2007MNRAS.381..194C

Two nights of phase-resolved medium-resolution Very Large Telescope spectroscopy of the extra-galactic low-mass X-ray binary LMCX-2 have revealed a 0.32±0.02 d spectroscopic period in the radial velocity curve of the HeII λ4686 emission line that we interpret as the orbital period. However, similar to previous findings, this radial velocity curve shows a longer term variation that is most likely due to the presence of a precessing accretion disc in LMCX-2. This is strengthened by HeII λ4686 Doppler maps that show a bright spot that is moving from night to night. Furthermore, we detect narrow emission lines in the Bowen region of LMCX-2, with a velocity of K_em= 351±28 km/s, that we tentatively interpret as coming from the irradiated side of the donor star. Since K_em must be smaller than K₂, this leads to the first upper limit on the mass function of LMCX-2 of f(M₁) ≥ 0.86 M_☉(95 per cent confidence), and the first constraints on its system parameters.