2023MNRAS.523.5510G

We report the results of optical échelle spectroscopy with the Southern African Large Telescope (SALT) of the mass donor star BSDL923 in the neutron star (NS) high-mass X-ray binary XMMU J051342.6-672412 associated with the LMC supernova remnant (SNR) MCSNR J0513-6724. We found that BSDL923 is a B0.7 III star with double peaked emission lines originating in a circumbinary disc-like structure. Modelling with the stellar atmosphere code FASTWIND was used to derive T_eff = 27 000 K, log g = 3.22, $v\sin i\approx 100\, {\rm \, km\, s^{-1}}$ and $\log (L_*/\rm \, L_\odot)=5.46$ of BSDL923, as well as to show that the surface of this star is polluted with α-elements from the supernova ejecta. We found also that the NS is orbiting BSDL923 in an eccentric orbit with the orbital period of 1.280 d and the semimajor axis of $17\pm 3 \,R_\odot$, which is less than or equal to the radius of BSDL923 of $25\pm 5 \,R_\odot$. We speculate that the NS is embedded in the atmosphere of BSDL923 either because it was kicked at birth towards this star or because of inflation of BSDL923 caused by the energy input from the supernova blast wave. Using long-slit spectroscopy with SALT, we searched for possible signs of the SNR shell in the 2D spectrum, but did not find them. This lack of detection is consistent with the young age of this SNR, implying that it is still in the adiabatic phase.