Binary Stars in the Orion Trapezium Cluster Core

Details Binary Stars in the Orion Trapezium Cluster Core Binary Stars in the Orion Trapezium Cluster Core

Jun 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...500..825p&link_type=abstract

Astrophysical Journal v.500, p.825

Astronomy and Astrophysics

Astronomy

123

Stars: Binaries: Close, Stars: Individual Constellation Name: Theta Orionis, Galaxy: Open Clusters And Associations: Individual Name: Orion Nebula Cluster, Stars: Pre-Main-Sequence, Techniques: Interferometric

Scientific paper

We have obtained high angular resolution (0."13 FWHM) near-infrared images of the central ~40" x 40" of the Trapezium cluster, using a speckle holography technique that we describe in detail. A search for close binary systems was made in Ks (2.16 mu m) and H (1.65 mu m) mosaic images, in which 45 and 35 stars were detected, respectively. The sensitivity limits for stellar detections are Ks ~= 14.8 and H ~= 14.9 over the whole mosaics and Ks ~= 16.0 and H ~= 15.9 for those regions of the mosaics where most data were accumulated, thus potentially including objects with substellar masses down to ~0.04 M&sun;. In total, four binary systems were identified with projected linear separations in the range of 0."14-0."5 (63-225 AU). The resulting binary fraction for low-mass pre-main-sequence stars is 5.9% +/- 4.0%. This fraction agrees well with the binary frequency observed for main-sequence field stars, but is lower by a factor of ~3 than the fraction found from observations of young stars in Taurus-Auriga over the same range of separations. The difference in binary frequency between the core of the Trapezium cluster and the low-mass, low stellar density dark cloud Taurus-Auriga is established at a statistical significance level of 96% and suggests that binary frequencies are affected by the local star-forming environment. We show that the massive Trapezium star theta 1 Ori A has a nearby companion separated by ~0."2 (~90 AU). The location of this companion is coincident, within the positional uncertainties, with a nonthermal and variable VLA radio source, which was previously associated with theta 1 Ori A itself. We give H photometry for 32 stars, Ks photometry for 43 stars, and present a color-magnitude diagram for the Trapezium core.

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