def tms( mass ):
    """ Return time on main sequence for given mass

    """

    nom = 2.5E3 + (6.7E2 * mass ** 2.5) + mass**4.5
    denom = (3.3E-2 * mass ** 1.5) + (3.5E-1 * mass**4.5)

    return 1E-3 * (nom / denom)