The WIYN Open Cluster Study Photometric Binary Survey: Initial Findings for NGC 188

TL;DR

This study combines multi-wavelength photometry and radial velocity data to identify and analyze binary star populations in the open cluster NGC 188, revealing a binary fraction of 36-49%.

Contribution

It introduces a photometric method using spectral energy distribution fitting across multiple wavelengths to identify binaries in open clusters.

Findings

Binary fraction in NGC 188 is 36-49%.

Photometric binary identification agrees with radial velocity data.

Multi-wavelength approach enhances binary detection accuracy.

Abstract

The WIYN open cluster study (WOCS) has been working to yield precise magnitudes in the Johnson-Kron-Cousins UBVRI system for all stars in the field of a selection of ``prototypical'' open clusters. Additionally, WOCS is using radial velocities to obtain orbit solutions for all cluster binary stars with periods of less than 1000 days. Recently, WOCS is being expanded to include the near-infrared JHK_s (deep ground-based plus 2MASS) and mid-infrared ([3.6], [4.5], [5.8], [8.0]) photometry from Spitzer/IRAC observations. This multi-wavelength data (0.3--8.0 microns) allows us photometrically to identify binaries, with mass ratios from 1.0--0.3, across a wide range of primary masses. The spectral energy distribution (SED) fitter by Robitaille et al. (2007) is used to fit the fluxes of 10--12 bands, converted from the observed magnitudes, to Kurucz stellar models. Using this photometric technique, we find that NGC 188 has a binary fraction of 36--49% and provide a star-by-star comparison to the WOCS radial velocity-based binary study.