2026ApJ...998...10I

We present the discovery of a young, close-in companion to the early B-type Herbig Be star MWC 340 (V1685 Cyg), a rare system known to host a protoplanetary disk. Herbig Be stars often show complex circumstellar environments shaped by accretion and multiplicity. Using near-infrared (NIR) interferometric observations with the Center for High Angular Resolution Astronomy (CHARA) array over 5 yr in the H band (λ = 1.5-1.7 μm) and K band (λ = 2.1-2.4 μm), we resolve the binary and constrain its orbital and stellar properties through image reconstruction, model fitting, and spectral energy distribution analysis. Orbital modeling suggests a 16 yr minimum period and a 27.5 mas projected separation (≈25 au). Assuming an M_A+B = 14.65 M_⊙ total mass, we find a best-fit semimajor axis of 21 mas and eccentricity e = 0.69. The reconstructed images reveal a slightly elongated primary that is roughly 3 times brighter than the secondary (flux B/A = 0.28 in the H band, 0.3 in the K band), contributing 65% of the NIR flux. The secondary contributes 21%, with the remainder from extended emission. Stellar photospheres account for only ∼20% of total H- and K-band emission. Isochrone fitting yields masses and ages of 7.5-9 M_⊙, 0.13-0.19 Myr for the primary, and 5.8-7 M_⊙, 0.28-0.45 Myr for the secondary, suggesting non-coevality unless the secondary is more extinguished. The apparent age discrepancy and high eccentricity ruled out by mass constraints may reflect differential reddening or point to dynamical influence from an unresolved third component. Continued CHARA monitoring and Gaia astrometry will help clarify the system's architecture.