Hoyle-Lyttleton Accretion onto Accretion Disks

We investigate Hoyle-Lyttleton accretion for the case where the centralsource is a luminous accretion disk. %In classical Hoyle-Lyttleton accretiononto a ``spherical'' source, accretion takes place in an axially symmetricmanner around a so-called accretion axis. The accretion rate of the classicalHoyle-Lyttleton accretion onto a non-luminous object and $\Gamma$ theluminosity of the central object normalized by the Eddington luminosity. %Ifthe central object is a compact star with a luminous accretion disk, theradiation field becomes ``non-spherical''. %Although the gravitional fieldremains spherical. In such a case the axial symmetry around the accretion axisbreaks down; the accretion radius $R_{acc}$ generally depends on an inclinationangle $i$ between the accretion axis and the symmetry axis of the disk and theazimuthal angle $\phi$ around the accretion axis. %That is, the cross sectionof accretion changes its shape. Hence, the accretion rate $\dot{M}$, which isobtained by integrating $R_{acc}$ around $\phi$, depends on $i$. % as well as$M$, $\Gamma$, and $v_\infty$. %In the case of an edge-on accretion($i=90^{\circ}$), The accretion rate is larger than that of the spherical caseand approximately expressed as $\dot{M} \sim \dot{M}_{HL} (1-\Gamma)$ for$\Gamma \leq 0.65$ and $\dot{M} \sim \dot{M}_{HL} (2-\Gamma)^2/5$ for $\Gamma\geq 0.65$. %Once the accretion disk forms and the anisotropic radiation fieldsare produced around the central object,the accretion plane will be maintainedautomatically (the direction of jets associated with the disk is alsomaintained). %Thus, the anisotropic radiation field of accretion disksdrastically changes the accretion nature, that gives a clue to the formation ofaccretion disks around an isolated black hole.Comment: 5 figure