Identification of partially resolved binaries in Pan-STARRS1 data

TL;DR

This paper presents a shape measurement method adapted from weak lensing surveys to identify partially resolved ultracool binary stars in Pan-STARRS1 data, successfully discovering three new binaries and demonstrating potential for large-scale surveys.

Contribution

The study introduces a novel shape-based technique for detecting unresolved binaries in wide-field survey data, validated with known binaries and applied to ultracool dwarfs.

Findings

Successfully recovered known binaries wider than 0.3"

Identified three new ultracool binaries, confirmed with follow-up imaging

Demonstrated method's potential for future large-scale surveys like LSST and DES

Abstract

Using shape measurement techniques developed for weak lensing surveys we have identified three new ultracool binaries in the Pan-STARRS1 survey. Binary companions which are not completely resolved can still alter the shapes of stellar images. These shape distortions can be measured if PSF anisotropy caused by the telescope is properly accounted for. We show using both a sample of known binary stars and simulated binaries that we can reliably recover binaries wider than around 0.3" and with flux ratios greater than around 0.1. We then applied our method to a sample of ultracool dwarfs within 30pc with 293 objects having sufficient Pan-STARRS1 data for our method. In total we recovered all but one of the 11 binaries wider than 0.3" in this sample. Our one failure was a true binary detected with a significant but erroneously high ellipticity which led it to be rejected in our analysis. We identify three new binaries, one a simultaneous discovery, with primary spectral types M6.5, L1 and T0.5. These latter two were confirmed with Keck/NIRC2 follow-up imaging. This technique will be useful for identifying large numbers of stellar and substellar binaries in the upcoming LSST and DES sky surveys.