An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



Number of Results: 18
  نقطه‌ی ِ X   
noqte-te X

Fr.: point X   

A configuration of magnetic field lines around a → magnetic null point resembling a cross. See also → O-point.

X, the letter of alphabet whose shape evokes the configuration; → point.

  پرتو ِ ایکس   
partow-e iks (#)

Fr.: rayon X   

The → electromagnetic radiation with → wavelengths shorter than that of → ultraviolet radiation and greater than that of → gamma rays. Typical X-rays have a wavelength ranging from 0.1 to 100 Å (0.01 to 10 → nanometers), corresponding to frequencies in the range 3 × 1016 to 3 × 1019 Hz and energies in the range 100 eV to 100 → keV. X-rays are produced artificially when high-speed → electrons collide with a heavy metal target such as tungsten. Astrophysical sources of X-rays include → plasmas with → temperatures in the range 106-108 K, and deceleration process of rapidly moving charges upon interaction with matter (→ bremsstrahlung). X-rays were discovered in 1895 by Wilhelm Röntgen, a German physics professor (→ roentgen). For this discovery he won the first Nobel prize in physics in 1901. See also: → soft X-rays, → hard X-rays.

X stand for "unknown," since Röntgen was not sure what they were; → ray.

X-ray astronomy
  اخترشناسی ِ پرتوهای ِ ایکس   
axtaršenâsi-ye partowhâ-ye iks (#)

Fr.: astronomie en rayons X   

The study of celestial bodies using their X-ray emission. X-ray astronomy deals mainly with Galactic and extragalactic phenomena involving very high-energy photon emissions, covering a band of energies between 0.1 keV and 500 keV. The research field includes: → X-ray binaries, → cataclysmic variables, → pulsars, → black holes, → dark matter, → active galaxies, → galactic clusters → X-ray transients. The Earth's atmosphere absorbs most X-rays coming from outer space. X-ray astronomy therefore requires observations to be done above atmosphere. The first rocket flight which successfully detected a cosmic source of X-ray emission was launched in 1962 by an American research group. A very bright source was detected that they named → Scorpius X-1. Since then several dedicated X-ray astronomy satellites have been launched, among which: Uhuru, INTEGRAL, ROSAT, Rossi X-ray Timing Explorer (RXTE), → Chandra X-ray Observatory, and → XMM-Newton, which have contributed to important advances in astronomy.

X-ray; → astronomy.

X-ray background
  پس-زمینه‌ی ِ ایکس، زمینه‌ی ِ ~   
pas-zamine-ye iks, zamine-ye ~ (#)

Fr.: fond de rayons X   

A diffuse background radiation in X-ray wavelengths which has several origins. At very low energies it is due to hot gas in the → Local Bubble. In the → soft X-ray energy band it comes from active galaxies at moderate redshifts. In → hard X-ray range the background is thought to be due to integrated emission from many → quasars at various redshifts.

X-ray; → background.

X-ray binary
  دورین ِ پرتو ِ ایکس   
dorin-e partow-e iks

Fr.: binaire X   

A binary star system where one of the stars has evolved and collapsed into an extremely dense body such as a → white dwarf, a → neutron star, or a → black hole. The enormous gravitational attraction of the massive, dense, but dim component pulls material from the brighter, less massive star in an → accretion disk. The gravitational potential energy of the accreted matter is converted to heat by → viscosity and eventually to high-energy photons in the X-ray range. The brightest X-ray binary is → Scorpius X-1.

X-ray; → binary.

X-ray burst
  بلک ِ پرتو ِ ایکس   
belk-e partow-e iks

Fr.: sursaut de rayonnement X   

A rapid and intense surge of X-ray emission from some sources. They often last less than one second followed by an exponential decrease of typically a few seconds to a minute. Most X-ray bursts are believed to arise in → X-ray binary systems due to nuclear fusion of material accreted onto a compact companion.

X-ray; → burst.

X-ray diffraction
  پراش ِ پرتو ِ ایکس   
parâš-e partow-e iks

Fr.: diffraction de rayons X   

The diffraction of X-rays by the atoms or ions of a crystal. The wavelength of X-rays are comparable to the size of interatomic spacings in solids. Since the atoms in a crystal are arranged in a set of regular planes, crystals serve as three-dimensional diffraction gratings for X-rays. Planes of repetition within the atomic structure of the mineral diffract the X-rays. The pattern of diffraction thus obtained is therefore used to identify minerals by bombarding them with X-rays.

X-ray; → diffraction.

X-ray Dim Isolated Neutron Star (XDINS)
  ستاره‌ی ِ نوترونی با پرتوهای ِ ایکس ِ نزار   
setâre-ye notroni bâ partowhâ-ye X-e nazâr

Fr.: étoile à neutron de faibles rayons X   

A member of a class of isolated, radio-silent → pulsars with peculiar properties. They show a purely thermal spectrum at X-ray energies with no evidence for a high-energy, power-law component often detected in other → isolated neutron star classes. The X-ray luminosity is 1031 - 1032 erg s-1, fully consistent with surface blackbody emission with temperatures ~ 40-100 eV and (radiation) radii of a few kilometers, as derived from X-ray spectral fits. With the only exception of RX J1856.5-3754, broad absorption features have been found in all XDINSs. These features have energies ~ 300 - 700 eV, equivalent widths of ~ 50 - 150 eV and, as in the case of RX J0720.4-3125, may be variable.

X-ray; → dim; → isolated; → neutron; → star.

X-ray Dissociation Region (XDR)
  ناحیه‌ی ِ واهزش ِ پرتوهای ِ ایکس   
nâhiye-ye vâhazeš-e partowhâ-ye X

Fr.: région de dissociation par rayons X   

A region of → molecular clouds whose chemistry is affected by → X-rays from neighboring sources.

X-ray; → dissociation; → region.

X-ray persistent
  پرتو ِ X پریستنده   
partow-e X paristandé

Fr.: rayons X persistants   

An → X-ray source that does not display emission → outbursts, in contrast to → X-ray transients.

X-ray; → persistent.

X-ray pulsar
  پولسار ِ پرتوهای ِ ایکس، تپار ِ ~ ~   
pulsâr-e partowhâ-ye iks, tapâr-e ~ ~

Fr.: pulsar X   

A regularly variable X-ray source in which the pulsation is associated with the rotation of a magnetized neutron star in an → X-ray binary. Periods range from a few seconds to a few minutes. Examples include Hercules X-1, Centaurus X-3, Cygnus X-3.

X-ray; → pulsar.

X-ray source
  خن ِ پرتو ِ ایکس   
xan-e partow-e iks

Fr.: source de rayons X   

An astronomical object whose dominant mechanism of radiation is through X-ray emission. X-ray sources contain an extremely hot gas at temperatures from 106 to 108 K. They are generated by various physical processes involving high energies, such as accretion on to a compact object, shock waves from supernovae, stellar winds, hot gas in stellar coronae, or hot spaces between galaxies in a cluster. The first celestial X-ray source, after the Sun, to be detected was → Scorpius X-1 by means of rocket flight (Giacconi et al. 1962).

X-ray; → source.

X-ray spectrometer
  بیناب‌سنج ِ پرتو ِ ایکس   
binâb-sanj-e partow-e iks (#)

Fr.: spectromètre de rayons X   

An instrument for producing an X-ray spectrum and measuring the wavelengths of its components.

X-ray; → spectrometer.

X-ray telescope
  تلسکوپ ِ پرتو ِ ایکس، دوربین ِ ~ ~   
teleskop-e patow-e iks (#), durbin-e ~ ~

Fr.: télescope de rayons X   

A telescope designed to focus X-rays from astronomical objects. X-ray telescopes function from orbital satellites because X-rays are absorbed by the Earth's atmosphere. These telescopes require special techniques since the conventional methods used in optical and radio telescopes are not adequate. → grazing-incidence telescope; → Bragg angle.

X-ray; → telescope.

X-ray transient
  پرتو ِ X گذرا   
partow-e X gozarâ

Fr.: rayons X transitoire   

An → X-ray source that enhances its emission well above its usual level for a period typically longer than a week. Recurrences can be → periodic or → aperiodic, but there is no obvious correlation between recurrence time and the luminosity amplitude of the → outburst. X-ray transients seem to be divided into two classes: those associated with → high-mass X-ray binary (HMXB) stars and those associated with → low-mass X-ray binary (LMXB) stars. The HMXBs contain a → neutron star or → black hole paired with a → massive star. Often, the stellar companion is a → Be star, Be star, which sometimes sheds material from its equatorial region. In these systems, the transient event is characterized by having more higher energy X-rays in the spectrum. The LMXBs contain a neutron star or black hole orbiting around a cooler, → low-mass star. These transient events often generate more lower-energy X-rays.

X-ray; → transient.

X-wind model
  مدل ِ باد ِ X   
model-e bâd-e X

Fr.: modèle de vent X   

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.

gezenon (#)

Fr.: xénon   

A colorless, odorless, tasteless, chemically un-reactive gas, belonging to the → inert gas group, occurring in exceedingly minute amounts in the air; symbol Xe. → Atomic number 54; → atomic weight 131.29; → melting point -111.9°C; → boiling point -107.1°C. Xenon was discovered spectroscopically in 1898 by William Ramsay and M. W. Travers, who obtained it by fractional distillation of an impure sample of liquid → krypton. The lightest → isotopes of xenon (124Xe and 126Xe) are produced during → supernova explosions; intermediate-mass isotopes (127Xe, 128Xe, 129Xe, 130Xe, 131Xe and 132Xe) are produced during the → Asymptotic Giant Branch phase of evolved low- and intermediate-mass stars; the heaviest isotopes (134Xe and 136Xe) are produced during the → merger of → neutron stars.

From Gk. xenon, neuter of xenos "strange," introduced by the discoverers.

   XMM نیوتن   

Fr.: XMM-Newton   

A European Space Agency's satellite, launched on 10 December 1999 and designed for the observation of → X-rays emitted by astronomical objects. The satellite carries three very advanced X-ray telescopes. The three corresponding European Photon Imaging Cameras (EPIC) are sensitive over the energy range 0.2 keV to 12 keV. Other instruments on-board are two reflection grating spectrometers which are sensitive below about 2 keV, and a 30 cm diameter → Ritchey-Chretien optical/UV telescope. The telescope moves in a highly elliptical orbit, traveling out to nearly one third of the distance to the Moon and enabling long, uninterrupted observations of faint → X-ray sources. The original mission lifetime was two years, it has now been extended for further observations until at least 2010. Among recent results obtained using XMM-Newton one can mention an intermediate-mass black hole of over 500 solar masses in the galaxy ESO 243-49 (Nature 460, 73, 2009) and broad line emission from iron K- and L-shell transitions in the active galaxy 1H 0707-495 (Nature 459, 540, 2009). See also → X-ray astronomy.

XMM, from "X-ray Multi-Mirror;" Newton, in honor of Sir Isaac Newton, → newton.