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

Studies of the primary star wind and innermost wind-wind collision zone^⋆,⋆⋆

¹ Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: weigelt@mpifr.de
² South African Astronomical Observatory, PO Box 9, 7935 Observatory, South Africa
³ CRESST and X-ray Astrophysics Laboratory, Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁴ Universities Space Research Association, 10211 Wincopin Circle, Suite 500, Columbia, MD 21044, USA
⁵ Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Rua do Matão 1226, Cidade Universitária, São Paulo 05508-900, Brazil
⁶ European Southern Observatory, Casilla 19001, Santiago 19, Chile
⁷ I. Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany
⁸ School of Physics, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
⁹ Code 667, Astrophysics Science Division, Goddard Space Flight Center, Greenbelt, MD 20771, USA
¹⁰ Department of Physics and Astronomy & Pittsburgh Particle Physics, Astrophysics, and Cosmology Center (PITT PACC), University of Pittsburgh, 3941 O’Hara Street, Pittsburgh, PA 15260, USA
¹¹ European Southern Observatory, Karl Schwarzschild Strasse 2, 85748 Garching, Germany
¹² University of Exeter, Astrophysics Group, Stocker Road, Exeter, EX4 4QL, UK
¹³ Laboratoire Lagrange, UMR7293, Université de Nice Sophia-Antipolis, CNRS, Observatoire de la Côte d’Azur, 06300 Nice, France
¹⁴ Département de physique and Centre de Recherche en Astrophysique du Québec (CRAQ), Université de Montréal, CP 6128 Succ. A., Centre-Ville, Montréal, Québec H3C 3J7, Canada
¹⁵ Universidad Católica del Norte, Instituto de Astronomía, Avenida Angamos 0610, Antofagasta, Chile
¹⁶ Osservatorio Astrofisico di Arcetri, 5 Largo Enrico Fermi, 50125 Firenze, Italia
¹⁷ Indian Institute of Astrophysics, Koramangala, 560034 Bengaluru, India
¹⁸ Ritter Observatory, Department of Physics and Astronomy, The University of Toledo, Toledo, OH 43606-3390, USA

Received: 1 May 2016
Accepted: 25 August 2016

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.