AMBER/VLTI observations of η Carinae with high spatial resolution and spectral resolutions of λ/Δ λ = 1500 and 12 000

Abstract

We present the first NIR interferometric observations of the LBV η Carinae with high spectral resolution [Weigelt et al., 2007. Near-infrared interferometry of η Carinae with spectral resolutions of 1500 and 12000 using AMBER/VLTI. A&A 464, 87.]. Our observations demonstrate the potential of AMBER/VLTI to unveil new structures on the scales of milliarcseconds. The aim of this work is to study the wavelength dependence of η Car’s optically thick wind region with a high spatial resolution of 5 mas (11 AU) and high spectral resolution. The observations were carried out with three 8.2 m VLTI Unit Telescopes. The raw data are interferograms obtained with spectral resolutions of λ/Δ λ = 1500 (MR-K mode) and 12 000 (HR-K mode). The observations were performed in the wavelength range around both the HeI 2.059 μm and the Brγ 2.166 μm emission lines. The spectrally dispersed AMBER interferograms allow us to investigate the wavelength dependence of the visibility, differential phase, and closure phase of η Car. If we fit [Hillier, D.J., Davidson, K., Ishibashi, K., Gull, T., 2001. On the Nature of the Central Source in η Carinae. ApJ 553, 837] model visibilities (Hillier et al., 2001) to the observed AMBER visibilities, we obtain 50% encircled-energy diameters of 4.3, 6.5, and 9.6 mas in the 2.17 μm continuum, the HeI, and the Brγ emission lines, respectively. We find good agreement between the measured visibilities and the predictions of the radiative transfer model of Hillier et al. (2001). Our observations support theoretical models of anisotropic winds from fast-rotating, luminous hot stars with enhanced high-velocity mass loss near the polar regions.