An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

The → mechanism that imparts or transfers power to a → telescope so that it can move along the → right ascension direction. See also → tacking.

→ alpha, → right ascension; → drive.

The transfer of photon momentum to free electrons. The acceleration by → continuum emission can be given by: a_c = (σ/m)(L_*/4πR²c), where σ is the → Thomson scattering  → cross section, m is the mass per free electron, L_* is → stellar luminosity, R_* is radius, and c the → speed of light. The ratio of a_c to the → surface gravity is ≅ 2 × 10^-5L_*/M_*, with M_* and L_* in solar units. The atmosphere is is stable if a_c very smaller than g_grav. If L_* is above the → Eddington limit, the radiation pressure in the continuum leads to very heavy → mass loss and thus to expanding envelopes (K.S. de Boer & W. Seggewiss, 2008, Stars and Stellar Evolution, EDP Sciences).

→ continuum; → drive; → wind.

The → mechanism that imparts or transfers power to a → telescope so that it can move along the → declination direction. See also → tracking.

→ delta; → drive.

1a) To cause to move, to force to act. → continuum-driven wind, → dust-driven wind, → line-driven wind, → radiation-driven implosion, → radiation-driven mass loss, → radiation-driven wind.
1b) To cause and → guide the → motion of a → telescope.
2a) The act of driving.
2b) The → mechanism that imparts or transfers → power to a telescope so that it can move. → alpha drive, → delta drive, → drive accuracy, → slewing drive .

M.E. driven; O.E. drifan; cf. O.N. drifa, Goth. dreiban.

Rândan "to cause to go," causative of raftan "to go, walk, proceed" (present tense stem row-, Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- "to go; to attack").

The accuracy with which a telescope is moved by alpha or delta drives.

→ drive; → accuracy.

A → stellar wind generated by the action of → radiation pressure on dust grains. This occurs in the case of cool stars, such as → AGB stars, with → effective temperatures below 2500 K when the density is sufficiently large. Since dust is a very good continuum absorber, the dust grains will be radiatively accelerated outward.

→ dust; → drive; → wind.

Same as → radiation-driven wind.

→ line; → drive; → wind.

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.

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

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

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.

Same as → radiation-driven wind

→ radiative; → drive; → wind.

A motor designed to drive a high-speed radar antenna for slewing to monitor a target.

→ slewing; → drive