Microturbulence

<h2 id="stellar">Stellar</h2>
<p>Microturbulence is one of several mechanisms that can cause <a href="/facts/Spectral_line/HuI4Bj5f">broadening</a> of the <a href="/facts/Absorption_line/HuI4Bj5f">absorption lines</a> in the stellar spectrum.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> Stellar microturbulence varies
with the effective temperature and the surface gravity.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a>
</p><p>The microturbulent velocity is defined as the microscale
non-thermal component of the gas velocity in the region of spectral
line formation.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>
Convection is the mechanism believed to be responsible for the observed turbulent velocity field, both in low mass stars and massive stars.
When examined by a <a href="/facts/Spectroscope/BjshQbA8">spectroscope</a>, the velocity of the convective gas along the line of sight produces <a href="/facts/Doppler_shift/bzrK1BKf">Doppler shifts</a> in the absorption bands. It is the distribution of these velocities along the line of sight that produces the microturbulence broadening of the absorption lines in low mass stars that have convective envelopes. In massive stars convection can be present only in small regions below the surface; these sub-surface convection zones can excite turbulence at the stellar surface through the emission of acoustic and gravity waves.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a>
The strength of the microturbulence (symbolized by <a href="/facts/Xi_(letter)/q66nzcM5">ξ</a>, in units of <a href="/facts/Metre_per_second/hSEkho3J">km s−1</a>) can be determined by comparing the broadening of strong lines versus weak lines.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a>
</p>
<h2 id="magnetic-nuclear-fusion">Magnetic nuclear fusion</h2>
<p>Microturbulence plays a critical role in energy transport during magnetic nuclear fusion experiments, such as the <a href="/facts/Tokamak/kDtb8Bsw">Tokamak</a>.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a>
</p>

<h2 id="external-links">External links</h2>
<ul><li>Landstreet, J. D. (August 21–25, 2006). "Observing Atmospheric Convection in Stars". <i>Symposium no. 239 – Convection in Astrophysics</i>. Prague, Czech Republic: <a href="/facts/International_Astronomical_Union/GMFPImXo">International Astronomical Union</a>. <a href="/facts/Bibcode_(identifier)/9HtdQSGB">Bibcode</a>:<a href="https://ui.adsabs.harvard.edu/abs/2006IAUS..239E...7L">2006IAUS..239E...7L</a>.</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>De Jager, C. (1954). "High-energy Microturbulence in the Solar Photosphere". Nature. 173 (4406): 680–1. Bibcode:1954Natur.173..680D. doi:10.1038/173680b0. S2CID 4188420. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Montalban, J.; Nendwich, J.; Heiter, U.; Kupka, F.; et al. (1999). "The Effect of the microturbulence parameter on the Color-Magnitude Diagram". Reports on Progress in Physics. 61 (S239): 77–115. Bibcode:2007IAUS..239..166M. doi:10.1017/S1743921307000361. <a href="https://doi.org/10.1017%2FS1743921307000361" target="_blank">https://doi.org/10.1017%2FS1743921307000361</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Cantiello, M. et al. (2008) (15 February 2024). "On the origin of Microturbulence in hot stars" (PDF). {{cite journal}}: Cite journal requires |journal= (help)CS1 maint: numeric names: authors list (link) <a href="http://www.astro.uu.nl/~cantiell/articles/liege1.pdf" target="_blank">http://www.astro.uu.nl/~cantiell/articles/liege1.pdf</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>Cantiello, M. et al. (2009); Langer, N.; Brott, I.; De Koter, A.; Shore, S. N.; Vink, J. S.; Voegler, A.; Lennon, D. J.; Yoon, S.-C. (2009). "Sub-surface convection zones in hot massive stars and their observable consequences". Astronomy and Astrophysics. 499 (1): 279. arXiv:0903.2049. Bibcode:2009A&A...499..279C. doi:10.1051/0004-6361/200911643. S2CID 55396719.{{cite journal}}:  CS1 maint: numeric names: authors list (link) <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>Briley, Michael (July 13, 2006). "Stellar Properties from Spectral Lines: Introduction". University of Wisconsin. Archived from the original on November 23, 2007. Retrieved 2007-05-21. <a href="https://web.archive.org/web/20071123121917/http://www.phys.uwosh.edu/mike/exercises/lines/lines.html" target="_blank">https://web.archive.org/web/20071123121917/http://www.phys.uwosh.edu/mike/exercises/lines/lines.html</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>Nevins, W.M. (August 21, 2006). "The Plasma Microturbulence Project". Lawrence Livermore National Laboratory. Archived from the original on July 20, 2011. Retrieved 2007-05-21. <a href="https://web.archive.org/web/20110720152817/http://www.scidac.gov/FES/FES_PMP/reports/PMP2004Annual.html" target="_blank">https://web.archive.org/web/20110720152817/http://www.scidac.gov/FES/FES_PMP/reports/PMP2004Annual.html</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
</ol>

Microturbulence open-in-new

Microturbulence