Self-consistent modeling of the outflow from the O-rich Mira IRC –20197

Abstract

We present a self-consistent time-dependent model for the oxygen-rich Mira variable IRC -20197. This model includes a consistent treatment of the interactions among hydrodynamics, thermodynamics, radiative transfer, equilibrium chemistry, and heterogeneous dust formation with TiO 2 nuclei, The model is determined by the stellar parameters, stellar mass M * = 1.3 M O ., stellar luminosity L * = 1.4 × 10 4 L O ., stellar temperature T * = 2400 K, and solar abundances of the elements. The pulsation of the star is simulated by a piston at the inner boundary where the velocity varies sinusoidally with a period of P = 636 d and an amplitude of Δν p = 8 km s - 1 . Based on the atmospheric structure resulting from this hydrodynamic calculation at different phases, we have performed angle- and frequency-dependent continuum radiation transfer calculations, which result in the spectral energy distributions at different phases of the pulsation cycle and in synthetic light curves at different wavelengths. These are in good agreement with the infrared observations of IRC -20197. The model yields a time averaged outflow velocity of 11.9 km s - 1 and an average mass loss rate of 7.3 × 10 - 6 M O . yr - 1 which are in good agreement with the values derived from radio observations. Furthermore, the chemical composition of the resulting grains is discussed.