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
Parameters
    ----------
    m1, m2 : float
        M in Msun.
    r : float
        Distance in Rsun.
        
    Returns
    -------
    Epot
        Epot in erg.