论文标题
关于VX Sagitarii的性质：是TZO，RSG还是高质量AGB明星？
On the nature of VX Sagitarii: Is it a TZO, a RSG or a high-mass AGB star?
论文作者
论文摘要
目标。我们基于高分辨率观测值与AAVSO光曲线数据相结合，对极发红星VX SGR进行了光谱分析。鉴于VX SGR的令人困惑的特征，我们探索了三种情况的性质：巨大的红色超级巨人（RSG）或超级巨星（RHG），一个Thorne Zytkow物体（TZO），以及极端渐近的巨型分支（AGB）。 方法。我们通过使用最先进的凤凰大气模型来取得多个光度变异性的整个周期，从而得出了出色的大气参数。我们将它们与光学和近红外光谱类型进行比较。我们报告了一些关键特征，原因是中性元素原子物种，例如李I，CA I和RB。 结果。我们提供有关其亮度，进化阶段及其脉动时期的新见解。基于所有数据，有两个强烈的理由相信VX SGR是某种极端AGB恒星。首先，其在活动阶段中的mira样行为。 VX SGR显示出振幅的光变化，其幅度比任何已知的RSG大得多，并且显然比所有RHG大。此外，它显示了Balmer线的发射，如前首次显示，其金属光谱在最大光线下加倍，这是MIRAS的典型特征。其次，与任何已知的RSG或RHG不同，VX SGR显示出强RB I线条。除了有时会看到的光谱线外，它始终显示出与信封中的OH MASERS膨胀速度兼容的间隔组件，表明外部气氛连续富集具有S过程的元素，这种行为只能在热脉冲阶段通过第三挖掘来解释这种行为。
Aims. We present a spectroscopic analysis of the extremely luminous red star VX Sgr based on high-resolution observations combined with AAVSO light curve data. Given the puzzling characteristics of VX Sgr, we explore three scenarios for its nature: a massive red supergiant (RSG) or hypergiant (RHG), a Thorne Zytkow object (TZO), and an extreme Asymptotic Giant Branch (AGB) star. Methods. Sampling more than one whole cycle of photometric variability, we derive stellar atmospheric parameters by using state-of-the-art PHOENIX atmospheric models. We compare them to optical and near infrared spectral types. We report on some key features due to neutral elemental atomic species such as Li I, Ca I, and Rb I. Results. We provide new insights into its luminosity, evolutionary stage as well as its pulsation period. Based on all the data, there are two strong reasons to believe that VX Sgr is some sort of extreme AGB star. Firstly, its Mira-like behaviour during active phases. VX Sgr shows light variations with amplitudes much larger than any known RSG and clearly larger than all RHGs. In addition, it displays Balmer line emission and, as shown here for the first time, line doubling of its metallic spectrum at maximum light, both characteristics typical of Miras. Secondly, unlike any known RSG or RHG, VX Sgr displays strong Rb I lines. In addition to the photospheric lines that are sometimes seen, it always shows circumstellar components whose expansion velocity is compatible with that of the OH masers in the envelope, demonstrating a continuous enrichment of the outer atmosphere with s-process elements, a behaviour that can only be explained by third dredge up during the thermal pulse phase.
