MESA inlists and scripts for, 'Blue Straggler in the Making: An X-ray Active Binary in Algol Configuration'

Article Abstract: We report an extremely rare X-ray active Blue Straggler Star (BSS) in Collinder 261, undergoing ongoing Roche-lobe overflow in a semi-detached binary in an Algol-type configuration with an orbital period of $P_{\mathrm{orb}}\sim$ 2.112 days, providing direct observational evidence for the ongoing binary mass transfer formation channel of BSS. Light curve modeling with \texttt{PHOEBE} reveals a low mass ratio of $q\sim0.19$, corresponding to a mass of $1.67$ M$_{\odot}$ for BSS primary and a mass of $0.32$ M$_{\odot}$ for Roche-lobe–filling companion. Reflection effects and a hotspot near the inner Lagrangian point ($L_{1}$) reproduce the observed light curve asymmetries, while the observed X-ray luminosity is consistent with direct-impact accretion-driven emission, supporting ongoing mass transfer. Radial velocities from VLT/GIRAFFE are also consistent with the photometric solution and reveal enhanced primary rotation of $v\sin i \sim 69.55$ km\,s$^{-1}$, consistent with spin-up through direct-impact accretion. Evolutionary model with \texttt{MESA} reproduce the observed configuration for an initially detached system with $M_{\mathrm{d}}\sim1.12$ M$_{\odot}$, $M_{\mathrm{a}}\sim0.92$ M$_{\odot}$, $P_{\rm ini}\sim0.83$ day. Roche-lobe overflow and mass transfer begin at $\sim5.46$ Gyr with mass ratio reversal at $\sim5.58$ Gyr. The present configuration at $\sim7$ Gyr, consistent with the cluster age, corresponds to stable MT of $\dot{M}\sim$$2 \times 10^{-10}$ M$_{\odot}{\rm yr^{-1}}$. These results indicate that the system represents a very rare case of a BSS currently forming through binary mass transfer. MESA details: MESA: 25.12.1, MESA SDK:23.7.3