HIP 99770 b

HIP 99770 b^[1] is a directly imaged superjovian planetary mass companion orbiting the dusty A-type star HIP 99770 (29 Cygni), detected with Gaia/Hipparcos precision astrometry and high-contrast imaging.^[3] HIP 99770 b is the first joint direct imaging + astrometric discovery of a planetary mass companion and the first planetary mass companion discovered using precision astrometry from the Gaia mission.

HIP 99770 b

Subaru Telescope detection of HIP 99770 b
Discovery
Discovered by	Currie et al.[1]
Discovery site	Subaru Telescope
Discovery date	November 30, 2022
Detection method	Direct imaging
Orbital characteristics
Semi-major axis	15.8+1.7 −1.0[2] AU
Eccentricity	0.31+0.06 −0.12[2]
Inclination	152+10 −8[2] °
Star	HIP 99770
Physical characteristics
Mean radius	1.5±0.3[2] RJ
Mass	17+6 −5[2] MJ
Temperature	1,400 K[1]
Spectral type	L8[2]

Discovery

HIP 99770 b was discovered by a team led by Thayne Currie, Mirek Brandt, and Tim Brandt using the Subaru Telescope on Mauna Kea. The Subaru data utilized the observatory's extreme adaptive optics system, SCExAO, to correct for atmospheric turbulence and the CHARIS integral field spectrograph to detect HIP 99770 b at 22 different near-infrared wavelength passbands from 1.1 microns to 2.4 microns. It was also detected at longer wavelengths using the NIRC2 camera on the Keck Observatory.

Atmosphere

With a spectral type of L7.5--L9, HIP 99770 b lies at the L/T transition for substellar objects, transition from cloudy atmospheres without methane absorption to clear atmospheres with methane absorption. Atmospheric modeling favors an effective temperature of 1400 K and a Jupiter-like radius. The companion is likely intermediate in cloudiness between older, more massive field brown dwarfs and young L/T transition exoplanets like HR 8799 d.

Orbit and mass

Jointly modeling relative astrometry of HIP 99770 b with absolute astrometry of the primary as measured by Gaia and Hipparcos yields precise estimates for the companion's orbit and mass. HIP 99770 b lies at about 16.9 au from its host star. The host star is significantly more luminous than the Sun: HIP 99770 b receives roughly as much light as Jupiter receives from the Sun. HIP 99770 b is a super-jovian planetary mass companion with a mass of roughly 16.1 times that of Jupiter. Its mass ratio -- mass divided by the mass of the host star -- is comparable to that of many planets detected through methods such as radial velocity and transits and is similar to that of HR 8799 d.

See also

• List of exoplanets discovered in 2023