Publications
of the
MPIfR Optical & Infrared Interferometry Group
Hofmann,
K.-H., Beckmann, U., Berger, J.,
Blöcker,
T., Brewer, M.K., Lacasse, M., Malanushenko, V., Millan-Gabet, R.,
Monnier,
J., Ohnaka, K., Pedretti, E., Schertl, D., Schloerb, P., Scholz, M.,
Traub,
W. A., Weigelt, G., and Yudin, B.
Near-infrared
IOTA interferometry of the symbiotic star CH Cyg
in: W.A. Traub
(ed.),
Interferometry for Optical Astronomy II, SPIE Conf. Vol. 4838
(2003)
Abstract.
We present observations of the symbiotic star CH Cyg with a new
JHK-band beam
combiner mounted to the IOTA interferometer. The new beam combiner
consists
of an anamorphic cylindrical lens system and a grism, and allows the
simultaneous
recording of spectrally dispersed J-, H- and K-band Michelson
interferograms.
The observations of CH Cyg were conducted on 5, 6, 8 and 11 June 2001
using
baselines of 17m to 25m. From the interferograms of CH Cyg, J-, H-, and
K-band
visibility functions can be determined. Uniform-disk fits to the
visibilities
give, e.g., stellar diameters of (7.8 +/- 0.6) mas and (8.7 +/- 0.8)
mas
in H and K, respectively. Angular stellar filter radii and Rosseland
radii are derived from the measured visibilities by fitting theoretical
center-to-limb
intensity variations (CLVs) of Mira star models. The available
HIPPARCOS
parallax of CH Cyg allows us to determine linear radii. For example, on
the
basis of the K-band visibility, Rosseland radii in the range of 214 to
243
solar radii can be derived utilizing CLVs of different fundamental mode
Mira
models as fit functions. These radii agree well within the error bars
with
the corresponding theoretical model Rosseland radii of 230 to 282 solar
radii.
Models of first overtone pulsators are not in good agreement with the
observations.
The wavelength dependence of the stellar diameter can be well studied
by
using visibility ratios V(λ1)/V(λ2) since ratios
of visibilities of different spectral channels can be measured with
higher precision
than absolute visibilities. We found that the 2.03 μm uniform disk
diameter
of CH Cyg is approximately 1.1 times larger than the 2.15 μm and 2.26
μm
uniform-disk diameter.
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