Abstract
We combine corrected Gaia DR3 astrometry with non-conservative MESA modelling to retrace the evolution of the FS-CMa binary MWC 728. The revised parallax sets the distance at d=1.2±0.1 kpc, leading—after Monte-Carlo error propagation—to luminosities of log(L/L⊙)acc=2.6±0.1 and log(L/L⊙)don=1.5±0.1, corresponding to the accretor and donor, respectively. A fiducial binary track that starts with Mdon=3.6±0.1M⊙, Macc=1.8±0.1M⊙, and P0=21.0±0.2 d reproduces the observations provided the Roche-lobe overflow, which is moderately non-conservative: only 39% of the transferred mass is retained by the accretor, while the remainder leaves the system via (i) a fast isotropic wind from the donor (α=0.01), (ii) isotropic re-emission near the accretor (β=0.45), and (iii) outflow into a circumbinary torus (δ=0.15, lever arm γ=1.3). These channels remove sufficient angular momentum to expand the orbit to the observed Pobs=27.5±0.1 d while sustaining the dusty circumbinary outflow. At t≃223 Myr, the model matches every current observable: Mdon=1.30±0.05M⊙, Macc=2.67±0.05M⊙, mass ratio q=2.0±0.1, and an ongoing transfer rate of M˙≃(1±0.3)×10−6M⊙yr−1. MWC 728 thus serves as a benchmark intermediate-mass binary for testing how non-conservative outflows regulate angular-momentum loss and orbital growth.