Pulsation-induced atmospheric dynamics in M-type AGB stars. Effects on wind properties, photometric variations and near-IR CO line profiles

Abstract

Wind-driving in asymptotic giant branch (AGB) stars is commonly attributed to a two-step process. First, matter in the stellar atmosphere is levitated by shock waves, induced by stellar pulsation, and second, this matter is accelerated by radiation pressure on dust, resulting in a wind. In dynamical atmosphere and wind models the effects of the stellar pulsation are often simulated by a simplistic prescription at the inner boundary. We test a sample of dynamical models for M-type AGB stars, for which we kept the stellar parameters fixed to values characteristic of a typical Mira variable but varied the inner boundary condition. The aim was to evaluate the effect on the resulting atmosphere structure and wind properties. The results of the models are compared to observed mass-loss rates and wind velocities, photometry, and radial velocity curves, and to results from 1D radial pulsation models. Dynamical atmosphere models are calculated, using the DARWIN code for different combinations of photospheric velocities and luminosity variations. The inner boundary is changed by introducing an offset between maximum expansion of the stellar surface and the luminosity and/or by using an asymmetric shape for the luminosity variation. Models that resulted in realistic wind velocities and mass-loss rates, when compared to observations, also produced realistic photometric variations. For the models to also reproduce the characteristic radial velocity curve present in Mira stars (derived from CO $\Delta v=3$ lines), an overall phase shift of 0.2 between the maxima of the luminosity and radial variation had to be introduced. We find that a group of models with different boundary conditions (29 models, including the model with standard boundary conditions) results in realistic velocities and mass-loss rates, and in photometric variations.

References in corpus (25)

• Dust formation in the oxygen-rich AGB star IK Tau
• A close halo of large transparent grains around extreme red giant stars
• Mass loss rates of a sample of irregular and semiregular M-type AGB-variables
• `Thermal' SiO radio line emission towards M-type AGB stars: a probe of circumstellar dust formation and dynamics
• On the reliability of mass-loss-rate estimates for AGB stars
• Global 3D radiation-hydrodynamics models of AGB stars. Effects of convection and radial pulsations on atmospheric structures
• Line formation in AGB atmospheres including velocity effects. Molecular line profile variations of long period variables
• Dynamic atmospheres and winds of cool luminous giants, I. Al${}_2$O${}_3$ and silicate dust in the close vicinity of M-type AGB stars
• The pulsation modes, masses and evolution of luminous red giants
• Synthetic photometry for M and K giants and stellar evolution: hydrostatic dust-free model atmospheres and chemical abundances
• Dynamical Opacity-Sampling Models of Mira Variables. II: Time-Dependent Atmospheric Structure and Observable Properties of 4 M-Type Model Series
• New insights into the dust formation of oxygen-rich AGB stars
• Synthetic photometry for carbon-rich giants. IV. An extensive grid of dynamic atmosphere and wind models
• Clumpy dust clouds and extended atmosphere of the AGB star W Hya revealed with VLT/SPHERE-ZIMPOL and VLTI/AMBER
• Dynamical Opacity-Sampling Models of Mira Variables. I: Modelling Description and Analysis of Approximations
• Exploring wind-driving dust species in cool luminous giants III. Wind models for M-type AGB stars: dynamic and photometric properties
• Atmospheric dynamics in carbon-rich Miras. I. Model atmospheres and synthetic line profiles
• Synthetic photometry for carbon-rich giants II. The effects of pulsation and circumstellar dust
• Atmospheric dynamics in carbon-rich Miras. II. Models meet observations
• Exploring wind-driving dust species in cool luminous giants II. Constraints from photometry of M-type AGB stars
• Dust-driven winds of AGB stars: The critical interplay of atmospheric shocks and luminosity variations
• Silicate condensation in Mira variables
• Spatially resolving the outer atmosphere of the M giant BK Vir in the CO first overtone lines with VLTI/AMBER
• The shapes of light curves of Mira-type variables
• 4mu spectra of AGB stars I: Observations

Cited by in corpus (15)

• ALMA spectral line and imaging survey of a low and a high mass-loss rate AGB star between 335 and 362 GHz
• An extensive grid of DARWIN models for M-type AGB stars I. Mass-loss rates and other properties of dust-driven winds
• The evolution of DARWIN: current status of wind models for AGB stars
• Exploring the origin of clumpy dust clouds around cool giants. A global 3D RHD model of a dust-forming M-type AGB star
• Tomography of cool giant and supergiant star atmospheres II. Signature of convection in the atmosphere of the red supergiant star $\mu$ Cep
• Atmospheres and wind properties of non-spherical AGB stars
• Dynamic atmospheres and winds of cool luminous giants, II. Gradual Fe enrichment of wind-driving silicate grains
• Circumstellar ammonia in oxygen-rich evolved stars
• Carbon stars with increased oxygen and nitrogen abundances: hydrostatic dust-free model atmospheres
• Evidence for localized onset of episodic mass loss in Mira
• Meandering periods and asymmetries in light curves of Miras: Observational evidence for low mass-loss rates
• The Great Dimming of Betelgeuse: the photosphere as revealed by tomography over the past 15 years
• Contemporaneous high-angular-resolution imaging of the AGB star W Hya in vibrationally excited H2O lines and visible polarized light with ALMA and VLT/SPHERE-ZIMPOL
• High-angular-resolution ALMA imaging of the inhomogeneous dynamical atmosphere of the asymptotic giant branch star W Hya
• Spectroscopic and photometric monitoring of a poorly known high-luminous OH/IR star: IRAS 18278+0931