isolated massive star formation
diseš-e vâyutide-ye setâre-ye porjerm
Fr.: formation isolée d'étoile massive
Massive star formation outside → OB associations. Recent observational findings suggest that → massive star formation is a collective process. In other words, massive stars form in → cluster environments and the mass of the most massive star in a cluster is correlated with the mass of the cluster itself. Nevertheless, other observational results give grounds for supposing that massive stars do not necessarily form in clusters but that they can be formed as isolated stars or in very small groups. According to statistical studies nearly 95% of Galactic → O star population is located in clusters or OB associations. This means that a small percentage, about 5%, of high mass stars may form in isolation. Isolation is meant not traceable to an origin in an OB association. This definition therefore excludes → runaway massive stars, which are thought to result from either dynamical interaction in massive dense clusters, or via a kick from a → supernova explosion in a → binary system. Alternatively, isolated massive star has been defined as follows: An O-type star belonging to a cluster whose total mass is < 100 Msun and moreover is devoid of → B stars (Selier et al. 2011, A&A 529, A40 and references therein).
isolated neutron star (INS)
setâre-ye notroni-ye vâyutidé
Fr.: étoile à neutron isolée
A → neutron star which does not belong to a → binary system, does not have radio emission, and is not surrounded by a progenitor → supernova remnant. INSs appear to be thermally cooling with no emission outside the → soft X-ray band, except for faint optical/UV counterparts. Although these properties are similar to those of → compact central object (CCO)s, they are a distinct class because they lack any observable associated supernova remnant or nebula. There are presently seven confirmed INSs (sometimes referred to as The Magnificent Seven), six of which have measured weakly modulated X-ray pulsations with periods between 3 s and 11 s, much longer than those of CCOs (A. K. Harding, 2013, Front. Phys. 8, 679).
Fr.: système isolé
An act or instance of isolating; the state of being isolated.
Verbal noun of → isolate.
Physics: Any of two or more nuclei having the same atomic number A and mass number Z
but different half-lives.
Back formation from isomeric, from → iso- + mer a combining form meaning "part," from Gk. meros "part, portion, share."
Izomer, loan from Fr. isomère.
A line drawn through all points on a weather map having the same amount of → cloud cover.
From Gk. → iso- + nephos "cloud," cognate with Pers. nam "humidity, moisture;" Av. napta- "moist," nabās-câ- "cloud," nabah- "sky;" Skt. nábhas- "moisture, cloud, mist;" L. nebula "mist," nimbus "rainstorm, rain cloud;" O.H.G. nebul; Ger. Nebel "fog;" O.E. nifol "dark;" from PIE *nebh- "cloud, vapor, fog, moist, sky."
Of or relating to → isophotes.
Fr.: rayon isophotal
The size attributed to a galaxy corresponding to a particular level of → surface brightness. The reason is that galaxies do not have sharp edges.
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."
The quality of an imaging system which is characterized by → isoplanatism.
Izobirâh, from izo-, → iso-, + birâh "a devious path; a wanderer, who deviates, errs."
Fr.: angle isoplanatique
The angle in which the → point spread function of the atmosphere/telescope system is space invariant. Because of the presence of → turbulence in high layers of the atmosphere, this angle is extremely small, often only a few seconds of arc at visible wavelengths. See also → aplanatism.
pac-e izobirâh, teke-ye ~
Fr.: tache isoplanatique
The spatial region where the variation of the → point spread function of an imaging system is considered negligible.
In an imaging system, the unvarying of the → point spread function over an extended field of view.
The condition in which the wavefronts arriving from different parts of a region of sky undergo almost identical phase perturbations. See also → isoplanatic patch.
A line on a map connecting points of equal value. For example the contour lines joining points of equal altitude on a topographic map. Some other examples of isopleths are: → isobar, → isoneph, and → isohel.
Izocand, from izo-, → iso-, + cand replacing candi (after prefix) "quantity," from Mid.Pers. candih "amount, quantity," from cand "how many, how much; so many, much;" O.Pers. yāvā "as long as;" Av. yauuant- [adj.] "how great?, how much?, how many?," yauuat [adv.] "as much as, as far as;" cf. Skt. yāvant- "how big, how much;" Gk. heos "as long as, until."
sebar-e do-pahlu-barâbar (#)
Fr.: triangle équilatéral
A triangle having two sides equal.
From L.L. isosceles, from Gk. isoskeles "with equal legs; that can be divided into two equal parts," from isos "equal, identical," → iso-, + skelos "leg."
A quantum number based on the assumption that the nucleon (proton and neutron) is a single entity having two states, like → spin. It is conserved by the strong interaction. Same as isotopic spin, isobaric spin.
Meteo.: A line on a map or graph joining points of equal temperature.
Isotherm, back formation from → isothermal.
1) Relating to or having a constant temperature.
Isothermal, from → iso- + therm, from Gk. therme "heat" thermos "warm;" cognate with Pers. garm "warm" (garmâ "heat, warmth," from Mid.Pers. garmâg; O.Pers./Av. garəma- "hot, warm;" cf. Skt. gharmah "heat;" L. formus "warm," fornax "oven;" P.Gmc. *warmaz; O.E. wearm; E. warm; O.H.G., Ger. warm; PIE *ghworm-/*ghwerm- "warm") + → -al; → process.