[Paper Review] Bispectrum speckle interferometry of the Orion Trapezium stars: detection of a close (33 mas) companion of Theta1 Ori C

G. Weigelt, Yuri Balega+4 more|arXiv (Cornell University)|Jun 14, 1999

Stellar, planetary, and galactic studies4 citations

TL;DR

Using bispectrum speckle interferometry at the 6 m SAO telescope, the authors achieved diffraction-limited resolution of 57 mas (H-band) and 76 mas (K-band), detecting a close 33 mas binary companion to Theta1 Ori C—the first direct imaging of this close binary system. The study confirms multiple companions in the Orion Trapezium, revealing a higher multiplicity rate (1.75 companions per primary) than in low-mass star populations, suggesting distinct formation mechanisms for high-mass multiple systems in dense clusters.

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 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.

Motivation & Objective

• To resolve the close binary nature of Theta1 Ori C using high-angular-resolution imaging techniques.
• To confirm and characterize the multiplicity of the four brightest stars in the Orion Trapezium cluster.
• To investigate the stellar properties of companions using their magnitudes and colors in the H- and K-bands.
• To compare the multiplicity frequency of Trapezium stars with low-mass stars in the Orion Nebula Cluster and the field population.
• To explore whether different formation mechanisms operate for high-mass multiple systems in dense stellar environments.

Proposed method

• Bispectrum speckle interferometry was applied to data collected with the 6 m SAO telescope to suppress atmospheric turbulence effects and enhance image resolution.
• The technique enabled diffraction-limited imaging at 57 mas (H-band) and 76 mas (K-band), achieving unprecedented resolution for the Orion Trapezium.
• The bispectrum analysis was used to reconstruct high-fidelity images from short-exposure frames, improving signal-to-noise and resolving close companions.
• Photometric and color measurements of detected companions were used to infer their stellar parameters via the Hertzsprung-Russell (HR) diagram.
• The multiplicity frequency was calculated by combining visual detections with known spectroscopic companions of the four primary Trapezium stars.

Experimental results

Research questions

• RQ1 Is Theta1 Ori C resolved as a close binary system using high-resolution speckle interferometry?
• RQ2 What is the angular separation and photometric properties of the companion to Theta1 Ori C?
• RQ3 How does the multiplicity frequency of the Trapezium stars compare to that of low-mass stars in the Orion Nebula Cluster and the field?
• RQ4 Do the observed stellar properties of the companions align with evolutionary models in the HR diagram?
• RQ5 What do the multiplicity statistics suggest about the formation mechanisms of high-mass multiple systems in dense clusters?

Key findings

• Theta1 Ori C was resolved as a close binary system with a projected separation of 33 mas in the H-band, marking the first direct imaging of this binary.
• The H- and K-band images achieved diffraction-limited resolutions of 57 mas and 76 mas, respectively, enabling sub-arcsecond resolution of the Trapezium stars.
• The companions of Theta1 Ori A and Theta1 Ori B, previously reported by Petr et al. (1998), were confirmed using the new high-resolution data.
• Stellar parameters derived from magnitudes and colors suggest the companions are consistent with main-sequence or pre-main-sequence stars in the HR diagram.
• The Trapezium stars host at least 7 companions across the 4 primary stars, yielding an average of 1.75 companions per primary, significantly higher than for low-mass stars in the cluster or field.
• The elevated multiplicity rate implies distinct formation mechanisms for high-mass multiple systems in dense environments compared to low-mass stars.