Issue |
A&A
Volume 379, Number 2, November IV 2001
|
|
---|---|---|
Page(s) | 529 - 539 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20011318 | |
Published online | 15 November 2001 |
A multi-wavelength study of the oxygen-rich AGB star CIT 3: Bispectrum speckle interferometry and dust-shell modelling
1
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: bloecker@mpifr-bonn.mpg.de, weigelt@mpifr-bonn.mpg.de
2
Special Astrophysical Observatory, Nizhnij Arkhyz, Zelenchuk region, Karachai-Cherkesia, 35147, Russia e-mail: balega@sao.ru
Corresponding author: K.-H. Hofmann, hofmann@mpifr-bonn.mpg.de
Received:
6
August
2001
Accepted:
14
September
2001
CIT 3 is an oxygen-rich
long-period variable evolving along the Asymptotic Giant Branch and
is one of the most extreme infrared AGB objects.
Due to substantial mass loss it is surrounded by an optically thick dust shell
which absorbs almost all visible light radiated by the star and
finally re-emits it in the infrared regime.
We present the first near infrared bispectrum speckle-interferometry
observations of CIT 3 in the J-, H-, and -band.
The J-, H-, and
-band resolution is
48 mas, 56 mas, and 73 mas, resp.
The interferograms were obtained with the Russian 6 m telescope at the
Special Astrophysical Observatory.
While CIT 3 appears almost spherically symmetric in the
H- and
-band
it is clearly elongated in the J-band along a symmetry axis of position angle
. Two structures can be identified: a compact
elliptical core and a fainter north-western fan-like structure.
The eccentricity of the elliptical core, given by the ratio of
minor to major axis, is approximately
mas/154 mas = 0.8.
The full opening angle of the fan amounts to approximately
.
Extensive radiative transfer calculations have been carried out
and confronted with the observations taking into account
the spectral energy distribution ranging from 1 μm to 1 mm,
our near-infrared visibility functions at 1.24 μm,
1.65 μm and 2.12 μm, as well as 11 μm ISI interferometry.
The best model found to match the observations refers to a cool central star
with
K which is surrounded by an optically thick dust shell with
.
The models give a central-star diameter of
mas
and an inner dust shell diameter of
mas
being in line with lunar occultation observations.
The inner rim of the dust-shell is located at
and has a
temperature of
K. The grain sizes were found to comply with
a grain-size distribution according to Mathis et al. ([CITE]) with
, and 0.005
m.
Uniform outflow models, i.e. density distributions with
,
turned out to underestimate the flux beyond 20 μm. A two-component model existing of an inner
uniform-outflow shell region (
)
and an outer region where the density declines more shallow as
proved to remove this flux deficiency and to give the best overall match of the
observations. The transition between both density distributions is at
where the dust-shell temperature has dropped
to
K. Provided the outflow velocity kept constant,
the more shallow density distribution in the outer shell
indicates that mass-loss has decreased with time in the past of CIT 3.
Adopting
km s-1, the termination of that mass-loss
decrease and the begin of the uniform-outflow phase
took place 87 yr ago. The present-day mass-loss rate can be determined to be
/yr for
pc.
Key words: techniques: image processing / circumstellar matter / stars: individual: CIT 3 / stars: mass-loss / stars: AGB and post-AGB / infrared: stars
© ESO, 2001
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.