ionization correction factor (ICF)
karvand-e aršâyeš-e yoneš
Fr.: facteur de correction d'ionisation
A quantity used in studies of → emission nebulae to convert the → ionic abundance of a given chemical element to its total → elemental abundance. The elemental abundance of an element relative to hydrogen is given by the sum of abundances of all its ions. In practice, not all the ionization stages are observed. One must therefore correct for unobserved stages using ICFs. A common way to do this was to rely on → ionization potential considerations. However, → photoionization models show that such simple relations do not necessarily hold. Hence, ICFs based on grids of photoionization models are more reliable. Nevertheless here also care should be taken for several reasons: the atomic physics is not well known yet, the ionization structure of a nebula depends on the spectral energy distribution of the stellar radiation field, which differs from one model to another, and the density structure of real nebulae is more complicated than that of idealized models (see, e.g., Stasińska, 2002, astro-ph/0207500, and references therein).
Fr.: énergie d'ionisation
Same as → ionization potential.
Fr.: front d'ionisation
An abrupt discontinuity between an H II region and the molecular cloud in which it has formed. In this transition region interstellar gas changes from a mostly neutral state to a mostly ionized state.
Fr.: paramètre d'ionisation
A ratio representing the number of ionizing photons to the number of electrons in a nebular emitting region.
Fr.: potentiel d'ionisation
The energy required to remove an electron from an isolated atom or molecule. The ionization potential for hydrogen is 13.6 eV, which corresponds to an ultraviolet ionizing photon with a wavelength of 912 A. Also called → ionization energy.
Fr.: stratification d'ionisation
The spatial distribution of ionic species around an ionization source according to their → ionization potentials. The higher the ionization potential, the nearer to the source the corresponding ions will be.
ionization-bounded H II region
nâhiye-ye H II-e yoneš-karânmand
Fr.: région H II bornée par ionisation
To change into ions. Verbal form of → ionization.
Converted into ions.
P.p. of → ionize.
gâz-e yonidé (#)
Fr.: gaz ionisé
A gas composed partially or totally of → ions.
ionized hydrogen region
nâhiye-ye hidrožen-e yonidé (#)
Fr.: région d'hydrogène ionisé
Same as → H II region.
tâbeš-e yonandé (#)
Fr.: rayonnement ionisant
A photon that has enough energy to remove an electron from an atom or molecule, thus producing an ion and free electrons.
The region of the Earth's upper atmosphere containing a small percentage of free electrons and ions produced by photoionization of the constituents of the atmosphere by solar ultraviolet radiation.
A general purpose software package for the reduction and analysis of astronomical data. It is aimed specifically at the reduction of imaging and spectroscopy data obtained using → CCD detector systems. IRAF is developed by the National Optical Astronomy Observatories (NOAO).
Short for Image Reduction and Analysis Facility.
gâhšomâr-e Irâni (#)
Fr.: calendrier iranien
The most accurate solar calendar in use, which is based on two successive passages of the Sun through the true vernal equinox. The year length, defined by an ingenious intercalation system devised by the mathematician Omar Khayyâm (A.D. 1048-1131), is 365.2424.. solar days, in perfect agreement with the → vernal-equinox year of 365.24236 solar days (epoch +2000). This interval should not be confounded with the → tropical year of 365.2422 solar days. The most remarkable feature of the calendar is Nowruz, the spring festival, which has its profound roots in the Zoroastrian worldview. Same as → Persian calendar. Click here for more details.
Iranian, of or pertaining to Iran "(land of) the Aryans," as below; → calendar.
Gâhšomâr, → calendar; Irâni adj. of Irân, from Mid.Pers. Êrân "(land of) the Aryans," pluriel of êr "noble, hero," êrîh "nobility, good conduct;" Parthian Mid.Pers. aryân; O.Pers. ariya- "Aryan;" Av. airya- "Aryan;" cf. Skt. ārya- "noble, honorable, respectable."
From L. iris (genitive iridis) "rainbow," + → -escence.
Producing a display of lustrous, rainbow-like colors.
A metallic chemical element; symbol Ir. Atomic number 77; atomic weight 192.22; melting point about 2,410°C; boiling point about 4,130°C; specific gravity 22.55 at 20°C. Iridium is a very hard, usually brittle, extremely corrosion-resistant silver-white metal with a face-centered cubic crystalline structure. The unusually high concentration of iridium found in the thin clay layer that marks the boundary between the Cretaceous and Tertiary rocks is attributed to an asteroid impact with Earth 65 million years ago.
Iridium coined 1804 by its discoverer, E. chemist Smithson Tennant (1761-1815) from Gk. → iris "rainbow;" so called for the varying color of its compounds.
1) The circular diaphragm forming the colored portion of the eye and perforated by
the pupil in its center. → pupil = mardomak
Iris, M.E., from L. irid-, iris "colored part of the eye, rainbow, iris plant, a precious stone," from Gk. iris, iridos "rainbow, iris plant, iris of the eye," initially "a messenger of the gods, regarded as the goddess of the rainbow." The eye portion was so called for being the colored part.
Titak, from Kermâni, Tâleši, variants Lori tiya, Dehxodâ dictionary tuk, probably from didan "to see," Mid.Pers. ditan "to see, regard, catch sight of, contemplate, experience;" O.Pers. dī- "to see;" Av. dā(y)- "to see," didāti "sees;" cf. Skt. dhī- "to perceive, think, ponder; thought, reflection, meditation," dādhye; Gk. dedorka "have seen."
miyânband-e titaki, ~ titakvâr
Fr.: diaphragme iris
A mechanical device, consisting of thin overlapping plates, designed to smoothly vary the effective diameter of a lens, thereby controlling the amount of light allowed through.