Resolve the nature of the Type II candidates

Determine whether the five Type II long-period single-lined binary candidates host compact objects, faint stellar companions, or hierarchical systems through continued long-term radial-velocity monitoring and other follow-up observations.

Background

The five Type II systems have substantial dynamically inferred minimum companion masses, ranging from 0.86 to 2.42 solar masses, but their expected luminosity ratios under a main-sequence companion assumption are modest. Consequently, the available photometry cannot establish that the companions are compact objects.

The authors identify faint stellar companions and hierarchical configurations as alternatives that remain viable. Continued long-term radial-velocity monitoring is required to refine the orbital solutions and clarify the physical nature of these systems.