Orbital motion of the massive multiple stars in the Orion Trapezium

We present bispectrum speckle interferometry of the multiple Orion Trapezium stars theta ¹Ori A, theta ¹Ori B, and theta ¹Ori C obtained with the SAO 6 m telescope in Russia over a period of 5.5 years (epochs 1995-2001). Our diffraction-limited images have a resolution lambda /D of 42 mas (J-band), 57 mas (H-band) and 76 mas (K-band). We clearly detect motion of the companions relative to their primary stars in the systems theta ¹Ori A1-2 (mean separation rho ~ 220 mas, change in position angle Delta PA = 6degr ), theta ¹Ori B2-3 (rho ~ 205 mas, Delta PA = 8degr ), and theta ¹Ori C1-2 (rho ~ 37 mas, Delta PA = 18degr ). In our K-band image of theta ¹Ori B we resolve a fourth visual component, confirming its discovery by Simon et al. (\cite{Sim99}). We determine the J, H, and K magnitudes of the system components and estimate the stellar masses of the companions in the HR-diagram. The companions theta ¹Ori C2 and theta ¹Ori B2 show clear evidence of near-infrared excess in the color-color diagram. The companions theta ¹Ori A2 and theta ¹Ori B3 show much stronger extinction than their primary stars, providing evidence of the presence of circumstellar material around the companions.