space Astrophysics), Germany.
The discovery work has been published in the refereed journal Monthly Notices of the Royal Astronomical Society, titled “Discovery of an inflated hot Jupiter around a slightly evolved star TOI-1789”.