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

The speed at which the → stellar wind is forced away from the star. Wind velocities of → hot stars are directly measured from → P Cygni profiles, which indicate velocities from several hundred to several thousand km s^-1. See also → escape velocity, → terminal velocity, → velocity law, → radiation-driven wind, → CAK model.

→ wind; → velocity.

The problem encountered in the explanation of the → spiral arms of galaxies if the material making up a spiral arm is static, that is remains in the arm. Since galaxies exhibit → differential rotation, stars near the center take less time to orbit the center than those farther from the center. The arm would, after a few → galactic rotations, become increasingly curved and wind around the → galaxy ever tighter until it ultimately disappears. This is inconsistent with observations.

1) Anything likened to a window in appearance or function.
2) In particular, the wavelength region in the electromagnetic spectrum that is relatively unaffected by atmospheric absorption. → atmospheric windows; → infrared window; → optical window; → radio window.

Window literally "wind eye," from O.N. vindauga, from vindr, → wind, + auga, → eye.

Rowzané, from rowzan "window, aperture;" Mid.Pers. rocânak "window," rôšn "light; bright, luminous," from Av. raocana- "bright, shining, radiant," raocah- "light, luminous; daylight," related to Mod.Pers. ruz "day," from Mid.Pers. rôc, O.Pers. raucah-; akin to Skt. rocaná- "bright, shining," roka- "brightness, light;" Gk. leukos "white, clear;" L. lux "light" (also lumen, luna); PIE base *leuk- "light, brightness." The Persian words rowšan "bright, clear," foruq "light," and afruxtan "to light, kindle" also belong to this family, as well as the E. light, Ger. Licht, and Fr. lumière; forusorx→ infrarouge.

A function whose value is zero outside a given interval. Applications of window functions include signal filtering and spectral analysis. The various types of windw functions include: → rectangular window, cosine window, triangular window, Gaussian window, Hanning window, and so on.

→ window; → function.

A → magnetocentrifugal model for → accretion and → outflow in → protostars, which considers the interaction between the → magnetosphere of a → young stellar object and an & rarr; accretion disk. The model assumes that the → magnetic field originates from the protostar, and the outflow is driven from a small region near the inner edge of the disk, called X, where the inner disk corotates with the star (→ corotation radius). The accretion disk is → truncated in its central region, that is the disk does not extend to the protostar. The matter spiraling toward the protostar is either funneled by the magnetic field connecting the star to the disk, or blown outward under the effect of → centrifugal force. The X-wind model is able to account for many observations in one fairly self-consistent model. The observations include time variable accretion/wind phenomena in → T Tauri stars, the slow rotation rates of T Tauri stars, protostellar X-ray activity, and a number of the properties of → bipolar jets and → molecular outflows (F. H. Shu et al., 2000, in Protostars and Planets IV, V. Mannings et al. (eds.), Tucson: Univ. Arizona Press, 789).

X, referring to a configuration of the magnetic field where the lines of force intersect with an "X" shape; → wind; → model.