Thermal Infrared MMTAO Observations of the HR 8799 Planetary System

TL;DR

This paper presents thermal infrared direct imaging observations of the HR 8799 planetary system, providing new constraints on the atmospheres and temperatures of its planets, and comparing observations with atmospheric models.

Contribution

First thermal infrared imaging observations of HR 8799 planets at multiple wavelengths, constraining their atmospheres and effective temperatures, and testing atmospheric models including non-equilibrium chemistry.

Findings

Detection of all three planets at L' band.

c and d detected at 3.3 microns; upper limits at 4.8 microns.

Estimated effective temperatures: b < 960 K, c = 1300 K, d = 1170 K.

Abstract

We present direct imaging observations at wavelengths of 3.3, 3.8 (L',band), and 4.8 (M band) microns, for the planetary system surrounding HR 8799. All three planets are detected at L'. The c and d component are detected at 3.3 microns, and upper limits are derived from the M band observations. These observations provide useful constraints on warm giant planet atmospheres. We discuss the current age constraints on the HR 8799 system, and show that several potential co-eval objects can be excluded from being co-moving with the star. Comparison of the photometry is made to models for giant planet atmospheres. Models which include non-equilibrium chemistry provide a reasonable match to the colors of c and d. From the observed colors in the thermal infrared we estimate T_eff < 960 K for b, and T_eff=1300 and 1170 K for c and d, respectively. This provides an independent check on the effective temperatures and thus masses of the objects from the Marois 2008 results.