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

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 1042
photoionization
  شید-یونش، نور-یونش   
šid-yoneš, nur-yoneš

Fr.: photoionisation   

The physical process in which an incident high-energy photon ejects one or more electrons from an atom, ion, or molecule.

photo- + → ionization.

photoionize
  شید-یونیدن، نور-یونیدن   
šid-yonidan, nur-yonidan

Fr.: photoioniser   

To cause, or to undergo → photoionization.

photo-; → ionize.

photoionized
  شید-یونیده، نور-یونیده   
šid-yonidé, nur-yonidé

Fr.: photoionisé   

Subject to, or produced by → photoionization.

photo-; → ionized.

photoluminescence
  شید-فروزستی   
šid-foruzesti

Fr.: photoluminescence   

A process in which → absorption of photons at → ultraviolet (UV) / → optical wavelengths is followed by → electronic transitions associated with the emission of longer wavelength optical and → near-IR photons. Photoluminescence has two types: → phosphorescence and → luminescence. The excitation of the photoluminescence process under astrophysical conditions results from the absorption of a single UV/optical photon, leading to an electronic transition from a → ground state (1) to a higher state (2). State (2) typically is a bound, high-lying vibrational-rotational level of the first or second electronically excited state of a molecule or molecular ion, or a high state in the → conduction band of a semiconductor particle. The excited system relaxes through a series of → vibrational-rotational transitions until the electron finds itself in an intermediate state (3), from where an optical electronic transition back to the ground state (1) is possible. In a → polycyclic aromatic hydrocarbon (PAH) molecule, for example, state (3) can either be the lowest state in the → singlet or → triplet vibrational-rotational manifold of the first excited electronic level (Witt, A. N., Vijh, U. P., 2003, astro-ph/0309674).

photo-; → luminescence.

photometer
  شید-سنج، نور-سنج   
šidsanj, nursanj

Fr.: photomètre   

An instrument for measuring the amount of light.

photo- + → -metry.

photometric
  شید-سنجی، شید-سنجیک، نور-سنجی، نور-سنجیک   
šidsanji, šidsanjik, nursanji, nursanjik

Fr.: photométrique   

Pertaining to or related to → photometry.

photometer + → -ic.

photometric band
  باند ِ شیدسنجیک، ~ نورسنجیک   
bând-e šid-sanjik, ~ nur-sanjik

Fr.: bande photométrique   

The range of → wavelengths allowed by a → filter used in a → photometric system.

photometric + → band.

photometric binary
  دُرین ِ شید-سنجیک، ~ نور-سنجیک   
dorin-e šidsanjik, ~ nursanjik

Fr.: binaire photométrique   

A binary star whose binarity is detectable from its variability and light-curve that has certain specific characteristics.

photometric + → binary.

photometric calibration
  کبیزش ِ شید-سنجیک، ~ سنور-سنجیک   
kabizeš-e šidsanjik, ~ nursanjik

Fr.: calibration photométrique   

A calibration which converts the measured relative magnitudes into an absolute photometry.

photometric + → calibration.

photometric parallax
  دیدگشت ِ شیدسنجیک   
didgašt-e šidsanjik

Fr.: parallaxe photométrique   

A method of deriving the distance of a star using its → apparent magnitude and the → absolute magnitude inferred from its → spectral type.

This is a misnomer, because the method has nothing to do with parallax; → photometric; → parallax.

photometric system
  راژمان ِ شید-سنجیک، ~ نور-سنجیک   
râžmân-e šidsanjik, ~ nursanjik

Fr.: système photométrique   

A system of → magnitudes, each of them characterized by a set of well-defined → passbands (or → filters) with known → response curves. The system is defined by the values given for the → standard stars. See also:
AB magnitude system, → five-color system, → Stromgren system, → JHK system, → UBV system, → uvby system.

photometric; → system.

photometry
  شید-سنجی، نور-سنجی   
šidsanji, nursanji

Fr.: photométrie   

In astronomy, the measurement of the light of astronomical objects, generally in the visible or infrared bands, in which a wavelength band is normally specified.

photo- + → -metry.

photomultiplier
  شید-بستاگر، نور-بستاگر   
šid-bastâgar, nur-bastâgar

Fr.: photomultiplicateur   

Electronic tube which converts photons into electrons, multiplies the electrons via a series of electrodes, and produces a measurable current from a very small input signal.

photo- + → multiplier.

photon
  فوتون   
foton (#)

Fr.: photon   

The → quantum of the → electromagnetic field, which mediates the interaction between charged particles. It is the mass-less → boson with zero → electric charge, which propagates with the → speed of light in vacuum. The energy of a photon is connected to its → frequency ν, through the formula E = hν, where h is → Planck's constant.

From phot-, variant of → photo- before a vowel + → -on a suffix used in the names of subatomic particles (gluon; meson; neutron), quanta (photon, graviton), and other minimal entities or components. The term photon was coined by Gilbert N. Lewis in 1926 in a letter to the editor of Nature magazine (Vol. 118, Part 2, December 18, page 874).

photon escape time
  زمان ِ گریز ِ فوتون   
zamân-e goriz-e foton

Fr.: temps d'échappement des photons   

The time required for a photon created in the Sun's core to attain the → photosphere and leave the Sun. If the photons were free to escape, they would take a time of only R/c (a couple of seconds) to reach the surface, where R is the Solar radius and c the speed of light. The solar material is, however, very opaque, so that photons travel only a short distance before interacting with other particles. Therefore, photons undergo a very large number of → random walks before arriving at the surface by chance. The typical time is approximately 5 x 104 years for a constant density Sun.

photon; → escape; → time.

photon hardening
  سختش ِ فوتون   
saxteš-e foton

Fr.: durcissement des photons   

An effect occurring in the outer zones of → H II regions where the number of high-energy ultraviolet photons with energies well above the → ionization potential of hydrogen increases with respect to the number of → Lyman continuum photons. The effect is due to stronger absorption of weaker photons.

hard; → photon.

photon noise
  نوفه‌ی ِ فوتون   
nufe-ye foton

Fr.: bruit de photons   

An intrinsic noise caused by the quantum nature of light. Same as → quantum noise.

photon; → noise.

photon sphere
  سپهر ِ فوتون   
sepehr-e foton

Fr.: sphère de photons   

A surface where if a photon is emitted from one of its points the photon follows a closed orbit and returns periodically to its departure point. Such a surface exists only near sufficiently → compact objects where the → curvature of → space-time is very important. In other words, a body can take a stable orbit around a → black hole provided that it moves with the → speed of light. However, only photons can have such a velocity; hence the term "photon sphere." For a non-rotating → Schwarzschild black hole, the photon sphere has a radius of R = 3GM/c2 = 3 RS/2, where G is the → gravitational constant, M is the mass, c is the → speed of light, and RS is the → Schwarzschild radius. For a rotating, → Kerr black hole, the situation is much more complex due to the → Lense-Thirring effect. In that case circular paths exist for radii whose values depend on the rotation direction. More specifically, in the equatorial plane there are two possible circular light paths: a smaller one in the direction of the rotation, and a larger one in the opposite direction.

photon; → sphere.

photon tiring limit
  حد ِ خستگی ِ فوتون   
hadd-e xastegi-ye foton

Fr.: limite par fatigue du photon   

The maximum → mass loss rate of a star when the → wind luminosity equals the total available → stellar luminosity. The mechanical luminosity of the wind at infinity is given by: Lwind = Mdot (v2/2 + GM/R) = Mdot (v2/2 + vesc2/2). For Lwind = L*, the mass loss rate is Mdotmax = 2L*/(v2 + vesc2). Following Owoki & Gayly (1997), Mdottir is the maximum mass loss rate when the wind just escapes the gravitational potential, with v tending toward zero. Mdottir is much larger than typical mass loss rates from → line-driven winds, where the driving lines become saturated with increasing density limiting the wind mass loss rates to about 10-4 Msun yr-1 in even the most luminous stars.

photon; tiring, from tire "to weary; become weary," → tired; → limit.

photon-baryon plasma
  پلاسما فوتون-باریون   
plâsmâ foton-bâriyon

Fr.: plasma photon-baryon   

The plasma filling space before the → recombination epoch that mainly consisted of → cosmic microwave background radiation photons, electrons, protons, and → light elements.

photon; → baryon; → plasma.

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