An Etymological Dictionary of Astronomy and Astrophysics
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The interval of time during which an object turns once about its axis.

→ rotation; → period.

A position parameter used in → stellar magnetic field studies. Its zero value represents the moment when, during → stellar rotation, the positive → magnetic pole is nearest to the → line of sight.

→ rotation; → phase.

A type of → turbulence with motions more vigorous in the horizontal than in the vertical direction occurring in internal radiation zone of → rotating stars. Same as → shear turbulence.

→ rotation; → induced; → turbulence.

A → neutron star that is spinning down as a result of → torques from → magnetic dipole radiation and particle emission. RPPs derive their energy primarily from the → rotation of the neutron star. The energy from their → spin-down appears as broad-band pulsations from → radio to → gamma-ray wavelengths and as a → wind of energetic particles flowing into their surrounding → pulsar wind nebulae. Since the discovery of RPPs through their radio → pulsations in 1967, more than 2000 → radio pulsars are now known with periods ranging from a few milliseconds to several seconds (A. K. Harding, 2013, Front. Phys. 8, 679).

→ rotation; → power; → pulsar.

The spectrum of a molecule resulting from the simultaneous rotation and vibration of its constituent atoms.

→ rotation; → vibration; → spectrum.

Of or pertaining to → rotation.

Rotational, adj., from → rotation + → -al.

The → angular momentum of a body rotating about an axis. The rotational angular momentum of a solid homogeneous sphere of mass M and radius R rotating about an axis passing through its center with a period of T is given by: L = 4πMR²/5T.

→ rotational; → angular; → momentum.

An imaginary line about which a solid object rotates. Same as → rotation axis and → axis of rotation.

→ rotational; → axis.

The spectral line broadening caused by stellar rotation. Light from two rims of the star will be Doppler shifted in opposite directions, resulting in a line broadening effect. The line broadening depends on the inclination of the star's pole to the line of sight. The derived value is a function of v_e. sini, where v_e is the rotational velocity at the equator and i is the inclination, which is not always known. The fractional width (Δλ/λ) is of the order of 10^-3 for B stars.

→ rotational; → broadening.

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.

The → kinetic energy due to the → rotation of and object. Rotational energy is part of the total kinetic energy of the body. It is given by: (1/2)Iω², where I is the → moment of inertia and ω is the → angular velocity. Same as → angular kinetic energy.

→ rotational; → energy.

A consequence of → stellar rotation that deforms the star, triggers instabilities (→ shear turbulence and → meridional currents) leading to → transport of chemical species in the star. The efficiency of rotational mixing (measured for instance by the degree of surface → enrichments at a given → evolutionary stage) increases when the initial mass and rotation increase. This efficiency increases also when the initial → metallicity decreases. This is due to the fact that when the metallicity is lower, the stars are more compact. This makes the → gradients of the → angular velocity steeper in the stellar interiors. Steeper gradients produce stronger shear turbulence and thus more mixing. Rotational mixing can bring to the surface heavy elements newly synthesized in the stellar core. Rotation thus produces an increase of the → opacity of the outer layers and activates strong → mass loss through → radiatively driven winds. This effect may be responsible for the loss of large fractions of the initial mass of the star (Meynet et al. 2007, arXiv:0709.2275).

→ rotational; → mixing.

A very small variation in the surface brightness of a single star due to its rotation. Several types of stars are known to have photospheric spots. Brightness variation occurs as rotation carries star spots or other localized activity across the line of sight.

→ rotational; → modulation.

Of a → rigid body, a motion in which there are always two points of the body which remain motionless.

→ rotational; → motion.

→ rotation period.

→ rotational; → period.

A slight change in the energy level of a molecule due to the rotation of its constituent atoms about their center of mass.

→ rotational; → transition.

The velocity of a → rotational motion; same as → angular velocity.

→ rotational; → velocity.

An integral constraint used to quantify the uncertainty on the extent of → convective overshooting and its effect on models of stars.

Roxburgh, I. 1989, A&A, 211, 361; → criterion.

Same as → significance testing and → test of significance.

→ rule; → decision.

A fundamental constant of atomic physics appearing in the → Rydberg formula. The Rydberg constant for hydrogen is 109,739 cm^-1.

→ rydberg; → constant.