A. J. Fleischer

Temporal Variations of CO Infrared Lines in Cool-Star Winds

High-resolution infrared spectroscopy of molecular lines provides a powerful diagnostic probe to investigate the spatial structure and temporal evolution of the cool, dusty winds of Miras and long—period variables, such as the carbon rich IR-Mira IRC+10216 (Keady et al. 1988). For this object, high-resolution spectra of the CO fundamental and first overtone transitions at 5μm and 2μm have been obtained repeatedly over an interval spanning more than ten years. The unsaturated overtone lines reflect the actual conditions and their temporal changes in the acceleration region of the wind. The line profiles show a multi-component absorption structure, and spectra from different epochs reveal changes of the line profiles (e.g., the emergence of a new absorption component) on time scales that are much longer than the period of the star (Sada 1993).

Diffraction-limited 76 mas speckle-masking interferometry of the carbon star IRC+10 216 and related AGB objects with the SAO 6 m telescope

We present high-resolution J-, H-, and K-band observations of the carbon star IRC+10216. The images were reconstructed from 6m telescope speckle interferograms using the speckle masking bispectrum method. The H image has the unprecedented resolution of 70 mas. The H and K images consist of at least five dominant components within a 0.21 arcsec radius and a fainter asymmetric nebula. The J-, H-, and K-band images seem to have an X-shaped bipolar structure. A comparison of our images from 1995, 1996, 1997, and 1998 shows that the separation of the two brightest components A and B increased from 193 mas in 1995 to 246 mas in 1998. The cometary shapes of component A in the H and J images and the 0.79 micron and 1.06 micron HST images suggest that the core of A is not the central star, but the southern (nearer) lobe of the bipolar structure. The position of the central star is probably at or near the position of component B, where the H-K color has its largest value of H-K = 4.2. If the star is located at or near B, then the components A, C, and D are located close to the inner boundary of the dust shell at separations of 200 mas = 30 AU (projected distance) = 6 stellar radii for a distance of 150 pc, in agreement with our 2-dimensional radiative transfer modelling. In addition to IRC+10216 we studied the stellar disks and the dust shells of several related objects. Angular resolutions of 24 mas at 700 nm or 57 mas at 1.6 micron were achieved.

Dynamical Modeling of Circumstellar Outflows

We review dynamical models of circumstellar dust shells around long-period variables which include time-dependent hydrodynamics and a detailed treatment of dust formation, growth and evaporation. Important effects caused by the complex interaction between the dynamics of the pulsating atmosphere and the dust complex which only can be revealed in the dynamical approach are summarized. Special emphasis is given to the treatment of the dust and gas opacity.

Infrared Appearance of Time-Dependent Models of Dust—Enshrouded Carbon-Mira Atmospheres

We present a consistent time-dependent model.1 for the circumstellar dust shell (CDS) around GL 3068 with a detailed treatment of hydrodynamics, thermodynamics, equilibrium chemistry, formation, growth and evaporation of carbon grains and radiative transfer. We consider a spherically symmetric atmosphere surrounding a pulsating red giant, characterized by mass M ⋆ effective temperature T ⋆ luminosity L ⋆ pulsation period P and the photospheric element abundances єi. To simulate the interior pulsation of the star, we apply a sinusoidal variation of the velocity with amplitude Δ u and period P at the inner boundary r i of the model. Thus, our models are defined by the prescription of the four fundamental stellar parameters (T ⋆ L ⋆ M ⋆ єi) and of (P Δ u) to describe the interior pulsation. Fleischer et al. (1992) give details of the hydrodynamical modelling and the basic equations. For the determination of the equilibrium temperature the radiative transfer problem is solved in grey approximation in the hydrodynamical calculation, which does not yield the spectral energy distribution, the lightcurves or the surface brightness profiles of the dust shell model. Therefore, in a second step, we solve the frequency-dependent stationary radiative transfer equation in spherical geometry for a given radial structure of the dust shell model i.e. at a fixed instant of time. Details of the radiative transfer calculation are described in Winters et al. (1994a,b)

Winds of Red Giants and Supergiants: Basic Physical Processes, Structure and Appearance

Red giants and supergiants usually exhibit three important phenomena: i) effective grain formation manifested by large infrared excesses, ii) considerable mass loss carried by slow, massive stellar winds, and iii) pronounced spectral variability induced by more or less regular stellar pulsations.

Brightness Profiles and Spatial Spectra of Dynamical Models for C-Rich Circumstellar Dust Shells Around Long-Period Variables

Based on dynamical models of circumstellar dust shells (CDS) around long-period variables (LPVs), which include time-dependent hydrodynamics and a detailed treatment of the processes of formation, growth and evaporation of carbon grains, angle- and frequency-dependent radiative transfer calculations have been carried out. The models are completely determined by 6 parameters, comprising the 4 fundamental stellar parameters (M * , T * , L * , ∈ i ) and the pulsation period and velocity amplitude at the base of the atmosphere (P, Aup). It turns out that these models result in a discrete onion-like structure of the CDS (cf. Fleischer et al. 1992) which decisively influences the shape of the synthetic lightcurves (Winters et al. 1994) as well as the calculated spatial intensity profiles and the corresponding spatial spectra (Winters et al. 1995).

Infrared Appearance of Dynamical Models for Circumstellar Dust Shells around Long–Period Variables

Synthetic brightness profiles resulting from consistent dynamical models for circumstellar dust shells around long-period variables are presented and discussed with respect to a corresponding observation of IRC +10216.