Showing papers by "Scott Tremaine published in 1984"

Dynamical friction in spherical systems

Abstract: On etudie la friction dynamique sur un objet test (tel qu'une barre ou un satellite) qui tourne ou evolue dans un systeme stellaire spherique. On trouve que les effets de friction proviennent entierement des etoiles proches de la resonance et on obtient une formule pour la friction dynamique, analogue a celle de Chandrasekhar, qui s'applique aux systemes spheriques. On montre qu'une formule de ce type demeure valide tant que la vitesse angulaire de l'objet test change suffisamment rapidement

A kinematic method for measuring the pattern speed of barred galaxies.

Abstract: Il est possible de mesurer Ω p d'une galaxie disque barree sans utiliser de modele dynamique particulier. Dans sa forme la plus simple, la methode necessite la mesure de la brillance de surface et de la vitesse radiale le long d'une bande parallele a la ligne des nœuds. On a teste la methode sur une simulation numerique de disque barre construit par Sellwood; on trouve qu'il est possible d'obtenir Ω p a ±15% pres

Excitation of inclinations in ring-satellite systems

Abstract: Resonant gravitational interactions between a ring and a satellite produce secular variations of their orbital inclinations. Interactions at vertical resonances, analogous to Lindblad resonances but involving inclinations instead of eccentricities, excite inclinations. There is no inclination analog of the corotation resonance. An equatorial ring changes the inclination of a nearby satellite in qualitatively the same way that a satellite in an equatorial orbit changes the inclination of a nearby ring. Viscous dissipation in a ring leads to an equilibrium value of its inclination. These results provide a basis for discussing the origins of the inclinations of planetary rings.

Sharp Edges of Planetary Rings

Abstract: The ring systems of Saturn and Uranus exhibit several sharp edges across which the optical depth drops from order unity to essentially zero. At least two and perhaps all of these features are associated with the location of orbital resonances between a satellite and the ring particles. It is remarkable that the optical depth varies on a distance scale which is much finer than that over which angular momentum can be transferred between a satellite and the ring material. The important features of this phenomenon are: (1) A perturbed band of width Δa/a ≃ (M_s/M_p)^(½) adjacent to the edge within which the angular momentum transfer occurs. (2) Streamlines perturbed such that the angular momentum luminosity decreases smoothly across the band to zero at the edge even though the optical depth remains constant. (3) Dynamical equilibrium requires a relation between the random velocity, the rate of deformation and the optical depth.