Publications of the MPIfR
Optical & Infrared
Interferometry Group
Visual/infrared interferometry of Orion
Trapezium stars:
Preliminary dynamical orbit and aperture synthesis imaging of the Theta
1 Orionis C system
Kraus, S., Balega, Y.Y., Berger, J.-P.,
Hofmann, K.-H., Millan-Gabet, R., Monnier, J.D., Ohnaka, K., Pedretti,
E., Preibisch, Th.,
Schertl, D., Schloerb, F.P., Traub, W.A. , Weigelt, G.
Astronomy & Astrophysics, 466, pg.649-659 (2007)
Abstract
Located in the Orion Trapezium cluster, Theta 1 Orionis C is one of the
youngest and nearest high-mass stars (O5-O7) and also known to be a
close binary system. Using new multi-epoch visual and near-infrared
bispectrum speckle interferometric observations obtained at the BTA 6 m
telescope, and IOTA near-infrared long-baseline interferometry, we
trace the orbital motion of the Theta 1 Ori C components over the
interval 1997.8 to 2005.9, covering a significant arc of the orbit.
Besides fitting the relative position and the flux ratio, we apply
aperture synthesis techniques to our IOTA data to reconstruct a
model-independent image of the Theta 1 Ori C binary system.
The orbital solutions suggest a high eccentricity (e approx. 0.91) and
short-period (P approx. 10.9 yrs) orbit. As the current astrometric
data only allows rather weak constraints on the total dynamical mass,
we present the two best-fit orbits. From these orbital solutions one
can be favoured, implying a system mass of 48 M_sun and a distance to
the Trapezium cluster of 434 pc. When also taking the measured flux
ratio and the derived location in the HR-diagram into account, we find
good agreement for all observables, assuming a spectral type of O5.5
for Theta 1 Ori C1 (M=34.0 M_sun) and O9.5 for C2 (M=15.5 M_sun).
We find indications that the companion C2 is massive itself, which
makes it likely that its contribution to the intense UV radiation field
of the Trapezium cluster is non-negligible. Furthermore, the high
eccentricity of the preliminary orbit solution predicts a very small
physical separation during periastron passage (approx. 1.5 AU, next
passage around 2007.5), suggesting strong wind-wind interaction between
the two O stars.
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