WIYN Open Cluster Study. LX. Spectroscopic Binary Orbits in NGC 6819

TL;DR

This study presents a comprehensive spectroscopic binary orbit survey in the open cluster NGC 6819, revealing a 22% binary fraction among main-sequence stars and analyzing various notable binary systems within the cluster.

Contribution

First detailed spectroscopic binary orbit survey of NGC 6819, providing new data on binary fraction, orbital periods, and notable binaries in this 2.5 Gyr old cluster.

Findings

Binary fraction for MS stars <10,000 days is 22% +/- 3%.

Tidal circularization period is 6.2 +/- 1.1 days.

Identified notable binaries including eclipsing and Kepler asteroseismology targets.

Abstract

We present the current state of the WOCS radial-velocity (RV) survey for the rich open cluster NGC 6819 (2.5 Gyr) including 93 spectroscopic binary orbits with periods ranging from 1.5 to 8,000 days. These results are the product of our ongoing RV survey of NGC 6819 using the Hydra Multi-Object Spectrograph on the WIYN 3.5 m telescope. We also include a detailed analysis of multiple prior sets of optical photometry for NGC 6819. Within a 1-degree field of view, our stellar sample includes the giant branch, the red clump, and blue straggler candidates, and extends to almost 2 mag below the main-sequence (MS) turnoff. For each star observed in our survey we present all RV measurements, the average RV and velocity variability information. Additionally, we discuss notable binaries from our sample, including eclipsing binaries (WOCS 23009, WOCS 24009, and WOCS 40007), stars noted in Kepler asteroseismology studies (WOCS 4008, WOCS 7009, and WOCS 8007), and potential descendants of past blue stragglers (WOCS 1006 and WOCS 6002). We find the incompleteness-corrected binary fraction for all MS binaries with periods less than 10,000 days to be 22% +/- 3% and a tidal circularization period of 6.2 +/- 1.1 days for NGC 6819.