Showing papers on "Stellar-wind bubble published in 1978"

The Interstellar Wind and its Influence on the Interplanetary Environment

Abstract: The existence of diffuse matter between the stars has been known for decades. How­ ever, only recently have we known of its presence in the immediate environs of the solar system. The discovery in 1970 of neutral interstellar gas pervading the solar system was a by-product of space exploration -specifically of the study of planetary atmospheres by ultraviolet photometry and spectroscopy. Because most of the work in this field was done by aeronomers using techniques borrowed from studies of the ultraviolet airglow, these new findings have not yet been widely disseminated in the astronomical community. However, studies of the interstellar medium have much to gain from these new results. To illustrate this point, wc considcr the hierarchy of sizes of neutral interstellar gas in numbers of parsecs ( 1 pc = 3 X 1018 cm): the galaxy ( 104), large interstellar clouds and spiral arms ( 102-103), small clouds (10°), intercloud eddies (10-2-10-1), and the mean free path ( 10-3-10-2). Radio­ astronomical techniques probe the largest scales ( 102-104), and absorption spectroscopy applies to smaller distances (101_103). In contrast, the ultraviolet back­ scattering of solar resonance lines from the local gas constitutes literally a micro­ scopic probe on a scale of 10-4 pc. It is as if a geologist were suddenly given the magnifying power to examine an individual atom of a rock sample, where before he was able to view only the individual grains. Unfortunately, we have only a single sample of the interstellar gas that we can study with such microscopic precision. Offsetting this disadvantage is the fact that for this "tiny" scale, the relevant laws of physics are simply those of single-particle motion (this is not true of the ionized component of the gas), and it is straightforward to infer the dynamical and chemical properties of the neutral gas. These properties can in turn be extrapolated to larger scales to infer the gas temperature and the chemical composition of at least the smallest irregularity in which the Sun is imbedded. This extrapolation is far safer

On the interaction between a strong stellar wind and a surrounding disk nebula

Abstract: The interaction between a strong stellar wind carrying no intrinsic angular momentum and a surrounding disk nebula is investigated. We analyze the shape and stability of the wind-nebula interface, the strength and direction of the ensuing mass motions and the time scales for nebular disruption. The resultant time scale is given by Equation (44). The dominant physical process is one of nebular accretion onto the central star due to turbulent viscosity in the disk. The turbulence will be driven in the upper layers of the disk by the wind. We note that if the accretion supplies mass for the wind (after the absorption of stellar energy), then the particle fluxes may undergo a runaway increase until the energy or momentum flux in the wind is limited by the total stellar luminosity. This may explain the origin of strong, pre-Main-Sequence winds.