# Homework Help: Mass uncertainties and the calculation of accretion disks

1. Jul 29, 2009

### Ikendo

I'm currently writing an extended essay about black holes in binary systems and accretion disks, and I wonder how I should proceed when calculating the size of the accretion disk.

Take, for instance, the binary system A 0620-00 where the mass of the black hole is said to be 5-10 solar masses, and the companion star is said to be 0.2-0.7 solar masses. The period is 0.323 days. To calculate the size of the accretion disk I use these equations:

The distance between the star and the black hole (assuming circular orbits):
a=2.9 ×10^6 x M_1^(1/3) x (1+q)^(1/3) x P^(2/3) km

q=M_2/M_1

The size of the accretion disk:
R_circ/a=(q+1) x (0.500 - 0.227log q)^4

Will it be very wrong to use the min. value of the black hole and the min. value of the companion star to calculate the min. size of the accretion disk, and then the max. values for the max. size? Or should I use the max. value of the black hole and the min. value of the companion star, and then the other way around?

I suddenly feel like I lack some very basic knowledge in this...