An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



Number of Results: 20 Search : luminosity
absolute luminosity
  تابندگی ِ ا َوَست   
tâbandegi-ye avast

Fr.: luminosité absolue   

A star's → intrinsic brightness, i.e. the total amount of energy radiated by the star per second. → Luminosity is often expressed in units of watts or erg/sec. The Sun's absolute luminosity is 3.86 × 1033 erg/sec.

absolute; → luminosity.

anomalous luminosity effect
  اسکر ِ تابندگی ِ ناسان   
oskar-e tâbandegi-ye nâsân

Fr.: effet luminosité anormale   

Discrepant luminosity classes derived for the same → Am star when different criteria are used. Lore specifically, a luminosity criterion may indicate a → giant star, wheras another criterion indicates a → supergiant.

anomalous; → luminosity; → effect.

bolometric luminosity
  تابندگی ِ تاوسنجی، ~ تاوسنجیک   
tâbandegi-ye tâvsanji, ~ tâvsanjik

Fr.: luminosité bolométrique   

The total rate of energy output of an object integrated over all wavelengths.

bolometric; → luminosity.

break luminosity
  تابندگی ِ بره   
tâbandegi-ye boré

Fr.: luminosité de coupure   

A characteristic luminosity around which the → luminosity function of a sample of galaxies changes to a steeper slope or exponentially declines.

break; → luminosity.

color-luminosity diagram
  نمودار ِ رنگ-تابندگی   
nemudâr-e rang-tâbandegi

Fr.: diagramme couleur-luminosité   

A form of → Hertzsprung-Russell diagram in which the luminosity is the vertical axis and the → color index the horizontal axis.

color; → luminosity, → diagram.

Eddington luminosity
  تابندگی ِ ادینگتون   
tâbandegi-ye Eddington

Fr.: luminosité d'Eddington   

Same as → Eddington limit.

Eddington limit; → luminosity.

H II region luminosity
  تابندگی ِ ناحیه‌ی ِ H II   
tâbandegi-ye nâhiye-ye H II

Fr.: luminosité de région H II   

The total number of → Lyman continuum photons emitted by an → H II region. It is usually derived using → radio continuum observations which are less affected by → interstellar extinction. The measured value is often a lower limit because of photon leakage from the H II region and absorption. See also → density-bounded H II region.

H II; → region; → luminosity.

intrinsic luminosity
  تابندگی ِ درونگین   
tâbandegi-ye darungin

Fr.: luminosité intrinsèque   

The energy per second emitted by an astronomical object.

intrinsic; → luminosity.

tâbandegi (#)

Fr.: luminosité   

The → total → brightness of a star or other astronomical object. It is expressed in watts and represents the total amount of → energy that the object radiates each → second over all wavelength regions of the → electromagnetic spectrum. Because this quantity is independent of distance, it is an → intrinsic brightness.
See also:
absolute luminosity, → anomalous luminosity effect, → bolometric luminosity, → color-luminosity diagram, → Eddington luminosity, → H II region luminosity, → intrinsic luminosity, → luminosity class, → luminosity distance, → luminosity function, → luminosity problem, → mass-luminosity ratio, → mass-luminosity relation, → peak luminosity, → period-luminosity relation, → solar luminosity, → stellar luminosity, → wind luminosity.

Verbal noun of → luminous.

luminosity class
  رده‌ی ِ تابندگی   
rade-ye tâbandegi (#)

Fr.: classe de luminosité   

A classification of stellar spectra according to luminosity for a given → spectral type. The luminosity class is an indication of a star's → surface gravity. It is shown by a Roman numeral as follows: I (→ supergiants), II (bright → giants), III (normal giants), IV (→ subgiants), and V (→ dwarf stars, or → main-sequence stars). Luminosity classes VI (→ subdwarfs) and VII (→ white dwarfs) are rarely used. Subclasses a, b, and c are especially used for supergiants, while the most luminous → hypergiants are assigned luminosity class Ia-0.

luminosity; → class.

luminosity distance
  اپست ِ تابندگی   
apast-e tâbandegi

Fr.: distance de luminosité   

1) Distance derived by comparison of → observed and → intrinsic luminosities. If an object has a known luminosity L, and the observed flux is S, the luminosity distance is defined by DL = (L/4πS)1/2.

2) In cosmology, the → expansion of the Universe results in a diminution of the photon flux and the above equation fails. The reason is that for a homogeneous and isotropic Universe (→ Robertson-Walker metric), the luminosity decreases by a factor (1 + z)4. Therefore, the luminosity distance is related to the → angular diameter distance (DA) by: DL = (1 + z)2.DA.

luminosity; → distance.

luminosity function
  کریا‌ی ِ تابندگی   
karyâ-ye tâbandegi

Fr.: fonction de luminosité   

Number → distribution of → stars or galaxies (→ galaxy) with respect to their → absolute magnitudes. The luminosity function shows the → number of stars of a given intrinsic luminosity (or the number of galaxies per integrated magnitude band) in a given → volume of space.

luminosity; → function.

luminosity problem
  پراسه‌ی ِ تابندگی   
parâse-ye tâbandegi

Fr.: problème de luminosité   

Low-mass → protostars are about an order of magnitude less luminous than expected. Two possible solutions are that → low-mass stars form slowly, and/or protostellar → accretion is episodic. The latter accounts for less than half the missing luminosity. The solution to this problem relates directly to the fundamental question of the time required to form a low-mass star (McKee & Offner, 2010, astro-ph/1010.4307).

luminosity; → problem.

mass-luminosity ratio
  وابر ِ جرم-تابندگی   
vâbar-e jerm-tâbandegi

Fr.: rapport masse-luminosité   

The ratio of the mass of a system, expressed in solar masses, to its visual luminosity, expressed in solar luminosities. The Milky Way Galaxy has a mass-luminosity ratio in its inner regions of about 10, whereas a rich cluster of galaxies such as the Coma Cluster has a mass-luminosity ratio of about 200, indicating the presence of a considerable amount of dark matter.

mass; → luminosity; → ratio.

mass-luminosity relation
  باز‌آنش ِ جرم-تابندگی   
bâzâneš-e jerm-tâbandegi

Fr.: relation masse-luminosité   

A relationship between luminosity and mass for stars that are on the main sequence, specifying how bright a star of a given mass will be. Averaged over the whole main sequence, it has been found that L = M3.5, where both L and M are in solar units. This means, for example, that if the mass is doubled, the luminosity increases more than 10-fold.

mass; → luminosity; → relation.

peak luminosity
  تابندگی ِ ستیغ   
tâbandegi-ye setiq

Fr.: luminosité du pic   

The → bolometric luminosity of a → supernova corresponding to the highest brightness in its → light curve. The peak luminosity occurs after the → supernova explosion; it is directly linked to the amount of radioactive 56Ni produced in the explosion and can be used to test various explosion models. Following → Arnett's rule, one can derive the 56Ni mass from the peak luminosity of a → Type Ia supernova.

peak; → luminosity.

period-luminosity relation
  باز‌آنش ِ دوره-تابندگی   
bâzâneš-e dowré-tâbandegi

Fr.: relation période-luminosité   

A correlation between the periods and luminosities of → Cepheid variable stars. Once the period of a Cepheid variable is determined from observations, the period-luminosity relation can be used to derive its luminosity. Since luminosity is a function of distance, the distance can then be calculated with the luminosity. The period-luminosity relation is an invaluable tool for the measurements of distances out to the nearest galaxies and thus for studying the structure of our own Galaxy and of the Universe. The relation was discovered by Henrietta Leavitt in 1912 when studying Cepheids in the → Small Magellanic Cloud.

period; → luminosity; → relation.

solar luminosity
  تابندگی ِ خورشید   
tâbandegi-ye xoršid (#)

Fr.: luminosité solaire   

The total → radiant energy, in all wavelengths, emitted by the Sun in all directions. It is 3.828 × 1026 W or 3.828 × 1033 erg sec-1 (International Astronomical Union, Resolution B3, 14 August 2015, Honolulu, USA). This is the luminosity unit conventionally used to give the luminosities of stars. See also: → solar constant.

solar; → luminosity.

stellar luminosity
  تابندگی ِ ستاره   
tâbandegi-ye setâré

Fr.: luminosité stellaire   

The total amount of energy emitted by a star per unit time. According to the → Stefan-Boltzmann law, the stellar luminosity is given by: L* = 4πR*2σTeff4, where R* is radius, σ is the → Stefan-Boltzmann constant, and Teff is → effective temperature. A star's luminosity depends, therefore, on two factors, its size and its surface temperature. Stellar luminosity is measured either in ergs per second or in units of → solar luminosity or in → absolute magnitude. See also → luminosity class.

stellar; → luminosity.

wind luminosity
  تابندگی ِ باد   
tâbandegi-ye bâd

Fr.: luminosité de vent   

The final kinetic energy of the → stellar wind expressed by: (1/2)Mdot.v2 = (1/2)(v/c)L For an O6 star, L ~ 3 x 105Lsun and v ~ 2000 km s-1, which give a wind luminosity of ~ 1 x 1037 erg s-1, about 1% of the → stellar luminosity. See also → photon tiring limit.

wind; → luminosity.