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Optical & Infrared
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A. Gauger, J.M. Winters, A. Fleischer
and J. Keady:
Temporal Variations of CO Infrared Lines in
Cool Star Winds
Proceedings of the ESO workshop
Cyclical Variability in Stellar Winds,
L. Kaper and A. Fullerton (eds.), Springer, Berlin, p. 309 (1998)
Abstract.
High resolution infrared spectroscopy of molecular lines provides a
powerful diagnostic probe to investigate the spatial structure and
temporal evolution of the cool dusty winds from Miras and long-period
variables, such as the carbon-rich IR-Mira IRC+10216 (Keady et al.
1988). For this object high resolution spectra of the CO fundamental
and first overtone transitions at 5 micron and 2 micron
have been obtained repeatedly, covering more than ten years.
Especially the unsaturated overtone lines reflect the actual
conditions and their temporal changes in the acceleration region of
the wind. The line profiles show a multicomponent absorption
structure, and spectra from different epochs reveal changes of the
line profiles (e.g. the emergence of a new absorption component) on
timescales much longer than the period of the star (Sada 1993).
In order to model these observations, we have calculated the synthetic
CO fundamental and first overtone line spectra for a dynamical model
of the circumstellar dust shell around IRC+10216, which is obtained
from the consistent treatment of time-dependent hydro- and
thermodynamics, radiative transfer, chemistry, and carbon grain
formation (Fleischer et al.\ 1992). Due to the interaction between
interior stellar pulsation and grain condensation in the circumstellar
shell, such wind models are characterized by an inhomogeneous
onion-like grain distribution, strong shocks accelerated by radiation
pressure on dust, and cycle-to-cycle variations of the spatial
structure (either periodic or non-periodic).
Our synthetic CO first overtone line profiles resemble the
multicomponent absorption structure and the time variations of the
corresponding observed line spectra, which thus can be interpreted as
a result of the time-dependent dynamics in the inner parts of the
wind. In particular, the emergence and subsequent evolution of the
low-velocity absorption feature is reproduced by the model and can be
explained by the formation of a new dust layer and the subsequent
acceleration of the matter by radiation pressure on dust.
References:
Fleischer A.J., Gauger A., Sedlmayr E., 1992, A&A 266, 321
Keady J.J., Hall D.N.B., Ridgway S.T., 1988, ApJ 326, 832
Sada P.A.V., 1993, PhD thesis, New Mexico State University, Las Cruces
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