Mason, A. B.; Norton, A. J.; Clark, S. J.; Negueruela, I. and Roche, P.
The masses of the neutron and donor star in the high-mass X-ray binary IGR J18027-2016.
Astronomy & Astrophysics, 532, article no. A124.
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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 km s-1. Combined with other measured system parameters, a dynamically determined neutron star mass of 1.4 ± 0.2-1.6 ± 0.3 M⊙ is found. The mass range of the B0-B1 I donor was 18.6 ± 0.8-21.8 ± 2.4 M⊙. These lower and upper limits were obtained under the assumption that the system is viewed edge-on (i = 90° with β = 0.89) for the lower limit and the donor fills its Roche lobe (β = 1 with i = 73.1°) for the upper limit respectively.
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