Chemical and Isotopic Homogeneity between the L Dwarf CD-35 2722 B and Its Early M Host Star

Abstract CD-35 2722 B is an L dwarf companion to the nearby, ∼50–200 Myr old M1 dwarf CD-35 2722 A. We present a detailed analysis of both objects using high-resolution ( R ∼ 35,000) K -band spectroscopy from the Keck Planet Imager and Characterizer combined with archival photometry. With a mass of 3 0 − 4 + 5 M Jup (planet-to-host mass ratio 0.05) and projected separation of 67 ± 4 au from its host, CD-35 2722 B likely formed via gravitational instability. We explore whether the chemical composition of the system tells a similar story. Accounting for systematic uncertainties, we find [ M / H ] = − 0 . 16 − 0 . 02 + 0 . 03 ( stat ) ± 0 . 25 ( sys ) dex and 12 C / 13 C = 13 2 − 14 + 20 for the host, and [ M / H ] = 0 . 27 -0.06 +0.07 ( stat ) ±0.12 ( sys ) dex, 12 CO / 13 CO = 159 − 24 + 33 ( stat ) − 33 + 40 ( sys ) , and C/O = 0.55 ± 0.01 (stat) ± 0.04 (sys) for the companion. The chemical compositions for the brown dwarf and host star agree within the 1.5 σ level, supporting a scenario where CD-35 2722 B formed via gravitational instability. We do not find evidence for clouds on CD-35 2722 B despite it being a photometrically red mid-L dwarf and thus expected to be quite cloudy. We retrieve a temperature str