Polychromatic Interferometry of Mira
Variables
Wittkowski, M.; Boboltz, D.A.; Driebe,
T.; Ohnaka, K.
"Why Galaxies Care About AGB Stars: Their
Importance as Actors and Probes"
ASP Conference Series held from August 7-11, 2006 in Vienna, Austria
Vol. 378, pg.262-267(2007)
Abstract
We report on our project to study the atmospheric structure and
circumstellar environment of evolved stars using optical and radio
long-baseline interferometry. VLTI observations of the cool giants ψ
Phe, γ Sge, and α Cet have previously been used to calibrate stellar
model atmospheres of regular non-pulsating cool giants as well as to
derive high-precision fundamental parameters. Previous VLTI
observations of the Mira variable R Leo are consistent with
self-excited dynamic Mira model atmospheres that include molecular
shells close to the continuum-forming layers. Coordinated observations
of evolved stars at near-infrared, mid-infrared, and radio wavelengths
have been conducted, aiming at a better understanding of the stellar
pulsation, the mass-loss process, and the triggering and formation of
asymmetric structures. Results from our pilot study on the Mira
variable S Ori show that the SiO masers reside at a distance of about 2
photospheric radii, a result that is virtually free of the usual
uncertainty inherent in comparing observations of variable stars often
widely separated in time. Preliminary results of new coordinated
VLTI/midi and VLBA observations of S Ori at concurrent epochs are shown.
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