docs: def am_orb(m1,m2,a,e):
      ''' 
      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
          
      '''
  
      a_cm  = a * rsun_cm
      m1_g = m1 * msun_g
      m2_g = m2 * msun_g
  
      J_orb=np.sqrt(grav_const*a_cm*(old_div((m1_g**2*m2_g**2),(m1_g+m2_g))))*(1-e**2)
      return J_orb