docs: def energ_orb(m1,m2,r):
      ''' 
      Parameters
      ----------
      m1, m2 : float
          M in Msun.
      r : float
          Distance in Rsun.
          
      Returns
      -------
      Epot
          Epot in erg.
          
      '''
      epo = -grav_const * m1 * m2 * msun_g**2 / (r * rsun_cm)
      return epo