In order to explain the variance of the solar rotation law during the activity minima and maxima, the angular momentum transport by rotating magnetoconvection is simulated in a convective box penetrated by an inclined azimuthal magnetic field. Turbulence-induced kinetic and magnetic stresses { and} the Lorentz force of the large-scale magnetic background field are the basic transporters of angular momentum. Without rotation, the sign of the magnetic stresses naturally depends on the signs of the field components as positive (negative) $B_θB_ϕ$ transport the angular momentum poleward (equatorward). For fast enough rotation, however, the turbulence-originated Reynolds stresses start to dominate the transport of the angular momentum flux. The simulations show that positive ratios of the two meridional magnetic field components to the azimuthal field reduce the inward radial as well as the equatorward latitudinal transport,%by the rotating magnetoconvection which result from hydrodynamic calculations. Only for $B_θB_ϕ>0$ (generated by solar-type rotation laws with an accelerated equator) does the magnetic-influenced rotation at the solar surface prove to be flatter than the nonmagnetic profile together with the observed slight spin-down of the equator. The latter phenomenon does not appear for antisolar rotation with polar vortex as well as for rotation laws with prevailing radial shear.
Searching for rotational X-ray modulation on TIC 277539431
Leibniz Institute for Astrophysics Potsdam (AIP)（波茨坦莱布尼茨天体物理研究所）；Universität Potsdam（波茨坦大学）；Netherlands Institute for Radio Astronomy, ASTRON（荷兰射电天文研究所）
Context. Results from global magnetoconvection simulations of solar-like stars are at odds with observations in many respects: They show a surplus of energy in the kinetic power spectrum at large scales, anti-solar differential rotation profiles, with accelerated poles and a slow equator, for the solar rotation rate, and a transition from axi- to non-axisymmetric dynamos at a much lower rotation rate than what is observed. Even though the simulations reproduce the observed active longitudes in fast rotators, their motion in the rotational frame (the so-called azimuthal dynamo wave, ADW) is ret…
Since the end of 2018, the Transiting Exoplanet Survey Satellite (TESS) has provided stellar photometry to the astronomical community. We have used TESS data to study rotational modulation in the light curves of a sample of chemically peculiar stars with measured large-scale magnetic fields (mCP stars). In general, mCP stars show inhomogeneous distributions of elements in their atmospheres that lead to spectroscopic (line profile) and photometric (light curve) variations commensurate with the rotational period. We analyzed the available TESS data from 50 sectors for eight targets after post-pr…
We investigate the relation between rotation periods $P_\mathrm{rot}$ and photometric modulation amplitudes $R_\mathrm{per}$ for $\approx 4,000$ Sun-like main-sequence stars observed by Kepler, using $P_\mathrm{rot}$ and $R_\mathrm{per}$ from McQuillan et al. (2014), effective temperature $T_\mathrm{eff}$ from LAMOST DR6, and parallax data from Gaia EDR3. As has been suggested in previous works, we find that $P_\mathrm{rot}$ scaled by the convective turnover time $τ_\mathrm{c}$, or the Rossby number $\mathrm{Ro}=P_\mathrm{rot}/τ_\mathrm{c}$, serves as a good predictor of $R_\mathrm{per}$: $R_\…
Characterizing the dynamical magnetosphere of the extremely slowly rotating magnetic O9.7 V star HD 54879 using rotational modulation of the H $α$ profile
研究通过近十年分光偏振与 H α/H β 观测，推断 HD 54879 为周期 7.41 年、极区磁场 ≥2 kG 的慢转强磁约束恒星，并用赤道磁层捕获盘解释 H α 发射及轮廓调制。
In this study, we report on the analysis of 701 stars in a solar vicinity defined in three categories namely subsolar, solar, and supersolar with rotation periods between 1 and 70 days, based on rotational modulation signatures inferred from time series from the Kepler mission's Public Archives. In our analysis, we performed an initial selection based on the rotation period and position in the period-H diagram, where H denotes the Hurst exponent extracted from fractal analysis. To refine our analysis, we applied a fractal approach known as the R/S method, taking into account the fluctuations o…
Lithium enrichment on the single active K1-giant DI Piscium -- Possible joint origin of differential rotation and Li enrichment
我们研究了快速旋转的富锂活动单K巨星DI Psc的表面斑点活动，以测量表面微分旋转并了解锂富集背后的机制。多普勒成像被应用于恢复的表面温度分布的DI Psc在两个随后的旋转周期中使用单独的映射线Ca I 6439，Fe I 6430，Fe I 6421和Li I 6708。通过后续地图的互相关推导出表面差异旋转。差图的产生，以研究锂富集的均匀性的表面上。这些地图进行了比较与旋转调制的Li I 6708线等效宽度。多普勒图像获得的钙和铁映射线同意，并揭示了强大的极地斑点，以及在低纬度地区的凉爽功能。对连续的地图进行互相关，得到切变系数为-0.083 +-0.021的反日差异自转。平均值和Li图的差异表明锂丰度与活动无关。也有一个显着的旋转调制的Li等效宽度。
The Kepler mission revealed a plethora of stellar variability in the light curves of many stars, some associated with magnetic activity or stellar oscillations. In this work, we analyse the periodic signal in 162 intermediate-mass stars, interpreted as Rossby modes and rotational modulation - the so-called \textit{hump \& spike} feature. We investigate whether the rotational modulation (\textit{spike}) is due to stellar spots caused by magnetic fields or due to Overstable Convective (OsC) modes resonantly exciting g~modes, with frequencies corresponding to the convective core rotation rate. As…
NGTS clusters survey. I. Rotation in the young benchmark open cluster Blanco 1
我们使用下一代凌日巡天（NGTS）的200天光度监测，确定了1.15亿年前的布兰科1疏散星团中127颗恒星的自转周期。这些恒星跨越F5-M3光谱类型（1.2 $\gtrsim M \gtrsim$ 0.3 M $_{\odot}$），并将布兰科1的已知旋转周期增加了四倍。我们确定旋转周期使用三种方法：高斯过程（GP）回归，广义自相关（G-ACF）和Lomb-Scargle（LS）周期图，并发现GP和G-ACF更适用于不断发展的斑点调制模式。在中F和中K光谱类型之间，单颗恒星遵循一个明确的旋转序列，从2到10天，而在光度多系统中的恒星通常旋转得更快。这可能表明，一个中等到高质量比的伴星的存在抑制了早期前主序期间的角动量损失机制，并且这个特征在~ 1亿年时没有被抹去。大多数中F到中K星显示不断变化的调制模式，而大多数M星显示稳定的调制信号。这种形态上的变化与从一个定义明确的旋转序列（中F到中K星）到一个广泛的旋转周期分布（晚K和M星）的转变相吻合。最后，我们比较了我们对Blanco 1和类似年龄的昂宿星团的旋转结果：两个星团中的单恒星种群具有一致的旋转周期分布，这表明恒星的角动量演化遵循一个明确的路径，至少对于中F到中K恒星来说，强烈的印记是~ 1亿年。
We introduce a model for the orbital period modulation in systems with close-by giant planets based on a spin-orbit coupling that transfers angular momentum from the orbit to the rotation of the planet and viceversa. The coupling is produced by a permanent non-axisymmetric gravitational quadrupole moment assumed to be present in the solid core of the planet. We investigate two regimes of internal planetary rotation, that is, when the planet rotates rigidly and when the rotation of its deep interior is time dependent as a consequence of a vacillating or intermittent convection in its outer shel…
In this work, a state-of-the-art vortex detection method, Instantaneous Vorticity Deviation, is applied to locate three-dimensional vortex tube boundaries in numerical simulations of solar photospheric magnetoconvection performed by the MURaM code. We detected three-dimensional vortices distributed along intergranular regions and displaying coned shapes that extend from the photosphere to the low chromosphere. Based on a well-defined vortex center and boundary, we were able to determine averaged radial profiles and thereby investigate the dynamics across the vortical flows at different height …
Light Curve Modulation of Low Mass Stars in K2. I. Identification of 508 Fast Rotators in the Solar Neighborhood
K2任务的目标是从SUPERBLINK自行巡天中选出的大量邻近（d<100 pc）GKM矮星（mu>40 mas yr^-1，V<20）。此外，该任务的目标是与本地（d<500 pc）星系晕人口相关的低质量，高自行恒星，也是从SUPERBLINK中选择的。K2活动0到8总共监测了27，382颗这样的冷主序星。我们使用的自关联函数，以寻找快速旋转识别短周期光度调制的K2光变曲线。我们确定了508个旋转周期<4天的候选快速旋转体，它们的光变曲线调制与恒星黑子一致。它们的运动学显示出较低的平均横向速度，这表明它们是年轻盘人口的一部分。在这些目标中发现了一个快速旋转子的子集（13个），其颜色和运动学与当地的星系晕人口一致，可能代表在密近双星系统中由潮汐相互作用旋转起来的恒星。我们进一步证明了从K2光变曲线中选择的M矮星快速旋转体更有可能具有UV过量，并讨论了K2任务在其快速旋转速率的基础上识别新的附近年轻GKM矮星的潜力。最后，我们讨论了可能使用的本地晕星作为基准，在开普勒领域的非变量源。
Accurate tracers of the stellar magnetic field and rotation are cornerstones for the study of M dwarfs and for reliable detection and characterization of their exoplanetary companions. Such measurements are particularly challenging for old, slowly rotating, fully convective M dwarfs. To explore the use of new activity and rotation tracers, we examined multi-year near-infrared spectroscopic monitoring of two such stars -- GJ 699 (Barnard's Star) and Teegarden's Star -- carried out with Habitable Zone Planet Finder spectrograph. We detected periodic variations in absorption line widths across th…
