Chemical Sciences: A Manual for CSIR-UGC National Eligibility Test for Lectureship and JRF/Microturbulence

Microturbulence is a form of turbulence that varies over small distance scales. (Large-scale turbulence is called macroturbulence.) Stellar Microturbulence is one of several mechanisms that can cause broadening of the absorption lines in the stellar spectrum.De Jager C. High-energy Microturbulence in the Solar Photosphere Nature 1954 173 680–1 http://www.nature.com/nature/journal/v173/n4406/abs/173680b0.html 2007-05-21 10.1038/173680b0 Stellar microturbulence varies with the effective temperature and the surface gravity.Montalban, J.; Nendwich, J.; Heiter, U.; Kupka, F.; Paunzen, E.; Smalley, B. The Effect of the microturbulence parameter on the Color-Magnitude Diagram Reports on Progress in Physics 1999 61 77–115 http://adsabs.harvard.edu/abs/1998RPPh...61...77K 2007-05-21 10.1088/0034-4885/61/2/001 The microturbulent velocity is defined as the microscale non-thermal component of the gas velocity in the region of spectral line formation.Cantiello M. et al. (2008) On the origin of Microturbulence in hot stars http://www.astro.uu.nl/~cantiell/articles/liege1.pdf 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 spectroscope, the velocity of the convective gas along the line of sight produces Doppler shifts 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.Cantiello M. et al. (2009) Sub-surface convection zones in hot massive stars and their observable consequences http://adsabs.harvard.edu/abs/2009arXiv0903.2049C 10.1051/0004-6361/200911643 2009 Langer N. Brott I. De Koter A. Shore S. N. Vink J. S. Voegler A. Lennon D. J. Yoon S.-C. Astronomy and Astrophysics 499 279 The strength of the microturbulence (symbolized by ξ, in units of km s-1) can be determined by comparing the broadening of strong lines versus weak lines.Briley Michael July 13, 2006 http://www.phys.uwosh.edu/mike/exercises/lines/lines.html Stellar Properties from Spectral Lines: Introduction University of Wisconsin 2007-05-21 Magnetic nuclear fusion Microturbulence plays a critical role in energy transport during magnetic nuclear fusion experiments, such as the Tokamak.W.M. Nevins August 21, 2006 http://www.scidac.gov/FES/FES_PMP/reports/PMP2004Annual.html The Plasma Microturbulence Project Lawrence Livermore National Laboratory 2007-05-21 References