Jayasinghe et al. identified a dark ≈3 M _⊙ companion on a nearly edge-on ≈60 day orbit around the red giant star V723 Monoceros as a black hole candidate in the mass gap. This scenario was shown to explain most of the data presented by Jayasinghe et al., except for periodic radial velocity (RV) residuals from the circular Keplerian model. Here we show that the RV residuals are explained by orbital phase-dependent distortion of the absorption line profile associated with changing visible fractions of the approaching and receding sides of the red giant star, whose surface is tidally deformed by and rotating synchronously with the dark companion. Our RV model constrains the companion mass M _• = 2.95 0.17 M _⊙ and orbital inclination (medians and 68.3% highest density intervals of the marginal posteriors) adopting the radius of the red giant 24.0 0.9 R _⊙ as constrained from its SED and distance. The analysis provides independent support for the companion mass from ellipsoidal variations and the limits on the companion’s luminosity from the absence of eclipses, both derived by Jayasinghe et al. We also show that a common scheme to evaluate the tidal RV signal as the flux-weighted mean of the surface velocity field can significantly underestimate its amplitude for RVs measured with a cross-correlation technique, and present a modified prescription that directly models the distorted line profile and its effects on the measured RVs. The formulation will be useful for estimating the component masses and inclinations in other similar binaries.

贾亚辛哈等人。在围绕红巨星 V723 Monoceros 的近 60 天轨道上，确定了一个暗 ≈3 M _⊙伴星，作为质量间隙中的黑洞候选者。除了圆形开普勒模型中的周期性径向速度 (RV) 残差外，该场景可以解释 Jayasinghe 等人提供的大部分数据。在这里，我们展示了 RV 残差是通过吸收线轮廓的轨道相位相关失真来解释的. 我们的 RV 模型约束了伴生质量M _• = 2.95 0.17 M _⊙和轨道倾角（边缘后部的中位数和 68.3% 的最高密度间隔）采用红巨星的半径 24.0 0.9 R _⊙受其 SED 和距离的限制。该分析为来自椭球变化的伴星质量和因没有日食而对伴星光度的限制提供了独立的支持，两者都是由 Jayasinghe 等人推导出来的。我们还表明，将潮汐 RV 信号作为表面速度场的通量加权平均值来评估的通用方案可以显着低估其使用互相关技术测量的 RV 的幅度，并提出了一种直接模拟失真线的改进方案轮廓及其对测量 RV 的影响。该公式可用于估计其他类似双星中的分量质量和倾角。