Publications of the MPIfR
Optical & Infrared
Interferometry Group
Weigelt, G., Driebe, T., Hofmann,
K.-H., Kraus, S., Petrov, R., Schertl, D.
AMBER/VLTI observations of Eta Carinae with
high spatial resolution and spectral resolutions of λ/Δλ=1500 and 12000
Euro Summer School held from June 4-16, 2006 in
Goutelas, France
New Astronomy Reviews 51, pg.724-729 (2007)
Abstract
We present the first NIR interferometric observations of the LBV η
Carinae with
high spectral resolution (Weigelt et al. 2006, astro-ph/0609715). The
observations
were carried out with three 8.2 m VLTI Unit Telescopes in the K-band.
The raw
data are spectrally dispersed interferograms obtained with spectral
resolutions of
λ/Δλ=1500 (MR-K mode) and 12 000 (HR-K mode). The observations were
per-
formed in the wavelength range around both the He I 2.059 μm and the
Brγ 2.166 μm
emission lines. The spectrally dispersed AMBER interferograms allow us
to investi-
gate the wavelength dependence of the visibility, differential phase,
and closure phase
of η Car. If we fit Hillier et al. (2001) model visibilities (Hillier
et al. 2001, ApJ, 553,
837) 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 He I, and the
Brγ emission
lines, respectively. In the continuum near the Brγ line, an elongation
along a posi-
tion angle of approximately 120° was found, consistent with previous
VLTI/VINCI
measurements (van Boekel et al. 2003, A&A 410, L37). We find good
agreement be-
tween the measured visibilities and the predictions of the radiative
transfer model
of Hillier et al. (2001). For the interpretation of the non-zero
differential and clo-
sure phases measured within the Brγ line, we developed a simple
geometric model
of an inclined, latitude-dependent wind zone. Our observations support
theoretical
models of anisotropic winds from fast-rotating, luminous hot stars with
enhanced
high-velocity mass loss near the polar regions.
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