Fr.: pulsation non-radiale
A type of stellar pulsation in which waves run in different directions on and beneath the surface of a star.
The act of pulsating; beating or throbbing; vibration or undulation. → stellar pulsation.
Verbal noun of → pulse.
tarz-e tapeš, mod-e ~
Fr.: mode de pulsation
The way in which pulsations occur in a star due to the fact that stars act as resonant cavities, as studied in → asteroseismology. A star may pulsate either with approximately spherical symmetry (radial pulsation), or as a series of waves running across the surface (non-radial pulsation). Pulsation may occur in a single mode or in multiple modes, depending on the type of star. Three different modes of pulsations have been detected through the → helioseismology of the → Sun: → p mode, → g mode, and → f mode, generated by acoustic, gravity, and surface gravity waves respectively. Also called → oscillation mode.
Fr.: instabilitÃ© pulsationnelle
A term used to describe irregularly spaced, fine-scale structure in optically thick rings. The process relies on a combination of viscosity and self-gravity of ring material to produce this fine structure. Also known as overstability (Ellis et al., 2007, Planetary Ring Systems, Springer).
pulsational pair-instability supernova
abar-novâ-ye nâpâydâri-ye tapeši-ye joft, abar-now-axtar-e ~ ~ ~
Fr.: supernova à instabilité pulsationnelle de paires
A → supernova resulting from the → pair instability that generates several successive explosions. According to models, a first pulse ejects many solar masses of hydrogen layers as a shell. After the first explosion, the remaining core contracts and searches for a stable burning state. When the next explosion occurs a few years later, several solar masses of material are again ejected, which collide with the earlier ejecta. This collision can radiate 1050 erg of light, about a factor of ten more than an ordinary → core-collapse supernova. After each pulse, the remaining core contracts, radiates neutrinos and light, and searches again for a stable burning state. Later ejections have lower mass, but have higher energy. They quickly catch up with the first shell, where the collision dissipates most of their kinetic energy as radiation. The first SNe from → Population III stars are likely due to pulsational pair instability (Woosley et al. 2007, Nature 450, 390). See also → pair-instability supernova.
tapeš-e setâré, ~ setâre-yi
Fr.: pulsation stellaire
The expansion of a star followed by contraction so that its → surface temperature and → luminosity undergo periodic variation. Pulsation starts with a loss of → hydrostatic equilibrium, when, for example, a layer contracts. This layer heats up and becomes more opaque to radiation. Therefore, radiative diffusion slows down through the layer because of its increased → opacity and heat increases beneath it. Hence pressure rises below the layer. Eventually this increase in pressure starts to push the layer out. The layer expands, cools and becomes more transparent to radiation. Energy now escapes from below the layer and the pressure beneath the layer drops. The layer falls inward and the cycle starts over. See also → kappa mechanism; → gamma mechanism; → partial ionization zone; → pulsating star; → valve mechanism.