An Etymological Dictionary of Astronomy and Astrophysics
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The → process by which the relative → abundance of a given → chemical element or → species in an → astrophysical object is increased. For example the the → increase of the → heavy element content of the → interstellar medium due to → stellar evolution.

→ chemical; → enrichment.

The → enrichment of deuterium (D) with respect to → hydrogen (H) in → Solar System molecules when compared with the D/H ratio in the → interstellar → solar nebula. H-bearing molecules in → comets, → planets, and → chondrite  → meteorites show a systematic D enrichment relative to the → molecular hydrogen of the solar nebula. Because there is no nuclear source for D in the Universe, the observed → isotopic enrichment must have its origin in chemical reactions having faster reaction rates for D than for H. In the Solar nebula the → isotopic fractionation of D between → water and H followed the reversible reaction:
H₂O + HD ⇔ HDO + H₂.
At low temperatures, this reaction favors the concentration of D in HDO. In the → interstellar medium grain chemistry plays a crucial role in D enrichment. See also → enrichment factor.
Apart from → deuterium fractionation, D could be enriched through another mechanism. Since molecular hydrogen (H₂) is more → volatile than molecular deuterium (D₂), D/H ratio could increase in certain planets that orbit near their star.

→ deuterium; → enrichment.

The ratio between the D/H value in → water and in → molecular hydrogen, as expressed by:
f = [(1/2)HDO/H₂O]/[(1/2)HD/H₂] = (D/H)_H2O/(D/H)_H2.
When f> 1, there is → deuterium enrichment.

→ deuterium; → enrichment; → factor.

One of the following conditions for a → Fourier series to converge:
1) The function f(x) is defined and single valued, except possibly at a finite number of points in the interval -π, +π.
2) f(x) has a period of 2π.
3) f(x) and f'(x) are → piecewise continuous functions on -π, +π.
Then, the Fourier series converges to:
(a) f(x) if x is a point of continuity.
(b) (f(x + 0) + f(x - 0))/2, if x is a point of discontinuity.

Named after Peter Gustav Lejeune Dirichlet (1805-1859), German mathematician who made valuable contributions to → number theory, → analysis, and → mechanics; → condition.

To increase the → concentration or → abundance of a specified → component or → isotope in a material.

From en- a prefix forming verbs with a particular sense + → rich.

Pordâridan, pordâr kardan, infinitives from pordâr, → rich.

Supplied with abundance of something. → enriched gas, → enriched uranium.

Past participle of → enrich.

A gas, usually → interstellar, in which the → abundance of particular chemical or atomic species is higher than the expected values.

→ enriched; → gas.

Uranium in which the → proportion of the → isotope U-235 has been increased (above the 0.7% value in natural uranium).

→ enriched; → uranium.

1) A process that changes the → isotopic ratio in a material. For example, for uranium the ratio of U-235 to U-238 may be increased by gaseous diffusion of uranium hexafluoride.
2) → chemical enrichment.

Verbal noun of → enrich.

A galaxy, usually young, which has a relatively important gas content.

→ gas; → rich; → galaxy.

A → giant star whose observed → lithium abundance is much higher (A(Li) ~ 2.95) than that predicted by stellar → evolutionary models. Standard evolutionary models predict severe → depletion of surface Li → abundance, which is as low as 1.4 → dex in K giants, a factor of about 80 lower than the maximum value of about 3.3 dex observed in → main sequence stars. Observations confirm model predictions showing much less Li compared to model predictions in most → red giant branch (RGB) stars (Kumar et al., 2018, J. Astrophys. Astr. 39, 25 and references therein).

→ lithium; → rich; → giant.

An environment (→ galaxy, → nebula) whose → metallicity is larger than that of the → Milky Way galaxy.

→ metal; → rich; → environment.

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.

→ metal; → rich; → star.

Having large amounts of something specified. → metal-rich environment, → rich cluster; → enrich, → enrichment, → richness, → poor.

M.E., from O.E. rice "wealthy, powerful" (cf. Du. rijk, Ger. reich "rich"), from PIE base *reg- "move in a straight line," hence, "to direct, rule" (cf. Mod.Pers./Mid.Pers. râst "right, straight;" O.Pers. rāsta- "straight, true," rās- "to be right, straight, true;" Av. rāz- "to direct, put in line, set," razan- "order;" Skt. raj- "to direct, stretch," rjuyant- "walking straight;" Gk. orektos "stretched out;" L. regere "to lead straight, guide, rule," p.p. rectus "right, straight;" Ger. recht; E. right).

Por "full, much, very, too much" (Mid.Pers. purr "full;" O.Pers. paru- "much, many;" Av. parav-, pauru-, pouru-, from par- "to fill;" PIE base *pelu- "full," from *pel- "to be full;" cf. Skt. puru- "much, abundant;" Gk. polus "many," plethos "great number, multitude;" O.E. full); pordâr, literally "having much possession," from por + dâr "having, possessor," from dâštan "to have, to possess," → property.

A → galaxy cluster with a particularly large number of galaxies.

→ rich; → cluster.

Same as → energy cascade

Named after L. F. Richardson (1922), Weather Prediction by Numerical Process (Cambridge Univ. Press); → cascade.

A condition for the onset of → instability in multilayer fluids which compares the balance between the restoring force of → buoyancy and the destabilizing effect of the → shear.

Named after the British meteorologist Lewis Fry Richardson (1881-1953), who first arrived in 1920 to the dimensionless ratio now called → Richardson number. The first formal proof of the criterion, however, came four decades later for → incompressible flows (Miles, J. W. 1961, J. Fluid Mech., 10, 496; Howard, L. N., 1961, J. Fluid Mech., 10, 509). Its extension to → compressible flows was demonstrated subsequently (Chimonas 1970, J. Fluid Mech., 43, 833); → criterion.

A dimensionless number which is used according to the → Richardson criterion to describe the condition for the → stability of a flow in the presence of vertical density stratification. If the → shear flow is characterized by linear variation of velocity and density, with velocities and densities ranging from U₁ to U₂ and ρ₁ to ρ₂ (ρ₂>ρ₁), respectively, over a depth H, then the Richardson number is expressed as: Ri = (ρ₂ - ρ₁) gH / ρ₀ (U₁ - U₂)². If Ri < 0.25, somewhere in the flow turbulence is likely to occur. For Ri > 0.25 the flow is stable.

→ Richardson criterion; → number.

The property of being very abundant.

→ rich; → -ness.

A classification of → galaxy clusters into six groups (0 to 5), as in the → Abell catalog. It depends on the number of galaxies in a given cluster that lie within a → magnitude range m₃ to m₃₊₂, where m₃ is the magnitude of the 3rd brightest member of the cluster. The first group contains 30-49 galaxies and the last group more than 299 galaxies.

→ richness; → group.