Fr.: fibre à faible perte
Optical fiber that transmits a greater percentage of input light than does high-loss step-index fiber.
Fr.: galaxie de faible masse
A galaxy with stellar masses ≤ 109 → solar masses (Dawn K. Erb, 2015, Nature, 9 July).
setâre-ye kamjerm (#)
Fr.: étoile de faible masse
low-mass X-ray binary (LMXB)
dorin-e partow-e iks-e kam-jerm
Fr.: binaire X de faible masse
A member of one of the two main classes of
→ X-ray binary systems where one of the components is a
→ neutron star or → black hole
and the other component a → low-mass star with a spectral type A
or later. LMXBs mainly emit → soft X-rays.
The ratio of their optical to X-ray luminosities is less than 0.1. They belong
to → old stellar populations
with ages 5-15 × 109 years and are found in
→ globular clusters
and in the → bulge
of our → Milky Way
galaxy; some are also found in the disk.
Hercules X-1 is an example of LMXBs.
Fr.: environnement faible en métaux
A medium in which chemical elements have abundances smaller than the solar values.
Relatively low in position, rank, or order.
Comparative of → low.
havâsepehr-e zirin, javv-e ~
Fr.: atmosphère inférieure
Generally and quite loosely, that part of the atmosphere in which most weather phenomena occur (i.e., the → troposphere and lower → stratosphere); hence used in contrast to the common meaning for the → upper atmosphere. In other contexts, the term implies the lower troposphere (Meteorology Glossary, American Meteorological Society).
Fr.: culmination inférieure
The instant of culmination when the star passes between the pole and the horizon, having an hour angle of 12h. Lower culmination for non-circumpolar objects occur below the horizon and is thus unobservable. Same as → inferior culmination. See also → upper culmination.
Fr.: manteau inférieur
jofteš-e LS, jafsari-ye ~
Fr.: couplage LS
Same as → Russell-Saunders coupling.
Moderately warm; tepid.
M.E. lukewarme "tepid," from luke "tepid," of unknown origin, + → warm.
Velarm "lukewarm, tepid," of unknown origin.
The SI unit of luminous flux, equal to the luminous flux emitted per unit solid angle by a standard point source having a luminous intensity of 1 candela. → candela.
L. lumen (gen. luminis) "light," from lucere "to shine," related to lux "light," lucidus "clear," luna, "moon;" Fr. lumière "light;" cf. Pers. ruz "day," rowšan "bright, clear," rowzan "window, aperture;" foruq "light," afruxtan "to light, kindle;" Mid.Pers. rôšn "light; bright, luminous," rôc "day;" O.Pers. raucah-rocânak "window;" O.Pers. raocah- "light, luminous; daylight;" Av. raocana- "bright, shining, radiant;" akin to Skt. rocaná- "bright, shining," roka- "brightness, light;" Gk. leukos "white, clear;" O.E. leoht, leht, from W.Gmc. *leukhtam (cf. O.Fris. liacht, M.Du. lucht, Ger. Licht), from PIE *leuk- "light, brightness."
Lumen loanword, as above.
The luminous intensity in a given direction of a small element of surface area divided by the orthogonal projection of this area onto a plane at right angle to the direction. It is measured in candelas per square meter. Luminance is often called surface brightness of the object.
From lumin-, combining form of → lumen "light," + -ance a suffix used to form nouns either from adjectives in -ant or from verbs.
Tâbâni, from tâbidan "to shine," → luminous.
The emission of light at low temperatures by any process other than → incandescence, where a substance emits light without being strongly heated. Luminescence is a collective term for different phenomena, for example: → phosphorescence, → fluorescence, → chemiluminescence, → photoluminescence.
Capable of, suitable for, or exhibiting luminescence.
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.
Verbal noun of → luminous.
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.
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.
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.
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).