We aimed at finding a physical explanation for the occurrence of macroturbulence in the atmospheres of hot massive stars, a phenomenon found in observations since more than a decade but yet unexplained. We computed time series of line profiles for evolved massive stars broadened by rotation and by hundreds of low-amplitude nonradial gravity-mode pulsations which are predicted to be excited for evolved massive stars. In general, line profiles based on macrotubulent broadening can mimic those subject to pulsational broadening. In several cases, though, good fits require macroturbulent velocities that pass the speed of sound for realistic pulsation amplitudes. Moreover, we find that the rotation velocity can be seriously underestimated by using a simple parameter description for macroturbulence rather than an appropriate pulsational model description to fit the line profiles. We conclude that macroturbulence is a likely signature of the collective effect of pulsations. We provide line diagnostics and their typical values to decide whether or not pulsational broadening is present in observed line profiles, as well as a procedure to avoid an inaccurate estimation of the rotation velocity.
Pulsations in the Late-type B Supergiant Star HD 202850
HD 202850是一颗B型超巨星。众所周知，这类恒星的光球线是变化的。由于宏观湍流，谱线比预期的要宽得多。宏观湍流与恒星脉动有关。据报道，有几颗B超巨星经历了脉动。在我们以前的工作中，我们从Ondrejov 2-m望远镜拍摄的数据中检测到该物体的脉动周期为1.59小时。我们继续研究这个物体，并用DAO 1.2米望远镜拍摄了几个时间序列。我们的新数据表明，这颗恒星可能存在一些额外的脉动周期。我们在这张海报中展示了我们的新结果。
Large-scale variability in macroturbulence driven by pulsations in the rapidly rotating massive star Zeta Oph from high-cadence ESPRESSO spectroscopy and TESS photometry
Predicting Macroturbulence in F/G/K Dwarfs to 100 m/s Precision
University of California Los Angeles（加州大学洛杉矶分校）；Osaka University（大阪大学）；California Institute of Technology（加州理工学院）；SETI Institute（SETI研究所）；University of Hawai‘i（夏威夷大学）；Flatiron Institute（平顿研究所）；Indiana University（印第安纳大学）
Constraining general massive-star physics by exploring the unique properties of magnetic O-stars: Rotation, macroturbulence, and sub-surface convection
Is macroturbulent broadening in OB Supergiants related to pulsations?
O型和B型超巨星的光谱被认为会受到一种重要的额外谱线增宽（通常称为宏观湍流）的影响，这种增宽会增加恒星的自转。最近对高分辨率光谱的分析表明，将这种谱线展宽解释为大尺度湍流运动的结果将意味着高度超音速的速度场，使得这种情况非常不可能。恒星振荡被认为是一种可能的替代解释。我们首先介绍了一个旨在研究O和B超巨星中的$macroturbulent$增宽及其与光谱变率现象和恒星振荡的可能联系的观测项目的令人鼓舞的结果：a）所有研究的B超巨星都显示出谱线轮廓的变化，通过< v >谱线的一阶（）和三阶速度（< v^3 >）矩来量化; b）谱线和< v^3 >变率的峰-峰幅度与额外增宽的大小之间存在很强的相关性< v >。
Context. Massive stars are predicted to excite internal gravity waves (IGWs) by turbulent core convection and from turbulent pressure fluctuations in their near-surface layers. These IGWs are extremely efficient at transporting angular momentum and chemical species within stellar interiors, but they remain largely unconstrained observationally. Aims. We aim to characterise the photometric detection of IGWs across a large number of O and early-B stars in the Hertzsprung-Russell diagram, and explain the ubiquitous detection of stochastic variability in the photospheres of massive stars. Methods.…
The rotation rates of massive stars: How slow are the slow ones?
背景：自转在质量超过8 Msun的恒星的生命周期中起着关键作用。因此，准确了解这些大质量恒星的自转速率对于理解它们的性质和限制它们演化的模型至关重要。目的：本文研究了目前的方法的可靠性，用于获得投影旋转速度v sin i的大质量恒星的光球光谱线加宽签名，专注于不快速旋转的恒星。研究方法：我们使用缓慢旋转的磁性O-星与确定的旋转周期来测试傅立叶变换（FT）和拟合优度（GOF）的方法通常用于推断大质量恒星的投影旋转速率。结果：对于我们的两颗测得自转周期大于一年的磁性测试星，即，当vsin i < 1 km/s时，我们用FT和GOF方法都导出了vsin i ~ 40-50 km/s。这些严重的高估是最有可能造成的不充分治疗的竞争性增宽机制称为微观湍流和宏观湍流。结论：这些发现警告我们不要不加批判地依赖于当前标准技术的结果，以获得存在显著额外谱线增宽的大质量恒星的投影旋转速度，至少当v sin i <~ 50 km/s时。例如，这可能是至关重要的i）确定观测到的大质量恒星自转速率的统计分布，ii）解释旋转制动的B超巨星的演化状态和自旋下降历史，iii）解释观测到的O星的光谱推断v sin i ~ 0 km/s的不足。目前正在进一步调查上述技术的潜在缺点。
The IACOB project: IV. New predictions for high-degree non-radial mode instability domains in massive stars and connection with macroturbulent broadening
Observations indicate that turbulent motions are present on most massive star surfaces. Starting from the observed phenomena of spectral lines with widths much larger than thermal broadening (e.g. micro- and macroturbulence) to the detection of stochastic low-frequency variability (SLFV) in the Transiting Exoplanet Survey Satellite photometry, these stars clearly have large scale turbulent motions on their surfaces. The cause of this turbulence is debated, with near-surface convection zones, core internal gravity waves, and wind variability being proposed. Our 3D grey radiation hydrodynamic (R…
Behavior of Li abundances in solar-analog stars II.
Evidence of the connection with rotation and stellar activity
我们以前试图确定为什么Li I 6708线强度的类太阳恒星的差异如此显着，尽管表面相似的恒星参数。本文对118个太阳类似物进行了综合分析，发现Li丰度A_Li与谱线展宽宽度（v_r+m，主要由转动效应贡献）之间存在着密切的联系，从而得出恒星转动可能是控制表面Li含量的主要因素的结论。为了更详细地检验我们的说法，我们研究了恒星活动的程度是否与Li丰度具有类似的相关性，这是因为人们普遍认为旋转和活动之间存在密切联系。我们测量了所有样本星在强Ca II 8542线中心的剩余通量，r_0（8542），已知是一个有用的恒星活动指数，使用新获得的光谱在这个近红外区域。通过从我们已经建立的v_r+m中减去宏观湍流的贡献来估计投影旋转速度（v_esin i）。A_Li与（vs.）r_0（8542）图以及r_0（8542）与v_esin i和A_Li与v_esin i图中的结果，正如预期的那样。随着旋转相关恒星活动的确认，这清楚地表明，这些太阳类似物的表面Li丰度随着旋转速率的降低而逐渐降低。鉴于这一观测证据，我们得出结论，太阳型恒星的表面锂的耗尽，可能是由有效的信封混合，更有效地作为恒星自转减速。这可能是有希望的归属低锂倾向的行星主机G矮星，它们的不同性质的恒星角动量。
