felez-e qalyâyi (#)
Fr.: métal alcalin
Any of the chemical elements belonging to group A of the → periodic table, which burn vigorously in air; i.e. → lithium, → sodium, → potassium, → rubidium, → cesium, and → francium. Alkali metals have a → valence of one and are softer and less dense than other metals.
alkaline earth metal
felez-e qalyâyi-ye xâki (#)
Fr.: terre alcaline
Any of the metallic chemical elements belonging to group 2 of the → periodic table; i.e. → beryllium, → magnesium, → calcium, → strontium, → barium, and → radium. They are not found free in the nature because they are highly reactive.
Felez, → metal; qalyâyi, → alkaline; xâki "of or pertaining to soil," from xâk, → soil.
carbon-enhanced metal-poor star (CEMP)
setâre-ye kamfelez-e karbon bolandidé
Fr.: étoile pauvre en métaux enrichie en carbon
A star that presents very low → iron → abundances [Fe/H] < -4 but an → anomalous richness in carbon. CEMP stars have been defined as a subset of → metal-poor stars that exhibit elevated [C/Fe] ≥ +1.0. It has been recognized that ~15-20% of stars with [Fe/H] < -2.0 are carbon enhanced. This fraction rises to 30% for [Fe/H] < -3.0, to 40% for [Fe/H] < -3.5, and ~75% for [Fe/H] < -4.0. This increasing trend of CEMP-star frequency with declining [Fe/H] is confirmed by the observation of many thousands of CEMP stars (Daniela Carollo + ApJ 2014, 788, 180). See also → extremely metal-poor star (EMPS)
Fr.: métallicité critique
The → metallicity of a → star-forming → molecular cloud when → cooling → rates by → metals dominate the → gravitational → heating during → protostellar collapse. The minimum → Jeans mass achieved by gravitational → fragmentation depends on the presence/absence of → coolants in the cloud. Since cooling rate in metal lines is more efficient than in primordial molecular lines (H2 and HD), metals favor fragmentation in gas and formation of → low-mass stars.
→ critical; → metallicity.
extremely metal-poor star (EMPS)
stâre-ye ostomâné kamfelez
Fr.: étoile extrêmement pauvre en métaux
A star with an iron abundance [Fe/H] < -3 found in a → galactic halo. These stars, whose → metallicity is typically less than one thousandth of the solar value, are believed to have formed shortly after the → Big Bang, 13.7 billion years ago. The number of such stars depends on the primordial → initial mass function. If the IMF were steep, there could, in principle, be a lot of EMPSs formed at high → redshifts. Thus many of them could have ended up in the halos of galaxies. See also → Population III star.
Fr.: métallicité de gaz
The metallicity derived from observations of the gas component of a galaxy. It is mainly measured from optical → emission lines using primarily oxygen abundances. The gas → metallicity is one of the most important tools to investigate the evolutionary history of galaxies. The reason is that the gas metallicity of galaxies is basically determined by their star-formation history. Recent observational studies has allowed the investigation of the gas metallicity even in → high redshift beyond z = 1, such as → Lyman break galaxies, submillimeter-selected high-z galaxies, and so on. Such observational insights on the metallicity evolution of galaxies provide constraints on the theoretical understandings of the formation and the evolution of galaxies.
→ gas; → metallicity.
Fr.: environnement faible en métaux
A medium in which chemical elements have abundances smaller than the solar values.
→ low; → metallicity; → environment.
mass-metallicity relation (MZR)
Fr.: relation masse-métallicité
A correlation between the → stellar mass (or → luminosity) and the → gas metallicity of → star-forming galaxies (Lequeux et al. 1979) according to which massive galaxies have higher gas metallicities. Several large galaxy surveys, such as the → Sloan Digital Sky Survey (SDSS), have confirmed that galaxies at all → redshifts with higher stellar masses retain more metals than galaxies with lower stellar masses. Besides the dependence on stellar mass, other studies have found further dependences of gas metallicity on other physical properties at a given mass, such as → specific star formation rate, → star formation rate, and stellar age. These higher dimensional relations could provide additional constraints to the processes that regulate the metal enrichment in galaxies. In addition to gas metallicity, also the → stellar metallicity of galaxies is found to correlate with the stellar mass, suggesting the mass-metallicity relation already existed at early epochs of galaxy evolution (Lian et al., 2017, MNRAS 474, 1143, and references therein).
→ mass; → metallicity; → relation.
1) Chemistry: An → element in which the highest
occupied energy band (→ conduction band) is only partially
filled with electrons.
From O.Fr. metal, from L. metallum "metal, mine, quarry, what is got by mining," from Gk. metallon "metal, ore," originally "mine, quarry, pit," probably from metalleuein "to mine, to quarry," of unknown origin, but related somehow to metallan "to seek after."
Felez "metal," loanword from Ar. filizz.
Fr.: déficience en métaux
The quality of being metal deficient, e.g. → metal-deficient galaxy.
→ metal; deficiency from L. deficientem (nominative deficiens), pr.p. of deficere "to desert, fail," from → de- "down, away" + facere "to do, perform" + -ency a noun suffix, equivalent to -ence.
Kamfelezi, from kam "little, few; deficient, wanting; scarce" (Mid.Pers. kam "little, small, few," O.Pers./Av. kamna- "small, few," related to keh "small, little, slender" (related to kâstan, kâhidan "to decrease, lessen, diminish," from Mid.Pers. kâhitan, kâstan, kâhênitan "to decrease, diminish, lessen;" Av. kasu- "small, little;" Proto-Iranian *kas- "to be small, diminish, lessen") + felez→ metal + -i suffix denoting state.
Fr.: galaxie pauvre en métaux
A galaxy whose → metallicity is smaller than that of the → Milky Way galaxy.
Adj. from → metal deficiency; → galaxy.
Fr.: pauvre en métaux
Describing an → astronomical object in which the → chemical abundances of → heavy elements are lower than that of a reference value (usually solar or of Milky Way).
Fr.: galaxie pauvre en métaux
Same as → metal-deficient galaxy.
Fr.: environnement riche en métaux
An environment (→ galaxy, → nebula) whose → metallicity is larger than that of the → Milky Way galaxy.
→ metal; → rich; → environment.
Fr.: étoile riche en métaux
A star whose → metal content is higher than the → solar metallicity. The stars that harbor → extrasolar planets tend to be considerably more metal-rich than the average → Population I star in the Galactic neighborhood. See also → super-metal-rich star.
Any language that is used to describe a language. See also → object language.
Of, relating to, or consisting of metal.
Fr.: hydrogène métallique
A kind of → degenerate matter resulting from hydrogen gas when it is sufficiently compressed to undergo a phase change to liquid or solid state. Metallic hydrogen is thought to be present in compressed astronomical objects, such as the interiors of the solar system planets Jupiter and Saturn. Above the core of these planets (at a temperature of 10,000 degrees and a pressure of 3 million bars) the electrons are squeezed out of the hydrogen atoms and the fluid starts to conduct like a metal.
In a star, nebula, or galaxy, the proportion of the material that is made up of
→ metals, that is elements heavier than → helium.
It is generally denoted by Z.
The term "metallicity" is a misnomer used in astrophysics.
metallicity distribution function (MDF)
karyâ-ye vâbâžeš-e felezigi
Fr.: fonction de distribution de métallicité
A plot representing the number of stars (or systems) per metallicity interval, usually expressed in [Fe/H] (abundance of → iron relative to → hydrogen).
→ metallicity; → distribution; → function.