An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 38 Search : dwarf
blue compact dwarf galaxy
  کهکشان ِ کوتوله‌ی ِ آبی ِ همپک   
kahkešân-e kutule-ye âbi-ye hampak

Fr.: galaxie naine bleue compacte   

An small → irregular galaxy undergoing → violent star formation activity. These objects appear blue by reason of containing clusters of hot, → massive stars which ionize the surrounding interstellar gas. They are chemically unevolved since their → metallicity is only 1/3 to 1/30 of the solar value. Same as → H II galaxy.

blue; → compact; → dwarf; → galaxy.

brown dwarf
  کوتوله‌ی ِ قهوه‌ای   
kutule-ye qahvei

Fr.: naine brune   

A star-like object whose mass is too small to sustain → hydrogen fusion in its interior and become a star. Brown dwarfs are → substellar objects and occupy an intermediate regime between those of stars and giant planets. With a mass less than 0.08 times that of the Sun (about 80 → Jupiter masses), nuclear reactions in the core of brown dwarfs are limited to the transformation of → deuterium into 3He. The reason is that the cores of these objects are supported against → gravitational collapse by electron → degeneracy pressure (at early spectral types) and → Coulomb pressure (at later spectral types). Brown dwarfs, as ever cooling objects, will have late M dwarf spectral types within a few Myrs of their formation and gradually evolve as L, T and Y dwarfs → brown dwarf cooling. As late-M and early-L dwarfs, they overlap in temperature with the cool end of the stellar → main sequence (→ M dwarf, → L dwarf, → T dwarf, → Y dwarf). In contrast to the OBAFGKM sequence, the M-L-T-Y sequence is an evolutionary one. These objects were first postulated by Kumar (1963, ApJ 137, 1121 & 1126) and Hayashi & Nakano (1963, Prog. Theor.Phys. 30, 460).

The term brown dwarf was first used by Jill Tarter in her 1975 PhD thesis; → brown; → dwarf.

brown dwarf cooling
  سردش ِ کوتوله‌ی ِ قهوه‌ای   
sardeš-e kutule-ye qahve-yi

Fr.: refroidissement de naine brune   

The process whereby a → brown dwarf cools over time after the → deuterium burning phase, which lasts a few 107 years. The → effective temperature and luminosity decrease depending on the mass, age, and → metallicity. Even though massive brown dwarfs may start out with star-like luminosity (≥ 10-3solar luminosities), they progressively fade with age to the point where, after 0.5 Gyr all → substellar objects are less luminous than the dimmest, lowest mass stars. More explicitly, brown dwarfs may start as star-like objects hotter than 2200 K, with → M dwarf spectral types, and, as they get older, pass through the later and cooler L, T, and Y spectral types (→ L dwarf, → T dwarf, → Y dwarf).

brown; → dwarf; → cooling.

brown dwarf desert
  کویر ِ کوتوله‌های ِ قهوه‌ای   
kavir-e kutulehâ-ye qahvei

Fr.: désert des naines brunes   

The observational result indicating a deficit in the frequency of → brown dwarf companions to Sun-like stars, either relative to the frequency of less massive planetary companions or relative to the frequency of more massive stellar companions. However, this desert exists mainly for low-separation brown dwarfs detected using orbital velocity surveys. No brown dwarf desert is noticed at wide separations (J. E. Gizis et al. 2001, ApJ 551, L163).

brown; → dwarf; → desert.

DA white dwarf
  سفید‌کوتوله‌ی ِ DA   
sefid kutule-ye DA

Fr.: naine blanche DA   

A → white dwarf whose spectrum shows the → Balmer lines of hydrogen only, with no helium or metals.

D short for → dwarf; A a convention; → white.

DB white dwarf
  سفید‌کوتوله‌ی ِ DB   
sefid kutule-ye DB

Fr.: naine blanche DB   

A → white dwarf whose spectrum shows strong He I in the absence of hydrogen or metal lines.

D short for → dwarf; B a convention; → white.

DC white dwarf
  سفید‌کوتوله‌ی ِ DC   
sefid kutule-ye DC

Fr.: naine blanche DC   

A → white dwarf showing a continuous spectrum with no readily apparent lines.

D short for → dwarf; C a convention; → white.

degenerate dwarf
  کوتوله‌ی ِ واگن   
kutule-ye vâgen

Fr.: naine dégénérée   

Same as → white dwarf.

degenerate; → dwarf.

DO white dwarf
  سفید‌کوتوله‌ی ِ DO   
sefid kutule-ye DO

Fr.: naine blanche DO   

A → white dwarf whose spectrum shows strong lines of singly ionized helium He II; He I or H may be present. As a DO star cools, the He II will recombine with free electrons to form He I, eventually changing the DO type into a DB white dwarf.

D short for → dwarf; O a convention; → white.

double white dwarf
  سفیدکوتوله‌ی ِ دوتایی   
sefid kutule-ye dotâyi

Fr.: naine blanche double   

A → double-lined binary with two → white dwarf components. Short-period double white dwarfs can lose → orbital angular momentum by emitting → gravitational radiation and if the total mass of the binary exceeds the → Chandrasekhar limit, their eventual → merger might produce a → Type Ia supernova.

double; → white; → dwarf.

DQ white dwarf
  سفید‌کوتوله‌ی ِ DQ   
sefid kutule-ye DQ

Fr.: naine blanche DQ   

A → white dwarf whose spectrum shows carbon features of any kind.

D short for → dwarf; Q a convention; → white.

Draco Dwarf
  کوتوله‌ی ِ اژدها   
kutule-ye eždahâ

Fr.: Naine du Dragon   

A dwarf elliptical galaxy that is a satellite of our Galaxy and lies at a distance of about 250,000 light-years from the Galactic center. Its diameter is only about 3,500 light-years, and its absolute magnitude -8.6, making it the least luminous galaxy known.

Draco; → dwarf.

dwarf
  کوتوله   
kutulé (#)

Fr.: nain   

1) General: A person of abnormally small height owing to a pathological condition; an animal or plant much smaller than the average of its kind or species.
2) Astro.: An adjective characterizing a particular type of object, as in → dwarf star, → dwarf galaxy, → dwarf planet.
See also:
blue compact dwarf galaxy, → brown dwarf, → brown dwarfcooling, → brown dwarfdesert, → DA white dwarf, → DB white dwarf, → DC white dwarf, → DO white dwarf, → double white dwarf, → DQ white dwarf, → Draco Dwarf, → dwarf Cepheid, → dwarf elliptical galaxy, → dwarf irregular galaxy, → dwarf nova, → dwarf spheroidal galaxy, → dwarf spiral galaxy, → DZ white dwarf, → L dwarf, → M dwarf, → OB subdwarf, → red dwarf, → Sagittarius Dwarf Elliptical Galaxy, → Sagittarius Dwarf Irregular Galaxy, → Sculptor Dwarf Elliptical Galaxy, → subdwarf, → T dwarf, → tidal dwarf galaxy, → white dwarf, → white dwarf cooling track, → white dwarf crystallization, → Y dwarf.

Dwarf, from ME dwerg, dwerf, O.E. dweorg, dweorh, O.H.G. twerg "dwarf," from P.Gmc. *dweraz.

Kutulé, from kut "small, short" + Pers. diminutive suffix -ulé, → -ula. The first component kut is the base of kutâh "short, small, little," kudak "child, infant," Mid.Pers. kôtâh "low," kôtak "small, young; baby;" the Mid/Mod.Pers. kucak "small," belongs to this fammily; Av. kutaka- "little, small."

dwarf Cepheid
  کفیءوسی ِ کوتوله   
Kefeusi-ye kutulé

Fr.: céphéide naine   

An old name for a class of pulsating variable stars with small variations in amplitude, also called an AI Velae star or delta Scuti star. They lie in the lower part of the Cepheid instability strip.

dwarf; → Cepheid.

dwarf elliptical galaxy
  کهکشان ِ بیضی‌گون ِ کوتوله   
kahkašân-e beyzigun-e kutulé (#)

Fr.: galaxie elliptique naine   

A galaxy that is much smaller than other members of the elliptical class; it is designated as dE. A subtype of dwarf ellipticals is called a → dwarf spheroidal galaxy (dSph). The basic characteristics of the class are low surface brightness and smooth light distribution. They range in luminosity from that of the faintest dSph galaies MV ~ -9 to about -17. In the → Local Group there are 19 known dEs. They are very common in → galaxy clusters.

dwarf; → elliptical; → galaxy.

dwarf galaxy
  کهکشان ِ کوتوله   
kahkešân-e kutulé (#)

Fr.: galaxie naine   

A small, low luminosity galaxy that is associated with a larger spiral galaxy and may make up part of a galactic halo. There are many of them in the Local Group, and often orbit around larger galaxies such as the Milky Way and the Andromeda Galaxy. There are three main types of them: → dwarf elliptical galaxy (dE), → dwarf irregular galaxy (dI), and → dwarf spiral galaxy (dSA).

dwarf; → galaxy.

dwarf irregular galaxy
  کهکشان ِ بی‌سامان ِ کوتوله   
kahkašân-e bisâmân-e kutulé

Fr.: galaxie irrégulière naine   

An irregular galaxy that is much smaller than other irregulars. Dwarf irregulars are generally metal poor and have relatively high fractions of gas. They are thought to be similar to the earliest galaxies that populated the Universe, and are therefore important to understand the overall evolution of galaxies.

dwarf; → irregular; → galaxy.

dwarf nova
  نو‌اختر ِ کوتوله   
nowaxtar-e kutulé

Fr.: nova naine   

A class of → novae and → cataclysmic variables that have multiple observed → eruptions. Their prototype is → U Geminorum star. Optically, dwarf nova eruptions have amplitudes of 2-6 mag in V, a duration of a few to 20 days and a recurrence time-scale of weeks to years. Dwarf novae are thought to be → semidetached binary stars consisting of a → white dwarf  → primary accreting via → Roche lobe overflow from a → companion which is usually a → late-type, generally → main-sequence star. DN outbursts are usually attributed to the release of gravitational energy resulting from an → instability in the → accretion disk or by sudden mass transfers through the disk.

dwarf; → nova.

dwarf planet
  سیاره‌ی ِ کوتوله   
sayyâre-ye kutulé (#)

Fr.: planète naine   

A new category of → astronomical objects in the → solar system introduced in a resolution by the 26th General Assembly of the → International Astronomical Union (IAU) on August 24, 2006. The characterizing properties are as follows: 1) It is in orbit around the Sun; 2) It has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a → hydrostatic equilibrium (nearly round) shape; 3) It has not "cleared the neighbourhood" around its orbit; and 4) It is not a → satellite of a → planet, or other non-stellar body. The property 3 reclassified → Pluto from a planet to a dwarf planet because it has not cleared the neighborhood of its orbit (the → Kuiper Belt). The largest known dwarf planets are: → Eris, → Pluto, → Ceres, → Makemake, and → 2015 RR245.

dwarf; → planet.

dwarf spheroidal galaxy (dSph)
  کهکشان ِ کره‌وار ِ کوتوله   
kahkašân-e korevâr-e kutulé (#)

Fr.: galaxie sphéroïdale naine   

A subtype of dwarf ellipticals (→ dwarf elliptical galaxy), which are companion to the Milky Way and other similar galaxies. The first example of such objects was discovered by Harlow Shapley (1938) in the constellation → Sculptor. Nine such galaxies are known currently to orbit the Milky Way. Nearby galaxy clusters such as the Virgo, Fornax, Centaurus, and Coma clusters contain hundreds to thousands of individual dSph galaxies. These galaxies have very low surface brightnesses, as low as only 1% that of the night sky (faintest MV ~ -9). They are also among the smallest, least luminous galaxies known. Most of the radiation from dSph galaxies is emitted by stars in the optical portion of the electromagnetic spectrum. The lack of strong emission lines, infrared, or radio radiation suggests that these galaxies are generally devoid of an → interstellar medium. The velocities of stars within dSph galaxies are so high that these galaxies must be disrupting. However, the bulk of mass in these galaxies might be undetected. Dynamical models that include → dark matter do adequately explain the → velocity dispersion of the stars in all dSph systems. In the most extreme cases, only 1% of the mass of the galaxy is visible. Many of the → Local Group dSph galaxies show evidence for star formation more recent than 10 Gyr.

dwarf; → spheroidal; → galaxy.

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