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Astron. Astrophys. 346, 892-896 (1999)

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1. Introduction

Z CMa is a pre-main-sequence (Herbig, 1960) binary (Koresko et al., 1991) located at a distance of 1150 pc (Clariá 1974). One component, the secondary , dominates the continuum at optical wavelengths (Thiébaut, 1994, Barth et al., 1994, Thiébaut et al., 1995) whereas the primary dominates the IR continuum and total luminosity of the system (Koresko et al., 1991). The secondary is an FU Ori object (Hartmann et al., 1989), and the primary is a Herbig Ae/Be star (Withney et al., 1993, hereinafter refered as W93).

The system is associated with a powerful bipolar jet that extends up to 2 pc along position angle 60 deg (Poetzel et al., 1989). In 1987 Z CMa suffered an outburst in which the typical FU Ori absorption line spectrum changed into an emission line spectrum on top of a bluer continuum (Hessmann et al., 1991). Spectropolarimetry observations showed that the emission lines were more polarized than the continuum (W93). This was interpreted as an evidence for their origin in the embedded companion. This interpretation also had the advantage of attributing the outburst to the primary thus solving several difficulties in explaining the emission line spectra in the FU Ori scenario (Hessmann et al.). However, Fischer et al. (1998) found that at 2.2 µm both components are polarized, the secondary having the higher intrinsic polarization. In order to explain both their observations and W93's assumption that the secondary has a negligible contribution to the optical polarization, they invoked an inclined and flared thick disk for the secondary. Recently Lamzin et al. (1998) argued that the emission lines originate from the secondary and that the higher polarization results from Thompson scattering in the wind, thus opening the discussion of which component is the emission line object.

Here we present integral field spectrographic observations of the Z CMa system using OASIS 1, coupled to the PUE'O adaptive optics bonnette (Rigaut et al., 1998). These observations allowed us to image the jet with a 0.24" resolution, and to measure the image centroids with an accuracy beyond the telescope diffraction limit (which is 0.036" for the CFHT at [OI]). We combined this information with the binary parameters derived from speckle interferometry to recover for the first time the spectrum of each Z CMa component.

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© European Southern Observatory (ESO) 1999

Online publication: June 17, 1999
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