Publications of the MPIfR
Optical & Infrared
Interferometry Group
T. Preibisch, Y. Balega, K.-H. Hofmann,
G. Weigelt,
and H. Zinnecker:
Multiplicity of the massive stars in the
Orion Nebula cluster
New Astronomy 4, 531-542 (1999)
Abstract.
We present bispectrum speckle interferometry observations of 13 bright
Orion Nebula cluster member stars of spectral type O or B.
Diffraction-limited images with a resolution lambda/D of 75 mas in the
K'-band were obtained with the SAO 6 m telescope.
In our speckle images we find 8 visual companions in total.
Using the flux ratios of the resolved systems to estimate the masses of
the companions, we find that the systems generally have mass ratios
below 1/2. The distribution of mass ratios seems to be consistent with
a companion
mass function similar to the field IMF. Considering both, the visual
and the spectroscopic companions of the 13 target stars, the total
number of companions is at least 14.
Extrapolation with correction for the unresolved systems
suggests that there are at least 1.5 companions per primary star on
average. This number is clearly higher than the mean number of ~ 0.5
companions per primary star
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 Orion
Nebula cluster than for low-mass stars.
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