Three Dimensional Radiative Transfer in Winds of Massive Stars: Wind3D

Source: arXiv


We discuss the development of the new radiative transfer code Wind3D. It solves the non-LTE radiative transport problem in moving stellar atmosphere models in three geometric dimensions. The code accepts arbitrary 3D velocity fields in Cartesian geometry without assumptions of axial symmetry. Wind3D is currently implemented as a fully parallelized (exact) accelerated lambda iteration scheme with a two level atom formulation. The numerical transfer scheme is efficient and very accurate to trace small variations of local velocity gradients on line opacity in strongly scattering dominated extended stellar winds. We investigate the detailed formation of P Cygni line profiles observed in ultraviolet spectra of massive stars. We compute the detailed shape of these resonance lines to model local enhancements of line opacity that can for instance be caused by clumping in supersonically expanding winds. Wind3D will be applied to hydrodynamic models to investigate physical properties of discrete absorption line components.

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    ABSTRACT: Fourier analysis of two spectroscopic time series obtained with the IUE observatory confirm that the ultraviolet stellar wind profiles of HD 64760 (B0.5 Ib) are periodically variable. The periodic component consists of modulations that extend over most of the P Cygni absorption trough, and can frequently be traced through the emission lobe. The modulations coexist with variations due to the propagation of discrete absorption components, but there does not seem to be a direct link between these two types of variability. In a long time series obtained in 1995 January during the IUE MEGA Campaign, the modulations in the P Cygni profiles of the Si III, Si IV, C IV, and N V resonance lines were dominated by two sinusoidal variations with semi-amplitudes between ~5-10% of the continuum flux and periods of 1.202+/-0.004 and 2.44+/-0.04days. The weak emission-lobe variability was predominantly due to the 2.4-day modulation. In the absorption trough, the ratio of the amplitude of the 1.2-day modulation to the amplitude of the 2.4-day modulation increased systematically as a function of ionization potential. For both periods, the distribution of the phase constant with position in the absorption trough exhibited a maximum near -710km/s, and decreased symmetrically toward larger and smaller velocities. There was a systematic decrease in the value of the maximum phase between Si IV and N V. Only the 2.4-day period was present in a shorter time series obtained in 1993 March, when its amplitude was nearly twice its 1995 value and it was more concentrated toward smaller velocities in the absorption trough. There is no clear evidence for phase bowing in the 1993 data. Since the 2.4- and 1.2-day periods are approximately a half and a quarter of the estimated rotational period of HD 64760, respectively, we interpret the modulations in terms of 2 (1993) and 4 (1995) broad, corotating circumstellar structures that modulate the optical depth of the stellar wind. The bowed distribution of phase implies that the structures are azimuthally extended, probably spiral-shaped arms, and we develop a kinematic interpretation of the projected velocity associated with the phase turnover in terms of the degree of bending of the spirals. We derive a value for the exponent governing the radial expansion of the wind of β=~1, which is in good agreement with the canonical value for smooth, spherically symmetric winds and suggests that the spiral structures are long-lived perturbations through which material flows. The systematic phase lag associated with higher ions suggests that they are preferentially located along the inner, trailing edge of the spiral, as expected if the structures are formed by the collision of fast and slow winds originating from equally-spaced longitudinal sectors of the stellar surface. Although a photospheric process is implicated in the origin of these structures, it is not clear that magnetic fields or nonradial pulsations could readily account for the switch between 2- and 4-equally spaced surface patches that evidently occurred between 1993 and 1995.
    Astronomy and Astrophysics 10/1997; 327:699-720. · 4.38 Impact Factor
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    ABSTRACT: A finite volume method is applied to the three-dimensional radiative line transfer in accretion disks. The two-level-atom approximation with complete redistribution is used. It is assumed that the disks are homogeneous in temperature and pressure. Monochromatic images of the intensity distribution on the surface of disks are given for several assumptions on the scattering and the disk thickness. In the LTE case, earlier results are confirmed. However, for scattering conditions a rather different intensity pattern is obtained. In a parameter study for geometrically thin and thick disks, obtain in a variety of line profile shapes is obtained.
    Astronomy and Astrophysics 11/1990; 240:541-550. · 4.38 Impact Factor
  • Line Formation in Accretion Disks The UV Universe: Stars from birth to death 6 rLobel & Blomme Wind3D. .

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