# Binary Star initial positions and velocities

• Astro_Husky

#### Astro_Husky

Hi all,

I've been tasked with computing binary star orbits based on their initial parameters, positions and velocities.
In this problem everything must be expressed in terms of the masses, but I am struggling to define positions and velocities in terms of mass.
It is assumed that the stars are in circular orbits around a common center of mass at the origin (0,0) and the stars are on the x-axis (y=0) at time t=0. The primary star is on the negative x-axis and the secondary is on the positive x axis.

Using the relevant dimensionless properties:
Massprimary ≡ Massprimary/M
Masssecondary ≡ Masssecondary/M
where M = Massprimary + Masssecondary

Distance = Xprimary ≡ Xprimary/a
Xsecondary ≡ Xsecondary/a
where, a = initial binary separation

Time = t ≡ t/(sqrt(a^3/GM))

## The Attempt at a Solution

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I got as far as determining the masses of the stars: Primary = 4/5, Secondary = 1/5.
I cannot even begin to express the initial positions and velocities in terms of mass.
Any help would be very much appreciated.