It has long been suspected that tidal forces in close binary stars could modify the orientation of the pulsation axis of the constituent stars. Such stars have been searched for, but until now never detected. Here we report the discovery of tidally trapped pulsations in the ellipsoidal variable HD 74423 in Transiting Exoplanet Survey Satellite (TESS) space photometry data. The system contains a δ Scuti pulsator in a 1.6 d orbit, whose pulsation mode amplitude is strongly modulated at the orbital frequency, which can be explained if the pulsations have a much larger amplitude in one hemisphere of the star. We interpret this as an obliquely pulsating distorted dipole oscillation with a pulsation axis aligned with the tidal axis. This is the first time that oblique pulsation along a tidal axis has been recognized. It is unclear whether the pulsations are trapped in the hemisphere directed towards the companion or in the side facing away from it, but future spectral measurements can provide the solution. In the meantime, the single-sided pulsator HD 74423 stands out as the prototype of a new class of obliquely pulsating stars in which the interactions of stellar pulsations and tidal distortion can be studied.

长期以来，人们一直怀疑封闭双星中的潮汐力会改变组成恒星脉动轴的方向。已经搜寻了此类恒星，但直到现在仍未发现。在这里，我们报告在瞬变系外行星勘测卫星（TESS）空间光度学数据中，椭圆形变量HD 74423中被潮汐捕获的脉动的发现。该系统在1.6 d轨道上包含一个δScuti脉动器，其脉动模式振幅在轨道频率上受到强烈调制，如果脉动在恒星的一个半球中具有更大的振幅，则可以解释这一点。我们将其解释为脉动轴与潮汐轴对齐的倾斜脉动畸变偶极子振荡。这是首次识别出沿潮汐轴的倾斜脉动。尚不清楚是将脉动捕获在指向同伴的半球中还是将其捕获在背离同伴的一侧中，但是未来的频谱测量可以提供解决方案。同时，单侧波轮HD 74423是新型斜脉动星的原型，在其中可以研究恒星脉动和潮汐畸变的相互作用。