van Soelen, Brian, Bordas, Pol, Negueruela, Ignacio, de Oña Wilhelmi, Emma, Papitto, Alessandro, Ribó, Marc
NIR spectral classification of the companion in the gamma-ray binary HESS J1832−093 as an O6 V star
Monthly Notices of the Royal Astronomical Society: Letters. 2024, 529(1): L102–L107. https://doi.org/10.1093/mnrasl/slae007
URI: http://hdl.handle.net/10045/140169
DOI: 10.1093/mnrasl/slae007
ISSN: 1745-3925 (Print)
Abstract: 
HESS J1832−093 is a member of the rare class of gamma-ray binaries, as recently confirmed by the detection of orbitally modulated X-ray and gamma-ray emission with a period of ∼86 d. The spectral type of the massive companion star has been difficult to retrieve as there is no optical counterpart, but the system is coincident with a near-infrared source. Previous results have shown that the infrared counterpart is consistent with an O or B-type star, but a clear classification is still lacking. We observed the counterpart twice, in 2019 and 2021, with the X-Shooter spectrograph operating on the Very Large Telescope (VLT). The obtained spectra classify the counterpart as an O6 V-type star. We estimate a distance to the source of 6.7 ± 0.5 kpc, although this estimate can be severely affected by the high extinction towards the source. This new O6 V classification for the companion star in HESS J1832−093 provides further support to an apparent grouping around a given spectral type for all discovered gamma-ray binaries that contain an O-type star. This may be due to the interplay between the initial mass function and the wind momentum–luminosity relation.
Keywords:Binaries: spectroscopic, Stars: neutron, Gamma-rays: stars, X-rays: binaries, X-rays: individual: (HESS J1832−093, 2MASS J18324516−0921545)
Oxford University Press
info:eu-repo/semantics/article