发表机构
Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège; FRS-FNRS; BRIXIIS Observatory; BAV Bundesdeutsche Arbeitsgemeinschaft Veränderliche Sterne; American Association of Variable Stars Observers (AAVSO); Piera Remote Observatory; SMM Remote Observatory; NSF OIR Lab; Université de Strasbourg, CNRS, Observatoire Astronomique de Strasbourg, UMR 7550; Tennessee State University（列日大学空间科学、技术和天体物理研究（STAR）研究所; 比利时国家科研基金会; BRIXIIS天文台; 德国变星观测协会; 美国变星观测者协会; 皮耶拉远程天文台; 圣玛丽亚德蒙马加斯特雷尔远程天文台; 美国国家科学基金会光学红外实验室; 斯特拉斯堡大学，法国国家科学研究中心，斯特拉斯堡天文台; 田纳西州立大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究监测休眠γ Cas星HD45314的光学和X射线变化，发现其星周盘消退伴随X射线低态，长期振荡与脉动并存，并探讨了与伴星间距或辐射烧蚀相关的可能机制。
AI 中文摘要
γ Cas星是呈现明亮且硬X射线辐射的Oe/Be星。HD45314曾属于此类，但随着其星周盘开始消退，它失去了γ Cas特征。该星在光学光谱、光学测光和X射线光谱方面受到监测，以跟踪其在小时至年时间尺度上的变化。利用傅里叶方法分析了星等、颜色、谱线等值宽度以及紫端与红端峰值强度比的时间序列，以揭示可能的周期性。在五年间，HD45314在230天的时间尺度上表现出星等和谱线强度的振荡。随后，它降至几乎无盘阶段，目前正在缓慢重建其星周盘。在这些阶段中，紫端与红端峰值强度比表现出约1190天时间尺度的调制。在整个监测期间，显著的短期测光变化（尤其在3.369天$^{-1}$的频率上）可能源于β Cep型脉动。这些脉动的振幅在整体亮度变化阶段更强。与此同时，X射线光谱在振荡阶段开始时转为低态，并自此保持在该低态。尽管如此，仍观测到一些残余的硬辐射。HD45314的长期光学变化与光滑粒子流体动力学计算的预测有相似之处，尽管仔细审视确实揭示了一些不一致之处。与其他一些γ Cas星（其X射线辐射在星周盘发生重大变化时几乎保持恒定）不同，HD45314的X射线特性在星周盘开始消散时发生了显著变化。这些差异可能源于Oe星与其假定的白矮星伴星之间更宽的轨道间距，或源于Oe星辐射场对星周盘的烧蚀作用。
英文摘要
$γ$ Cas stars are Oe/Be stars that exhibit bright and hard X-ray emission. HD45314 belonged to this category, but lost its $γ$ Cas characteristics as its circumstellar disc started to fade away. The star was monitored in optical spectroscopy, optical photometry, and X-ray spectroscopy to follow its variability on timescales of hours to years. Time series of magnitudes, colours, line equivalent widths and violet over red peak intensity ratios were analysed with Fourier methods to uncover possible periodicities. For five years, HD45314 exhibited oscillations of its magnitude and line strengths on a timescale of 230 d. It then declined towards a nearly disc-free stage and is now slowly rebuilding its disc. During these phases, the violet over red peak intensity ratio exhibited a modulation on a timescale of about 1190 d. Over the whole campaign, prominent short-term photometric variations, notably at a frequency of 3.369 d$^{-1}$, were probably due to $β$ Cep-type pulsations. The amplitude of these pulsations was stronger during phases of overall brightness changes. In parallel, the X-ray spectrum switched to a low state at the onset of the oscillation phase and has remained in this low state since then. Some residual hard emission is nonetheless observed. HD45314's long-term optical variations bear resemblance with the predictions of smooth particle hydrodynamics calculations, although a close look does reveal some inconsistencies. Unlike some other $γ$ Cas stars, where the X-ray emission remained nearly constant despite major changes of the circumstellar disc, HD45314's X-ray properties changed dramatically as the disc begun to dissipate. These differences might arise from a wider orbital separation between the Oe star and its putative white dwarf companion or from the ablation of the disc by the radiation field of the Oe star.
CommentsAccepted for publication in A&A
