The masses of the neutron and donor star in the high-mass X-ray binary IGR J18027-2016 (Research Note)

Aims. We report near-infrared observations of the supergiant donor to the eclipsing high mass X-ray binary pulsar 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. Methods. 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. Results. The spectral type of the donor was confirmed as B0-1 I. The radial velocity curve constructed has a semi-amplitude of 23.8 +/- 3.1 kms(-1). Combined with other measured system parameters, a dynamically determined neutron star mass of 1.4 +/- 0.2-1.6 +/- 0.3 M-circle dot is found. The mass range of the B0-B1 I donor was 18.6 +/- 0.8-21.8 +/- 2.4 M-circle dot. These lower and upper limits were obtained under the assumption that the system is viewed edge-on (i = 90 degrees. with beta = 0.89) for the lower limit and the donor fills its Roche lobe (beta = 1 with i = 73.1 degrees.) for the upper limit respectively.