Publications
of the
MPIfR Optical & Infrared Interferometry Group
Weigelt,
G., Beckmann, U., Berger, J., Blöcker, T., Brewer, M.K.,
Hofmann, K.-H., Lacasse, M., Malanushenko, V., Millan-Gabet, R.,
Monnier, J., Ohnaka, K., Pedretti, E., Schertl, D., Schloerb, P.,
Scholz, M., Traub, W.A., and Yudin, B.
Spectro-interferometry
of the Mira star T Cep with the IOTA
interferometer and comparison with models
in: W.A. Traub
(ed.),
Interferometry for Optical Astronomy II, SPIE Conf. Vol. 4838
(2003)
Abstract.
Our new IOTA JHK-band beam combiner allows the simultaneous recording
of spectrally
dispersed J-, H- and K-band Michelson interferograms. In this paper we
present
our IOTA observations of the Mira star T Cep with this beam combiner
(observations
in June 2001; four baselines in the range of 14 m to 27 m). The beam
combiner
optics consists of an anamorphic cylindrical lens system and a prism.
From
the interferograms of T Cep we derive the visibilities and the J-, H-,
and
K-band uniform-disk diameters of 14.0 +/- 0.6 mas, 13.7 +/- 0.6 mas and
15.0
+/- 0.6 mas, respectively. Angular stellar filter radii and Rosseland
radii
are derived from the measured visibilities by fitting theoretical
center-to-limb
intensity variations (CLVs) of different Mira star models. The
available
HIPPARCOS parallax (4.76 +/- 0.75 mas) of T Cep allows us to determine
linear
radii. For example, from the K-band visibility we derive a Rosseland
radius
of 329-50/+70 solar radii if we use the CLVs of
the M-models as fit functions. This radius is in good agreement with
the theoretical
M-model Rosseland radius of 315 solar radii. The comparison of measured
stellar
parameters (e.g. diameters, effective temperature, visibility shape)
with
theoretical parameters indicates whether any of the models is a fair
representation
of T Cep. The ratios of visibilities of different spectral channels can
be
measured with higher precision than absolute visibilities. Therefore,
we
use the visibility ratios V(λ1)/V(λ2) to
investigate
the wavelength dependence of the stellar diameter. We find that the
2.03 μm
uniform-disk diameter of T Cep is about 1.26 times larger than the 2.26
μm
uniform-disk diameter.
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