Publications
of the
MPIfR
Optical & Infrared
Interferometry Group
K.-H. Hofmann, G. Weigelt, Y. Balega,
and M. Scholz:
Diffraction-limited Speckle Masking
Observations of the
Mira Variables R Cas and R Leo with the 6 m SAO Telescope
Astronomische Gesellschaft Meeting Abstracts
(AGM 14, P52)
Poster presented at the Annual Scientific Meeting of the Astronomische
Gesellschaft
at Heidelberg, September 14-19, 1998
Abstract.
We present the first diffraction-limited optical and infrared speckle
masking
observations of Mira stars with the 6 m SAO telescope.
A resolution of 24 mas was achieved at 700 nm wavelength. The speckle
interferograms were recorded through various narrow-band interference
filters between 673 nm and 1045 nm covering strong and weak TiO
absorption
bands and the continuum. Mira stars show substantial variations of
their angular size with wavelength caused by the wavelength dependence
of
TiO opacity. Our reconstructions show that the disk of R Cas is
non-uniform
and elongated. The size (elliptical uniform disk fit) of the elongated
disk is
35 mas x 40 mas in the 700 nm pseudo-continuum filter and
42 mas x 56 mas in the 714 nm TiO absorption band filter.
In the 1045 nm continuum image the disk of R Cas shows no asymmetry and
has a
uniform disk diameter of 30 mas.
The goal of our Mira star project is to provide the basic observations
for a
quantitative analysis of the photospheric structure of Mira variables
and
thus to test Mira star models. We compare our observations of R Cas and
R Leo
with the models of Bessell et al. (1996). Using the E model series of
Bessell et al. we find, for instance, for R Cas a photospheric
(Rosseland)
radius of 380+/-70 Rsol and a low effective temperature of
approximately 1900 K near minimum phase.
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