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The temperature of the corona is about 3.0 million K.
On 13 November 2008, Christian Marois of the National Research Council of Canada's Herzberg Institute of Astrophysics and his team announced they had directly observed three planets orbiting the star with the Keck and Gemini telescopes in Hawaii, A precovery observation of the outer 3 planets was later found in infrared images obtained in 1998 by the Hubble Space Telescope's NICMOS instrument, after a newly developed image-processing technique was applied.
The system is more likely to be stable if the planets "e", "d" and "c" are in a 4:2:1 resonance, which would imply that the orbit the planet d has an eccentricity exceeding 0.04 in order to match the observational constraints.
Planetary systems with the best-fit masses from evolutionary models would be stable if the outer three planets are in a 1:2:4 orbital resonance (similar to the Laplace resonance between Jupiter's inner three Galilean satellites: Io, Europa and Ganymede as well as three of the planets in the Gliese 876 system).
Because of this special status, stars like HR 8799 have a very complex spectral type.
The luminosity profile of the Balmer lines in the star's spectrum, as well as the star's effective temperature, best match the typical properties of an F0 V star.
It is part of a system that also contains a debris disk and at least four massive planets.
Those planets, along with Fomalhaut b, were the first extrasolar planets whose orbital motion was confirmed via direct imaging.
Because of the inverse square law relating radiation intensity to distance from the source, comparable radiation intensities are present at distances These objects are near the upper mass limit for classification as planets; if they exceeded 13 Jupiter masses, they would be capable of deuterium fusion in their interiors and thus qualify as brown dwarfs under the definition of these terms used by the IAU's Working Group on Extrasolar Planets.This may indicate that the observed element abundances are the result of the accretion of metal-poor gas from the environment around the star.Astroseismic analysis using spectroscopic data indicates that the rotational inclination of the star is constrained to be greater than or approximately equal to 40°.Detailed analysis of the star's spectrum reveals that it has a slight overabundance of carbon and oxygen compared to the Sun (by approximately 30% and 10% respectively).
While some Lambda Boötis stars have sulfur abundances similar to that of the Sun, this is not the case for HR 8799; the sulfur abundance is only around 35% of the solar level.
More accurately, asteroseismology also suggests an age of approximately a billion years.