Observational predictions for Thorne–Zytkow objects

Model data, input files, and plotting scripts for the paper : Observational predictions for Thorne–Zytkow objects Abstract Thorne–Zytkow objects (TZO) are potential end products of the merger of a neutron star with a non-degenerate star. In this work, we have computed the first grid of evolutionary models of TZOs with the MESA stellar evolution code. With these models, we predict several observational properties of TZOs, including their surface temperatures and luminosities, pulsation periods, and nucleosynthetic products. We expand the range of possible TZO solutions to cover $3.45\( \lesssim\) log (T/Teff) \( \lesssim\) 3.65 and 4.85 \( \lesssim\)log (L/L_sun) \( \lesssim\)5.5. Due to the much higher densities our TZOs reach compared to previous models, if TZOs form we expect them to be stable over a larger mass range than previously predicted, without exhibiting a gap in their mass distribution. Using the GYRE stellar pulsation code we show that TZOs should have fundamental pulsation periods of 1000--2000 days, and period ratios of ~0.2--0.3. Models computed with a large 399 isotope fully-coupled nuclear network show a nucleosynthetic signal that is different to previously predicted. We propose a new nucleosynthetic signal to determine a star's status as a TZO: the isotopologues \(^{44}\rm{Ti O}\) and \(^{44}\rm{Ti O_2}\), which will have a shift in their spectral features as compared to stable titanium-containing molecules. We find that in the local Universe (~SMC metallicities and above) TZOs show little heavy metal enrichment, potentially explaining the difficulty in finding TZOs to-date. MESA version: r22.11.1本数据集包含用于论文《Thorne–Zytkow天体的观测预言》（Observational predictions for Thorne–Zytkow objects）的模型数据、输入文件与绘图脚本。 摘要 索恩-齐特科夫天体（Thorne–Zytkow objects, TZO）是中子星与非简并恒星并合的潜在最终产物。本研究首次利用MESA恒星演化代码（MESA stellar evolution code）构建了TZO的演化模型网格。基于这些模型，我们预言了TZO的多项观测特性，包括其表面温度与光度、脉动周期以及核合成产物。我们将TZO的可行解范围拓展至覆盖3.45 ≲ log(T/Teff) ≲ 3.65 与4.85 ≲ log(L/L☉) ≲ 5.5。相较于此前的模型，本研究中的TZO可达到更高的物质密度，因此若TZO真实形成，其稳定存在的质量范围将比此前预言的更广，且质量分布不存在间隙。借助GYRE恒星脉动代码（GYRE stellar pulsation code），我们证明TZO的基频脉动周期应为1000~2000天，周期比约为0.2~0.3。利用包含399种同位素的全耦合大核网络计算得到的模型，其核合成信号与此前的预言存在差异。我们提出了一种可用于判定恒星是否为TZO的新型核合成信号：⁴⁴TiO与⁴⁴TiO₂同位素分子，相较于稳定的含钛分子，它们的光谱特征将发生位移。我们发现在局部宇宙（约小麦哲伦星系（Small Magellanic Cloud, SMC）金属丰度及更高金属丰度环境中），TZO的重金属富集程度极低，这或许可以解释迄今为止难以观测到TZO的原因。 MESA版本：r22.11.1