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A Clear View of a Cloudy Brown Dwarf Companion from High-Resolution Spectroscopy

Presentation #102.37 in the session Poster Session.

Published onJun 20, 2022
A Clear View of a Cloudy Brown Dwarf Companion from High-Resolution Spectroscopy

Direct imaging surveys have used low-resolution spectroscopy (LRS; R ~ 20-100) to study the atmospheres of giant exoplanets and brown dwarf companions, but encountered hurdles in measuring reliable atmospheric abundances (e.g. C/O, metallicity). This precludes clear insights into their formation mechanisms. The Keck Planet Imager and Characterizer (KPIC) uses single-mode fibers to transport light into NIRSPEC (R ~ 35,000 in K band), and aims to address these challenges with high-resolution spectroscopy (HRS). Using an atmospheric free retrieval framework, we analyzed both KPIC HRS and archival LRS (1-2.2 μm) of the benchmark brown dwarf companion HD 4747 B (m ≈ 67 MJup, a ≈ 10 au, Teff ≈ 1400 K). We find that the measured abundances from LRS can vary by 3σ depending on the cloud model, while the HRS is insensitive to clouds. We show this is because HRS is sensitive to lower pressures where cloud opacity is minimal, while LRS probes higher pressures where clouds condense. From the KPIC HRS, we also measure the C/O and metallicity of the brown dwarf to be consistent with its host star to within 1-2σ, as expected for binary star-like formation. With more than 20 companions observed by KPIC so far, these results pave the way for a statistical study of giant planet and brown dwarf atmospheres.

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