Microturbulence
Encyclopedia
Microturbulence is a form of turbulence
that varies over small distance scales. (Large-scale turbulence is called macroturbulence.)
of the absorption lines in the stellar spectrum. Stellar microturbulence varies
with the effective temperature and the surface gravity.
The microturbulent velocity is defined as the microscale
non-thermal component of the gas velocity in the region of spectral
line formation.
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.
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.
.
Turbulence
In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...
that varies over small distance scales. (Large-scale turbulence is called macroturbulence.)
Stellar
Microturbulence is one of several mechanisms that can cause broadeningSpectral line
A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from a deficiency or excess of photons in a narrow frequency range, compared with the nearby frequencies.- Types of line spectra :...
of the absorption lines in the stellar spectrum. Stellar microturbulence varies
with the effective temperature and the surface gravity.
The microturbulent velocity is defined as the microscale
non-thermal component of the gas velocity in the region of spectral
line formation.
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.
The strength of the microturbulence (symbolized by ξ, in units of km s-1
Metre per second
Metre per second is an SI derived unit of both speed and velocity , defined by distance in metres divided by time in seconds....
) can be determined by comparing the broadening of strong lines versus weak lines.
Magnetic nuclear fusion
Microturbulence plays a critical role in energy transport during magnetic nuclear fusion experiments, such as the TokamakTokamak
A tokamak is a device using a magnetic field to confine a plasma in the shape of a torus . Achieving a stable plasma equilibrium requires magnetic field lines that move around the torus in a helical shape...
.