EMISSA：探索太阳-恒星活动的毫米指标 III. 三维模型大气中 Ca II 指数与毫米连续谱的比较
EMISSA: Exploring millimetre indicators of solar-stellar activity III. Comparison of Ca II indices and millimetre continua in a 3D model atmosphere
AI总结：
本研究利用 Bifrost 三维 rMHD 模型及 RH1.5D、ART 辐射转移计算，比较 Ca II 活动指数与 ALMA 毫米连续谱，揭示其相关性和斜率随分辨率、波长的变化，为毫米活动指标校准提供依据。
摘要：
Ca II H & K 线是强大的色球诊断工具，可用于确定太阳大气的温度分层和磁结构。阿塔卡马大型毫米/亚毫米波阵列（ALMA）利用毫米连续谱辐射提供关于恒星大气热结构的互补信息。总体目标是通过将 ALMA 观测与经典诊断（如 s 指数和红外三重态（IRT）指数）进行比较，建立更可靠的太阳/恒星活动指标。本研究使用 1.5D 辐射转移代码 RH1.5D 和高级辐射转移（ART）代码，以及由最先进的三维辐射磁流体动力学（rMHD）Bifrost 代码生成的增强网络大气模型，计算了 Ca II 谱线和毫米连续谱的合成光谱。为考虑 ALMA 有限的空间分辨率，我们使用高斯点扩散函数（PSF）模拟了其影响。此外，我们分析了原始分辨率和降级分辨率下 Ca II 指数与毫米连续谱之间散点图的相关性和斜率，并分别聚焦于整个模拟区域、宁静太阳区域和增强网络斑块。由这些谱线生成的活动指数可进一步用于将类太阳恒星的光谱与太阳光谱进行比较。在高分辨率下，Ca II 活动指数与毫米亮温之间存在弱相关，其中在对应 ALMA band 10 的 0.3 mm 波长处观测到最高相关性。随着分辨率降低，相关性持续增强。相反，斜率随波长增加呈下降趋势，而分辨率降级不会显著影响计算得到的斜率。因此，这些关系对于校准通过 ALMA 观测获得的毫米连续谱图可能具有重要价值。
英文摘要：
The Ca II H & K lines are strong chromospheric diagnostics that can be used to determine the temperature stratification and magnetic structure of the solar atmosphere. The Atacama Large Millimetre/Submillimetre Array (ALMA) offers complementary information on the thermal structure of stellar atmospheres using mm continuum radiation. The overall aim is to establish more robust solar/stellar activity indicators using ALMA observations in comparison with classical diagnostics, such as the s index and infrared triplet (IRT) index. A study was conducted using 1.5D radiative transfer codes RH1.5D and advanced radiative transfer (ART), along with an enhanced network atmosphere model generated by the state-of-the-art 3D radiation magnetohydrodynamics (rMHD) Bifrost code, to compute synthetic spectra for both Ca II lines and mm continua. To account for the limited spatial resolution of ALMA, we simulated the effect using a Gaussian point spread function (PSF). Additionally, we analysed the correlations and slopes of scatter plots between the Ca II indices and mm continuum for the original and degraded resolutions, focusing on the entire simulation box, quiet Sun regions, and enhanced network patches separately. The activity indices generated from these lines could further be used to compare the spectra of Sun-like stars with the solar spectrum. The Ca II activity indices and mm brightness temperatures are weakly correlated at the high resolution, with the highest correlation observed at a wavelength of 0.3 mm, corresponding to ALMA band 10. As the resolution decreases, the correlation consistently increases. Conversely, the slopes exhibit a decreasing trend with increasing wavelength, while the degradation of resolution does not noticeably affect the calculated slopes. Consequently, these relationships could be valuable for calibrating the mm continuum maps obtained through ALMA observations.
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