Searching for Binary Y dwarfs with the Gemini Multi-Conjugate Adaptive Optics System (GeMS)

TL;DR

This study used the GeMS adaptive optics system to search for binary Y-type brown dwarfs, finding no companions and providing insights into their binary properties and comparison with hotter ultra-cool dwarfs.

Contribution

First high-resolution adaptive optics search for binary Y dwarfs, establishing limits on their binary separations and energies, and comparing with known properties of hotter brown dwarf binaries.

Findings

No binary companions detected in the sample.

Binary binding energies are consistent with those of hotter ultra-cool dwarfs.

Binary separations larger than ~0.5-1.9 AU are unlikely for these Y dwarfs.

Abstract

The NASA Wide-field Infrared Survey Explorer (WISE) has discovered almost all the known members of the new class of Y-type brown dwarfs. Most of these Y dwarfs have been identified as isolated objects in the field. It is known that binaries with L- and T-type brown dwarf primaries are less prevalent than either M-dwarf or solar-type primaries, they tend to have smaller separations and are more frequently detected in near-equal mass configurations. The binary statistics for Y-type brown dwarfs, however, are sparse, and so it is unclear if the same trends that hold for L- and T-type brown dwarfs also hold for Y-type ones. In addition, the detection of binary companions to very cool Y dwarfs may well be the best means available for discovering even colder objects. We present results for binary properties of a sample of five WISE Y dwarfs with the Gemini Multi-Conjugate Adaptive Optics System (GeMS). We find no evidence for binary companions in these data, which suggests these systems are not equal-luminosity (or equal-mass) binaries with separations larger than ~ 0.5-1.9 AU. For equal-mass binaries at an age of 5 Gyr, we find that the binary binding energies ruled out by our observations (i.e. 10^42 erg) are consistent with those observed in previous studies of hotter ultra-cool dwarfs.