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: http://star.arm.ac.uk/~ambn/abstract328.html
Дата изменения: Mon Mar 27 15:58:11 2000
Дата индексирования: Mon Oct 1 23:59:29 2012
Кодировка:
Поисковые слова: etacarinae
We model the spectral chanages of late oxygen-rich Miras observed in different
pulsation phases. From a combination of variable near-IR spectra and UKIRT
spectrophotometry of the 9.7 \mu m silicate dust emission feature in different
phases we study the influence of the changing atmospherical circumstances on the
conditions in the circumstellar dust shell. From a detailed modelling of TiO
and VO bands in the near-IR spectra we determine changes of the effective
temperature and the effective atmospheric acceleration of the central star. The
corresponding model spectra energy distribution is redistributed through the
dust shell by means of radiative transfer calculations in order to perform a
detailed modelling of shape changes observed in the silicate feature. We show
that the latter are mainly caused by changes in the flux distribution of the
incident radiation field with stellar pulsation, whereas intensity changes of
the dust emission result from stellar luminosity changes as they are enshrouded
by very optically thin dust shells. In the case of Mira (o Cet) we compute that
the effective temperature increases from T_{eff}=2400 K in the minimum phase to
3000 K (\pm 100 K) around maximum phase. The amplified momentum transfer around
maximum light enhances the acceleration of the dust outflow near the dust
condensation radius of \sim 6 R\ast . This produces variations of the terminal dust
outflow velocity with phase (\Delta \nu \infty \backsimeq 5 km s^(-1) at larger
distance from the star. The corresponding small changes in flux mean opacity
and gas mass-loss rates (from 2.8 to 3.2 10^{-7} M\odot y^{-1}) are sufficient
to model the shape changes observed in the dust emission feature. A comparision
with the modelling results for another long period Mira U Ori is also provided.