HR 8799 is a roughly 30 million-year-old main-sequence star located 133.3 light-years (40.9 parsecs) away from Earth in the constellation of Pegasus.

It has a magnitude 5.96 and it is located inside the western edge of the great square of Pegasus almost exactly halfway between Beta and Alpha Pegasi.

Given the star's position on the Hertzsprung–Russell diagram of luminosity versus temperature, it has an estimated age in the range of 30–1,128 million years.

The best accepted value for an age of HR 8799 is 30 million years, consistent with being a member of the Columba association co-moving group of stars.

[11] Earlier 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).

[8] Astroseismic analysis using spectroscopic data indicates that the rotational inclination of the star is constrained to be greater than or approximately equal to 40°.

The temperature of the stellar corona is about 3.0 million K.[15] 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,[22][23][24][25] in both cases employing adaptive optics to make observations in the infrared.

[b] 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.

It is one of the most massive disks known around any star within 300 light years of Earth, and there is room in the inner system for terrestrial planets.

[16] Near-infrared observations with the Project 1640 integral field spectrograph on the Palomar Observatory have shown that compositions between the four planets vary significantly.

[31] A number of studies have used the spectra of HR 8799's planets to determine their chemical compositions and constrain their formation scenarios.

[33] The first simultaneous spectra of all four known planets in the HR 8799 system were obtained in 2012 using the Project 1640 instrument at Palomar Observatory.

The near-infrared spectra from this instrument confirmed the red colors of all four planets and are best matched by models of planetary atmospheres that include clouds.

[clarification needed] Later, in November 2018, researchers confirmed the existence of water and the absence of methane in the atmosphere of HR 8799 c using high-resolution spectroscopy and near-infrared adaptive optics (NIRSPAO) at the Keck Observatory.

Three components of the debris disk were distinguished: The halo is unusual and implies a high level of dynamic activity which is likely due to gravitational stirring by the massive planets.

[37] The Spitzer team says that collisions are likely occurring among bodies similar to those in the Kuiper Belt and that the three large planets may not yet have settled into their final, stable orbits.

Specifically, it is easier to obtain images when the planet is especially large (considerably larger than Jupiter), widely separated from its parent star, and hot so that it emits intense infrared radiation.

However, in 2010 a team from NASAs Jet Propulsion Laboratory demonstrated that a vortex coronagraph could enable small telescopes to directly image planets.