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Astron. Astrophys. 318, 472-484 (1997)

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1. Introduction

From the beginning and by their definition (as showing line emission and being associated with reflection luminosity, Herbig 1960) the Herbig Ae/Be stars were thought of as the higher mass counterparts of the T Tau stars, covering the mass range of about 2-8 [FORMULA] just above that of the T Tau stars. High spatial resolution near infrared observations of their circumstellar environment started when the technique of speckle interferometry became available. The initial work on a few selected objects (Beckwith et al.  1984, De Warf and Dyck 1993) resulted in the detection of circumstellar matter in the form of flattened halos, with conclusions on the dynamics and characteristics of the circumstellar dust. Our near-infrared speckle observations of Herbig Ae/Be stars, started in 1985, also aimed at a study of circumstellar diffuse material. However, these data also have shown hitherto unknown close companions to these stars. We present here this aspect of the study. As in the case of the lower mass T Tau stars, the study of duplicity among Herbig Ae/Be stars is expected to give valuable information not only on the formation of binaries but also on the mechanisms of star formation for intermediate-mass stars in general. Although our sample is too incomplete and heterogeneous for a systematic study of duplicity, its results appear typical and represent a first step toward a future systematic evaluation. In addition, we discuss in Sect. 5 the individual binaries, in particular those, where measurements at several near-infrared wavelengths allow us to comment on the nature of the companions. A preliminary account of part of these data can be found in Leinert et al.  (1994).

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© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998