We used long high-quality unresolved (Sun-as-a-star observations) data collected by GOLF and VIRGO instruments on board the ESA/NASA SOHO satellite to investigate the amplitude variation with solar cycle 23 in the high-frequency band (5.7 < nu< 6.3 mHz). We found an enhancement of acoustic emissivity over the ascending phase of about 18+-3 in velocity observations and a slight enhancement of 3+-2 in intensity. Mode conversion from fast acoustic to fast magneto-acoustic waves could explain the enhancement in velocity observations. These findings open up the possibility to apply the same technique to stellar intensity data, in order to investigate stellar-magnetic activity.
Sunspots are known to be strong absorbers of solar oscillation modal power. The most convincing way to demonstrate this is done via Fourier-Hankel decomposition (FHD), where the local oscillation field is separated into in- and outgoing waves, showing the reduction in power. Due to the Helioseismic and Magnetic Imager's high-cadence Doppler measurements, power absorption can be investigated at frequencies beyond the acoustic cutoff frequency. We perform an FHD on five sunspot regions and two quiet-Sun control regions and study the resulting absorption spectra $α_\ell(ν)$, specifically at frequ…
Activity-related variations in the solar oscillation properties have been known for 30 years. However, the relative importance of the different contributions to the observed variations is not yet fully understood. Our goal is to estimate the relative contribution from sunspots to the observed activity-related variations in the frequencies of the acoustic modes. We use a variational principle to relate the phase differences induced by sunspots on the acoustic waves to the corresponding changes in the frequencies of the global acoustic oscillations. From the sunspot properties (area and latitude…
Magneto-acoustic waves in sunspots from observations and numerical simulations
本文研究了黑子光球层到色球层的波的传播。从时间序列的同空间钙II H（包括其线混合）的强度谱和偏振光谱的Si I 1082.7 nm和He I 1083.0 nm，我们检索的视线速度在几个高度。相位差和放大谱的分析示出了频率低于4 mHz的驻波和更高频率的传播波，并且允许我们推断线形成的温度和高度。利用这些观测数据，我们建立了一个太阳黑子模型，并介绍了用光球Si I 1082.7nm谱线作为驱动源测量的速度。数值传播的波型与使用在较高层形成的线观察到的相当吻合，并且模拟再现了许多观察到的特征。观测到的波是沿磁力线纵向传播的慢磁流体动力学波。
We examine the solar-cycle variation of the power in the low-degree helioseismic modes by looking at binned power spectra from 45 years of observations with the Birmingham Solar Oscillations Network, which provides a more robust estimate of the mode power than that obtained by peak fitting. The solar-cycle variation of acoustic mode power in the five-minute band is clearly seen. Unusually, even though Cycle 24 was substantially weaker in terms of surface magnetic activity than Cycle 23, the reduction in mode power at solar maximum is very similar for the two cycles, suggesting that the relatio…
We examine the acoustic and magnetic energy generation and propagation in beta Hydri (G2 IV). The underlying motivation for this work is based on the solar, stellar, and galactic relevance of beta Hydri (a star in the Southern hemisphere), which is readily understood as a prime example and proxy of the future Sun - thus allowing assessments and analyses of the secular decay of solar activity. Regarding the magnetic energy generation, we consider longitudinal flux tube waves. We also assess acoustic waves. For the acoustic wave energy flux, the difference between the results obtained for beta H…
Wave propagation and energy transport in the magnetic network of the Sun
我们调查波的传播和能量输运的磁性元素，这是小规模的磁通量集中在太阳上的磁网络的代表。这是Hasan et al.（2005）早期工作的延续。在本调查的新功能包括定量评估的能量传输的各种模式和不同的场强，以及边界层厚度对波传播的影响。对强、中磁场下的磁通量集中进行了二维MHD数值模拟。波在管和周围介质中由下边界的横向脉冲运动激发。激发的模式的性质取决于β的值。模式转换发生在中等场的情况下，当快速模式穿过β =1的轮廓。在强场的情况下，当波从通量集中的内部泄漏到周围介质时，快模式经历从主要是磁性到主要是声学的转换。我们还估计了声模和磁模的能流。我们的工作主要有两个方面的结论：第一，对于横向脉冲激励，强场的通量管/片比弱场的通量管/片更有效地向色球层提供声通量。然而，即使在强场情况下，声通量中的能量也不足以平衡网络中的色球辐射损失。第二，通量集中区与周围介质交界面的声发射随边界层宽度的增加而减少。
Current state-of-the-art models of the solar convection zone consist of solutions to the Navier-Stokes equations in rotating, 3D spherical shells. Such models are highly sensitive to the choice of boundary conditions. Here, we present two suites of simulations differing only in their outer thermal boundary condition, which is either one of fixed-entropy or fixed-entropy-gradient. We find that the resulting differential rotation is markedly different between the two sets. The fixed-entropy-gradient simulations have strong differential rotation contrast and isocontours tilted along radial lines …
Technical University of Cluj-Napoca（克卢日-纳波卡技术大学）；National Center for Atmospheric Research（美国国家大气研究中心）；Astronomical Institute of the Romanian Academy（罗马尼亚科学院天文研究所）
Sunquakes are seismic emissions visible on the solar surface, associated with some solar flares. Although discovered in 1998, they have only recently become a more commonly detected phenomenon. Despite the availability of several manual detection guidelines, to our knowledge, the astrophysical data produced for sunquakes is new to the field of Machine Learning. Detecting sunquakes is a daunting task for human operators and this work aims to ease and, if possible, to improve their detection. Thus, we introduce a dataset constructed from acoustic egression-power maps of solar active regions obta…
A new time--distance far-side imaging technique was recently developed by utilizing multiple multi-skip acoustic waves. The measurement procedure is applied to 11 years of Doppler observations from the Solar Dynamics Observatory / Helioseismic and Magnetic Imager, and over 8000 far-side images of the Sun have been obtained with a 12-hour temporal cadence. The mean travel-time shifts in these images unsurprisingly vary with the solar cycle. However, the temporal variation does not show good correlations with the magnetic activity in their respective northern or southern hemisphere, but show ver…
The solar acoustic oscillations are likely stochastically excited by convective dynamics in the solar photosphere, though few direct observations of individual source events have been made and their detailed characteristics are still unknown. Wave source identification requires measurements that can reliably discriminate the local wave signal from the background convective motions and resonant modal power. This is quite challenging as these 'noise' contributions have amplitudes several orders of magnitude greater than the sources and the propagating wave fields they induce. In this paper, we e…
The Sun is a well-studied astrophysical source of axion-like particles (ALPs), produced mainly through the Primakoff process. Moreover, in the Sun there exist large-scale magnetic fields that catalyze an additional ALP production via a coherent conversion of thermal photons. We study this contribution to the solar ALP emissivity, typically neglected in previous investigations. Furthermore, we discuss additional bounds on the ALP-photon coupling from energy-loss arguments, and the detection perspectives of this new ALP flux at future helioscope and dark matter experiments.
