The giant exoplanet AF Leporis b orbits a 1.2-solar-mass star in the 24-million-year-old beta Pictoris moving group.
The direct image of the giant exoplanet AF Lep b. Image credit: Franson et al., doi: 10.3847/2041-8213/acd6f6.
AF Leporis is a bright F8V star located about 87.5 light-years away from Earth in the constellation of Lepus.
Also known as AF Lep, HD 35850, HIP 25486 and HR 1817, the star has an age of 24 million years and a mass of 1.2 solar masses.
The star hosts a young exoplanet, AF Leporis b (AF Lep b), which is located about 8 times the Earth-Sun distance and is among the first ever discovered using a technique called astrometry.
This method measures the subtle movements of a host star over many years to help astronomers determine whether hard-to-see orbiting companions, including planets, are gravitationally tugging at it.
“When we processed the observations using the NIRC2 vector vortex coronagraph (VVC) at the Keck II telescope at the W.M. Keck Observatory on Maunakea, Hawai’i, in real time to carefully remove the glare of the star, the planet immediately popped out and became increasingly apparent the longer we observed,” said Kyle Franson, a graduate student at the University of Texas at Austin.
The direct images of AF Lep b revealed that the planet is about three times the mass of Jupiter.
“This is the first time this method has been used to find a giant planet orbiting a young analog of the Sun,” said Dr. Brendan Bowler, an astronomer at the University of Texas at Austin.
“This opens the door to using this approach as a new tool for exoplanet discovery.”
Despite having a much smaller mass than its host star, an orbiting planet causes a star’s position to wobble slightly around the center of mass of the planetary system.
Astrometry uses this shift in a star’s position on the sky relative to other stars to infer the existence of orbiting planets.
“Imaging planets is challenging. We only have about 15 examples, and we think this new ‘dynamically informed’ approach made possible by the Keck II telescope and NIRC2 adaptive optics imaging will be much more efficient compared to blind surveys which have been carried out for the past two decades,” Franson said.
The astronomers plan to continue studying AF Lep b.
“This will be an excellent target to further characterize with the NASA/ESA/CSA James Webb Space Telescope and the next generation of large ground-based telescopes like the Giant Magellan Telescope and the Thirty Meter Telescope,” Dr. Bowler said.
“We’re already planning more sensitive follow-up efforts at longer wavelengths to study the physical properties and atmospheric chemistry of this planet.”
The results were published in the Astrophysical Journal Letters.
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Kyle Franson et al. 2023. Astrometric Accelerations as Dynamical Beacons: A Giant Planet Imaged inside the Debris Disk of the Young Star AF Lep. ApJL 950, L19; doi: 10.3847/2041-8213/acd6f6
