VLTI-AMBER velocity-resolved aperture-synthesis imaging ofηCarinae with a spectral resolution of 12 000

Abstract

Context. The mass loss from massive stars is not understood well. η Carinae is a unique object for studying the massive stellar wind during the luminous blue variable phase. It is also an eccentric binary with a period of 5.54 yr. The nature of both stars is uncertain, although we know from X-ray studies that there is a wind-wind collision whose properties change with orbital phase. Aims. We want to investigate the structure and kinematics of η Car's primary star wind and wind-wind collision zone with a high spatial resolution of ∼6 mas (∼14 au) and high spectral resolution of R = 12 000. Methods. Observations of η Car were carried out with the ESO Very Large Telescope Interferometer (VLTI) and the AMBER instrument between approximately five and seven months before the August 2014 periastron passage. Velocity-resolved aperture-synthesis images were reconstructed from the spectrally dispersed interferograms. Interferometric studies can provide information on the binary orbit, the primary wind, and the wind collision.Results. We present velocity-resolved aperture-synthesis images reconstructed in more than 100 different spectral channels distributed across the Brγ 2.166 µm emission line. The intensity distribution of the images strongly depends on wavelength. At wavelengths corresponding to radial velocities of approximately −140 to −376 km s −1 measured relative to line center, the intensity distribution has a fan-shaped structure. At the velocity of −277 km s −1 , the position angle of the symmetry axis of the fan is ∼126 • . The fan-shaped structure extends approximately 8.0 mas (∼18.8 au) to the southeast and 5.8 mas (∼13.6 au) to the northwest, measured along the symmetry axis at the 16% intensity contour. The shape of the intensity distributions suggests that the obtained images are the first direct images of the innermost wind-wind collision zone. Therefore, the observations provide velocity-dependent image structures that can be used to test three-dimensional hydrodynamical, radiative transfer models of the massive interacting winds of η Car.

First light for GRAVITY: Phase referencing optical interferometry for the Very Large Telescope Interferometer

“…At this velocity, η Car shows an asymmetric elongated structure with a size of ∼15 mas, with a major axis in the south-east direction. This result is consistent with the fanshaped morphology found by Weigelt et al (2016) for similar velocities using the Astronomical Multi-Beam Combiner (AM-BER, Petrov et al 2007) at the VLTI. The morphology of the Brγ blue wing could be also affected by an additional contribution from the fossil winds at the core of η Car (Gull et al 2011(Gull et al , 2016.…”

Numerical simulations and infrared spectro-interferometry reveal the wind collision region in γ2 Velorum

“…All of this contributes to the final observables and would not have been accounted for with analytic models. As the current dataset does not allow for complete reconstruction of the image (as in Weigelt et al (2016) for η Carinae), one has to construct a model for the system and compare its observables with the data. While the model we propose has a strong physical motivations, a unique solution for the system's emission cannot be formally identified with the continuum data.…”

“…Direct observations of the WCZ in the optical and infrared remains a challenge, as it is strongly overshadowed by the wind and/or photospheric emission of the binary. It has only been possible for the very bright η Carinae system, where the angular separation between the stars is much larger (Weigelt et al 2016). While signatures of the WCZ are likely present in the data presented in Paper I, a firmer answer requires more data and a detailed model of the structure and dynamics of the interaction region.…”

The high energy Universe at ultra-high resolution: the power and promise of X-ray interferometry

“…In Vela X-1, where high and low ionization lines from different elements [31,69] are simultaneously present, we will thus, for the first time, be able to trace whether the cold material is concentrated in the accretion wake or directly embedded in the wind as denser, colder clumps. In interacting binary systems, we will be able to directly image the X-ray emitting interaction region, similarly to the optical [70], constraining the location and structure of the most energetic interactions. Tracing the variability of the radiation zone through multiple observations in both kinds of systems will give us further constraints on wind variability and thus wind driving as well as system geometry.…”