Models of Winds from Late Type Stars: the Stability of Dust-Driven Winds and the Hydrodynamics of Dusty Winds in Binary Systems

Details Models of Winds from Late Type Stars: the Stability of Dust-Driven Winds and the Hydrodynamics of Dusty Winds in Binary Systems Models of Winds from Late Type Stars: the Stability of Dust-Driven Winds and the Hydrodynamics of Dusty Winds in Binary Systems

Aug 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998phdt.........9m&link_type=abstract

Thesis (PHD). UNIVERSITY OF CALIFORNIA, LOS ANGELES , Source DAI-B 59/02, p. 694, Aug 1998, 295 pages.

Mathematics

Logic

2

Circumstellar Envelopes, Red Giants, Wind Accretion

Scientific paper

In this thesis we investigate two distinct problems that arise in the general context of mass loss in late stages of stellar evolution. We have numerically investigated the dynamical effects of dust drifting on the detailed structure of winds from late-type, pulsating variables. We examine the stability of dust-gas coupling in the presence of luminosity variations, by constructing two-fluid time-dependent wind models. At large distances from the star dust streaming and gas-dust viscous heating smooth out the wind. The outer parts of circumstellar envelopes are not subject to growing instabilities. Mass-losing giant stars and objects in transition to planetary nebulae often display a bipolar symmetry in their outflowing circumstellar envelopes. In the second part of the thesis we initiate a detailed study of the hypothesis that the observational characteristics of asymmetric and bipolar preplanetary nebulae result from the effects of a detached binary companion upon the otherwise spherical wind of a single mass-losing star. We follow the gas flows in this system using 3-dimensional smoothed particle hydrodynamics models. We investigate the formation of accretion disks about the binary companion of the mass-losing star and the morphology of the extended circumstellar envelope as a function of wind velocity, binary separation and mass of secondary. We find that permanent accretion disks of various sizes form around the binary companion. The disks are geometrically thin and their equilibrium structure has elliptical streamlines with a range of eccentricities. Our results also indicate that such disks may be susceptible to tilt or warping instabilities. The mass accretion rates computed are lower than the predicted ones from Bondi-Hoyle theory. Over large scales the wind exhibits a broad range of density contrasts. The morphologies found are classified in the categories of bipolar, for large density contrasts, elliptical for intermediate ones and quasi-spherical. The last category represents a hitherto unknown type of hydrodynamic solution, forming a helical shock which covers most of the solid angle around the binary, with observational implications that we discuss. The quasi-spherical type is the most common morphological type in parameter space. From current binary statistics data, we estimate that approximately 40% of binaries will give rise to bipolar planetary nebulae.

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