The close environment of high-mass X-ray binaries at high angular resolution. I. VLTI/AMBER and VLTI/PIONIER near-infrared interferometric observations of
Context. Recent improvements in the sensitivity and spectral resolution of X-ray observations have led to a better understanding of the properties of matter in the near vicinity of high-mass X-ray binaries (HMXB) hosting a supergiant star and a compact object. However, the geometry and physical properties of their environments on larger scales (up to a few stellar radii) are currently only predicted by simulations but have never been directly observed.
Aims: We aim to explore the environment of
Methods: We observed
Results: We resolved a structure of 8 ± 3 R⋆ from the AMBER K-band observations, and 2.0-1.2+0.7R* from the PIONIER H-band data. From the closure phase observable, we found that the circumstellar environment of
Conclusions: We propose three possible scenarios for this discrepancy between the two measurements: 1) there is a strong temperature gradient in the supergiant wind, leading to a hot component that is much more compact than the cool part of the wind observed in the K band; 2) we observed a diffuse shell in 2010, possibly triggered by an off-state in the accretion rate of the neutron star that was dissolved in the interstellar medium in 2012 during our second observations; or 3) the structure observed in the H band was the stellar photosphere instead of the supergiant wind.
Astronomy and Astrophysics
- Pub Date:
- January 2014
- techniques: interferometric;
- circumstellar matter;
- stars: individual: Vela X-1;
- Astrophysics - Solar and Stellar Astrophysics
- Accepted for publication in A&