An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) Composed of two like parts or members.
2) Twice as large, heavy, strong, etc.
3) Anything that is twofold in size or amount or twice the usual size, quantity, strength, etc.

From O.Fr. duble, from L. duplus "twofold" (Gk. diplos "double"), from duo "two" + -plus "fold."

Dotâyi, from dotâ, from do "two," akin to L. duo, + tâ "fold, plait, ply; piece, part," Mid.Pers. tâg "piece, part."

An electron-photon interaction that can be thought of as a → Compton scattering event associated with the production or destruction of an extra photon.

→ double; → Compton; → scattering.

The simplest case of a → multiple integral.

→ double; → integral.

A → binary pulsar consisting of two pulsars. The only known example is PSR J0737-3039 (A and B), discovered in 2003 (Burgay et al. Nature 426, 531). The rotation periods of the pulsars are 22.7 and 2.8 milliseconds respectively. Each of them has a mass about 1.3 times that of the Sun and revolves around their → center of gravity with a period of 2.4 hours. According to the theory of → general relativity, such a binary should lose energy through the emission of → gravitational waves. As deduced from the change in orbital period, the separation of the pulsars is reducing by about 7 mm per day, in exact agreement with theory. It is expected that the pulsars will eventually merge in about 85 million years.

→ double; → pulsar.

Formation of two refracted rays of light from a single incident ray; property of certain crystals, notably calcite.

→ double; → refraction.

A → root x₀ of function f(x), if f(x₀) = 0, df/dx | x₀ = 0, and d²f/dx² | x₀≠ 0. See also → simple root.

→ double; → root.

A situation in the evolution of an → asymptotic giant branch star whereby both hydrogen and helium shells provide energy alternatively. As the burning → helium shell approaches the hydrogen-helium discontinuity, its luminosity decreases because it runs out of the fuel. As a consequence, the layers above contract in response, thus heating the extinguished → hydrogen shell until it is re-ignited. However, the shells do not burn at the same rate: the He burning shell becomes thermally unstable and undergoes periodic → thermal pulses.

→ double; → shell; → burning.

A pair of adjacent holes or slits made on a dark and plane surface, used in optical experiments, such as interference and diffraction.

→ double; → slit.

An apparently single star which better observational resolution shows it to be a pair of closely lying stars. They may or may not be physically related.

→ double; → star.

Same as → diplopia.

→ double; → vision.

A → double-lined binary with two → white dwarf components. Short-period double white dwarfs can lose → orbital angular momentum by emitting → gravitational radiation and if the total mass of the binary exceeds the → Chandrasekhar limit, their eventual → merger might produce a → Type Ia supernova.

→ double; → white; → dwarf.

A system of evolved → binary stars in which both → components have ejected their envelopes and evolve toward → white dwarf stage. So far a half dozen double-degenerate → binary systems are known, for example Henize 2-248 (M. Santander-Garcia et al., 2015, 518, 5).

→ double; → degenerate; → binary; → system.

An instability involving two layers of fluid with opposite gradients of properties. Same as → fingering instability. See also → salt finger. Double-diffusive instabilities commonly occur in any astrophysical fluid that is stable according to the → Ledoux criterion, as long as the entropy and chemical stratifications have opposing contributions to the dynamical stability of the system. They drive weak forms of convection, and can cause substantial heat and compositional → mixing. Two cases can be distinguished. In fingering convection, entropy is stably stratified (∇ - ∇ad < 0), but chemical composition is unstably stratified (∇μ < 0); it is often referred to as → thermohaline convection by analogy with the oceanographic context in which the instability was first discovered. In oscillatory double-diffusive convection, entropy is unstably stratified (∇ - ∇ad > 0), but chemical composition is stably stratified (∇μ > 0); it is related to semiconvection, but can occur even when the → opacity is independent of composition (P. Garaud, 2014, arXiv:1401.0928).

→ double;→ diffusive; → system.

A → spectroscopic binary in which the → spectral lines of both stars are seen and the lines are alternatively double and single. Same as → SB2 binary. See also: → single-lined binary.

→ double; → line; → binary

A → double-lined spectroscopic binary whose → light curve is typical of an → eclipsing binary.

→ double; → line; → eclipsing; → binary.

Same as → double-lined binary.

→ double; → line; → spectroscopic; → binary.

A → galaxy that emits radio energy from two regions located on opposite sides of the galaxy.

→ double; → lobe; → radio; → source.

An experiment of → diffraction and → interference of two light beams using a → double slit; → Young's experiment.

→ double; → slit; → experiment.

A pair of forbidden spectral lines of the same atom arising from a common upper excitation level, for example [O III] λ 5007 and [O III] λ 4959, [N II] λ 6584 and [N II] λ 6548, and [S II] λ 6717, [S II] λ 6731.
A pair of associated lines arising from transitions having a common lower energy level in a spectrum characteristic of the alkali metals.

From O.Fr. doublet, from → double + -et diminutive suffix.

Dotâyé, from dotâ→ double + -(y)é nuance suffix.

A pair of stars that lie close to each other in the sky by chance, but are not physically associated, in contrast to a true → binary star.

→ optical; → double star.