Pre-Discovery 2007 Image of the HR 8799 Planetary System

TL;DR

This paper presents a pre-discovery H-band image of the HR 8799 planetary system from 2007, confirming all three planets and providing insights into their luminosity and atmospheric properties, along with limits on debris disk brightness.

Contribution

It provides the earliest image of the HR 8799 planets, confirming their association and characterizing their luminosity and atmospheric features compared to brown dwarfs.

Findings

Confirmed all three planets in 2007 image.

Planets are 2-3 mag fainter than similar brown dwarfs.

Placed upper limit on debris disk scattered light.

Abstract

We present a pre-discovery H-band image of the HR 8799 planetary system that reveals all three planets in August 2007. 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 under-luminosity 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/CH_4 chemistry in their atmospheres. Finally, we place an upper limit of 18 mag per square arc second on the >120 AU H-band dust-scattered light from the HR 8799 debris disk. The upper limit on the integrated scattered light flux is 1e-4 times the photospheric level, 24 times fainter than the debris ring around HR 4796A.