1) The process by which a system reaches → thermal equilibrium.
Thermalization results from energy exchange between the
components constituting the system and their exchange with the outside medium.
In a gas at a given temperature, molecules move with different velocities.
The gas temperature corresponds to the mean velocity of the molecules, but individual
molecules may deviate largely from the mean velocity. Some move very fast others
slowly and change velocity upon collisions. Collisions reduce the energy of
fast moving molecules and increase that of slow ones.
In the process of thermalization
→ matter and → radiation
are in constant interaction such that their → temperatures
The process goes on until energy distribution reaches
The system is said to be → thermalized.
Verbal noun of → thermalize.
Fr.: raie thermalisée
A collisionally excited spectral line formed in high density condition well above the → critical density. At such densities the → excitation temperature is at (or very near) the → kinetic temperature of the gas. At low densities, below the critical density, the excitation temperature will be only slightly above the radiation temperature and the emission line will be practically invisible.
very late thermal pulse (VLTP)
tape-ye garmâyi-ye besyâr dir
Fr.: flash de l'hélium très tardif
In evolutionary models of → post-asymptotic giant branch stars, the occurrence of the helium shell burning when the star has reached the → white dwarf cooling track. This leads to the possibility of a violent → helium shell flash and expansion on a time-scale of ≤ 10 years. The rapid expansion and prompt change in surface composition observed in → Sakurai's Object are thought to be due to such a very late thermal pulse.