def am_orb(m1,m2,a,e):
a_cm  = a * rsun_cm<EOL>m1_g = m1 * msun_g<EOL>m2_g = m2 * msun_g<EOL>J_orb=np.sqrt(grav_const*a_cm*(old_div((m1_g**<NUM_LIT:2>*m2_g**<NUM_LIT:2>),(m1_g+m2_g))))*(<NUM_LIT:1>-e**<NUM_LIT:2>)<EOL>return J_orb<EOL>
orbital angular momentum.

e.g Ge etal2010

Parameters
----------
m1, m2 : float
    Masses of both stars in Msun.
A : float 
    Separation in Rsun.
e : float
    Eccentricity