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, $\sim 50-200$ Myr old M1 dwarf CD-35 2722 A. We present a detailed analysis of both objects using high-resolution ($R\sim 35,000$) $K$ band spectroscopy from the Keck Planet Imager and Characterizer (KPIC) combined with archival photometry. With a mass of $30_{-4}^{+5}{M}_{\mathrm{Jup}}$ (planet-to-host mass ratio 0.05) and projected separation of $67\pm 4$ 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 $[M/H]=-0.16_{-0.02}^{+0.03}(\mathrm{stat})\pm 0.25(\mathrm{sys})$ dex and ${}^{12}\mathrm{C}{/}^{13}\mathrm{C}=132_{-14}^{+20}$ for the host, and $[M/H]=0.27_{-0.06}^{+0.07}(\mathrm{stat})\pm 0.12(\mathrm{sys})$ dex, ${}^{12}\mathrm{CO}{/}^{13}\mathrm{CO}=159_{-24}^{+33}{(\mathrm{stat})}_{-33}^{+40}(\mathrm{sys})$, and $C/O=0.55\pm 0.01(\mathrm{stat})\pm 0.04(\mathrm{sys})$ for the companion. The chemical compositions for the brown dwarf and host star agree within the $1.5\ddot{I}ƒ$ 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 structure which is more isothermal than models and investigate its impact on our measurements, finding that constraining the temperature structure to self-consistent models does not significantly impact our retrieved chemical properties. Our observations highlight the need for data from complementary wavelength ranges to verify the presence of aerosols in likely cloudy L dwarfs.

17 pages, 9 figures, 3 tables. Accepted to ApJ