Spectroscopic Follow-Up of Candidate Runaway Stars

TL;DR

This study targets 188 A‑ and later-type candidate runaway stars to obtain precise radial velocities and identify binarity, enabling robust Galactic traceback. Through a long-term spectroscopic campaign complemented by Gaia DR3 data, the authors derive 44 orbital solutions (39 new), revealing a high multiplicity fraction and significantly improving space-velocity estimates with respect to the Local Standard of Rest. A pilot traceback against four Magnificent Seven neutron stars finds no credible past encounters, highlighting the challenges of associating late-type runaways with compact-object progenitors. The work provides a rich catalog of RVs and binary orbits, facilitating future, larger-scale traceback analyses and a more complete census of runaway star origins. The enhanced kinematic dataset will support refined studies of stellar ejection mechanisms and Galactic dynamics.

Abstract

Runaway stars are characterized by higher space velocities than typical field stars. They are presumed to have been ejected from their birth places by one or more energetic mechanisms, including supernova explosions. Accurate radial velocities are essential for investigating their origin, by tracing back their Galactic orbits to look for close encounters in space and in time with neutron stars and young associations. While most studies of runaways have focused on OB stars, later-type stars have also been considered on occasion. Here we report the results of a long-term high-resolution spectroscopic monitoring program with the goal of providing accurate radial velocities for 188 runaway candidates of spectral type A and later, proposed by Tetzlaff et al. (2011). We obtained multiple measurements over a period of about 13 yr to guard against the possibility that some may be members of binary or multiple systems, adding archival observations going back another 25 yr in some cases. We report new spectroscopic orbital solutions for more than three dozen systems. Many more are also found to be binaries based on available astrometric information. A small-scale study carried out here to trace back the paths of our targets together with those of four well-studied, optically-visible neutron stars among the so-called Magnificent Seven, resulted in no credible encounters.