An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 31 Search : limit
photon tiring limit
  حد ِ خستگی ِ فوتون   
hadd-e xastegi-ye foton

Fr.: limite par fatigue du photon   

The maximum → mass loss rate of a star when the → wind luminosity equals the total available → stellar luminosity. The mechanical luminosity of the wind at infinity is given by: Lwind = Mdot (v2/2 + GM/R) = Mdot (v2/2 + vesc2/2). For Lwind = L*, the mass loss rate is Mdotmax = 2L*/(v2 + vesc2). Following Owoki & Gayly (1997), Mdottir is the maximum mass loss rate when the wind just escapes the gravitational potential, with v tending toward zero. Mdottir is much larger than typical mass loss rates from → line-driven winds, where the driving lines become saturated with increasing density limiting the wind mass loss rates to about 10-4 Msun yr-1 in even the most luminous stars.

photon; tiring, from tire "to weary; become weary," → tired; → limit.

Roche limit
  حد ِ رُش   
hadd-e Roche

Fr.: rayon de Roche   

The smallest distance at which a → satellite under the influence of its own → gravitation and that of a central mass about which it is describing a → Keplerian orbit can be in equilibrium. This does not, however, apply to a body held together by the stronger forces between atoms and molecules. At a lesser distance the → tidal forces of the → primary body would break up the → secondary body. The Roche limit is given by the formula d = 1.26 RMMm)1/3, where RM is the radius of the → primary body, ρM is the → density of the primary, and ρm is the density of the secondary body. This formula can also be expressed as: d = 1.26 Rm (MM/Mm)1/3, where Rm is the radius of the secondary. As an example, for the Earth-Moon system, where RM = 6,378 km, ρM = 5.5 g cm-3, and ρm = 2.5 g cm-3 is 1.68 Earth radii.

Named after Edouard Albert Roche (1820-1883), the French astronomer who first calculated this theoretical limit in 1848; → limit.

rotational Eddington limit
  حد ِ ادینگتون ِ چرخشی   
hadd-e Eddington-e carxeši

Fr.: limite d'Eddington avec rotation   

The → Eddington limit of luminosity for a → rotating star in which both the effects of → radiative acceleration and rotation are important. Such objects mainly include → OB stars, → LBV, → supergiants, and → Wolf-Rayet stars. It turns out that the maximum permitted luminosity of a star is reduced by rotation, with respect to the usual Eddington limit (Maeder & Meynet, 2000, A&A, 361, 159).

rotational; → Eddington limit.

Schönberg-Chandrasekhar limit
  حدّ ِ شونبرگ-چاندراسکهار   
hadd-e Schönberg-Chandrasekhar

Fr.: limite de Schönberg-Chandrasekhar   

During the → main sequence stage, a star burns the hydrogen in its core and transforms it into helium. When the helium mass amounts to about 10% of the initial stellar mass, the star can no longer maintain the → hydrostatic equilibrium in its core; the star increases its volume and leaves the main sequence in order to become a → red giant.

Named after the Brazilian astrophysicist Mario Schönberg (1914-1990) and Subramahmanyan Chandrasekhar, → Chandrasekhar limit, who were the first to point out this limit and derive it (1942, ApJ 96, 161).

solar ecliptic limit
  حد ِ هورپهی ِ خورشید   
hadd-e hurpehi-ye xoršid

Fr.: limite écliptique du Soleil   

The greatest angular distance from a → lunar orbit node within which a → solar eclipse may occur when the Sun and Moon are in conjunction there. The solar ecliptic limit extends about 17° on each side of the node.

solar; → ecliptic; → limit.

static limit
  حد ِ ایستا   
hadd-e istâ

Fr.: limite stationnaire   

Same as → stationary limit.

static; → limit.

stationary limit surface
  رویه‌ی ِ حدّ ِ ایست‌ور   
ruye-ye hadd-e istvar

Fr.: surface limite stationnaire   

A property of → space-time outside a → rotating black hole, which consists of a surface which geometrically bounds the → ergosphere outward. At the stationary limit a particle would have to move with the local light velocity in order to appear stationary to a distant observer. This is because the space here is being dragged at exactly the speed of light relative to the rest of space. Outside this limit space is still dragged, but at a rate less than the speed of light. Also known as → static limit.

stationary; → limit; → surface.

substellar limit
  حدّ ِ زیر-ستاره‌ای   
hadd-e zir-setâre-yi

Fr.: limite sous-stellaire   

The mass limit below which → hydrogen fusion cannot take place, and the cloud collapse cannot lead to the formation of a star. The limit is 0.075 → solar masses, corresponding to about 80 Jupiter masses.

substellar; → limit.

upper limit
  حدِ بالا، ~ زبرین   
hadd-e bâlâ (#), ~ zabarin (#)

Fr.: limite supérieure   

Of an integral operator, the point at which the integration ends.

upper; → limit.

upper mass limit
  حد ِ بالایی ِ جرم، ~ زبرین ِ ~   
hadd-e bâlâyi-ye jerm, ~ zabarin-e ~

Fr.: limite supérieure de masses   

The highest mass range admitted in a star formation model. The high mass end of the → initial mass function. The upper mass limit is a critical parameter in understanding → stellar populations, → star formation, and → massive star feedback in galaxies.

upper; → mass; → limit.

volume-limited survey
  بردید با گنج ِ حدمند   
bardid bâ gonj-e hyaddmand

Fr.: relevé limité en volume   

A survey in which the observed objects are contained in a given volume of space.

volume; → limited; → survey.

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