Publications
of the
MPIfR
Optical & Infrared
Interferometry Group
K. Ohnaka, T. Blöcker, K.-H. Hofmann,
N.R. Ikhsanov, G. Weigelt, Y. Balega, V.I. Shenavrin, B.F. Yudin, and
Y.S. Efimov:
Diffraction-limited speckle interferometry
and modeling of the circumstellar envelope of R CrB at maximum and
minimum light
in
Planetary Nebulae: Their Evolution and Role in the Universe ,
IAU Symp. 209, Canberra, Australia, November 19-23, 2001,
M. Dopita, S. Kwok, R. Sutherland (eds.), Astron. Soc. Pac., v.209,
p.88 (2003)
Abstract.
We present the first speckle interferometric observations of R CrB, the
prototype of a class of peculiar stars which undergo irregular declines
in their visible light curves. The observations were carried out with
the 6 m telescope at the Special Astrophysical Observatory near maximum
light (V=7, 1996 Oct. 1) and at minimum light (V=10.61, 1999 Sep. 28).
A spatial resolution of 75mas was achieved in the K-band. The dust
shell around R CrB is partially resolved, and the visibility is
approximately 0.8 at a spatial frequency of 10 cycles/arcsec. The
two-dimensional power spectra obtained at both epochs do not show any
significant deviation from circular symmetry. The visibility function
and spectral energy distribution obtained near maximum light can be
simultaneously fitted with a model consisting of the central star and
an optically thin dust shell with density proportional to r^-2. The
inner boundary of the shell is found to be 82 Rstar (19 mas) with a
temperature of 920 K. However, this simple model fails to
simultaneously reproduce the visibility and spectral energy
distribution obtained at minimum light. We show that this discrepancy
can be attributed to thermal emission from a newly formed dust cloud.