Sub-systems in nearby solar-type wide binaries

TL;DR

This study used adaptive optics imaging to survey wide binary systems with solar-type stars within 67 parsecs, identifying new sub-systems and analyzing their properties to inform star formation theories.

Contribution

It provides the first complete census of sub-systems in wide binaries within 100 AU, revealing their frequency, mass ratio distribution, and independence from separation.

Findings

Detected 7 sub-systems, 6 of which were previously unknown.

Estimated sub-system frequency above 5 AU as 0.12 +- 0.04.

Found a flat mass ratio distribution with a power-law index of 0.2 +- 0.5.

Abstract

We conducted a deep survey of resolved sub-systems among wide binaries with solar-type components within 67 pc from the Sun. Images of 61 stars in the K and H bands were obtained with the NICI adaptive-optics instrument on the 8-m Gemini-South telescope. Our maximum detectable magnitude difference is about 5mag and 7.8mag at 0.15" and 0.9" separations, respectively. This enables a complete census of sub-systems with stellar companions in the projected separation range from 5 to 100 AU. Out of 7 such companions found in our sample, only one was known previously. We determine that the fraction of sub-systems with projected separations above 5 AU is 0.12 +- 0.04 and that the distribution of their mass ratio is flat, with a power-law index 0.2 +- 0.5. Comparing this with the properties of closer spectroscopic sub-systems (separations below 1 AU), it appears that the mass-ratio distribution does not depend on the separation. The frequency of sub-systems in the separation ranges below 1 AU and between 5 and 100 AU is similar, about 0.15. Unbiased statistics of multiplicity higher than two, advanced by this work, provide constraints on star-formation theory.