The discovery was led by Prof Abhijit Chakraborty and included his students, team members, and international collaborators from Europe and the US. This 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”.
“This discovery was made using PRL Advanced Radial-velocity Abu-sky Search (PARAS) optical fibre-fed spectrograph, the first of its kind in India, on the 1.2-metre Telescope of PRL at its Mt. Abu Observatory. Using PARAS, which has the capability to measure the mass of an exoplanet, the exoplanet’s mass is found to be 70% and size about 1.4 times that of Jupiter,” Isro said.
While these measurements were carried out between December 2020 and March 2021, further follow-up measurements were obtained from TCES spectrograph from Germany in April 2021, and also independent photometric observations from the PRL’s 43-cm telescope at Mt. Abu.
“The star is known as HD 82139 as per the Henry Draper catalogue and TOI 1789 as per the TESS catalogue. Hence, the planet is known as TOI 1789b or HD 82139b as per the IAU (International Astronomical Union) nomenclature,” the researchers said.
This newly discovered star-planet system is very unique — the planet orbits the host star in just 3.2 days, thus placing it very-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 known so far. Because of the close proximity of the planet to its host star, it is extremely heated with a surface temperature reaching up to 2000 K, and hence an inflated radius, making it one of the lowest density planets known (density of 0.31 gram per cc),” an Isro statement read.
Such close-in exoplanets around stars (with distance less than 0.1 AU) with masses between 0.25 to a few Jupiter masses are called “Hot-Jupiters”, the researchers said.
“The detection of such a system enhances our understanding of various mechanisms responsible for inflation in hot Jupiters and the formation and evolution of planetary systems around evolving and ageing stars,” they added.
The research findings have been authored by Akanksha Khandelwal, Abhijit Chakraborty, Rishikesh Sharma, Ashirbad Nayak, Dishendra and Neelam JSSV Prasad from PRL; Priyanka Chaturvedi, Eike W Guenther, Artie P Hatzes, Massimiliano Esposito and Sireesha Chamarthi, from TLS Tautenburg, Germany; Carina M Persson and Malcolm Fridlund from the Department of Space, Earth and Environment, Chalmers University of Technology, Sweden and Steve B Howell from NASA Ames Research Centre.
This is the second exoplanet discovered by PRL scientists using PARAS at 1.2 m Mt. Abu telescope; the first exoplanet K2-236b, a sub-Saturn size at 600 light-years away, was discovered in 2018.