Spectroscopic and photometric behaviour of the FU Orionis variable Z Canis Majoris^*

¹ Osservatorio Astronomico di Capodimonte, Via Moiariello 16, I-80131 Napoli, Italy
² Istituto di Astrofisica Spaziale, CNR, Via E.Fermi 21, C.P. 67, I-00044 Frascati (Roma), Italy
³ Istituto Astronomico, Universita' "La Sapienza" di Roma, Via Lancisi 29, I-00161 Roma, Italy

Send offprint request to: A.A. Vittone

Received: 25 July 1996
Accepted: 3 March 1997

Abstract

We present optical and IR photometry, optical multi-dispersion spectroscopy, and IR spectrophotometry of the FU Ori variable Z Canis Majoris, obtained in the years 1984, 1985, 1989 and 1996. A comparison of data obtained in 1984 and 1985 confirms that in 1985 Z CMa underwent a low-power eruption. The enhancement of emission line, the transition of and Fe ii lines from pure absorption to emission with or without a P Cygni profile, the appearance of the He i 6678 Å  absorption line, a radial velocity increase of about 30% of the P Cygni absorption components, and finally a 0.2-0.3 mag increase of IR luminosity, were all dinstinctive characteristics of this state. Further observations in 1996 show that Z CMa is in a low-luminosity state at while the appearance of a double-peaked emission, with the blue component much weaker than the red one, is the most significant spectroscopic variation. Energy distributions in the range , obtained during 1984 and 1985 observational runs, are also presented.