Astronomers using NASA’s Transiting Exoplanet Survey Satellite (TESS) have discovered a massive gaseous exoplanet orbiting a subgiant star called HD 221416 (also known as TOI-197 and HIP 116158). Named HD 221416b, it is the first transiting exoplanet identified by TESS for which asteroseismology — a powerful observational technique used to determine stellar parameters and properties — of the host star is possible.
An artist’s impression of a massive gas giant in orbit around its parent star. Image credit: NASA / JPL-Caltech / R. Hurt, SSC & Caltech.
Astronomers use asteroseismic modeling to determine the radius, mass and age of a host star.
That data can be combined with other observations and measurements to determine the properties of orbiting exoplanets.
In the case of the host star HD 221416, which is about 312 light-years away, Dr. Daniel Huber from the University of Hawaii at Manoa’s Institute for Astronomy and colleagues used its oscillations to determine it’s about 5 billion years old and is a little heavier and larger than the Sun.
The astronomers also determined that the planet HD 221416b is a gas giant with a radius of about 9.2 times that of Earth, making it roughly the size of Saturn.
The planet is also 1/13th the density of Earth and about 60 times Earth’s mass.
“HD 221416 provides a first glimpse at the strong potential of TESS to characterize exoplanets using asteroseismology,” Dr. Huber and co-authors said.
HD 221416b is also very close to its star, completing an orbit in just 14 days, and therefore very hot.
“This planet is a ‘hot Saturn’ and joins a small but growing population of close-in, transiting planets orbiting evolved stars,” the scientists said.
“Based on its incident flux, radius and mass, HD 221416b may be a precursor to the population of gas giants that undergo radius re-inflation due to the increased irradiance as their host star evolves up the red-giant branch.”
The team’s work will be published in the Astronomical Journal.
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Daniel Huber et al. 2019. A Hot Saturn Orbiting An Oscillating Late Subgiant Discovered by TESS. AJ, in press; arXiv: 1901.01643
