1. A spectroscopic investigation of P Cygni. I. H and Hel lines;Najarro,1997
2. The distance, temperature, and luminosity of the hypergiant P Cygni (B1IA +);Lamers,1983
3. On the spectrum and nature of P Cygni;de Groot,1969
4. Adaptive optics imaging of P Cygni in H$_{\alpha}$