Ejection velocity spectra for indicated terminal accretor masses (M_WD, t). M_d and v_ej are the terminal mass and expected ejection velocity with respect to the center of mass of the progenitor binary of the remnant runaway hot subdwarf. The blue dots indicate the exact state of the system when the accretor reaches the indicated M_WD, t. Lines indicate the evolution of the system in an envelope from M_WD, t − 0.025 ⋅ M_⊙ <  M_WD, t <  M_WD, t + 0.025 ⋅ M_⊙. The dotted purple line indicates M_rem = 0.3 M_⊙, below which core helium burning ceases. The inferred ejection velocity of US 708 according to Geier et al. (2015) and current proper motions provided by Gaia DR2 (Gaia Collaboration 2018), represented by the solid red and dashed purple lines respectively, and local Galactic escape velocity according to Piffl et al. (2014), including error bars, are given for orientation.