Estimating effective temperatures of Mira Variables by fitting phase resolved spectra.
Matthias Dehn (Hamburger Sternwarte)
Schweitzer, Andreas (Hamburger Sternwarte)
Using an automatic procedure we compared the observed spectra
of the Mira Variables R Leo, R CVn, V CVn, S Car and RZ Car with
synthetic spectra which were generated with the PHOENIX
atmosphere package. The observations were done by Castelaz
et al. and Lancon et al. over several years in order to cover
several pulsation phases.
We calculated a model grid with Teff = 2000 … 4500 and
log(g) = -1.0 … 2.5. Furthermore we changed the abundances of
carbon and oxygen to obtain a C/O-ratio of 0.4, 0.8, 1.2 and 0.48
(solar) in order to get better fits. The models assume LTE and consider
the condensation of dust inside the atmosphere.
The fit parameters (correlation coefficient and chi-square sum)
are most sensitive to variations of temperature and C/O, whereas
variations of log(g) are too small to resolve. A clear correlation
between phase and temperature cannot be seen. Therefore, the
temperatures were accounted as mean values which agree to calculations
from Alvarez et al. (1997) for R Leo and R CVn and Shinkawa (1973)
for S Car.