Disk Evolution and Planet Formation in the Triple HD 104237 System

Planets are rare in close ( a < 10 au) binaries, consistent with millimeter surveys showing that circumbinary disks in such systems are typically fainter than disks around wide binaries or single stars. However, a few bright circumbinary disks deviate from this trend, suggesting that planet-forming reservoirs can sometimes survive severe dynamical truncation. We present high-angular-resolution (0 . ″ 1; 11 au) Atacama Large Millimeter/submillimeter Array Band 6 observations of the triple system HD 104237, a young Herbig Ae spectroscopic binary ( a = 0.22 au) with a tertiary companion at 134 au in the ϵ Cha association. The data reveal a compact circumbinary dust disk with outer radius R dust ≈ 8 au and a characteristic CO gas radius R CO ≈ 18 au, with faint CO emission extending farther outward. Despite its small size, the disk remains relatively massive, consistent with the high stellar accretion rates observed in the system. Modeling the CO kinematics with a Markov Chain Monte Carlo fit to the visibilities yields a dynamical mass for the central binary of M * = 2.42 ± 0.36 M ⊙ , lower than previous estimates. The CO velocity field is well described by Keplerian rotation, with no significant residuals. Hydrodynamic simulations reproduce the observed disk truncation and velocity structure, indicating that the tertiary companion limits the outer disk. Nevertheless, a substantial gaseous reservoir persists within the compact inner disk, compatible with ongoing planet formation. HD 104237 is therefore an outlier to the general trend of disk depletion in close binaries, demonstrating that compact massive circumbinary disks can survive in dynamically complex multiple systems. We also report millimeter continuum and 12 CO(2–1) emission from the disk surrounding HD 104237 E.