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The formation of massive stars remains one of the most intriguing questions in astrophysics today. The main limitations result from the difficulty to obtain direct observational constraints on the formation process itself. In this context, the Carina High-contrast Imaging Project of massive Stars (CHIPS) aims to observe all 80+ O stars in the Carina nebula using the new VLT 2nd-generation extreme-AO instrument SPHERE. This instrument offers unprecedented imaging contrast allowing us to detect the faintest companions around massive stars. These novel observational constraints will help to discriminate between the different formation scenarios by comparing their predictions for companion statistics and properties.
High-mass X-ray Binaries (HMXBs) are keys to study stellar remnants that are otherwise extremely faint and difficult to observe when isolated. Vela X-1 is a well-known eclipsing HMXB composed of a very massive neutron star orbiting a B0.5I supergiant with a period of 9 days. The supergiant wind is the main feeding material for the accreting neutron star, and its properties are of prime interest to understand the physics at stakes in the accretion process.
In order to characterize the geometry and physical properties of the dense wind at a scale of a few stellar radii, we obtained infrared interferometric observations of Vela X-1 in 2010 using the VLTI/AMBER instrument in the K band (2.2 μm), and in 2012 using the VLTI/PIONIER instrument in the H band (1.6 μm).
Although the apparent disk of the supergiant and the orbital separation of the two objects are beyond the present resolution limit of the VLTI, the K-band observations partially resolve the wind envelope on the two longest baselines. We were able to measure the radius of 265±82 R⊙ for the circumstellar wind at a temperature of 1300 K, assuming a distance of 1.9 kpc. The H-band observations do not resolve the system, and we were able to set an upper limit of 112 R⊙ for the envelope radius at a temperature of 1800 K.
First results of near-IR adaptive optics (AO)-assisted imaging, interferometry, and spectroscopy of this Luminous Blue Variable (LBV) are presented. They suggest that the Pistol Star is at least double. If the association is physical, it would reinforce questions concerning the importance of multiplicity for the formation and evolution of extremely massive stars.
Optical and IR spectra, optical to sub-mm photometry, visual imaging polarimetry, and IR high-resolution spectro-interferometry are being used to monitor the new outburst of 28 CMa, which started in 2008 and so far closely resembles previous ones. First modeling based on viscous decretion and focused on constraining the disk viscosity parameter, α, is presented.
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