Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions

TL;DR

This paper introduces a new method for analyzing sparse radial velocity data to identify and characterize stellar companions, resulting in a catalog of thousands of potential and confirmed companions from the APOGEE survey.

Contribution

The authors developed 'The Joker', a Monte Carlo sampler that reliably estimates orbital parameters from limited data, and applied it to create a comprehensive companion catalog from APOGEE DR14.

Findings

Catalog of 320 confirmed stellar companions.

Identification of 4,898 likely companion hosts needing more data.

Characterization of systems with confidently determined properties.

Abstract

Multi-epoch radial velocity measurements of stars can be used to identify stellar, sub-stellar, and planetary-mass companions. Even a small number of observation epochs can be informative about companions, though there can be multiple qualitatively different orbital solutions that fit the data. We have custom-built a Monte Carlo sampler (The Joker) that delivers reliable (and often highly multi-modal) posterior samplings for companion orbital parameters given sparse radial-velocity data. Here we use The Joker to perform a search for companions to 96,231 red-giant stars observed in the APOGEE survey (DR14) with $\geq 3$ spectroscopic epochs. We select stars with probable companions by making a cut on our posterior belief about the amplitude of the stellar radial-velocity variation induced by the orbit. We provide (1) a catalog of 320 companions for which the stellar companion properties can be confidently determined, (2) a catalog of 4,898 stars that likely have companions, but would require more observations to uniquely determine the orbital properties, and (3) posterior samplings for the full orbital parameters for all stars in the parent sample. We show the characteristics of systems with confidently determined companion properties and highlight interesting systems with candidate compact object companions.