Resolving stellar pulsational shock waves in the extreme helium star V652 Her

V652 Her正以8马赫的冲击波进行超音速脉动。我们建议使用强谱线中的线轮廓变化，以首次直接看到该星星中向外传播的冲击波。这将促进我们的理解的脉动冲击波的物理学，在一般情况下，直接应用到我们最近的模型的脉动冲击解释新发现的行为在强磁快速振荡Ap（roAp）恒星。它将使我们能够特别估计V652 Her高层大气中的能量损失，对模拟这种罕见的极端氦星星中的Fe不透明度驾驶具有重要意义。目前，没有模型包括能量损失;与斯巴鲁的观察，以指导我们，我们将首次介绍这种能量损失的物理到我们的模型。我们还将测量最小半径处的压缩。我们将获得大气层快速向外加速度的第一个时间分辨率--在大气层进入自由落体之前的令人震惊的短暂15分钟内，加速度为星星表面重力的10倍。2.5小时脉动周期。HDS的高分辨率和宽波长范围也将提供前所未有的高S/N光谱，从中我们将获得星星中hoc周期产生的元素的详细丰度，该恒星处于一个罕见的、尚未完全了解的恒星演化阶段--一个可能合并的白色矮双星。

V652 Her is pulsating supersonically with a Mach-8 shock wave. We propose to use line profile variations in strong spectral lines to see directly for the first time the outwardly propagating shock waves in this star. This will advance our understanding of the physics of pulsational shock waves, in general, with direct applications to our recent model of pulsational shocks to explain newly discovered behaviour in the strongly magnetic rapidly oscillating Ap (roAp) stars. It will allow us specifically to estimate energy losses in the upper atmosphere of V652 Her, with important implications for modelling the Fe-opacity driving in this rare extreme helium star. At present no models include energy losses; with Subaru observations to guide us, we will introduce for the first time the physics of such energy losses into our models. We will also measure the compression at minimum radius. We will have the first temporal resolution of the rapid outward acceleration of the atmosphere -- acceleration 10 times that of the surface gravity of the star for a stunningly brief 15 minutes before the atmosphere goes into free-fall for the rest of the 2.5-hr pulsation cycle. The high resolution and wide wavelength range of HDS will also give an unprecedented high S/N spectrum from which we will derive detailed abundances of the CNO-cycle produced elements in a star in a rare, and not fully understood, stage of stellar evolution -- a probable merged white dwarf binary.