2009ApJ...705L.204M

We present a pre-discovery H-band image of the HR 8799 planetary system that reveals all three planets in 2007 August. The data were obtained with the Keck adaptive optics system, using angular differential imaging and a coronagraph. We confirm the physical association of all three planets, including HR 8799d, which had only been detected in 2008 images taken two months apart, and whose association with HR 8799 was least secure until now. We confirm that the planets are 2-3 mag fainter than field brown dwarfs of comparable near-infrared colors. We note that similar underluminosity is characteristic of young substellar objects at the L/T spectral type transition, and is likely due to enhanced dust content and non-equilibrium CO/CH₄ chemistry in their atmospheres. Finally, we place an upper limit of ≳18 mag/arcsec2 on the >120 AU H-band dust-scattered light from the HR 8799 debris disk. The corresponding integrated scattered light flux is <10^–4 times the photospheric level, 24 times fainter than for the debris ring around HR 4796A.