Fr.: naine d'Antlia
A → dwarf spheroidal galaxy located about 4.3 million → light-years from. Earth. It is a very faint object, with an apparent magnitude of 16.2. The galaxy was not discovered until 1997. (PGC 29194) The Antlia Dwarf lies on the outer rim of the Local Group of galaxies, possibly even beyond it, and there is evidence suggesting that it is tidally interacting with another small galaxy, NGC 3109, in the → Hydra constellation.
blue compact dwarf galaxy
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.
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
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 (≥ 10-3→ solar 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 desert
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).
DA white dwarf
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.
DB white dwarf
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.
DC white dwarf
sefid kutule-ye DC
Fr.: naine blanche DC
A → white dwarf showing a continuous spectrum with no readily apparent lines.
Fr.: naine dégénérée
Same as → white dwarf.
→ degenerate; → dwarf.
DO white dwarf
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.
double white dwarf
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.
DQ white dwarf
sefid kutule-ye DQ
Fr.: naine blanche DQ
A → white dwarf whose spectrum shows carbon features of any kind.
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.
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
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."
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 elliptical galaxy
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.
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 irregular galaxy
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.
novâ-ye kutulé, nowaxtar-e ~
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.
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.