D. Nicholls, M. Dopita, H. Jerjen, und G. Meurer. (2011)cite arxiv:1107.3898Comment: 13 figures, 3 table. Accepted for publication in The Astronomical Journal.
D. Makarov, und R. Uklein. (2012)cite arxiv:1204.5406Comment: 17 pages, 6 figures, 2 tables, to be published in Astrophysical Bulletin 67, p.123 (2012).