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| {{About|gas ejected from the atmosphere of stars}}
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| A '''stellar wind''' is a flow of neutral or charged gas ejected from the [[stellar atmosphere|upper atmosphere]] of a [[star]]. It is distinguished from the [[bipolar outflow]]s characteristic of young stars by being less [[collimated]], although stellar winds are not generally spherically symmetric.
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| Different [[stellar classification|types]] of stars have different types of stellar winds.
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| Post-[[main sequence|main-sequence]] [[star]]s nearing the ends of their lives often eject large quantities of mass in massive (<math> \scriptstyle \dot{M} > 10^{-3}</math> solar masses per year), slow (v = 10 km/s) winds. These include [[red giant]]s and [[Red supergiants|supergiants]], and [[asymptotic giant branch]] stars. These winds are likely to be driven by [[radiation pressure]] on [[Cosmic dust|dust]] condensing in the upper atmosphere of the stars.
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| Massive stars of [[stellar classification|types]] [[O star|O]] and [[B V star|B]] have stellar winds with lower mass loss rates (<math>\scriptstyle \dot{M} < 10^{-6}</math> solar masses per year) but very high velocities (v > 1–2000 km/s). Such winds are driven by radiation pressure on the resonance absorption lines of heavy elements such as carbon and nitrogen.<ref>{{cite journal| bibcode=1975ApJ...195..157C| last= Castor| first=J.| coauthors=Abbott, D. C., & [[Richard Klein (astronomer)|Klein, R. I.]]| title=Radiation-driven winds in Of stars| year=1975| journal=Astrophys. J.| volume=195| pages=157–174| doi=10.1086/153315}}</ref> These high-energy stellar winds blow [[stellar wind bubble]]s.
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| [[G-type main-sequence star|G-type stars]] like the [[Earth|Earth's]] [[Sun]], have a wind driven by their hot, magnetized [[corona]]. The Sun's wind is called the [[solar wind]]. These winds consist mostly of high-energy [[electrons]] and [[proton]]s (about 1 [[electron volt|keV]]) that are able to escape the star's [[gravity]] because of the high [[temperature]] of the [[corona]].
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| Stellar winds from [[main sequence|main-sequence]] [[star]]s do not strongly influence the evolution of lower mass stars such as the Sun. However, for more massive stars such as O stars, the mass loss can result in a star shedding as much as 50% of its mass whilst on the main sequence: this clearly has a significant impact on the later stages of evolution. The influence can even be seen for intermediate mass stars, which will become [[white dwarf]]s at the ends of their lives rather than exploding as [[supernova]]e only because they lost enough mass in their winds.
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| ==See also==
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| {{Portal|Space}}
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| * [[Solar wind]]
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| * [[Cosmic ray]]
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| ==References==
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| <references/> | |
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| {{Star}}
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| {{DEFAULTSORT:Stellar Wind}}
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| [[Category:Stellar astronomy]] | |
Revision as of 07:47, 25 February 2014
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