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 gamma=5/3. 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 gamma<5/3, we show the
impossibility of subsonic accretion onto a point-like accretor when the entropy
of the flow is not uniform. The special case gamma=5/3 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
9/7<gamma<5/3.Comment: 22 pages, A&A LaTeX, submitted to A&
