A Deep Atmospheric Characterization of the Overlooked Red Planetary-Mass Companion BD+60 1417B

As a young planetary-mass companion that orbits a solar type star at a wide separation, BD+60B is rare. Widely-separated substellar companions that are free from contamination from their host stars are crucial, therefore BD+60B is an exemplary target for understanding atmospheres of extrasolar worlds and for understanding formation pathways. We present an atmospheric characterization study that includes atmospheric retrieval analysis on a set of young cloudy red L-dwarfs CWISER J124332.12+600126.2 (BD+60B) and its AB Doradus member clone WISEP J004701.06+680352, using the Brewster retrieval framework. The recently discovered, L6-L8γ planetary-mass companion, BD+60B (15 ± 5 M_Jup), lies at a separation of > 1000 AU from its K0 host star and has an age of 50 – 150 Myr. BD+60B joins a handful of companion objects with estimated masses < 20 M_Jup and separations > 1000 AU. The red (J – Ks) color of 2.72 shows that this companion is one of the reddest substellar objects characterized to date, suggesting that thick clouds and a complex, dusty atmosphere is present. In the complex cloudy L-dwarf regime the emergence of condensate cloud species complicates retrieval analysis most notably when only near-infrared spectra are available. In our retrieval analysis we find that for both objects, despite testing three different thermal profile parameterizations we are unable to constrain reliable abundance measurements and thus the C/O ratio. However, our best fits are those that prefer a cloudy atmosphere. We note that these results are consistent for both objects despite their different signal-to-noise ratios. The results presented in this work provide valuable lessons about retrieving young, low-surface gravity, cloudy L-dwarfs. We also present the first elemental abundance measurements of the young K-dwarf, BD+60 1417, using high resolution spectra taken with PEPSI/LBT. For the host we find a relatively high Mg/Si value and a near solar C/O ratio, which has implications for the types of clouds expected in the secondary. We also present new spectroscopic monitoring observations of BD+60B obtained with HST. We detect significant variability across the full 1.1-1.7 micron region probed by HST that is likely driven by inhomogeneous atmospheric features such as patchy clouds. Our observations allow us to measure the rotation rate and viewing angle of the companion BD+60B and thus test the spin axis alignment of the BD+60 system. This work provides continued evidence of missing information in models and the crucial need for JWST to guide and inform our understanding of extrasolar atmospheres in this regime.