Abstract
Our observations of cool, shock penetrated, expanding atmospheres of
M-type Mira stars (see Richter & Wood 2001, A&A 369, 1027)
showed that in particular the emission lines of Fe II and [Fe II] are
good diagnostic tools to study the physical conditions in the shocked
region close to the photosphere of these stars. The erratic appearance
of these particular emission lines in stars which had just had a bright
light maximum suggests that they require an exceptionally bright maximum
for excitation. Presumably, these are associated with stronger shock
waves. According to the phase of their appearance it can be estimated,
that the Fe II as well as the [Fe II] emission lines must originate
close to the star at ˜1 - 3 Rast.
To model the Fe II and [Fe II] emission lines and to analyze the
hydodynamical conditions which lead to their formation, detailed NLTE
radiative transfer calculations in spherical symmetry, applying a
co-moving frame formalism and using accelerated lambda iteration have
been carried out on a series of specific hydrodynamical shock
structures. Our basic parameter studies reveal that the lines from
ionized iron originate right from the shock front and that they are in
fact emitted close to the stars photosphere.
Work in progress will provide detailed line profiles to fit the observed
line shapes in order to extract the full information given by the
emission lines of ionized iron in M Miras. Dust formation takes place
approximately in the same regions were the Fe II and [Fe II] emission
lines originate. Hence a detailed study of these lines will offer the
unique possibility to determine the physical conditions in the dust
formation zone and thereby will shed some light on the basic mechanism
of dust formation in M-type Mira stars.
| Original language | English |
|---|---|
| Title of host publication | Stellar Atmosphere Modeling, ASP Conference Proceedings |
| Pages | 344 |
| Volume | 288 |
| Publication status | Published - 1 Jan 2003 |