The response of a gaseous disc to a binary encounter

Details The response of a gaseous disc to a binary encounter The response of a gaseous disc to a binary encounter

May 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995mnras.274...85k&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Volume 274, Issue 1, pp. 85-98.

Astronomy and Astrophysics

Astronomy

18

Accretion, Accretion Discs, Hydrodynamics

Scientific paper

We investigate the response of a two-dimensional inviscid, non-self-gravitating fluid disc around a point mass to a point-mass perturber flying by on a parabolic prograde orbit in the plane of the disc. We solve both the linearized equations, without any asymptotic approximations, and the full non-linear equations for the problem. We calculate the angular momentum flux due to inward-propagating waves, the torque exerted by the corotation resonance, and the total angular momentum change in the linear case. This is found to agree with the total angular momentum change found in the non-linear case for weakly perturbing encounters. For all calculations reported here, the net effect is such that the disc loses angular momentum. We investigate the effect of various parameters describing the characteristics of the disc and the encounter: the distance of closest approach, the sound speed, the disc surface-density profile, and the equation of state in a regime where the encounter is either linear or mildly non-linear. We find that most of the torque is applied impulsively near pericentre, with an excited wave propagating towards the disc centre with a speed which becomes close to the sound speed. The wave flux is always positive, leading to a loss of angular momentum and hence mass accretion by the inner parts of the disc. The corotation resonance causes a localized gain or loss of angular momentum in the outer parts of the disc; the value and even the sign depend on the details of the disc surface-density profile and rotation curve in the region near the outer edge of the disc. In the linear regime, for a disc with a profile such that the edge region is fairly large in extent, the corotation torque is positive, opposite in sign to the effect of the wave flux. However, non-linear effects may become important if the encounter is strong enough that material in the edge region moves through a distance comparable to the width of that region. The impulsive nature of the encounters suggests that a sequence of such non-interacting encounters can be used to describe the interaction of a disc with a companion in a highly eccentric orbit. Using such an approach, we discuss some implications for tidal truncation and circumstellar disc accretion in a highly eccentric binary system.

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