Abstract Details

Name: Nagendra Kumar
Affiliation: Department of Physics, IISc, Bangalore-560012
Conference ID: ASI2020_325
Title : A thermally driven wind in Keplerian disk - a hydrodynamic study
Authors and Co-Authors : Nagendra Kumar and Banibrata Mukhopadhyay
Abstract Type : Poster
Abstract Category : Stars, ISM and Galaxy
Abstract : The low mass X-ray binaries (LMXBs) exhibit often a wind outflow in high soft HS spectral state, the observed wind speed ranges from 0.001 to 0.04c, here c is speed of light. HS state is a blackbody dominated state and generally believes that it (HS state) has a thin/Keplerian accretion disk. To study the outflow, we formulated a steady and axisymmetric accretion disk, we solve this at given radius r along the vertical stream line (in cylindrical coordinate). We consider similar assumptions like thin disk except this,a) at launching radius we have very small vertical speed v_z(<< c_s sound speed), some factor to radial velocity, v_z=f*v_r; b) we consider both tangential components of shear stress;c) fluid is not in mechanical equilibrium, parametrized by a number x(<< 1), a possible cause is an irradiation of the disk from inner region. We initialize the flow variables to its Keplerian values at launching radius. We find an acceleration solutions in finite range of x for given f, it accelerates upto maximum height (termed z^m) where interstellar medium (ISM) conditions meet. And z^m increases with x. For any x after z^m height, the fluid will not longer rotationally bound, when radial-component-of-pressure-gradient (grad(p)_r >0 at z^m) becomes comparable to the radial-gravitational-force. We find that wind can escape the system after some z^m(or x) at large r. For given z^m, wind escapes the system from the inner disk for high accretion rate. At given launching radius, for lower z^m the wind velocity is mainly due to v_\phi and for higher z^m the v_r, v_z both contribute in wind velocity. Our results are consistent with wind observations in terms of wind's speed, density, etc.