发表机构
University of Exeter; Keele University（埃克塞特大学; 基尔大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究通过光谱和红外测光证实 sigma Orionis 星团中弱线 T Tauri 星存在覆盖表面 30-95% 的冷星斑，并排除双星、吸积和引力昏暗化解释，指出星斑会导致年龄和质量高估。
AI 中文摘要
T Tauri 星的光变曲线和光谱表明其光球层存在覆盖大面积区域的冷星斑。重度斑驳的恒星应具有比等效单温度光球更大的中红外通量。为验证这一预测，我们首先对 4 Myr 龄的 sigma Orionis 星团中年轻恒星的光谱以及一组较老场星的对照样本拟合了单温度和双温度模型。对年轻恒星的拟合倾向于双温度，而场星则无此偏好。利用红外测光对九颗可能的单 K 型弱线 T Tauri 星进行的独立模型检验证实了大型冷分量的存在。我们考虑并排除了双温度光球的解释：除一颗 WTTS 外，双星解释被排除；吸积解释因观测到的 H-alpha 等值宽度过小而排除；引力昏暗化因预测的温度差异过小而排除。这留下类似于星斑的冷区域覆盖表面 30-95% 作为合理解释。我们的结果显示，在表面分数 0.30-0.75 之间，冷温度无显著差异，暗示存在共同机制。这些冷表面分数在拟合无色等时线于颜色-星等图时将导致年龄和质量被显著高估。冷表面分数的离散性也可解释同年龄零龄主序星光谱中锂等值宽度的离散性。
英文摘要
The light curves and spectra of T Tauri stars indicate the presence of cool starspots covering large areas of their photospheres. Heavily spotted stars should have a larger mid-infrared flux than the equivalent single-temperature photospheres. To test this prediction we first fit single and two-temperature models to optical spectra of young stars in the 4 Myr-old sigma Orionis cluster and a control set of older field stars. The fits to the young stars favour two temperatures while the field stars show no preference. Independent tests of our models for nine probable single K-type weak-lined T Tauri stars using infrared photometry confirms the presence of large cool components. We consider and rule out as explanations of the two temperature photospheres: binary stars for all but one WTTS; accretion, as the observed H-alpha equivalent width is too small; gravity darkening as the predicted temperature differences are too small. This leaves cool areas akin to starspots covering 30-95 per cent of the surface as the plausible explanation. Our results show no significant difference in the cool temperature for surface fractions between 0.30-0.75, implying a common mechanism is responsible. These cool surface fractions would lead to significant overestimates in age and mass when fitting unspotted isochrones in colour-magnitude diagrams. The dispersion in cool surface fraction could also explain the dispersion in lithium equivalent width seen in the spectra of coeval zero-age main sequence stars.
Comments44 pages, 29 figures, 4 tables, accepted for publication in MNRAS
