|
Plummer Model
The Plummer model or Plummer sphere is a density law that was first used by H. C. Plummer to fit observations of globular clusters. It is now often used as toy model in N-body simulations of stellar systems. Description of the model The Plummer 3-dimensional density profile is given by \rho_P(r) = \frac \left(1 + \frac\right)^, where M_0 is the total mass of the cluster, and ''a'' is the Plummer radius, a scale parameter that sets the size of the cluster core. The corresponding potential is \Phi_P(r) = -\frac, where ''G'' is Newton's gravitational constant. The velocity dispersion is \sigma_P^2(r) = \frac. The isotropic distribution function reads f(\vec, \vec) = \frac \frac (-E(\vec, \vec))^, if E < 0, and otherwise, where is the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Henry Crozier Keating Plummer
Henry Crozier Keating Plummer FRS FRAS (24 October 1875 – 30 September 1946) was an English astronomer. Early years and education Born in Oxford, Plummer was the son of William Edward Plummer (1849–1928) and nephew of the distinguished astronomer John Isaac Plummer (1845-1925). He gained his education at St. Edward's School and then Hertford College at Oxford University. After studies in physics, he became a lecturer at Owen's College, Manchester, instructing in mathematics. Career In 1900, he became an assistant at the Radcliffe Observatory, Oxford, where his father had served previously. He remained there for most of the next twelve years, spending one year at Lick Observatory as a Research Fellow. In 1912, he was appointed to the position of Andrews Professor of Astronomy at Trinity College, Dublin, which carried with it the title of Royal Astronomer of Ireland. He was the last holder of both positions. He was the director of the Dunsink Observatory from 1912 to 1920. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Astronomy And Astrophysics
''Astronomy & Astrophysics (A&A)'' is a monthly peer-reviewed scientific journal covering theoretical, observational, and instrumental astronomy and astrophysics. It is operated by an editorial team under the supervision of a board of directors representing 27 sponsoring countries plus a representative of the European Southern Observatory. The journal is published by EDP Sciences and the current editors-in-chief are Thierry Forveille and João Alves. History Origins ''Astronomy & Astrophysics'' was created as an answer to the publishing situation found in Europe in the 1960s. At that time, multiple journals were being published in several countries around the continent. These journals usually had a limited number of subscribers, and articles were written in languages other than English. They were less widely read than American and British journals and the research they reported had therefore less impact in the community. Starting in 1963, conversations between astronomers from ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Monte Carlo Method
Monte Carlo methods, or Monte Carlo experiments, are a broad class of computational algorithms that rely on repeated random sampling to obtain numerical results. The underlying concept is to use randomness to solve problems that might be deterministic in principle. The name comes from the Monte Carlo Casino in Monaco, where the primary developer of the method, mathematician Stanisław Ulam, was inspired by his uncle's gambling habits. Monte Carlo methods are mainly used in three distinct problem classes: optimization, numerical integration, and generating draws from a probability distribution. They can also be used to model phenomena with significant uncertainty in inputs, such as calculating the risk of a nuclear power plant failure. Monte Carlo methods are often implemented using computer simulations, and they can provide approximate solutions to problems that are otherwise intractable or too complex to analyze mathematically. Monte Carlo methods are widely used in va ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Star Clusters
A star cluster is a group of stars held together by self-gravitation. Two main types of star clusters can be distinguished: globular clusters, tight groups of ten thousand to millions of old stars which are gravitationally bound; and open clusters, less tight groups of stars, generally containing fewer than a few hundred members. As they move through the galaxy, over time, open clusters become disrupted by the gravitational influence of giant molecular clouds, so that the clusters we observe are often young. Even though they are no longer gravitationally bound, they will continue to move in broadly the same direction through space and are then known as stellar associations, sometimes referred to as ''moving groups''. Globular clusters, with more members and more mass, remain intact for far longer and the globular clusters we observe are usually billions of years old. Star clusters visible to the naked eye include the Pleiades and Hyades open clusters, and the globular cluster ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
N-body Units
''N''-body units are a completely self-contained system of units used for ''N''-body simulations of self-gravitating systems in astrophysics. In this system, the base physical units are chosen so that the total mass, ''M'', the gravitational constant, ''G'', and the virial radius, ''R'', are normalized. The underlying assumption is that the system of ''N'' objects (stars) satisfies the virial theorem In mechanics, the virial theorem provides a general equation that relates the average over time of the total kinetic energy of a stable system of discrete particles, bound by a conservative force (where the work done is independent of path), with .... The consequence of standard ''N''-body units is that the velocity dispersion of the system, ''v'', is \scriptstyle \frac\sqrt and that the dynamical or crossing time, ''t'', is \scriptstyle 2\sqrt . The use of standard ''N''-body units was advocated by Michel Hénon in 1971. Early adopters of this system of units included H. Co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Cubic Function
In mathematics, a cubic function is a function of the form f(x)=ax^3+bx^2+cx+d, that is, a polynomial function of degree three. In many texts, the ''coefficients'' , , , and are supposed to be real numbers, and the function is considered as a real function that maps real numbers to real numbers or as a complex function that maps complex numbers to complex numbers. In other cases, the coefficients may be complex numbers, and the function is a complex function that has the set of the complex numbers as its codomain, even when the domain is restricted to the real numbers. Setting produces a cubic equation of the form :ax^3+bx^2+cx+d=0, whose solutions are called roots of the function. The derivative of a cubic function is a quadratic function. A cubic function with real coefficients has either one or three real roots ( which may not be distinct); all odd-degree polynomials with real coefficients have at least one real root. The graph of a cubic function always has a single infl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Circular Orbit
A circular orbit is an orbit with a fixed distance around the barycenter; that is, in the shape of a circle. In this case, not only the distance, but also the speed, angular speed, Potential energy, potential and kinetic energy are constant. There is no periapsis or apoapsis. This orbit has no Radial orbit, radial version. Listed below is a circular orbit in astrodynamics or celestial mechanics under standard assumptions. Here the centripetal force is the gravitational force, and the axis mentioned above is the line through the Center of mass, center of the central mass perpendicular to the orbital plane. Circular acceleration :wikt:transverse, Transverse acceleration (perpendicular to velocity) causes a change in direction. If it is constant in magnitude and changing in direction with the velocity, circular motion ensues. Taking two derivatives of the particle's coordinates concerning time gives the centripetal acceleration : a\, = \frac \, = where: *v\, is Kinetic e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Cubic Function
In mathematics, a cubic function is a function of the form f(x)=ax^3+bx^2+cx+d, that is, a polynomial function of degree three. In many texts, the ''coefficients'' , , , and are supposed to be real numbers, and the function is considered as a real function that maps real numbers to real numbers or as a complex function that maps complex numbers to complex numbers. In other cases, the coefficients may be complex numbers, and the function is a complex function that has the set of the complex numbers as its codomain, even when the domain is restricted to the real numbers. Setting produces a cubic equation of the form :ax^3+bx^2+cx+d=0, whose solutions are called roots of the function. The derivative of a cubic function is a quadratic function. A cubic function with real coefficients has either one or three real roots ( which may not be distinct); all odd-degree polynomials with real coefficients have at least one real root. The graph of a cubic function always has a single ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Specific Relative Angular Momentum
In celestial mechanics, the specific relative angular momentum (often denoted \vec or \mathbf) of a body is the angular momentum of that body divided by its mass. In the case of two orbiting bodies it is the vector product of their relative position and relative linear momentum, divided by the mass of the body in question. Specific relative angular momentum plays a pivotal role in the analysis of the two-body problem, as it remains constant for a given orbit under ideal conditions. " Specific" in this context indicates angular momentum per unit mass. The SI unit for specific relative angular momentum is square meter per second. Definition The specific relative angular momentum is defined as the cross product of the relative position vector \mathbf and the relative velocity vector \mathbf . \mathbf = \mathbf\times \mathbf = \frac where \mathbf is the angular momentum vector, defined as \mathbf \times m \mathbf. The \mathbf vector is always perpendicular to the instant ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Virial Theorem
In mechanics, the virial theorem provides a general equation that relates the average over time of the total kinetic energy of a stable system of discrete particles, bound by a conservative force (where the work done is independent of path), with that of the total potential energy of the system. Mathematically, the theorem states that \langle T \rangle = -\frac12\,\sum_^N \langle\mathbf_k \cdot \mathbf_k\rangle, where T is the total kinetic energy of the N particles, F_k represents the force on the kth particle, which is located at position , and angle brackets represent the average over time of the enclosed quantity. The word virial for the right-hand side of the equation derives from , the Latin word for "force" or "energy", and was given its technical definition by Rudolf Clausius in 1870. The significance of the virial theorem is that it allows the average total kinetic energy to be calculated even for very complicated systems that defy an exact solution, such as those co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Herwig Dejonghe
Herwig is both a masculine German given name and a surname. Notable people with the name include: Given name: *Herwig Ahrendsen (born 1948), German handball player *Herwig Dirnböck (born 1935), Austrian sprint canoeist *Herwig Drechsel (born 1973), Austrian footballer *Herwig Görgemanns (born 1931), German classical scholar * Herwig Kircher (born 1955), Austrian footballer *Herwig Kogelnik (born 1932), Austrian electrical engineer *Herwig Mitteregger (born 1953), Austrian musician * Herwig Reiter (born 1941), Austrian composer *Herwig Schopper (born 1924), German physicist *Herwig van Staa (born 1942), Austrian politician *Herwig Wolfram (born 1934), Austrian historian Surname: *Bob Herwig (1914–1974), American football player *Conrad Herwig (born 1959), American jazz trombonist *Holger Herwig (born 1941), German-Canadian historian *Malte Herwig (born 1972), German writer, journalist and literary critic *Walther Herwig (1838–1912), German jurist, biologist and politician *Chri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
