compact high-velocity clouds (CHVCs)
abrhâ-ye hampak-e tondrow
Fr.: nuages compacts à grande vitesse
A population of relatively small (typically < 2°) → high-velocity clouds, which are spatially and kinematically isolated from the gas distribution in their environment. They are thought to be located in the → intergalactic medium of the → Local Group.
boland (#); meh (#); por (#)
1) Situated above the ground or exceeding the common degree or
M.E. heigh, variants hegh, hey, heh; O.E. heh, heah "of great height, lofty, tall," (cf. Du. hoog, O.H.G. hoh, Ger. hoch, Goth. hauhs "high;" also Ger. Hügel "hill"); from PIE *koukos "hill."
Boland "high," variants bâlâ
"up, above, high, elevated, height," borz "height, magnitude"
(it occurs also in the name of the mountain chain Alborz),
Lori dialect berg "hill, mountain;"
Mid.Pers. buland "high;" O.Pers. baršan- "height;"
Av. barəz- "high, mount," barezan- "height;" cf.
Skt. bhrant- "high;" L. fortis "strong" (Fr. & E. force);
O.E. burg, burh "castle, fortified place," from P.Gmc.
*burgs "fortress;" Ger. Burg "castle," Goth. baurgs "city,"
E. burg, borough, Fr. bourgeois, bourgeoisie, faubourg);
PIE base *bhergh- "high."
High Energy Stereoscopic System (H.E.S.S.)
râžmân-e estereyo-ye meh kâruž (H.E.S.S.)
Fr.: Système stéréoscopique de haute énergie (H.E.S.S.)
An array of → IACT telescopes for studying cosmic → gamma rays in the 100 GeV to 100 TeV energy range. The HESS observatory is located in Namibia, southern Africa, at an altitude of 1800 m, and the project is an international collaboration of more than 100 scientists from nine countries. In its Phase I, HESS used four telescopes each consisting of a light collector with a diameter of 13 m and a focal length of 15 m placed at the corners of a square 120 m apart. Each telescope is segmented into 380 round mirror facets of 60 cm diameter and uses a camera consisting of 960 closely packed → photomultiplier tubes. The first of the telescopes went into operation in Summer 2002. Phase II includes a fifth telescope, called Large Cherenkov Telescope (LCT), of 27 m diameter, located in the centre of the initial array. This upgrade lowers the triggering threshold of the HESS array to about 20 GeV, thus broadening the energy window in which gamma-ray astronomy can be done, opening up more opportunities in astrophysical research (see, e.g., Bernlöhr et al. 2003, Astroparticle Physics 20, 111).
H.E.S.S., short for High Energy Stereoscopic System, is also intended to pay homage to Victor F. Hess (1883-1964), an Austrian-American physicist who received the Nobel Prize in Physics in 1936 for his discovery of → cosmic rays.
Fr.: hautes latitudes
The latitude belt roughly between 60 and 90 degrees North and South. Also referred to as the polar region.
high redshift object
Fr.: objet à grand décalage vers le rouge
A galaxy or quasar having a → redshift larger than about 0.8, corresponding to a → look-back time half the present age of the Universe. The qualifier "high" is, however, relative and depends on context and authors' assessment.
owpiš (#), kešand (#), madd (#)
Fr.: marée haute
The state of the → tide when at its highest level.
owpiš (#), barkešand (#), madd(#)
Fr.: marée haute
Also known as → high tide.
Fr.: astrophysique des hautes énergies
A branch of astrophysics that deals with objects emitting highly energetic radiation, such as X-ray astronomy, gamma-ray astronomy, and extreme ultraviolet astronomy, as well as neutrinos and cosmic rays.
high-energy cosmic rays
partowhâ-ye keyhâni-ye meh-kâruž, ~ ~ por-kâruž
Fr.: rayons cosmiques de hautes énergies
Cosmic rays which typically have energies in the range 1015 to 1020 electron volts. For the most part, they are protons and other atomic nuclei, and come from distant cosmos, perhaps even from outside our own Galaxy.
Fr.: neutrino haute énergie
A neutrino produced in high-energy particle collisions, such as those occurring when → cosmic rays strike atoms in the Earth's → atmosphere. Their energy range expands from a few → MeVs up to tenths of a → peta- (P) → electron-volts.
high-excitation blob (HEB)
A rare class of → H II regions in the → Magellanic Clouds. In contrast to the typical H II regions of the Magellanic Clouds, which are extended structures (sizes of several arc minutes corresponding to more than 50 pc, powered by a large number of exciting stars), HEBs are very dense and small regions (~ 4" to 10" in diameter corresponding to ~ 1-3 pc). They have a higher degree of → excitation ([O III] 5007Å /Hβ) with respect to the typical H II regions, and are, in general, heavily affected by local → dust. They are powered by a relatively smaller number of → massive stars.
setâre-ye meh-jerm (#), ~ por-jerm (#)
Fr.: étoile massive
high-mass X-ray binary (HMXB)
dorin-e partow-e iks-e por-jerm
Fr.: binaire X de forte 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 a black hole and the other one a → massive star. HMXBs emit relatively → hard X-rays and usually show regular pulsations, no X-ray bursts, and often X-ray eclipses. Their X-ray luminosity is much larger than their optical luminosity. In our Galaxy HMXBs are found predominantly in the → spiral arms and within the → Galactic disk in young → stellar populations less than 107 years old. One of the most famous HMXB is Cygnus X-1 which was the first stellar-mass black hole discovered. See also: → low-mass X-ray binary.
leyzer-e por-tavân (#)
Fr.: laser de puissance
A laser beam with the output power in the range 1012-1015 watts/cm2, capable of depositing kilo-joule order energies during nano-second time intervals in small volumes (about 1 mm3). High power lasers, which can produce temperatures of 10-50 million degrees and pressures of 10-100 million bars, are used to simulate astrophysical conditions in laboratories.
Fr.: observation à haute résolution
An observation that provides a particularly narrow, peaked image of a point source. → point spread function.
high-velocity clouds (HVCs)
Fr.: nuages à grande vitesse
A population of neutral or partly ionized gas clouds in the → Galactic halo which are seen as high-altitude structures in the atomic hydrogen 21 cm emission at high radial velocities (vLSR> 100 km/sec). They have substantial neutral column densities (> 1019 cm-2) and their metallicities range from 0.1 to about 1.0 times solar. The distances to the majority of them remain unknown. They may represent the continuing infall of matter onto the → Local Group. See also → compact high-velocity clouds.
Fr.: région montagneuse, hauts plateaux
A mountainous or elevated region; → plateau.
Fr.: hauts plateaux lunaires
ultra-high-energy cosmic ray (UHECR)
partowhâ-ye keyhâni-ye ultar-meh-kâruž
Fr.: rayons cosmiques de très haute énergie
A particle belonging to the most energetic population of → cosmic rays with an energy above ~ 1020 → electron-volts. The UHECRs constitute a real challenge for theoretical models, because their acceleration requires extreme conditions hardly fulfilled by known astrophysical objects. See also → UHECR puzzle, → Greisen-Zatsepin-Kuzmin cutoff.
Fr.: neutrino ultra haute énergie
A neutrino particle accelerated to energies above 1018 → electron-volts. They are produced by the interaction of → ultra-high-energy cosmic ray (UHECR)s with the → cosmic microwave background radiation. Also called → cosmogenic neutrinos. See also → Greisen-Zatsepin-Kuzmin limit.