VLTI-AMBER observations of Eta Carinae with the FINITO fringe tracker and spectral resolution 12000

Abstract

We present interferometric near-infrared observations of the Luminous Blue Variable (LBV) η Car using the Very Large Telescope Interferometer (VLTI) and the AMBER instrument of the European Southern Observatory (ESO). A high spatial resolution of 5 mas (~11.5 AU) and a high spectral resolution R = λ/Δλ=1500 and 12000 were obtained. Some of the data was recorded using the fringe tracker FINITO. The observations were obtained in the wavelength range around both the He I 2.059 μm and the Brγ 2.166 μm emission lines. The AMBER interferograms allow the investigation of the wavelength dependence of η Car's visibility, wavelength-differential phase, and closure phase. If we fit Hillier et al. model visibilities to the observations, we obtain 50% encircled-energy diameters of 4.2, 6.5 and 9.6 mas in the 2.17 μm continuum, the He I, and the Brγ emission lines, respectively. In the continuum, an elongation along a position angle of 120° ± 15° was derived from the visibilities. The VLTI observations support theoretical models of anisotropic winds from fast-rotating, luminous hot stars with enhanced high-velocity mass loss near the pole.