An Etymological Dictionary of Astronomy and Astrophysics
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An emission arising from the → maser process.

→ maser; → emission.

An → electromagnetic radiation emitted by → interstellar molecules through → transitions between → energy states of → molecules.

→ molecular; → emission.

A type of radioactive decay of atoms containing excess neutrons, in which a neutron is ejected from the nucleus.

→ neutron; → emission.

→ non-thermal radiation.

→ non-thermal; → emission.

A → continuum emission with frequencies in the radio range of the electromagnetic spectrum.

→ radio; → continuum; → emission.

→ Electromagnetic radiation carried by → radio waves.

→ radio; → emission.

The emission of → secondary electrons from the surface of a material when an incident particle (often, charged particle such as electron or ion) impacts the material with sufficient energy.

→ secondary; → emission.

The emission of electromagnetic radiation from an atom or molecule that does not depend on the presence of external fields.

→ spontaneous; → emission.

The process by which an electron, which is already in an excited state (an upper energy level, in contrast to its lowest possible level or "ground state"), can "stimulate" a transition to a lower level, producing a second photon of the same energy. The quantum energy of the incoming photon should be equal to the energy difference between its present level and the lower level. This process forms the basis of both the → laser and → maser. Same as → induced emission.

Stimulated, p.p. of → stimulate; → emission.

→ thermal radiation.

→ thermal; → emission.

Electrons gaining enough thermal energy to escape spontaneously from the cathode or dynodes and mimic photoelectrons.

thermion; → emission.

The simultaneous emission of two photons whose sum of energies is equal to that of a single electron transition. The energy of each individual photon of the pair is not fixed, so that the spectrum of two-photon emission is continuous from the wavelength of that transition to infinity. In practice, there is a peak in wavelength distribution of the emitted photons. Two-photon emission is studied atomic physics with application in astrophysics, as it contributes to the continuum radiation from → planetary nebulae. It was recently observed in condensed matter and specifically in → semiconductors.

→ two; → photon; → emission.

A member of a class of cntral stars of planetary nebula, → CSPN, which have weaker and narrower emission lines than → Wolf-Rayet-like CSPNe (Tylenda et al. 1993, A&AS 102, 595).

→ weak; → emission; → line.