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De Vaucouleur's Law
In astronomy, de Vaucouleurs's law, also known as the de Vaucouleurs profile or de Vaucouleurs model, describes how the surface brightness I of an elliptical galaxy varies as a function of apparent distance R from the center of the galaxy: \ln I(R) = \ln I_ - k R^. By defining ''Re'' as the radius of the isophote containing half of the total luminosity of the galaxy, the half-light radius, de Vaucouleurs profile may be expressed as: \ln I(R) = \ln I_ + 7.669 \left 1 - \left( \frac \right)^ \right or I(R) = I_ e^ where ''Ie'' is the surface brightness at ''Re''. This can be confirmed by noting \int^_0 I(r)2\pi r \, dr = \frac \int^_0 I(r)2\pi r \, dr . De Vaucouleurs model is a special case of Sersic's model, with a Sersic index of . A number of (internal) density profiles that approximately reproduce de Vaucouleurs's law after projection onto the plane of the sky include Jaffe's model and Dehnen's model. The model is named after Gérard de Vaucouleurs Gérard Henri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astronomy
Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest include planets, natural satellite, moons, stars, nebulae, galaxy, galaxies, meteoroids, asteroids, and comets. Relevant phenomena include supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, astronomy studies everything that originates beyond atmosphere of Earth, Earth's atmosphere. Cosmology is a branch of astronomy that studies the universe as a whole. Astronomy is one of the oldest natural sciences. The early civilizations in recorded history made methodical observations of the night sky. These include the Egyptian astronomy, Egyptians, Babylonian astronomy, Babylonians, Greek astronomy, Greeks, Indian astronomy, Indians, Chinese astronomy, Chinese, Maya civilization, M ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Elliptical Galaxy
An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the three main galaxy morphological classification, classes of galaxy described by Edwin Hubble in his Hubble sequence#Physical significance, Hubble sequence and 1936 work ''The Realm of the Nebulae'', with their intermediate scale disks, a subset of the "early-type" galaxy population. Most elliptical galaxies are composed of older, stellar evolution#Low-mass stars, low-mass stars, with a sparse interstellar medium, and they tend to be surrounded by large numbers of globular clusters. Star formation activity in elliptical galaxies is typically minimal; they may, however, undergo brief periods of star formation when merging with other galaxies. Elliptical galaxies are believed to make up approximately 10–15% of galaxies in the Virgo Supercluster, and they are not the dominant type of galaxy in the universe overall. They are preferentially fou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Contour Line
A contour line (also isoline, isopleth, isoquant or isarithm) of a Function of several real variables, function of two variables is a curve along which the function has a constant value, so that the curve joins points of equal value. It is a cross-section (geometry)#Definition, plane section of the graph of a function of two variables, three-dimensional graph of the function f(x,y) parallel to the (x,y)-plane. More generally, a contour line for a function of two variables is a curve connecting points where the function has the same particular value. In cartography, a contour line (often just called a "contour") joins points of equal elevation (height) above a given level, such as mean sea level. A contour map is a map illustrated with contour lines, for example a topographic map, which thus shows valleys and hills, and the steepness or gentleness of slopes. The contour interval of a contour map is the difference in elevation between successive contour lines. The gradient of t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Half-light Radius
Galaxy effective radius or half-light radius (R_e) is the radius at which half of the total light of a galaxy is emitted. This assumes the galaxy has either intrinsic circular symmetry, spherical symmetry or is at least circularly symmetric as viewed in the plane of the sky. Alternatively, a half-light Contour line, contour, or Contour line#Other phenomena, isophote, may be used for spherically and circularly asymmetric objects. R_e is an important length scale in \sqrt[4] R term in de Vaucouleurs's law, which characterizes a specific rate at which surface brightness decreases as a function of radius: I(R) = I_e \cdot e^ where I_e is the surface brightness at R = R_e. At R = 0, I(R=0) = I_e \cdot e^ \approx 2000 \cdot I_e Thus, the central surface brightness is approximately 2000 \cdot I_e. See also References Physical quantities Radii Equations of astronomy {{astronomy-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Jaffe Profile
The Jaffe profile (or Jaffe model) is a mathematical function that is used to describe the distribution of mass or light in elliptical galaxies and the bulges of spiral galaxies. It was proposed by the astronomer An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, natural satellite, moons, comets and galaxy, galax ... Walter Jaffe in 1983. Its usefulness derives from the fact that it accurately reproduces a de Vaucouleurs profile when projected onto the sky. The density in the Jaffe model is given by : \rho (r) = \left(\right)^ \left(1+\right)^. In this equation, \rho_0 and r_0 are parameters that can be varied to fit the observed density. Jaffe described how he arrived at his model: he formulawas derived heuristically from the observation that the brightness profiles of spherical galaxies seem to run as r^ and r^ in at least som ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gérard De Vaucouleurs
Gérard Henri de Vaucouleurs (25 April 1918 – 7 October 1995) was a French astronomer best known for his studies of galaxies. Life and career Gérard de Vaucouleurs was born on April 25, 1918 in Paris, he took the maiden name of his mother as his last name. He had an early interest in amateur astronomy and received his undergraduate degree in 1939 at the Sorbonne in that city. After military service in World War II, he resumed his pursuit of astronomy. He was married to fellow astronomer Antoinette de Vaucouleurs on October 31, 1944, and the couple would frequently collaborate on astronomical research. He was fluent in English and spent 1949-51 in England and 1951–57 in Australia at Mount Stromlo Observatory. He was at Lowell Observatory in Arizona from 1957-1958 and at Harvard from 1958-60. In 1960 he was appointed to the University of Texas at Austin, where he spent the rest of his career. He was one of the first five faculty in the newly formed astronomy departm ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astrophysics
Astrophysics is a science that employs the methods and principles of physics and chemistry in the study of astronomical objects and phenomena. As one of the founders of the discipline, James Keeler, said, astrophysics "seeks to ascertain the nature of the heavenly bodies, rather than their positions or motions in space—''what'' they are, rather than ''where'' they are", which is studied in celestial mechanics. Among the subjects studied are the Sun ( solar physics), other stars, galaxies, extrasolar planets, the interstellar medium, and the cosmic microwave background. Emissions from these objects are examined across all parts of the electromagnetic spectrum, and the properties examined include luminosity, density, temperature, and chemical composition. Because astrophysics is a very broad subject, ''astrophysicists'' apply concepts and methods from many disciplines of physics, including classical mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
