# IN-SYNC VI. Identification and Radial Velocity Extraction for 100+ Double-Lined Spectroscopic Binaries in the APOGEE/IN-SYNC Fields

## TL;DR

This paper reports radial velocity measurements for over 100 double-lined spectroscopic binaries in star-forming regions, identifying new binaries, deriving orbital parameters, and analyzing mass ratio distributions using APOGEE data.

## Contribution

It introduces a method to identify SB2 binaries from APOGEE spectra and provides initial orbital parameters for several systems, expanding the catalog of known binaries in star-forming regions.

## Key findings

- Mass ratio distribution peaks at q=1 with a tail toward lower q.
- Initial orbital parameters derived for two systems with extensive epoch coverage.
- Identification of new SB2 systems in star-forming regions.

## Abstract

We present radial velocity measurements for 70 high confidence, and 34 potential binary systems in fields containing the Perseus Molecular Cloud, Pleiades, NGC 2264, and the Orion A star forming region. 18 of these systems have been previously identified as binaries in the literature. Candidate double-lined spectroscopic binaries (SB2s) are identified by analyzing the cross-correlation functions (CCFs) computed during the reduction of each APOGEE spectrum. We identify sources whose CCFs are well fit as the sum of two Lorentzians as likely binaries, and provide an initial characterization of the system based on the radial velocities indicated by that dual fit. For systems observed over several epochs, we present mass ratios and systemic velocities; for two systems with observations on eight or more epochs, and which meet our criteria for robust orbital coverage, we derive initial orbital parameters. The distribution of mass ratios for multi-epoch sources in our sample peaks at q=1, but with a significant tail toward lower q values. Tables reporting radial velocities, systemic velocities, and mass ratios are provided online. We discuss future improvements to the radial velocity extraction method we employ, as well as limitations imposed by the number of epochs currently available in the APOGEE database. The Appendix contains brief notes from the literature on each system in the sample, and more extensive notes for select sources of interest.