Context :

Aims : We report near-infrared ( NIR ) observations of the mass donors of the eclipsing high-mass X-ray binary ( HMXB ) systems EXO 1722-363 and OAO 1657-415 in order to derive their accurate spectral classifications .

Methods : ESO/VLT observations of the targets with the NIR spectrometer ISAAC were compared with several published NIR spectral atlases of O and B supergiants , an identification of each object ’ s spectral characteristics was made , enabling the refinement of spectral classification of the mass donors .

Results : We determined that EXO 1722-363 was of spectral type B0 - B1Ia , positioned at a distance 8.0 _ { -2.0 } ^ { +2.5 } kpc with a progenitor mass in the range 30M _ { \odot } - 40M _ { \odot } .
Luminosity calculations imply that L _ { X } \sim 10 ^ { 35 } - 10 ^ { 37 } erg s ^ { -1 } for this distance range .
We conclude that EXO 1722-363 shares many of the properties associated with other X-ray binary B-type supergiant donors . We found that OAO 1657-415 correlates closely with the spectra of a class of transitional objects , the Ofpe/WNL stars , an intermediate evolutionary stage between massive O type stars leaving the main sequence and evolving into Wolf-Rayets .
Due to the wide range in luminosity displayed by Ofpe/WNL stars , ( log ( L/L _ { \odot } ) \sim 5.3 - 6.2 ) distance determinations are problematic .
For OAO 1657-415 we report a distance of 4.4 \leq d \leq 12 kpc , implying an X-ray luminosity of 1.5 \times 10 ^ { 36 } \leq L _ { X } \leq 10 ^ { 37 } erg s ^ { -1 } .
We have used our new classification of OAO 1657-415 to explain the physical processes responsible for its unique position within the Corbet diagram .
Ofpe/WNL stars demonstrate a high rate of mass-loss through a dense stellar wind combined with a low terminal velocity .
This combination of wind properties leads to a high accretion rate and transfer of angular momentum to the neutron star in this system .
We believe this in turn leads to a smaller instantaneous equilibrium spin period with respect to normal OB supergiants .

Conclusions :