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

TL;DR

This study uses near-infrared spectroscopy to determine the spectral type, radial velocity, and stellar masses of the components in the high mass X-ray binary IGR J18027-2016, providing new dynamical mass measurements.

Contribution

The paper presents the first dynamical mass measurements of the neutron star and donor star in IGR J18027-2016 using near-infrared spectroscopy and radial velocity analysis.

Findings

Neutron star mass estimated at 1.4 ± 0.2 - 1.6 ± 0.3 M☉

Donor star mass range is 18.6 ± 0.8 - 21.8 ± 2.4 M☉

Donor spectral type confirmed as B0-1 I

Abstract

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. 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 $23.8 \pm 3.1$ km s$^{-1}$. Combined with other measured system parameters, a dynamically determined neutron star mass of 1.4 $\pm$ 0.2 - 1.6 $\pm$ 0.3 M$_{\odot}$ is found. The mass range of the B0-B1 I donor was 18.6 $\pm$ 0.8 - 21.8 $\pm$ 2.4 ~M$_{\odot}$. These lower and upper limits were obtained under the assumption that the system is viewed edge-on (i = 90$^\circ$ with $\beta$ = 0.89) for the lower limit and the donor fills its Roche lobe ($\beta = 1$ with i = 73.1$^\circ$) for the upper limit respectively.