The stellar composition of the star formation region CMa R1 - III. A new outburst of the Be star component in Z CMa
van den Ancker, ME × Blondel, PFC Djie, HRETA Grankin, KN Ezhkova, OV Shevchenko, VS Guenther, E Acke, Bram #
Blackwell publishing ltd
Monthly notices of the royal astronomical society vol:349 issue:4 pages:1516-1536
We report on a recent event in which, after more than a decade of slow fading, the visual brightness of the massive young binary Z CMa suddenly started to rise by about 1 mag in 1999 December, followed by a rapid decline to its previous brightness over the next six months. This behaviour is similar to that exhibited by this system around its eruption in 1987 February. A comparison of the intrinsic luminosities of the system with recent evolutionary calculations shows that Z CMa may consist of a 16-M. B0 IIIe primary star and a similar to3-M. FUor secondary with a common age of similar to3 x 10(5) yr. We also compare new high-resolution spectra obtained in 2000 January and February, during the recent rise in brightness, with archive data from 1991 and 1996. The spectra are rich in emission lines, which originate from the envelope of the early B-type primary star. The strength of these emission lines increased strongly with the brightness of Z CMa. We interpret the collected spectral data in terms of an accretion disc with atmosphere around the Herbig B0e component of Z CMa, which has expanded during the outbursts of 1987 and 2000. A high-resolution profile of the 6300 Angstrom[O I] emission line, obtained by us in 2002 March, shows an increase in flux and a prominent blue shoulder to the feature extending to similar to-700 km s(-1), which was much fainter in the pre-outburst spectra. We propose that this change in profile is a result of a strong change in the collimation of a jet, as a result of the outburst at the start of this century.