Detecting New Visual Binaries in Gaia DR3 with Gaia and 2MASS Photometry I. New Candidate Binaries Within 200 pc of the Sun

TL;DR

This paper introduces a novel method to identify visual binary stars within 200 parsecs using Gaia and 2MASS photometry, enabling detection of close binaries without relying on parallax or proper motion data.

Contribution

The study develops a new photometric technique to detect likely binaries by analyzing PSF size differences and excess flux, expanding binary detection capabilities at small separations.

Findings

Identified 68,725 likely binaries within 200 pc, with 50,230 considered clean.

Discovered 590 previously unknown binaries, including some with separations less than 10 AU.

Achieved a completeness rate of approximately 75% and a contamination rate of about 14%.

Abstract

We present a method to identify likely visual binaries in Gaia eDR3 that does not rely on parallax or proper motion. This method utilizes the various PSF sizes of 2MASS/Gaia, where at $<2.5$" two stars may be unresolved in 2MASS but resolved by Gaia. Due to this, if close neighbors listed in Gaia are a resolved pair, the associated 2MASS source will have a predictable excess in the J-band that depends on the $\Delta G$ of the pair. We demonstrate that the expected relationship between 2MASS excess and $\Delta G$ differs for chance alignments, as compared to true binary systems, when parameters like magnitude and location on the sky are also considered. Using these multidimensional distributions, we compute the likelihood of a close pair of stars to be a chance alignment, resulting in a total(clean) catalog of 68,725(50,230) likely binaries within 200 pc with a completeness rate of $\sim75\%$($\sim64\%$) and contamination rate of $\sim14\%$($\sim0.4\%$). Within this, we find 590 previously unidentified binaries from Gaia eDR3 with projected physical separations $<30$ AU, where 138 systems were previously identified, and for $s<10$ AU we find that 4 out of 15 new likely binaries have not yet been observed with high-resolution imaging. We also demonstrate the potential of our catalog to determine physical separation distributions and binary fraction estimates, from this increase in low separation binaries. Overall, this catalog provides a good complement for the study of local binary populations by probing smaller physical separations and mass ratios, and provides prime targets for speckle monitoring.