SIMBAD references

We present bispectrum speckle interferometry observations with the SAO 6m telescope of the four brightest stars in the Orion Trapezium. Diffraction-limited images with an unprecedented resolution λ/D of 57mas and 76mas were obtained in the H- and K-band, respectively. The H and K images of Θ¹ Ori C (the star responsible for the proplyds) show for the first time that Θ¹ Ori C is a close binary with a separation of only ∼33mas (H-band observation). The sub-arcsecond companions of Θ¹ Ori A and Θ¹ Ori B reported by Petr et al. (1998) are confirmed. We use the magnitudes and colors of the companions to derive information about their stellar properties from the HR-diagram. In addition we briefly discuss the multiplicity of the Trapezium stars. Considering both, the visual and the spectroscopic companions of the 4 Trapezium stars, there are at least 7 companions, i.e. at least 1.75 companions per primary on average. This number is clearly higher than that found for the low-mass stars in the Orion Nebula cluster as well as in the field population. This suggests that a different mechanism is at work in the formation of high-mass multiple systems in the dense Trapezium cluster than for low-mass stars.