Humphreys, R.M. , Gordon, M., Martin, J., Weis, K., Hahn, D. Luminous and Variable Stars in M31 and M33. IV. Luminous Blue Variables, Candidate LBVs, and the B[e] Supergiants; How to Tell Them Apart. The Astrophysical Journal, 836:64.
Humphreys, R.M., Davidson, K., Hahn, D., Martin, J., Weis, K. Luminous and Variable Stars in M31 and M33. V. The Upper HR Diagram. The Astrophysical Journal, 844:40.
