Publications of the MPIfR Optical & Infrared
Interferometry Group
1) High-Resolution Near-Infrared Speckle
Interferometry and Radiative Transfer Modeling of the OH/IR star OH
104.9+2.4
Riechers, D., Balega, Y., Driebe, T.,
Hofmann, K.-H.,
Men'shchikov, A. B., Shenavrin, V.I., and Weigelt, G.
Astronomy and Astrophysics, 424, 165-177 (2004)
Abstract.
We present near-infrared speckle interferometry of the OH/IR star OH
104.9+2.4
in the K' band obtained with the 6m telescope of the Special
Astrophysical Observatory
(SAO). At a wavelength of lambda = 2.12 micron the diffraction-limited
resolution of
74 mas was attained. The reconstructed visibility reveals a spherically
symmetric,
circumstellar dust shell (CDS) surrounding the central star. The
visibility function
shows that the stellar contribution to the total flux at lambda = 2.12
micron is less
than ~50%, indicating a rather large optical depth of the CDS. The
azimuthally averaged
1-dimensional Gaussian visibility fit yields a diameter of 47 +/- 3mas
(FHWM),
which corresponds to 112 +/- 13 AU for an adopted distance of D = 2.38
+/- 0.24 kpc.
To determine the structure and the properties of the CDS of OH
104.9+2.4, radiative
transfer calculations using the code DUSTY were performed to
simultaneously model its
visibility and the spectral energy distribution (SED). We found that
both the ISO
spectrum and the visibility of OH 104.9+2.4 can be well reproduced by a
radiative
transfer model with an effective temperature T_eff = 2500 +/- 500 K of
the central
source, a dust temperature T_in = 1000 +/- 200 K at the inner shell
boundary
R_in = 9.1 R_star = 25.4 AU, an optical depth tau = 6.5 +/- 0.3 at 2.2
micron, and
dust grain radii ranging from a_min = 0.005 +/- 0.003 micron to a_max =
0.2 +/- 0.02
micron with a power law with index -3.5. It was found that even minor
changes in
a_max have a major impact on both the slope and the curvature of the
visibility
function, while the SED shows only minor changes. Our detailed analysis
demonstrates
the potential of dust shell modeling constrained by both the SED and
visibilities.
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2) A quasi-time-dependent radiative
transfer model
of OH 104.9+2.4
Riechers, D., Balega, Y., Driebe, T.,
Hofmann, K.-H.,
Men'shchikov, A. B., and Weigelt, G.
Astronomy
and
Astrophysics, 436, 925-931 (2005)
Abstract.
We
investigate the pulsation-phase dependent properties of the
circumstellar dust
shell (CDS) of the OH/IR
star OH 104.9+2.4 based on radiative transfer modeling (RTM) using the
code
DUSTY. Our previous study concerning
simultaneous modeling of the spectral energy distribution (SED) and
near-infrared (NIR) visibilities (Riechers
et al. 2004) has been extended by means of a more detailed analysis of
the
pulsation phase dependence of the
model parameters of OH 104.9+2.4. In order to investigate the temporal
variation of the spatial structure of the
CDS, additional NIR speckle interferometric observations in the K'
band were
carried out with the 6 m telescope
of the Special Astrophysical Observatory (SAO). At a wavelength
of λ =
2.12 m
the diffraction-limited resolution
of 74 mas was attained. As regards our previous best-fitting model,
several key
parameters had to be adjusted
in order to be consistent with the extended amount of observational
data. It
was found that a simple rescaling
of the bolometric flux Fbol is not suffcient to take into account the
variability of the source, as the change
in optical depth τ over a full pulsation cycle is rather high. On
the
other
hand, the impact of a change in effective
temperature Teff on SED and visibility is rather small. However,
observations as
well as models for other AGB
stars show the necessity to include a variation of Teff with pulsation
phase in
the radiative transfer models. Therefore,
our new best-fitting model accounts for these changes.
Key
words. radiative transfer -- stars: AGB and post AGB -- stars:
mass loss --
stars: circumstellar matter -- infrared:
stars -- stars: oscillations -- stars: individual: OH 104.9+2.4
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