The condition in which a physical system is capable of assuming either of two stable states.
Fr.: bistabilité par saut
An abrupt discontinuity in the → stellar wind properties of → hot stars near → effective temperatures about 21,000 K and 10,000 K, corresponding to O9.5-B3 supergiants (Castor et al. 1975, ApJ 195, 157; Lamers et al., 1995, ApJ 455, 269). At these temperatures the → terminal velocity of the wind drops steeply by about a factor two and the → mass loss rate increases steeply by about a factor three to five, when going from high to low temperatures. Bistability jump is related to the degree of ionization in the wind. With a little drop in the temperature, the dominant driving element (Fe) will recombine to lower ionization stages which produces a lower terminal velocity and a relatively high density in the wind. → wind momentum. Additional bistability jumps may occur at higher temperatures where CNO may provide the dominant line driving, especially for low metallicity stars (Vink et al. 2001, A&A 369, 574). However, a recent study using a larger sample finds that there is a gradual decline in the wind terminal velocities of early B supergiants and not a "jump" (Crowther et al. 2006, A&A 446, 279).
Fr.: mécanisme de bistabilité
The mechanism that accounts for the → bistability jump.
black hole surface gravity
gerâni-ye ruye-ye siyah câl
Fr.: gravité de surface de trou noir
tâbandegi-ye tafsanji, ~ tafsanjik
Fr.: luminosité bolométrique
The total rate of energy output of an object integrated over all wavelengths.
Fr.: luminosité de coupure
A characteristic luminosity around which the → luminosity function of a sample of galaxies changes to a steeper slope or exponentially declines.
Fr.: vitesse de rupture
The velocity of a → rotating star at which the → centrifugal force equals the → gravitational force. Also known as → critical velocity. The simplest expression of the break-up velocity for an OB star, ignoring the → Eddington luminosity, is given by the relation: v = (GM / R)1/2, where M and R are the mass and radius of the star respectively, and G the → gravitational constant. A more realistic expression takes into account not only the → radiation pressure, but also the non-uniformity of the brightness over the stellar surface, as indicated by → von Zeipel theorem. With these conditions, the break-up velocity has a more complicated formula, corresponding to the velocity reached when somewhere on the star the → total gravity becomes zero.
The ability to receive or contain.
From M.Fr. capacité, from L. capacitatem, from capax "able to hold much," from capere "to take, grasp."
Gonjâyeš "capacity, holding, containing," from gonjdan "to be contained; to hold exactly; to be filled;" Mid.Pers. winj- "to be contained;" Proto-Iranian *uiac-/*uic-; cf. Skt. vyac- "to contain, encompass," vyás- "extent, content, extension;" L. uincire "to bind."
Same as → capillary action.
The relationship between causes and effects
Causality, from → causal + -ity.
Bonârmandi, from bonâr→ cause + -mand suffix denoting relation, affinity + -i noun forming suffix.
Fr.: principe de causalité
The principle that cause must always precede effect.
The quality of being physically caustic.
1) An apparently hollow formation in the structure of an astronomical
object, for example a sizable hole on the surface of a
→ molecular cloud created by
→ ultraviolet photons of a
→ massive star.
From M.Fr. cavité, from L.L. cavitas "hollowness," from L. cavus "hollow."
Kâvâk, related to verb kâvidan (kâftan) "to dig; to examine, investigate," cf. L. cavus "hollow" (E. derivatives: cavity, concave, cave, excavate), Gk. koilos "hollow," Armenian sor, PIE *kowos "hollow."
center of gravity
Fr.: centre de gravité
Gerânigâh, from gerâni→ gravity + -gâh "place."
The condition of being → chaotic.
Fr.: densité de charge
The → electric charge per unit volume in space, or per unit area on a surface, or per unit length of a line. They are respectively called volume- (ρ), surface- (σ), or line (λ) charge density.
Fr.: symétrie charge-parité
The laws of physics should be the same if a particle is interchanged with its → antiparticle (→ charge conjugation), or swapped for its mirror image (→ parity symmetry). It is known that charge-parity (CP) symmetry holds for interactions involving → electromagnetism, → gravitation, and → strong interactions, but CP violation is known to occur during → weak interactions involved in → radio decay. Same as → CP-symmetry.
karvani-ye šimiyâyi, ~ šimik
Fr.: affinité chimique
The extent to which a chemical species, such as an atom or molecule, tends to combine with another to form a chemical compound.
The geometric property of a rigid object that is → chiral.