Abstract
view Abstract Citations (754) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Advection-dominated Accretion: Self-Similarity and Bipolar Outflows Narayan, Ramesh ; Yi, Insu Abstract We consider axisymmetric viscous accretion flows where a fraction f of the viscously dissipated energy is advected with the accreting gas as stored entropy and a fraction 1-f is radiated. When f is small (i.e. very little advection), our solutions resemble standard thin disks in many respects except that they have a hot tenuous corona above. In the opposite {\it advection-dominated} limit ($f\rightarrow1$), the solutions approach nearly spherical accretion. The gas is almost at virial temperature, rotates at much below the Keplerian rate, and the flow is much more akin to Bondi accretion than to disk accretion. We compare our exact self-similar solutions with approximate solutions previously obtained using a height-integrated system of equations. We conclude that the height- integration approximation is excellent for a wide range of conditions. We find that the Bernoulli parameter is positive in all our solutions, especially close to the rotation axis. This effect is produced by viscous transport of energy from small to large radii and from the equator to the poles. In addition, all the solutions are convectively unstable and the convection is especially important near the rotation axis. For both reasons we suggest that a bipolar outflow will develop along the axis of the flows, fed by material from the the surface layers of the equatorial inflow. Publication: The Astrophysical Journal Pub Date: May 1995 DOI: 10.1086/175599 arXiv: arXiv:astro-ph/9411058 Bibcode: 1995ApJ...444..231N Keywords: Accretion Disks; Advection; Analogies; Axisymmetric Flow; Bipolarity; Computational Astrophysics; Flow Equations; Viscous Flow; Approximation; Convection; Flow Characteristics; Hydrodynamics; Interstellar Matter; Stellar Rotation; Viscosity; Astrophysics; ACCRETION; ACCRETION DISKS; HYDRODYNAMICS; ISM: JETS AND OUTFLOWS; Astrophysics E-Print: 22 Pages, 5 Figures are available by request to yi@cfa.harvard.edu, Plain Tex, CfA Preprint No. 3931, To Appear in Astrophysical Journal 5/1/95 full text sources arXiv | ADS |
Highlights
In a previous paper (Narayan & Yi 1994, hereafter NY) we discussed the potential importance of advection effects in accretion flows
Both at very low and very high optical depths, the energy released through viscous stresses in an accretion disk may be trapped within the accreting gas
Most of the energy is advected with the flow as stored entropy. Such advectiondominated flows have been found in models of boundary layers in cataclysmic variables at low accretion rates (Narayan & Popham 1993) and in models of pre-main sequence stars such as the FU Orionis systems at very high accretion rates (Popham et al 1993)
Summary
In a previous paper (Narayan & Yi 1994, hereafter NY) we discussed the potential importance of advection effects in accretion flows We showed that, both at very low and very high optical depths, the energy released through viscous stresses in an accretion disk may be trapped within the accreting gas. Making the usual assumptions of steady state, axisymmetry, and α-viscosity, we obtained a set of ordinary differential equations for the gas variables as a function of the cylindrical radius R. We showed that these equations have an exact self-similar solution where all variables have power-law dependences on R and where the Mach number is independent of R. Before we can explore the consequences of these properties we need first to confirm that the self-similar solution itself is real and not just an artifact of the vertical integration of the equations
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