An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 742
radiation-dominated Universe
  گیتی ِ تابش‌چیره   
giti-ye tâbeš-ciré

Fr.: Univers dominé par le rayonnement   

An early epoch in the history of the → Universe when the radiation → density parameter was Ωr≈ 1, while other density parameters had negligible contributions. A radiation-dominated Universe is characterized by R/R0 ∝ t1/2, where R is the → cosmic scale factor and t is time. According to the → Big Bang model, the radiation-dominated phase was followed by the → matter-dominated phase.

radiation; → dominate; → Universe.

radiation-driven implosion (RDI)
  فروکفت از راه ِ تابش   
forukaft az râh-e tâbeš

Fr.: implosion induit par rayonnement   

A hydrodynamic process occurring in star forming regions where a neutral cloud (→ clump) is subjected to the intense ultraviolet radiation of a newly-born → massive star. The gas within the layer exposed to the radiation is ionized and forms an → ionization front at the front surface. The increased pressure due to temperature rise at the top layer drives an → isothermal  → shock front into the clump, which compresses the neutral gas ahead of it, below the surface. A density → gradient builds up leading rapidly to the formation of a condensed core. With further concentration of the gas, the hydrogen density in the center of the core increases drastically, reaching 108 cm-3 about 4 x 105 years after the first impact of the ionizing radiation on the clump, according to current models (e.g. Bertoldi 1989, ApJ 346, 735; Miao et al. 2006, MNRAS 369, 143, and references therein). The core can develop further to form a → cometary globule or → collapse under its self-gravity, eventually giving rise to new → low-mass stars (→ triggered star formation). In the process, the whole clump accelerates away from the initial ionizing star. Indeed, the gas evaporated off the side of the clump facing the ionizing star can create a rocket effect accelerating the clump away from the star (with a velocity of up to 5 km s-1), while losing part of its initial mass.

radiation; driven, p.p. of → drive; → implosion.

radiation-driven mass loss
  دسترفت ِ جرم از راه ِ باد ِ تابشی   
dastraft-e jerm az râh-e bâd-e tâbeši

Fr.: perte de masse par vent radiatif   

The → mass loss experienced by a → massive star due to the effect of → radiation-driven wind.

radiation; driven, p.p. of → drive; → mass; → loss.

radiation-driven wind
  باد ِ تابشی، ~ تابش‌زاد   
bâd-e tâbeši, ~ tâbešzâd

Fr.: vent radiatif   

The loss of matter from the → photosphere due to the acceleration imparted to the outer layers of the star by photons created inside the star. The coupling between radiation and matter creates a → radiative acceleration that may exceed the → gravity. This mechanism is particularly important in → massive stars, since the luminosity is high and therefore the number of energetic ultraviolet photons important. Same as → line-driven wind.

radiation; → drive; → wind.

radiationless relaxation
  واهلش ِ بی‌تابش   
vâhaleš-e bitâbeš

Fr.: relaxation sans rayonnement   

A process in which a molecule relaxes without emitting a → photon.

radiation; → -less; → relaxation.

tâbešisi (#)

Fr.: radiatif   

Of or pertaining to radiation.

Adjective of → radiation.

radiative acceleration
  شتاب ِ تابشی   
šetâb-e tâbeši

Fr.: accélération radiative   

The acceleration imparted to matter by → radiation pressure.

radiative; → acceleration.

radiative braking
  لگامش ِ تابشی   
legâmeš-e tâbeši

Fr.: freinage radiatif   

The slowing down of a star's rotation due to radiative momentum transfer caused by emission of electromagnetic radiation.

radiative; → braking.

radiative capture
  گیراُفت ِ تابشی، گیر‌اندازی ِ ~   
gir-oft-e tâbeši, gir-andâzi-ye ~

Fr.: capture radiative   

Capture of a free electron by an ion with the subsequent emission of photons; also called → radiative recombination.

radiative; → capture.

radiative collision
  همکوبش ِ تابشی   
hamkubeš-e tâbeši

Fr.: collision radiative   

A collision between charged particles in which part of the kinetic energy is converted into electromagnetic radiation.

radiative; → collision.

radiative cooling
  سردش ِ تابشی   
serdeš-e tâbeši

Fr.: refroidissement radiatif   

The process by which temperature decreases due to an excess of emitted radiation over absorbed radiation.

radiative; → cooling.

radiative decay
  تباهی ِ تابشی   
tabâhi-ye tâbeši

Fr.: désexcitation radiative   

The process when the energy difference between the excited and non excited states of an atom is taken away by radiation.

radiative; → decay.

radiative diffusion
  پخش ِ تابشی   
paxš-e tâbeši

Fr.: diffusion radiative   

A process of → radiative transfer in which photons are repeatedly absorbed and re-emitted by matter particles.

radiative; → diffusion.

radiative envelope
  پوشه‌ی ِ تابشی   
puše-ye tâbeši

Fr.: envelope radiative   

A → radiative zone occupying the outer parts of a star.

radiative; → envelope.

radiative equilibrium
  ترازمندی ِ تابشی   
tarâzmandi-ye tâbeši

Fr.: équilibre radiatif   

The balance between radiative emission and radiative absorption in a specified system.

radiative; → equilibrium.

radiative feedback
  بازخورد ِ تابشی   
bâzxord-e tâbeši

Fr.: rétroaction radiative   

The radiative energy put back to the environment through an astrophysical process. For example, in the process of → star formation  → accretion disks form around → protostars. The material in the disk spirals inward and on to the protostar, provided that there is an efficient mechanism to redistribute → angular momentum outward in the disk. During this process → gravitational energy is transformed into radiation due to → viscous dissipation in the disk and at the → accretion shock around the protostar. This radiation heats the region around the protostar and may → suppress subsequent → fragmentation and further star formation. Thus, radiative feedback plays a critical role in regulating the stellar → initial mass function.

radiative; → feedback.

radiative flux
  شار ِ تابشی   
šârr-e tâbeši

Fr.: flux radiatif   

The radiative energy per unit time and unit area.

radiative; → flux.

radiative heating
  گرمش ِ تابشی   
garmeš-e tâbeši

Fr.: chauffage radiatif   

The process by which temperature increases due to an excess of absorbed radiation over emitted radiation.

radiative; → heating.

radiative levitation
  بالاشد ِ تابشی   
bâlâšod tâbeši

Fr.: lévitation radiative   

A physical process occurring in → stellar atmospheres whereby → radiation pressure selectively pushes certain → chemical elements outward, leading to an atmospheric overabundance of such elements. See also → gravitational settling.

radiative; → levitation.

radiative phase
  فاز ِ تابشی   
fâz-e tâbeši

Fr.: phase radiative   

For a → supernova remnant (SNR), same as the → snowplow phase.

radiative; → phase.

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