Engle, S. G.; Guinan, E. F.; Harper, G. M.; Neilson, H. R.; Evans, N. R.. (2014). «THE SECRET LIVES OF CEPHEIDS: EVOLUTIONARY CHANGES AND PULSATION-INDUCED SHOCK HEATING IN THE PROTOTYPE CLASSICAL CEPHEID δ Cep» The Astrophysical Journal 794: 80. doi:10.1088/0004-637X/794/1/80. Bibcode: 2014ApJ...794...80E..
Engle, S. G.; Guinan, E. F.; Harper, G. M.; Neilson, H. R.; Evans, N. R.. (2014). «THE SECRET LIVES OF CEPHEIDS: EVOLUTIONARY CHANGES AND PULSATION-INDUCED SHOCK HEATING IN THE PROTOTYPE CLASSICAL CEPHEID δ Cep» The Astrophysical Journal 794: 80. doi:10.1088/0004-637X/794/1/80. Bibcode: 2014ApJ...794...80E..