标题： 蓝大振幅脉动子由低质量白矮星合并形成 显示英文标题

标题： Blue large-amplitude pulsators formed from the merger of low-mass white dwarfs

摘要： 蓝大振幅脉动星（BLAPs）是一类最近发现的高温恒星，它们以径向模式发生脉动。它们的起源需要解释，已经提出了几种形成情景。我们研究了BLAPs是否可以作为两个低质量白矮星（WDs）合并的产物形成，并估计通过这种演化通道可以形成多少BLAPs。我们使用MESA代码模拟了三种不同的双极端低质量（DELM）白矮星合并及其随后的演化。我们还利用COSMIC代码对银河系中的DELM白矮星进行了人口合成。我们发现，BLAPs可以从DELM白矮星形成，前提是系统的总质量在0.32到0.7 M$_\odot$之间。在这种情况下诞生的BLAPs要么完全没有热核聚变，要么显示出中心外氦燃烧。最终产物演化为热亚矮星，最终以冷却的氦白矮星或混合氦/碳氧白矮星结束其演化。合并产物在合并后几千年内成为BLAPs，并需要2万到7万年才能穿过BLAP区域。我们发现基频径向模的不稳定性与观测结果相当一致，但也观察到了径向一次过调的不稳定性。从人口合成中，我们发现当前银河系中可能存在多达几百个通过这种情景诞生的BLAPs。鉴于在所研究的DELM白矮星合并情景中形成的BLAPs数量估计，有很好的机会观测到来自这种情景形成的BLAPs。由于合并过程中可能产生强磁场，这一情景可能导致磁性BLAPs的形成。这很好地符合了发现的两个可能是磁性的BLAPs，其脉动可以用倾斜旋转模型来解释。 显示英文摘要

摘要： Blue large-amplitude pulsators (BLAPs) are a recently discovered group of hot stars pulsating in radial modes. Their origin needs to be explained, and several scenarios for their formation have already been proposed. We investigate whether BLAPs can originate as the product of a merger of two low-mass white dwarfs (WDs) and estimate how many BLAPs can be formed in this evolutionary channel. We used the MESA code to model the merger of three different double extremely low-mass (DELM) WDs and the subsequent evolution of the merger product. We also performed a population synthesis of Galactic DELM WDs using the COSMIC code. We find that BLAPs can be formed from DELM WDs provided that the total mass of the system ranges between 0.32 and 0.7 M$_\odot$. BLAPs born in this scenario either do not have any thermonuclear fusion at all or show off-centre He burning. The final product evolves to hot subdwarfs and eventually finishes its evolution either as a cooling He WD or a hybrid He/CO WD. The merger products become BLAPs only a few thousand years after coalescence, and it takes them 20 to 70 thousand years to pass the BLAP region. We found the instability of the fundamental radial mode to be in fair agreement with observations, but we also observed instability of the radial first overtone. From the population synthesis, we found that up to a few hundred BLAPs born in this scenario can exist at present in the Galaxy. Given the estimated number of BLAPs formed in the studied DELM WD merger scenario, there is a good chance to observe BLAPs that originated through this scenario. Since strong magnetic fields can be generated during mergers, this scenario could lead to the formation of magnetic BLAPs. This fits well with the discovery of two likely magnetic BLAPs whose pulsations can be explained in terms of the oblique rotator model.