米拉变星光变曲线中的蜿蜒周期与不对称性：低质量损失率的观测证据
Meandering periods and asymmetries in light curves of Miras: Observational evidence for low mass-loss rates
AI总结：
本文通过分析548颗太阳邻域米拉变星的长时标光变曲线，发现周期蜿蜒变化和光变曲线不对称性与较低的质量损失率相关，并可能由He壳层闪和第三次挖掘事件引起。
摘要：
一些米拉变星——处于晚期演化阶段的长周期变星——具有蜿蜒的脉动周期和光变曲线不对称性，其成因仍不清楚。我们旨在通过研究太阳邻域的一批米拉变星样本，更好地理解这些现象的起源。我们对这组恒星进行了特征刻画，并将其光变特征与其他恒星参数联系起来。我们分析了来自多个数据库的观测数据，以获得包含548颗米拉变星的样本在最大时间跨度和时间覆盖范围内的光变曲线。我们确定了它们在数十年时间跨度内的脉动周期演化，搜寻了周期变化，并确定了周期变化的幅度。我们还分析了傅里叶谱中可能存在的次级频率极大值。根据光变曲线中是否存在凸起，样本被分为两组。我们收集了红外颜色和第三次挖掘（third dredge-up）指标，以研究样本恒星的质量损失和深层混合性质。我们的分析揭示了一颗新恒星T Lyn，其周期在持续变化。具有蜿蜒周期变化的米拉变星群完全由M型恒星组成。蜿蜒周期米拉变星的傅里叶谱没有显著的附加峰，这表明额外的脉动模式不是蜿蜒周期的成因。我们证实凸起在S型和C型米拉变星中更为常见，并首次表明具有凸起的米拉变星比具有规则、对称光变曲线的米拉变星具有更低的质量损失率。具有蜿蜒周期变化的米拉变星质量损失也相对较小。我们得出结论：周期强烈变化或光变曲线不对称的米拉变星具有相对较低的尘埃质量损失率。蜿蜒周期变化和光变曲线不对称性可能与He壳层闪和第三次挖掘事件有关。
英文摘要：
Some Miras -- long-period variables in late evolutionary stages -- have meandering pulsation periods and light curve asymmetries, the causes of which are still unclear. We aim to understand better the origin of these phenomena by investigating a sample of solar-neighbourhood Miras. We characterised this group of stars and related their variability characteristics to other stellar parameters. We analysed observations from several databases to obtain light curves with maximum time span and temporal coverage for a sample of 548 Miras. We determined their pulsation period evolution over a time span of many decades, searched for changes in the periods, and determined the amplitude of the period change. We also analysed the Fourier spectra with respect to possible secondary frequency maxima. The sample was divided into two groups with respect to the presence of light curve bumps. IR colours and indicators of the third dredge-up were collected to study the sample stars' mass-loss and deep mixing properties. Our analysis revealed one new star, T~Lyn, with a continuously changing period. The group of Miras with meandering period changes is exclusively made up of M-type stars. The Fourier spectra of the meandering period Miras have no prominent additional peaks, suggesting that additional pulsation modes are not the cause of the meandering periods. We confirm that bumps are more common among S and C Miras and show, for the first time, that Miras with bumps have lower mass-loss rates than those with regular, symmetric light curves. Also Miras with meandering period changes have relatively little mass loss. We conclude that Miras with strongly changing periods or asymmetries in their light curves have relatively low dust mass-loss rates. Meandering period changes and light curve asymmetries could be connected to He-shell flashes and third dredge-up episodes.
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