Publications of the MPIfR
Optical & Infrared
Interferometry Group
G. Weigelt, Y. Balega, T. Preibisch, D.
Schertl,
M. Schöller, and H. Zinnecker:
Bispectrum speckle interferometry of the
Orion trapezium stars: Detection of a close (33 mas) companion of
Theta¹ Ori C
Astronomy and Astrophysics 347, L15-L18 (1999)
Abstract.
We present bispectrum speckle interferometry observations
with the SAO 6 m telescope of the four
brightest stars in the Orion Trapezium.
Diffraction-limited images with an unprecedented resolution
lambda/D of 57 mas
and 76 mas were obtained in the H- and K-band, respectively. The H and
K
images of Theta1 Ori C (the star responsible for the proplyds)
show for the first time that Theta1 Ori C is a close binary
with a separation of only ~33 mas (H-band observation). The
sub-arcsecond companions of Theta1 Ori A
and Theta1 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.
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