We present VLT intermediate resolution spectroscopy of UY Vol , the optical counterpart of the LMXB X-ray burster EXO 0748-676 .
By using Doppler tomography we detect narrow components within the broad He ii \lambda 4542 , \lambda 4686 and \lambda 5412 emission lines .
The phase , velocity and narrowness of these lines are consistent with their arising from the irradiated hemisphere of the donor star , as has been observed in a number of LMXBs .
Under this assumption we provide the first dynamical constraints on the stellar masses in this system .
In particular , we measure K _ { \mathrm { 2 } } > K _ { \mathrm { em } } = 300 \pm 10 { km } \ > { s } ^ { -1 } \ > .
Using this value we derive 1 ~ { } \mathrm { M } _ { \odot } \leq M _ { 1 } \leq 2.4 ~ { } \mathrm { M } _ { \odot } and 0.11 \leq q \leq 0.28 .
We find M _ { 1 } \geq 1.5 ~ { } \mathrm { M } _ { \odot } for the case of a main sequence companion star .
Our results are consistent with the presence of a massive neutron star as has been suggested by , although we can not discard the canonical value of \sim 1.4 ~ { } \mathrm { M } _ { \odot } .