Astronomy:HIP 99770 b

HIP 99770 b

Subaru Telescope detection of HIP 99770 b
Discovery
Discovered by	Currie et al.
Discovery site	Subaru Telescope
Discovery date	November 30, 2022
Detection method	Direct imaging
Orbital characteristics
Semi-major axis	15.7+3.5 −1.0 AU
Eccentricity	0.31+0.06 −0.12
Orbital period	47+14 −4 years
Inclination	151.3+8.4 −12.0 °
Longitude of ascending node	279°+72° −269°
astron|astron|helion}}	2,465,218+3,763 −771 JD
astron|astron|helion}}	250°+68° −218°
Star	29 Cygni
Physical characteristics
Mean radius	1.056 |♃|J}}}}}}
Mass	13.6+4.8 −5.1 or 15.2+4.6 −4.4 |♃|J}}}}}}
Physics	1,300 K
Spectral type	L8

HIP 99770 b (also known as 29 Cygni b) is a directly imaged planet or a brown dwarf orbiting the A-type star HIP 99770 (29 Cygni), detected with Gaia/Hipparcos precision astrometry and high-contrast imaging. HIP 99770 b is the first joint direct imaging + astrometric discovery of an extrasolar planet and the first planet discovered using precision astrometry from the Gaia mission.

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.

Characteristics

HIP 99770 b imaged by the James Webb Space Telescope

The orbit of HIP 99770 b has been measured using both absolute astrometry of HIP 99770 as measured by Gaia and Hipparcos, and its relative astrometry (location with respect to the host star) from VLTI/GRAVITY and SCExAO/CHARIS. The most recent orbital solution give an orbital period of 47 years, a semi-major axis of 15.8 astronomical units, an orbital eccentricity of 0.29, and an inclination of 151°. As the host star is significantly more luminous than the Sun, HIP 99770 b receives roughly as much light as Jupiter receives from the Sun. Atmospheric modelling give a temperature of about 1,300 K and a radius of 1.056 R_J. With a spectral type of L8, HIP 99770 b lies at L/T transition for substellar objects, from cloudy atmospheres without methane absorption to clear atmospheres with methane absorption. The companion is likely intermediate in cloudiness and gravity between older, more massive field brown dwarfs and young L/T transition exoplanets like HR 8799 d.

The mass of HIP 99770 b is directly measured from joint dynamical modeling of the planet's relative astrometry from direct imaging data and absolute astrometry of the host star. The most recent mass estimates range between 13.1 M_J and 15.0 M_J . Thus HIP 99770 b likely straddles the deuterium burning limit, and as of such it has been considered a super-Jupiter. While the deuterium burning limit has often been used as a mass criterion to distinguish between planets and brown dwarfs, the discovery paper showed that HIP 99770 b's mass and mass ratio (mass divided by the mass of the host star) were instead better consistent with values for planets than brown dwarfs . HIP 99770 b appears to have a moderate eccentricity of e ~ 0.3: more eccentric than most directly imaged planets with well-constrained orbits but broadly consistent with the either planets or brown dwarf population. Its relatively small orbital separation and location near the system's ice line suggests it may have formed in a protoplanetary disk.

See also

• List of exoplanets discovered in 2023

Further reading

• Nola Taylor Tillman (April 13, 2023), "New Planet-Hunting Technique Finds Worlds We Can See Directly", Scientific American, https://www.scientificamerican.com/article/new-planet-hunting-technique-finds-worlds-we-can-see-directly/