A metal-poor main-sequence star with spectral type later than M7 and luminosity class VI. They are population II dwarfs which appear less luminous than their solar metallicity counterparts due to the dearth of metals in their atmospheres. Subdwarfs are halo members with high proper motions and large heliocentric velocities. They are important tracers of the chemical enrichment history of the Galaxy and belong to the first generation of stars formed in the Galaxy (at least 10 billion years old).
A great number of things especially in motion. → meteorite swarm.
ME; OE swearm; cf. O.S., M.L.G. swarm, Swed. svärm, M.Du. swerm, O.H.G. swarm, Ger. Schwarm "swarm;" O.N. svarmr "tumult."
Qang in Lârestâni "swarm of bees, flies, or the like," Lori qem (qem zaye) "swarm of bees, ants, and the like."
Fr.: naine T
A type of → brown dwarf with an → effective temperature between about 1200 K and 500 K, i.e. colder than the preceding type → L dwarf. The spectra of T dwarfs are characterized by the presence of → methane (CH4) bands in the → near infrared. The presence of these bands, broad H2O features, and H2 collision-induced absorption radically alter the spectral energy distributions of T dwarfs compared to a black body at the same temperature. Hence near-infrared colors become increasingly blue (J - K ~ 0) as compared to L dwarfs. The first T dwarf, called → Gl 229B, was discovered by Nakajima et al. (1995, Nature 378, 463). The spectral classification scheme (subtypes T0 to T9) currently used was defined by Burgasser et al. (2002, ApJ 564, 421).
For the reasoning behind the choice of the letter T, see Kirkpatrick et al. 1993, ApJ 406, 701; → dwarf.
tidal dwarf galaxy
kahkešân-e kutule-ye kešandi
Fr.: naine de marée
A self-gravitating entity which has been formed from tidal material expelled during interactions between larger galaxies. TDGs are typically found at the tip of tidal tails at distances between 20 and 100 kpc from the merging galaxies, of which at least one should be a gas-rich galaxy. They are gas-rich objects that can be as massive as the Magellanic Clouds, form stars at a rate which might be as high as in blue compact dwarf galaxies and seem dynamically independent from their parent galaxies.
ultracompact dwarf galaxy (UCD)
kahkešân-e kutule-ye ultar-hampak
Fr.: galaxie naine ultracompacte
A type of very bright compact → stellar system (-14 ≤ MV≥ -12) that is intermediate between → globular clusters (GCs) and → compact elliptical galaxies (cEs). With masses of M > 2 × 106 Msun and radii > 10 → parsecs (pc), UCDs are among the densest stellar systems in the Universe. Nevertheless, the nature and origin of these objects is still widely debated. Early interpretations suggested that UCDs could be the most massive GCs or possibly the → tidally stripped remnants of → dwarf galaxies. However, there is evidence that both formation mechanisms could contribute to the UCD population. → Supermassive black holes (SMBHs) have been confirmed in most UCDs with masses M > 107 Msun. The most massive UCD discovered to date, M59-UCD3 (M* ~ 2 × 108 Msun, radius ~ 25 pc), hosts a SMBH (Ahn et al., 2018, arxiv/1804.02399, and references therein).
Fr.: naine ultrafroide
A star-like objects with an → effective temperature of less than 2,700 K. Ultracool dwarfs constitute a heterogeneous group including stars of extremely low mass as well as → brown dwarfs, and represent about 15% of the population of astronomical objects near the Sun.
Fr.: logiciel utilitaire
A part of the system software designed to support the operation of application software and is used to manage the computer files. Examples of utility software are disk diagnosis program, backup software, password generation software, and virus protection software. Also called utilities.
A state of armed conflict between states, or between groups within states.
From M.E. werre, from O.E. werre, wyrre, from Old Northern Fr. werre, akin to O.H.G. werra "confusion, strife, quarrel," Du. war "confusion, disarray," O.E. wyrsa, wiersa "worse," O.Norse verri "worse; confounded;" ultimately from PIE *wers- "to confuse, mix up."
Jang, from Mid.Pers. jang "struggle, battle, fight."
M.E.; O.E. wearm (cf. O.S., O.Fris., M.Du., O.H.G., Ger. warm, O.N. varmr, Goth. warmjan "to warm"); cognate with Pers. garm, as below.
Garm "warm;" Mid.Pers. garm "warm;" O.Pers. garma-pada "name of the fourth month" (June-July); Av. garəma- "warm; heat;" cf. Skt. gharmá "heat;" Gk. therme, thermos; L. formus "warm;" E. warm, as above; PIE base *ghworm-/*ghwerm- "warm."
Fr.: absorbeur chaud
A cloud of ionized gas within → active galactic nuclei (AGN) that causes absorption at → soft X-ray wavelengths. Warm absorbers were first suggested by Halpern (1984) to explain Einstein data of the quasar MR 2251-178. They are dubbed "warm" absorbers as they imply gas at temperatures of 104-105 K; the gas is → photoionized, not collisionally ionized. High resolution observations of warm absorbers have shown that they are outfowing. See also → cold absorber (Ceri Ellen Ashton, 2005, A Study of Warm Absorbers in Active Galactic Nuclei, Thesis, Mullard Space Science Laboratory Department of Space and Climate Physics University College London ).
Fr.: front chaud
Meteo.: A leading edge that advances in a mass of air and replaces cooler air by warm air.
warm intercloud medium
madim-e andarabri-ye garm
Fr.: milieu internuage chaud
A component of the → interstellar medium consisting of an extremely tenuous (density 0.1 to 10 cm-3) and relatively warm gas (temperature about 8,000 K) filling the space between denser neutral and ionized gas. Hydrogen is partly ionized, partly atomic and observed by the → 21-centimeter line in emission.
warm-hot intergalactic medium
madim-e andar-kahkašâni garm-dâq
Fr.: milieu intergalactique chaud
The space containing a cluster of galaxies filled with a tenuous gas of temperature 105 to 107 K and density 10-6 to 10-4 cm-3. WHIM has been continuously shock-heated during the process of structure formation. It is so highly ionized that it can only absorb or emit far-ultraviolet and soft X-ray photons, primarily at spectral lines of highly ionized C, O, Ne, and Fe. WHIM is thought to be the main reservoir of missing baryons.
The vertical twisting of a → galactic disk in its outer parts. Many → spiral galaxies, including our Milky Way, appear to have warps in the outer reaches of their stellar and gas disks. The rotating body of stars and gas that characterizes a spiral galaxy is generally flat, but the outer regions may deviate from the plane of the disk. The causes are multiple, some warps can come from spontaneous instability, some result from interactions between galaxies, and many reflect the external gas → accretion from intergalactic matter filaments.
M.E. werpen, OE weorpan "to throw;" cf. O.S. werpan, O.N. verpa "to throw," Swed. värpa "to lay eggs," Du. werpen, Ger. werfen "to throw; to distort." Related to warp "threads running lengthwise in a fabric."
Tâb "twisting, bending, waving, a curling lock," variants tâv, tow, tew, from tâbidan, tâftan "to twist, to spin, to bend, to crook," p.p. tâftah "spun, silk or linen cloth," loaned into E. as taffeta (from O.Fr. taffetas, from It. taffeta); similarly Gk. tapetion "little carpet" is probably from this Iranian origin (from which tapestry, tapis); Proto-Ir. *tâp- "to twist, to wind;" cf. L. tempus "time (span);" Lith. tempti "to stretch;" Russ. tepsti "to tighten."
gerde-ye tâbdâr, disk-e ~
Fr.: disque gauchi
Verbal noun from → warp (v.).
zegil (#), veruk (#)
A hard rough lump growing on the skin, caused by infection with certain viruses and occurring typically on the hands or feet (TheFreeDictionary.com).
M.E., from O.E. weart "wart," cf. O.Norse varta, O.Frisian warte, Du. wrat, O.H.G. warza, Ger. Warze, Swed. varta, Russ. vered "ulcer," perhaps ultimately from the same source as L. verruca "a steep place, swelling, wart" (Fr. verrue, Sp. verruga, Catalan berruga, It. verruca), ultimately from PIE *uer-s- "a steep place, height," from *uer- "highland, high place, top;" cf. Gk. ouranos "sky."
Zegil "wart," maybe related to Pers. gereh "knot,"
ultimately from prefixed (*uz-,
→ ex-) *graθH- "to tie (a knot)."
sefid kutulé, kutule-ye sefid (#)
Fr.: naine blanche
A compact star of high surface temperature, low luminosity, and high density (105-108 g cm-3), with roughly the mass of the Sun (mean mass ~ 0.6 Msun) and the radius of the Earth (R ~ 0.01 Rsun), representing the end-point of the evolution of all stars with masses less then ~ 5-9 → solar masses. A white dwarf is what remains after the central star of a → planetary nebula fades and becomes cool. The → Chandrasekhar limit of 1.43 solar masses is the highest mass that a white dwarf can achieve before electron → degeneracy pressure is unable to support it. In the → Hertzsprung-Russell diagram, white dwarfs form a well-defined sequence around 8 magnitudes fainter than the main sequence. They are composed of a core of carbon and oxygen nuclei and degenerate electrons surrounded by a thin shell of helium and an outer skin of hydrogen. White dwarf's radiation is the leftover heat from the star's past when its core was an active nuclear reactor. The star slowly cools as heat escapes through the non-degenerate envelope. → white dwarf crystallization; → cooling time; → Mestel theory. The first white dwarf to be discovered was Sirius B, the → companion of Sirius. White dwarfs are divided into several types, according to their spectral features, which depend on the type of → shell burning that dominated as it became a → planetary nebula: → DA white dwarf; → DB white dwarf; → DC white dwarf; → DO white dwarf; → DZ white dwarf; → DQ white dwarf. For a review see Kepler and Brdaley (1995, Baltic Astron. 4, 166).
white dwarf cooling track
râh-e sardeš-e sefid kutulé
Fr.: trajet de refroidissement de naine blanche
In the → Hertzsprung-Russell diagram, the evolutionary track followed by a → low-mass or an → intermediate-mass star when it can no longer produce thermonuclear energy. The track starts at the end of the → horizontal branch to lead the star to a → white dwarf phase.