Optical and Infrared Study of the Obscured B[e] Supergiant High-mass X-Ray Binary IGR J16318-4848

Abstract

The supergiant high-mass X-ray binary IGR J16318-4848 was the first source detected by the INTErnational Gamma-Ray Astrophysics Laboratory satellite in 2003 and distinguishes itself by its high intrinsic absorption and B[e] phenomenon. It is the perfect candidate to study both binary interaction and the environment of supergiant B[e] stars. This study targets the local properties of IGR J16318-4848. We aim to clarify the geometry of this system and distinguish different key emitting regions in the binary. We provide optical to near-infrared (NIR) spectra from the Very Large Telescope/X-Shooter and analyze both fine structures of the lines and the broadband spectral energy distribution by adding archival mid-infrared Spitzer and Herschel data. We also perform a stellar atmosphere and wind modeling of the optical to NIR spectrum using the Potsdam Wolf-Rayet code. We determine the contribution of the irradiated inner edge of the dusty circumbinary disk, derive the velocity of an equatorial stellar wind, and suggest the compact object orbits within the cavity between the star and the disk. We report on flat-topped lines originating from a spherically symmetric disk wind, along with the first detection of what is likely the polar component of the stellar wind. Stellar atmosphere and wind modeling shows that the central star may have a helium-enhanced atmosphere, likely because of its intense wind shedding part of its hydrogen envelope. Finally, we compare the properties of IGR J16318-4848 with a similar source, CI Cameleopardis. <SUP>*</SUP> Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO program 089.D-0056.