Unveiling the Evolution of MWC 728: Non-Conservative Mass Transfer in an FS CMa Binary

Vaidman N.L. Khokhlov S.A. Agishev A.T.
August 2025 Multidisciplinary Digital Publishing Institute (MDPI)

Galaxies
2025 #13 Issue 4

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 (Formula presented.) kpc, leading—after Monte-Carlo error propagation—to luminosities of (Formula presented.) and (Formula presented.), corresponding to the accretor and donor, respectively. A fiducial binary track that starts with (Formula presented.), (Formula presented.), and (Formula presented.) d reproduces the observations provided the Roche-lobe overflow, which is moderately non-conservative: only (Formula presented.) of the transferred mass is retained by the accretor, while the remainder leaves the system via (i) a fast isotropic wind from the donor ((Formula presented.)), (ii) isotropic re-emission near the accretor ((Formula presented.)), and (iii) outflow into a circumbinary torus ((Formula presented.), lever arm (Formula presented.)). These channels remove sufficient angular momentum to expand the orbit to the observed (Formula presented.) d while sustaining the dusty circumbinary outflow. At (Formula presented.) Myr, the model matches every current observable: (Formula presented.), (Formula presented.), mass ratio (Formula presented.), and an ongoing transfer rate of (Formula presented.). MWC 728 thus serves as a benchmark intermediate-mass binary for testing how non-conservative outflows regulate angular-momentum loss and orbital growth.

binary stars , B[e] stars , FS CMa , stellar evolution

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Faculty of Physics and Technology, Al-Farabi Kazakh National University, Al-Farabi Ave., 71, Almaty, 050040, Kazakhstan
Fesenkov Astrophysical Institute, Observatory, 23, Almaty, 050020, Kazakhstan

Faculty of Physics and Technology
Fesenkov Astrophysical Institute

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