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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.[1] Stellar microturbulence varies with the effective temperature and the surface gravity.[2]

The microturbulent velocity is defined as the microscale non-thermal component of the gas velocity in the region of spectral line formation.[3] 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.[4] 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.[5]
Magnetic nuclear fusion

Microturbulence plays a critical role in energy transport during magnetic nuclear fusion experiments, such as the Tokamak.[6]
References

De Jager, C. (1954). "High-energy Microturbulence in the Solar Photosphere". Nature. 173 (4406): 680–1. Bibcode:1954Natur.173..680D. doi:10.1038/173680b0.
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.
Cantiello, M. et al. (2008). "On the origin of Microturbulence in hot stars" (PDF).
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.
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.

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.

External links

Landstreet, J. D. (August 21–25, 2006). "Observing Atmospheric Convection in Stars". Symposium no. 239 – Convection in Astrophysics. Prague, Czech Republic: International Astronomical Union. Bibcode:2006IAUS..239E...7L.

vte

Stars
Formation

Accretion Molecular cloud Bok globule Young stellar object
Protostar Pre-main-sequence Herbig Ae/Be T Tauri FU Orionis Herbig–Haro object Hayashi track Henyey track

Evolution

Main sequence Red-giant branch Horizontal branch
Red clump Asymptotic giant branch
super-AGB Blue loop Protoplanetary nebula Planetary nebula PG1159 Dredge-up OH/IR Instability strip Luminous blue variable Blue straggler Stellar population Supernova Superluminous supernova / Hypernova

Spectral classification

Early Late Main sequence
O B A F G K M Brown dwarf WR OB Subdwarf
O B Subgiant Giant
Blue Red Yellow Bright giant Supergiant
Blue Red Yellow Hypergiant
Yellow Carbon
S CN CH White dwarf Chemically peculiar
Am Ap/Bp HgMn Helium-weak Barium Extreme helium Lambda Boötis Lead Technetium Be
Shell B[e]

Remnants

White dwarf
Helium planet Black dwarf Neutron
Radio-quiet Pulsar
Binary X-ray Magnetar Stellar black hole X-ray binary
Burster

Hypothetical

Blue dwarf Green Black dwarf Exotic
Boson Electroweak Strange Preon Planck Dark Dark-energy Quark Q Black Gravastar Frozen Quasi-star Thorne–Żytkow object Iron Blitzar

Stellar nucleosynthesis

Deuterium burning Lithium burning Proton–proton chain CNO cycle Helium flash Triple-alpha process Alpha process Carbon burning Neon burning Oxygen burning Silicon burning S-process R-process Fusor Nova
Symbiotic Remnant Luminous red nova

Structure

Core Convection zone
Microturbulence Oscillations Radiation zone Atmosphere
Photosphere Starspot Chromosphere Stellar corona Stellar wind
Bubble Bipolar outflow Accretion disk Asteroseismology
Helioseismology Eddington luminosity Kelvin–Helmholtz mechanism

Properties

Designation Dynamics Effective temperature Luminosity Kinematics Magnetic field Absolute magnitude Mass Metallicity Rotation Starlight Variable Photometric system Color index Hertzsprung–Russell diagram Color–color diagram

Star systems

Binary
Contact Common envelope Eclipsing Symbiotic Multiple Cluster
Open Globular Super Planetary system

Earth-centric
observations

Sun
Solar System Sunlight Pole star Circumpolar Constellation Asterism Magnitude
Apparent Extinction Photographic Radial velocity Proper motion Parallax Photometric-standard

Lists

Proper names
Arabic Chinese Extremes Most massive Highest temperature Lowest temperature Largest volume Smallest volume Brightest
Historical Most luminous Nearest
Nearest bright With exoplanets Brown dwarfs White dwarfs Milky Way novae Supernovae
Candidates Remnants Planetary nebulae Timeline of stellar astronomy

Related articles

Substellar object
Brown dwarf Sub-brown dwarf Planet Galactic year Galaxy Guest Gravity Intergalactic Planet-hosting stars Tidal disruption event

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