nemudâr-e Hertzsprung-Russell (#)
Fr.: diagramme de Hertzsprung-Russell
A display of stellar properties using a plot of
→ effective temperature (or instead
→ color or → spectral type)
along the abscissa versus
(or → absolute magnitude). The temperature is plotted
in the inverse direction, with high temperatures on the left and low temperatures on
the right. On the diagram the majority of stars are concentrated in a diagonal strip running
from upper left to lower right, i.e. from high temperature-high luminosity
→ massive stars to low
temperature-low luminosity → low-mass stars.
This feature is known as the
→ main sequence. This is the locus of stars burning hydrogen in
their cores (→ proton-proton chain).
The lower edge of this strip, known as the
→ zero age main sequence (ZAMS), designates the positions
where stars of different mass first begin to burn hydrogen in their cores. Well below
the main sequence there is a group of stars that, despite
being very hot, are so small that their luminosity is very small as a
consequence. These are the class of → white dwarfs.
These objects represent old and very evolved
stars that have shed their outer layers to reveal a very small but
extremely hot inner core. They are no longer generating energy
but are merely emitting light as they cool
(→ white dwarf cooling track).
Stars with high luminosities but relatively low temperatures occupy a wide region
above the main sequence. The majority of them have used up all
the hydrogen in their cores and have expanded and cooled as a result of internal
readjustment. Called → red giants, they are still
burning helium in their cores (→ helium burning,
→ carbon burning).
There are also stars with very high luminosities, resulting from their
enormous outputs of energy, because they are burning their fuel at a prodigious rate.
These are the → supergiants. They can be hot or cool,
hence blue or red in color. Same as → H-R diagram.
Named after the Danish Ejnar Hertzsprung (1873-1967) and the American Henry Norris Russell (1877-1957). However, the first H-R diagram was published not by Hertzpurung neither Russell, but by a PhD student of Karl Schwarzschild at Göttingen. The student was Hans Rosenberg (1879-1940), who in 1910 published the diagram for stars in the → Pleiades (Astronomische Nachrichten, Vol. 186 (4445), p. 71, 1910). Although Hertzpurung had a very preliminary diagram in 1908, his first proper diagram was published in 1911. Likewise, Russell published his version only in 1915 with the better and more numerous data then available (Nielsen, A.V., 1969, Centaurus 9, 219; Valls-Gabaud, D., 2002, Observed HR diagrams and stellar evolution, ASP Conf. Proceedings, Vol. 274. Edited by Thibault Lejeune and João Fernandes); → diagram.
Fr.: diagramme de Hess
A diagram showing the relative density of occurrence of stars at various → color-magnitude positions of the → Hertzsprung-Russell diagram for a given → galaxy.
Named after R. Hess who originated it in 1924: "Die Verteilungsfunktion der absoluten Helligkeiten in ihrer Abhängigkeit vom Spektrum". Probleme der Astronomie. Festschrift fur Hugo v. Seeliger. Springer, Berlin. p. 265; → diagram.
nemudâr-e sotuni (#)
A type of graphical representation, used in statistics, in which frequency distributions are illustrated by rectangles.
Histogram, from Gk. histo-, a combining form meaning "tissue," from histos "mast, loom, beam, warp, web," literally "that which causes to stand," from histasthai "to stand," from PIE *sta- "to stand" (cf. Pers. ist-, istâdan "to stand;" O.Pers./Av. sta- "to stand, stand still; set;" Skt. sthâ- "to stand;" L. stare "to stand;" Lith. statau "place;" Goth. standan); → -gram.
Nemudâr, → diagram + sotuni "column-like," from sotun "column," from Mid.Pers. stun, from O.Pers. stênâ "column," Av. stuna-, Skt. sthuna- "column."
A three-dimensional image produced with the technique of → holography.
nemudâr-e Hubble (#)
Fr.: diagramme de Hubble
A plot of the → redshift of galaxies against their distance or against their → apparent magnitude.
Fr.: diagramme de Hunter
A diagram where the surface → nitrogen → chemical abundance of stars is plotted against their → projected rotational velocity (v sini).
I. Hunter et al., 2009, A&A, 496, 841; → diagram.
The graphical record made by a → hygrograph.
Fr.: diagram de Jablonski
An energy schematic representing the → electronic states of a → molecule and the → transitions between them. The vertical axis shows energies whereas → energy states are grouped horizontally according to their spin → multiplicity. Radiation-less transitions are symbolized by usual arrows, while → radiative transitions are represented by wavy arrows. The vibrational ground states of each electronic state are indicated with thick lines and the higher → vibrational states with thinner lines.
Named after Aleksander Jablonski (1898-1980), a Polish physicist who was an expert in the field of luminescence and atomic optics; → diagram.
Fr.: diagramme de Kiel
A version of the → H-R diagram displaying stellar gravities (→ gravity, log g) against the corresponding → effective temperatures (Teff).
Named after the group of astrophysicists (W.-R. Hamann, W. Schmutz, U. Wessolowski) working at Kiel University (Germany), who introduced the diagram in 1980s; → diagram.
The basic unit of mass in the → International System of Units (SI) and → MKS versions of the → metric system, equal to 1,000 → grams. The kilogram was until 2019 defined as the mass of the standard (international prototype) kilogram, a platinum-iridium cylinder kept at the International Bureau of Weights and Measures (BIPM), at Sèvre, near Paris, France. Copies of this prototype are kept by the standards agencies of all the major industrial nations. A kilogram is equal to the mass of 1,000 cubic cm of water at 4°C (→ maximum density). According to the new (2019) definition, the kilogram is defined by taking the fixed numerical value of the → Planck constant (h) to be 6.62607015 × 10-34 when expressed in the unit J.s, which is equal to kg m2 s-1, where the meter and the second are defined in terms of c and Δν Cs.
A metric unit of force which is equal to a mass of one kilogram multiplied by the standard acceleration due to gravity on Earth (9.80665 m sec-2). Therefore one (1) kilogram-force is equal to 1 kg × 9.80665 m sec-2 = 9.80665 → newtons.
Fr.: diagrame de Kippenhahn
A plot representing the evolution of the internal structure of a star as a function of time. The x-axis indicates the time, the y-axis the mass, and a color or shading specifies convective regions. A vertical line through the graph corresponds to a model at a particular time.
Named after Rudolf Kippenhahn (1926-), a German astrophysicist; → diagram
Fr.: diagramme de Kruskal
A diagram used to plot trajectories in → space-time near a → black hole. The vertical and horizontal axes are two complicated functions of time and distance from the black hole. Lines of constant time radiate from the origin of the diagram, with steeper slopes corresponding to later times. Lines of constant distance are hyperbolas, lines of constant time pass through the origin; photons always travel along diagonal lines at ±45° to the vertical. The trajectory of an object falling into the black hole is shown as a curving line moving upward on the diagram at less than 45° to the vertical.
Named after the American physicist Martin David Kruskal (1925-2006); → diagram.
barnâme-sâzi-ye xatti (#)
Fr.: programmation linéaire
A procedure for finding the maximum or minimum of a → linear function where the → arguments are subject to linear → constraints. For problems involving more than two variables or problems involving a large number of constraints, solution methods used are those that are adaptable to computers. A well-known such → algorithm is the → simplex method.
→ linear; → programmings.
Fr.: diagramme logique
A diagram that uses special symbols called logic symbols to represent the detailed functioning of electronic logic circuits. The symbols do not represent the type of electronics used, but only their functions.
Fr.: périodogramme de Lomb-Scargle
An algorithm for detecting and characterizing periodic signals in unevenly-sampled data. The Lomb-Scargle periodogram has a particularly wide use within the astronomy community. This method allows efficient computation of a Fourier-like → power spectrum estimator from such unevenly-sampled data, resulting in an intuitive means of determining the period of oscillation (see VanderPlas, 2017, astro-ph/1703.09824 and references therein).
Named after Lomb, N. R. 1976, Ap&SS 39, 447 and Scargle, J. D. 1982, ApJ 263, 835; → periodogram.
A graphic representation of solar magnetic field strengths and polarity.
Fr.: diagramme de Minkowski
Same as → space-time diagram.
→ Minkowski metric; → diagram.
Fr.: programme orienté objet
In computer science a programming technique that uses → objects and their interactions to design applications and programs.
→ object; oriented, p.p. from the verb of → orientation; → programming.
Barnâme-sâzi, → programming; barâxt, → object; gerâ agent adj. of gerâyidan "to incline toward; to intend; to make for." The stem gerâ may be a variant of Mod.Pers. kil "bent, inclined" (k/g and l/r interchanges), from PIE base *klei- "to lean, incline," cognate with L. clinare "to bend" (E. declination, inclination, etc.), Gk. klinein "to cause to slope, slant, incline," Skt. sri- "to lean," O.Pers. θray-, Av. sray- "to lean," P.Gmc. *khlinen (Ger. lehnen, E. lean).
A four-sided → polygon whose opposite sides are parallel. A parallelogram all of whose angles are right angles is a → rectangle.
From Fr. parallélogramme, from L. parallelogrammum, from Gk. parallelogrammon "bounded by parallel lines," from parallelos, → parallel, + gramme "line," related to graphein "to write, draw" → -graph.