An Etymological Dictionary of Astronomy and Astrophysics
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Of a → CCD detector, a pixel that has higher charge loss. Hot pixels are a type of noise affecting almost every CCD camera. They are caused by small contamination or production faults in the CCD sensor area.

→ hot; → pixel.

A compact, highly luminous region in a cataclysmic binary located in the accretion disk where the stream of material hits it.

→ hot; → spot.

A member of a class of stars having high → effective temperatures (above some 15,000 K); mainly → massive stars, but also including → exciting stars of → planetary nebulae, → white dwarfs, and → symbiotic stars.

→ hot; → star.

The → photoelectric effect whereby photons absorbed by a solid (→ semiconductor) raise electrons from a lower to a higher → energy level (from → valence band to → conduction band). See also → external photoelectric effect.

→ internal; → photoelectric; → effect.

Of or relating to → isophotes.

→ isophote; → -al.

The size attributed to a galaxy corresponding to a particular level of → surface brightness. The reason is that galaxies do not have sharp edges.

→ isophotal; → radius.

A line joining points with the same surface brightness on a plot or in image of a celestial object such as a nebula or galaxy.

Isophote, from → iso- + a combining form of Gk. phos (gen. photos) "light."

Izošid, from izo-, → iso-, + šid "light, sunlight," from Mid.Pers. šêt "shining, radiant, bright;" Av. xšaēta- "shining, brilliant, splendid, excellent."

An → ultraviolet photon with an energy between 11.2 and 13.6 eV, corresponding to the energy range in which the Lyman and Werner absorption bands of → molecular hydrogen (H₂) are found (→ Lyman band, → Werner band). The first generation of stars produces a background of Lyman-Werner radiation which can → photodissociate molecular hydrogen, the key → cooling agent in metal free gas below 10⁴ K. In doing so, the Lyman-Werner radiation field delays the collapse of gaseous clouds, and thus star formation. After more massive → dark matter clouds are assembled, atomic line cooling becomes effective and H₂ can begin to shield itself from Lyman-Werner radiation.

→ Lyman; → Werner band; → photon.

Photometry using narrow-band filters to isolate a particular spectroscopic line or molecular band.

→ narrow band; → photometry.

The supersymmetric partner of the → photon.

From phot, from → photon + -ino supersymmetric particle suffix.

From Gk. combining form of phos (genitive photos).

Šid- "light, sunlight," from Mid.Pers. šÃªt "shining, radiant, bright;" Av. xšaēta- "shining, brilliant, splendid, excellent."
Nur-, → light.

A situation in which all of the energy of a photon is transferred to an atom, molecule, or nucleus.

→ photo- + → absorption.

Electrode capable of releasing electrons when illuminated.

→ photo- + → cathode.

The study of the chemical and physical changes occurring when a molecule or atom absorbs photons of light.

→ photo- + → chemistry.

Th desorption of surface substances by ultraviolet radiation.

→ photo-; → desorption.

The process by which atomic nuclei are broken apart into their constituent protons and neutrons by the impact of high energy gamma photons. Photodisintegration takes place during the core collapse phase of a → Type II supernova explosion.

→ photo- + → disintegration.

To dissociate a → molecule by → radiation. See also → photodissociation.

→ photo-; → dissociate.

The → dissociation of a → chemical compound by → radiation  → energy.

Verbal noun of → photodissociate; → -tion.

A neutral region at the boundary of a → molecular cloud created by the penetration of → far ultraviolet (FUV) radiation from associated stars. The FUV radiation (6 eV ≤ hν ≤ 13.6 eV) dissociates the molecules and heats the gas and dust. A warm, atomic → H I region is thus created and the chemistry and thermal balance of the region are determined by the penetrating FUV photons. The progressive absorption of FUV photons leads to the occurrence of transitions between atomic and molecular phases, such as H I/H₂ and C II/C I/CO transitions. By extension, any neutral region where the physics is controlled by FUV photons can be called a PDR, as it is the case for → diffuse interstellar clouds or the edge of → circumstellar disks. The PDR concept was first studied by A. G. G. M. Tielens and D. Hollenbach (1985, ApJ 291, 722).

→ photodissociation + → region.

Pertaining to electronic or other electrical effects that are due to the action of electromagnetic radiation, especially visible light.

→ photo- + → electric.