2011A&A...532A.124M

We report near-infrared observations of the supergiant donor to the eclipsing high mass X-ray binary pulsar object IGR J18027-2016 . We aim to determine its spectral type and measure its radial velocity curve and hence determine the stellar masses of the components. ESO/VLT observations of the donor utilising the NIR spectrograph ISAAC were obtained in the H and K bands. The multi-epoch H band spectra were cross-correlated with RV templates in order to determine a radial solution for the system. The spectral type of the donor was confirmed as B0-1 I. The radial velocity curve constructed has a semi-amplitude of 23.8±3.1km/s. Combined with other measured system parameters, a dynamically determined neutron star mass of 1.4±0.2-1.6±0.3M_☉ is found. The mass range of the B0-B1 I donor was 18.6±0.8-21.8±2.4M_☉. These lower and upper limits were obtained under the assumption that the system is viewed edge-o