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Astron. Astrophys. 320, 342-361 (1997)


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An analytic study of Bondi-Hoyle-Lyttleton accretion

I. Stationary flows

T. Foglizzo and M. Ruffert

Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, Postfach 1523, D-85740 Garching, Germany

Received 3 April 1996 / Accepted 28 August 1996

Abstract

We prove that the sonic surface of axisymmetric meridional stationary flows is always attached to the accretor, however small, if the adiabatic index of the gas is [FORMULA].

Using local expansions near a point-like accretor, we extend Bondi's classification of spherically symmetric flows to axisymmetric flows, introducing the possibility of angular sectors reached by no flow lines, and singular directions of infinite mass flux, in addition to the angular regions of subsonic and supersonic accretion. For [FORMULA], we show the impossibility of subsonic accretion onto a point-like accretor when the entropy of the flow is not uniform. The special case [FORMULA] is treated separately.

We analyse the influence of the adiabatic index and Mach number of the flow at infinity on the mass accretion rate of shocked spherical flows. We propose an interpolation formula for the mass accretion rate of axisymmetric flows as a function of the Mach number and the adiabatic index, in the range [FORMULA].

Key words: accretion, accretion disks – hydrodynamics – instabilities – shock waves – binaries: close – X-rays: stars

Send offprint requests to: foglizzo@cea.fr

© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998

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