# Near-infrared survey of High Mass X-ray Binary candidates

## TL;DR

This study uses infrared spectroscopy and photometry to classify and determine distances of high-mass X-ray binary candidates, revealing their stellar types, obscuration levels, and X-ray properties, and identifying new characteristics of several sources.

## Contribution

It provides the first intermediate-resolution spectra for two sources, refines classifications for two others, and discusses the nature of a puzzling source, advancing understanding of high-mass X-ray binaries.

## Key findings

- Four systems host early-type B supergiants.
- All sources are heavily obscured with high extinction.
- IGR J18027-2016 and IGR J19140+0951 are confirmed supergiant X-ray binaries.

## Abstract

We combine infrared spectra in the I, J, H and K bands together with JHK photometry to characterize the spectral type, luminosity class and distance to the infrared counterparts to five INTEGRAL sources. For SAX J18186-1703 and IGR J18483-0311, we present the first intermediate-resolution spectroscopy reported. We find that four systems harbour early-type B supergiants. All of them are heavily obscured, with E(B-V) ranging between 3 and 5, implying visual extinctions of ~ 9 to 15 magnitudes. We refine the published classifications of IGR J18027-2016 and IGR J19140+0951 by constraining their luminosity class. In the first case, we confirm the supergiant nature and rule out class III. In the second case, we propose a slightly higher luminosity class (Ia instead of Iab) and give an improved value of the distance based on new optical photometry. Owing to their infrared and X-ray characteristics, IGR J18027-2016 and IGR J19140+0951, emerge as Supergiant X-ray binaries with X-ray luminosities of the order of Lx ~ [1-2] x 10^{36} erg/s, while SAX J1818.6-1703 and IGR J18483-0311, turn out to be Supergiant Fast X-ray Transients at 2 and 3 kpc, respectively. Finally, XTE J1901+014 emerges as a puzzling source: its X-ray behaviour is strongly reminiscent of the SFXTs but a supergiant nature is firmly ruled out for the counterpart. We discuss several alternative scenarios to explain its behaviour.