Predicted semi-amplitude of the GP Vel RV curves for different assumed neutron star masses and model input parameters: open symbols: β₀ ~ 0.3; filled symbols: β₀ ~ 0.6. All models were run with dR/R₁ = 0.06. The dotted lines indicate the observed range of semi-amplitudes from Barziv et al. (2001) and Quaintrell et al. (2003). The Keplerian semi-amplitudes (crosses) are generally smaller than those predicted by the model calculations. Note that for the slow-rotation (β₀ ~ 0.3) models, masses as low as m_ns = 1.55 M_⊙ yield K₁ values within the observed range.