重新审视大麦哲伦云造父变星不稳定带内的非脉动候选恒星
Revisiting candidates for non-pulsating stars located in the Cepheid instability strip in the Large Magellanic Cloud
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中文总结 AI 辅助
本研究分析大麦哲伦云造父变星不稳定带内11颗非脉动候选星的测光与光谱数据，确定其大气参数等物理量，发现钡峰s过程元素增强，脉动缺失仍待探究。
中文摘要 AI 辅助
我们分析了大麦哲伦云（LMC）造父变星不稳定带（IS）内11颗非脉动候选恒星的测光与光谱数据，以探究它们缺乏脉动的原因。我们采用基于测光色指数的有效温度定标来估算候选星的有效温度，该温度作为光谱分析的初始参数；还应用针对造父变星、巨星与超巨星定标的表面亮度-色指数关系来估算恒星半径。光谱分析采用光谱合成法确定大气参数，包括有效温度、金属丰度、表面重力、微湍流速度、投影旋转速度，以及多达约30种元素的化学丰度。多数天体仅有1条光谱，对重复观测的恒星未探测到显著视向速度变化，因此分析中所有恒星均被视为单一天体。2颗恒星显示宽谱线，可能指示高旋转速度或潜在双星特性，但需额外光谱确认该解释；其中1颗还呈现不对称线轮廓，或与非径向脉动模式导致的线形状变化相关。所有分析候选星的共同特征是钡峰s过程元素相对于太阳值增强，这可能表明其在渐近巨星支后阶段曾发生伴星的质量转移。本研究为大麦哲伦云造父变星不稳定带内非脉动候选恒星的物理参数提供了认知，尽管脉动缺失仍是未解之谜，对脉动理论构成挑战。
英文摘要
We analyzed photometric and spectroscopic data for 11 candidates for non-pulsating stars located in the Cepheid instability strip (IS) of the Large Magellanic Cloud (LMC) in order to investigate the reasons for the lack of pulsations. We used available temperature calibrations based on photometric colors to estimate the effective temperatures of the candidates, which served as initial parameters for the spectroscopic analysis. We also applied surface brightness-color relations calibrated for Cepheid variables, giants, and supergiants to estimate stellar radii. The spectral analysis was performed using the spectral synthesis method to determine the atmospheric parameters; namely, the effective temperature, metallicity, surface gravity, microturbulent velocity, projected rotational velocity, and chemical abundances for up to ~30 elements. For most objects, only a single spectrum was available. However, no significant variations in radial velocities were detected among the stars with repeat observations; therefore, all stars were treated as single object in the analysis. Two stars exhibit broad spectral lines, which may indicate high rotational velocities or possible binarity; however, additional spectra are required to confirm this interpretation. One of these objects also shows asymmetric line profiles, which might be related to the presence of non-radial pulsation modes causing line-shape variations. A common feature among all analyzed candidates is an enhancement of barium-peak s-process elements compared to solar values. This may indicate past mass transfer from a companion during its post-asymptotic giant branch phase. This study provides an insight into the physical parameters of candidates for non-pulsating stars residing within the Cepheid IS in the LMC, although the lack of pulsations remains a mystery and challenges pulsation theory.
发表机构
- Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences（波兰科学院哥白尼天文学中心）
- Universidad de Concepción（康塞普西翁大学）
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