A geometrically thin accretion disc around a Maclaurin spheroid

Abstract

We investigated a semi-analytic and numerical model to study the geometrically thin and optically thick accretion disk around Maclaurin spheroid (MS). The main interest is in the inner region of the so called {\alpha}-disk, {\alpha} being the viscosity parameter. Analytical calculations are done assuming radiation pressure and gas pressure dominated for close to Eddington mass accretion rate and $\dot{M}\lesssim 0.1\dot{M_{Edd}}$ respectively. We found that the change in eccentricity of MS gives a change at high frequency region in the emitted spectra. We found that disk parameters are dependent on eccentricity of MS. Our semi-analytic results show that qualitatively an increase in eccentricity of MS has same behavior as decrease in mass accretion rate. Numerical work has been carried out to see the viscous time evolution of the accretion disk around MS. In numerical model we showed that if the eccentricity of the object is high the matter will diffuse slowly during its viscous evolution. This gives a clue that how spin-up or spin-down can change the time evolution of the accretion disk using a simple Newtonian approach. The change in spectra can be used to determine the eccentricity of MS and thus period of the MS.