A&A Supplement Series, Vol. 126, November II 1997, 91-103
Received July 25, 1996; accepted March 3, 1997
M. Teodorani
- L. Errico - A.A. Vittone
- F. Giovannelli
- C. Rossi
Send offprint request: A.A. Vittone
Osservatorio Astronomico di Capodimonte
, Via Moiariello 16,
I-80131 Napoli, Italy
Istituto di Astrofisica Spaziale,
CNR, Via E.Fermi 21, C.P. 67, I-00044
Frascati (Roma), Italy
Istituto Astronomico, Universita'
"La Sapienza" di Roma, Via Lancisi 29,
I-00161 Roma, Italy
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 FeII lines from pure absorption to emission
with or without a P Cygni profile, the appearance of the
HeI 6678Å
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 V = 10.24 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.
keywords: stars: individual: Z CMa -- stars: pre-main-sequence -- stars: Be -- stars: variables: other