def a2p(sep, m1, m2):
    """
    It computes the period (day) given m1 (Msun), m2 (Msun) and the sep (Rsun).
    """
    yeardy=365.24
    AURsun=214.95
    p = ((sep/AURsun)**3./(m1 + m2))**(0.5)
    return p, p*yeardy