Of or pertaining to an → asymptote.
Fr.: liberté asymptotique
The phenomenon wherein the → quarks within a → hadron get closer together, the force of containment gets weaker so that it asymptotically approaches zero for close confinement. According to → quantum chromodynamics, the quarks in close confinement are completely free to move about. On the contrary, the further we try to force the quarks apart, the greater the force of containment. The 2004 Nobel Prize in Physics was awarded to David Gross, Frank Wilczek, and David Politzer for their discovery of asymptotic freedom. This discovery established quantum chromodynamics as the correct theory of the → strong interaction.
→ asymptotic; → freedom.
asymptotic giant branch (AGB)
šâxe-ye nâhamsâvi-ye qulân
Fr.: branche asymptotique des géantes
A region of the → Hertzsprung-Russell diagram populated by evolving → low-mass to → intermediate-mass stars. These stars have an electron → degenerate core of carbon and oxygen surrounded by two burning shells of helium and hydrogen. The H and He-burning shells are activated alternately in the deep layers of the star. An extended and tenuous convection envelope, having a radius of 104-105 times the size of the core, lies above these shells. The loosely bound envelope is gradually eroded by the strong → stellar wind, which forms a dusty → circumstellar envelope out to several hundreds of stellar radii. The convective envelope, stellar atmosphere, and circumstellar envelope have a rich and changing chemical composition provided by → nucleosynthesis processes in the burning shells in the deep interior.
Fr.: vitesse asymptotique
For → stellar winds, same as → terminal velocity.
→ asymptotic; → velocity.
post-asymptotic giant branch star (post-AGB)
setâre-ye pasâ-šâxe-ye qulân-e nâhamsâvi
Fr.: étoile post-asymptotique
A star in a short-lived evolutionary stage evolving from the → asymptotic giant branch toward higher → effective temperatures. The majority of low and intermediate mass stars (1 to 8 → solar masses) are believed to pass through this stage on their way to becoming → planetary nebulae.
→ post-; → asymptotic giant branch.