HR 8799f/HD 218396f not Detected, Must be Less than 5 Jupiter Mass

Deep Thermal Infrared Imaging of HR 8799 bcde: New Atmospheric Constraints and Limits on a Fifth Planet

Authors:

Currie et al

Abstract:

We present new L′ (3.8 μm) and Br-α (4.05 μm) data and reprocessed archival L′ data for the young, planet-hosting star HR 8799 obtained with Keck/NIRC2, VLT/NaCo and Subaru/IRCS. We detect all four HR 8799 planets in each dataset at a moderate to high signal-to-noise (SNR ≳ 6-15). We fail to identify a fifth planet, "HR 8799 f", at r less than 15 AU at a 5-σ confidence level: one suggestive, marginally significant residual at 0.2" is most likely a PSF artifact. Assuming companion ages of 30 Myr and the Baraffe (Spiegel & Burrows) planet cooling models, we rule out an HR 8799 f with mass of 5 MJ (7 MJ), 7 MJ (10 MJ), and 12 MJ (13 MJ) at rproj ∼ 12 AU, 9 AU, and 5 AU, respectively. All four HR 8799 planets have red early T dwarf-like L′ - [4.05] colors, suggesting that their SEDs peak in between the L′ and M′ broadband filters. We find no statistically significant difference in HR 8799 cde's colors. Atmosphere models assuming thick, patchy clouds appear to better match HR 8799 bcde's photometry than models assuming a uniform cloud layer. While non-equilibrium carbon chemistry is required to explain HR 8799 bc's photometry/spectra, evidence for it from HR 8799 de's photometry is weaker. Future, deep IR spectroscopy/spectrophotometry with the Gemini Planet Imager, SCExAO/CHARIS, and other facilities may clarify whether the planets are chemically similar or heterogeneous.