def METHOD_NAME(self, logM, concentration):
    """
    :param logM: log10 mass in M200 stellar masses
    :param concentration: halo concentration c = r_200 / r_s
    :return: Rs (in arc seconds), alpha_Rs (in arc seconds)
    """
    if self._static is True:
        return self._Rs_static, self._alpha_Rs_static
    M = 10**logM
    Rs, alpha_Rs = self._lens_cosmo.nfw_physical2angle(M, concentration)
    return Rs, alpha_Rs