25 Orionis group
goruh-e 25-Šekârgar, ~ 25-Oryon
Fr.: groupe de 25 Orionis
A group of nearly 200 low-mass → pre-main-sequence stars, concentrated within ~ 1 of the early → B star → 25 Orionis, in the component a of the → Orion OB1 Association. The group also harbors the → Herbig Ae/Be star V346 Ori and a dozen other early-type stars. The velocity distribution for the low-mass stars shows a narrow peak at 19.7 km s-1, offset ~ 10 km s-1 from the velocity characterizing the younger stars of the Ori OB1b subassociation, and 4 km s-1 from the velocity of widely spread young stars of the Ori OB1a population. This indicates that the 25 Ori group is a distinct kinematic entity. The low-mass members follow a well-defined band in the → color-magnitude diagram, consistent with an age of ~ 7-10 Myr (Briceno et al., 2007, ApJ 661, 1119).
goruh-e karbonil (#)
Fr.: groupe carbonyl
The radical -C=O, which occurs in several compounds, such as → aldehydes and ketones.
Fr.: groupe cyclic
A group in which each element can be expressed as a power of any other element.
goruh-e gaz (#)
Fr.: groupe de jauge
The mathematical group associated with a particular set of gauge transformations.
1) goruh (#); 2) goruhândan; goruhidan
Fr.: 1) groupe; 2) grouper; se grouper
1a) Any collection or assemblage of persons or things considered together or
regarded as belonging together; e.g.
→ Local Group of galaxies.
From Fr. groupe "cluster, group," from It. gruppo "cluster, packet, knot," likely from P.Gmc. *kruppa "round mass, lump."
Goruh "group," from Mid.Pers. grôh "group, crowd."
negare-ye goruh (#)
Fr.: théorie des groupes
A branch of mathematics concerned with structures called → groups and the description of their properties. Group theory provides a powerful formal method of analyzing abstract and physical systems in which → symmetry is present. It has a very considerable use in physics, especially → quantum mechanics, notably in analyzing the → eigenstates of energy of a physical system.
Fr.: vitesse de groupe
The act or process of uniting into groups.
Verbal noun of → group.
Hickson Compact Group (HCG)
goruh-e hampak-e Hickson
Fr.: groupe compact de Hickson
A list of 100 compact groups of galaxies that were identified by a systematic search of the → Palomar Observatory Sky Survey red prints. Each group contains four or more galaxies, has an estimated mean surface brightness brighter than 26.0 magnitude per arcsec2 and satisfies an isolation criterion.
hydroxyl group (OH)
goruh-e hidroksil (#)
Fr.: groupe hydroxyle
The univalent radical or group consisting of one hydrogen and one oxygen atom, forming a part of a molecule of a compound.
From → hydro- + ox(y)- a combining form meaning "sharp, acute, pointed, acid," used in the formation of compound words, from Gk, oxys "sharp, keen, acid" + -yl a suffix used in the names of chemical radicals, from Fr. -yle, from Gk. hyle "matter, substance;" → group.
goruh-e mahali (#)
Fr.: Groupe local
A small → galaxy cluster of about 50 galaxies to which our → Milky Way galaxy belongs. The Local Group occupies a volume of space nearly 10 million → light-years across centered somewhere between the → Andromeda Galaxy (M31) and the Milky Way, which are the dominant galaxies of the group; Andromeda being the principal member. Both of these galaxies exhibit spiral structures, and each is attended by a large family of satellite → dwarf galaxies. The Local Group also includes a third spiral galaxy known as → Triangulum (M33), which is bound to Andromeda. The remaining members span a range of → Hubble classification types from dwarf spheroidal to Irr to Sb and Sc and cover a factor of 10 in → metallicity. The total mass of the Local Group is estimated to be about 2 × 1012 solar masses, although this value is still uncertain to within a factor of about 2. The velocities of the individual galaxies of the Local Group are not particularly high. Therefore no member is believed to be able to escape the group, which is thus considered to be gravitationally → bound. Another remarkable member of the Group is → IC 10.
Fr.: groupe mobile
A young → stellar population that shares a common space motion. A moving group remains kinematically distinct within the general field stars at ages < 1 billion years, before being dispersed. As progenitor gas is cleared by OB star winds, and the natal cluster expands, stars with sufficiently high velocities become unbound and form a young, coeval moving group, possibly leaving behind a bound open cluster. Because of their common origin, moving group members have a shared age and composition. The nearest moving group is the → TW Hydrae association.
platinum group element (PGE)
bonpâr-e goruh-e pelâtin
Fr.: élément du groupe du platine
One of the six metals → platinum (Pt), → iridium (Ir), → osmium (Os), → palladium (Pd), → rhenium (Rh), and → ruthenium (Ru) that are grouped together in the → periodic table. They are relatively hard and resistant to corrosion and are used in jewellery and in some industrial applications. All are resistant to chemical attack.
Fr.: groupe du Sculpteur
The nearest group of galaxies to our → Local Group, lying near the south Galactic pole at about 10 million → light-years distance. The Sculptor Group is dominated by five galaxies, four spiral (NGC 247, 253, 300, and 7793) and one irregular (NGC 55). The brightest of the five is NGC 253. The nearest galaxy in this group is NGC 55 which at a distance of 5 million light-years lies on the border of the Local Group.
Fr.: groupe d'espace
Set of operations (rotation about an axis, reflection across a plane, translation, or combination of these) which when carried out on a periodic arrangement of points in space brings the system of points to self-coincidence.
The word group comes from the mathematical notion of a group.
Fr.: groupe de symétrie
A group of symmetry-preserving operations composed of all rigid motions or similarity transformations of some geometric object onto itself.
goruh-e yekâyi, ~ yekâni
Fr.: groupe unitaire
The set of n × n unitary matrices (→ unitary matrix).
Fr.: groupe de travail
A group of people working together to achieve a stated goal.