Editing Stellar wind (section)

{{Short description|Flow of gas ejected from the upper atmosphere of a star}}
{{About|gas ejected from the atmosphere of stars}}
[[File:52706main hstorion lg.jpg|thumb|upright=1.2|This image shows the wind from the star LL Orionis generating a [[bow shock]] (the bright arc) as it collides with material in the surrounding [[Orion Nebula]].]]
A '''stellar wind''' is a flow of 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.

Different [[stellar classification|types]] of stars have different types of stellar winds.

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&nbsp;km/s) winds. These include [[red giant]]s and [[Red supergiant|supergiants]], and [[asymptotic giant branch]] stars. These winds are understood to be driven by [[radiation pressure]] on [[Cosmic dust|dust]] condensing in the upper atmosphere of the stars.<ref>{{Cite book |author=Lamers, Henny J. G. L. M. |title=Introduction to stellar winds |date=1999 |publisher=Cambridge University Press |others=Cassinelli, Joseph P. |isbn=0521593980 |location=Cambridge, England |oclc=38738913}}</ref><ref>{{cite web|title=Dust Envelopes|url=http://www.aip.de/groups/sternphysik/stp/dust-env_neu.html|work=Stellar Physics|publisher=Astrophysical Institute Potsdam|access-date=7 April 2014|archive-date=1 October 2016|archive-url=https://web.archive.org/web/20161001214442/http://www.aip.de/groups/sternphysik/stp/dust-env_neu.html|url-status=dead}}</ref><ref>{{Cite journal|last1=Mattsson|first1=L.|last2=Wahlin|first2=R.|last3=Höfner|first3=S.|date=January 2010|title=Dust driven mass loss from carbon stars as a function of stellar parameters|journal=Astronomy and Astrophysics|language=en|volume=509|pages=A14|doi=10.1051/0004-6361/200912084|issn=0004-6361|arxiv=1107.1771|s2cid=17360256}}</ref><ref>{{Cite journal|last1=Höfner|first1=S.|last2=Gautschy–Loidl|first2=R.|last3=Aringer|first3=B.|last4=Jørgensen|first4=U. G.|date=February 2003|title=Dynamic model atmospheres of AGB stars|journal=Astronomy & Astrophysics|language=en|volume=399|issue=2|pages=589–601|doi=10.1051/0004-6361:20021757|issn=0004-6361|doi-access=free}}</ref><ref>{{Cite journal|last1=Sandin|first1=C.|last2=Höfner|first2=S.|date=June 2003|title=Three-component modeling of C-rich AGB star winds|journal=Astronomy & Astrophysics|language=en|volume=404|issue=3|pages=789–807|doi=10.1051/0004-6361:20030515 |arxiv=astro-ph/0304278|issn=0004-6361|doi-access=free}}</ref><ref>{{Cite journal|last1=Sandin|first1=C.|last2=Höfner|first2=S.|date=January 2004|title=Three-component modeling of C-rich AGB star winds|journal=Astronomy & Astrophysics|language=en|volume=413|issue=3|pages=789–798|doi=10.1051/0004-6361:20031530|issn=0004-6361|arxiv=astro-ph/0309822|s2cid=15641925}}</ref>

Young [[T Tauri star]]s often have very powerful stellar winds.{{citation needed|date=August 2020}}

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&nbsp;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| last1=Castor| first1=J.| last2=Abbott|first2=D. C. | last3=Klein|first3=R. I. | author-link3=Richard Klein (astronomer) | title=Radiation-driven winds in Of stars| date=1975| journal=Astrophys. J.| volume=195| pages=157–174| doi=10.1086/153315}}</ref> These high-energy stellar winds blow [[stellar wind bubble]]s.

[[File:The long goodbye.jpg|thumb|upright=1.2|In [[planetary nebula]] [[NGC 6565]], a cloud of gas was ejected from the star after strong stellar winds.<ref>{{cite web|title=The long goodbye|url=http://www.spacetelescope.org/images/potw1530a/|access-date=27 July 2015}}</ref>]]

[[G-type main-sequence star|G-type stars]] like the [[Sun]] have a wind driven by their hot, magnetized [[stellar corona|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 [[stellar corona|corona]].

Stellar winds from main-sequence stars 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.{{citation needed|date=August 2020}}