Understanding the dynamics of the solar chromosphere is crucial to understanding energy transport across the solar atmosphere. The chromosphere is optically thick at many wavelengths and described by non-local thermodynamic equilibrium (NLTE), making it difficult to interpret observations. Furthermore, there is considerable evidence that the atmosphere is filamented, and that current instruments do not sufficiently resolve small scale features. In flares, it is likely that multithreaded models are required to describe the heating. The combination of NLTE effects and multithreaded modeling requires computationally demanding calculations, which has motivated the development of a model that can efficiently treat both. We describe the implementation of a solver in a hydrodynamic code for the hydrogen level populations that approximates the NLTE solutions. We derive an accurate electron density across the atmosphere, that includes the effects of non-equilibrium ionization for helium and metals. We show the effects on hydrodynamic simulations, which are used to synthesize light curves using a post-processing radiative transfer code. We demonstrate the utility of this model on IRIS observations of a small flare. We show that the Doppler shifts in Mg II, C II, and O I can be explained with a multithreaded model of loops subjected to electron beam heating, so long as NLTE effects are treated. The intensities, however, do not match observed values very well, which is due to assumptions about the initial atmosphere. We briefly show how altering the initial atmosphere can drastically alter line profiles, and therefore derived quantities, and suggest that it should be tuned to pre-flare observations.
Understanding how energy is released in flares is one of the central problems of solar and stellar astrophysics. Observations of high temperature flare plasma hold many potential clues as to the nature of this energy release. It is clear, however, that flares are not composed of a few impulsively heated loops, but are the result of heating on many small-scale threads that are energized over time, making it difficult to compare observations and numerical simulations in detail. Several previous studies have shown that it is possible to reproduce some aspects of the observed emission by consideri…
Solar Flare Chromospheric Line Emission: Comparison Between IBIS High-resolution Observations and Radiative Hydrodynamic Simulations
太阳耀斑涉及脉冲能量释放，这导致在宽光谱范围和宽高度范围内的辐射增强。特别是，从色球层的线发射可以提供等离子体加热过程的关键诊断。因此，高分辨率光谱观测和先进的数值模拟结果之间的直接比较可能是非常有价值的，但尚未尝试。在本文中，我们提出了在本文中这样一个自洽调查的M3.0耀斑观测的邓恩太阳望远镜的干涉二维光谱仪（IBIS）在2011年9月24日，我们与辐射流体动力学代码RADYN建模。我们用IBIS在H $α$ 6563和Ca II 8542中获得了耀斑区的图像和光谱，并用X射线的Ramaty高能太阳光谱成像仪（RHESSI）获得了耀斑区的图像和光谱。后者的观测被用来推断非热电子的人口，这是通过RADYN模拟大气响应电子碰撞加热。然后，我们合成了谱线，并将它们的形状和强度与IBIS观察到的进行了比较，发现两者基本一致。特别是，合成的Ca II 8542钙离子谱与观察到的谱拟合良好，而合成的H $α$谱在岩心中比观察到的更暗。这表明H $α$发射比Ca II 8542发射对非热电子通量更敏感。我们认为，有必要改进能量输入和其他过程是必要的，以解决这种差异。
As one of the most violent activities in the solar atmosphere, white-light flares (WLFs) are generally known for their enhanced white-light (or continuum) emission, which primarily originates in the solar lower atmosphere. However, we know little about how white-light emission is produced. In this study, we aim to investigate the response of the continua at 3600Å and 4250Å and also the H$α$ and Ly$α$ lines during WLFs modeled with radiative hydrodynamics simulations. We take non-thermal electron beams as the energy source for the WLFs in two different initial atmospheres and vary their paramet…
We present radiative hydrodynamic simulations of solar flares generated by the RADYN and RH codes to study the perturbations induced in photospheric Fe I lines by electron beam heating. We investigate how variations in the beam parameters result in discernible differences in the induced photospheric velocities. Line synthesis revealed a significant chromospheric contribution to the line profiles resulting in an apparent red asymmetry by as much as 40 m/s close to the time of maximum beam heating which was not reflective of the upflow velocities that arose from the radiative hydrodynamic simula…
Sunquakes are one of the more distinct secondary phenomena related to solar flares, where energy deposition in the lower layers of the Sun's atmosphere excites acoustic waves easily visible in Helioseismic and Magnetic Imager (HMI) dopplergrams. We explore two possible sources of sunquakes in the context of the electron beam hypothesis: an instantaneous transfer of momentum and a gradual applied force due to flare eruption. We model the sunquake excitation and compare with five observed sunquake events using a cross-correlation analysis. We find that at least half the events studied are consis…
Dynamic modeling of coronal abundances during flares on M-dwarf stars
Computational Physics, Inc.（计算物理公司）；University College London, Mullard Space Science Laboratory（伦敦大学学院穆拉德空间科学实验室）；Institute for Astronomy, University of Hawai’i（夏威夷大学天文研究所）；ESTEC, European Space Agency（欧洲空间局欧洲空间研究与技术中心）；National Solar Observatory（国家太阳观测台）
The Atmospheric Response to Large Electron Beam Fluxes in Solar Flares III: Comprehensive Modeling of the Brightest Observed Near-Ultraviolet Continuum Source in an X9 Solar Flare
Soft X-ray spectra 3.33 A - 6.15 A from the RESIK instrument on CORONAS-F constitute a unique database for the study of the physical conditions of solar flare plasmas, enabling the calculation of differential emission measures. The two RESIK channels for the shortest wavelengths overlap with the lower end of RHESSI spectral energy range, which is located around 3 keV, making it possible to compare both data sets. We aim to compare observations from RESIK and RHESSI spectrometers and cross-correlate these instruments. Observations are compared with synthetic spectra calculated based on the resu…
The forward fitting of solar flare observations with radiation-hydrodynamic simulations is a common technique for learning about energy deposition and atmospheric evolution during these explosive events. A frequent spectral line choice for this process is Ca II 854.2 nm due to its formation in the chromosphere and substantial variability. It is important to ensure that this line is accurately modeled to obtain the correct interpretation of observations. Here we investigate the importance of photoionisation of Ca II to Ca III by the hydrogen Lyman transitions; whilst the Lyman continuum is typi…
Radiative losses in the chromosphere are very important in the energy balance. There have been efforts to make simple lookup tables for chromospheric radiative losses in the quiet Sun. During solar flares, the atmospheric conditions are quite different, and the currently available recipe of Gan & Fang (1990) is constructed from semi-empirical models. It remains to be evaluated how these recipes work in flare conditions. We aim to construct an approximate recipe of chromospheric radiative losses for solar flares. We follow the method of Carlsson & Leenaarts (2012) to tabulate the optically thin…
Small scale transients occur in the Solar corona at much higher frequencies than flares and play a significant role in coronal dynamics. Here we study three well-identified transients discovered by Hi-C and also detected by the EUV channels of Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO). We use 0-D enthalpy-based hydrodynamical simulations and produce synthetic light curves to compare with AIA observations. We have modeled these transients as loops of ~ 1.0~Mm length depositing energies ~ 10^23 ergs in ~ 50 seconds. The simulated synthetic light curves show rea…
Type II WLFs have weak Balmer line emission and no Balmer jump. We carried out a set of radiative hydrodynamic simulations to understand how the hydrogen radiative losses vary with the electron beam parameters and more specifically with the low energy cutoff. Our results have revealed that for low energy beams, the excess flare Lyman emission diminishes with increasing low energy cutoff as the energy deposited into the top chromosphere is low compared to the energy deposited into the deeper layers. Some Balmer excess emission is always present and is driven primarily by direct heating from the…
Radiation-hydrodynamics of star-disc collisions: From system parameters to outflows and lightcurves
Institute of Physics of the Czech Academy of Sciences（捷克科学院物理研究所）；Department of Theoretical Physics and Astrophysics, Masaryk University（马萨里克大学理论与天体物理学系）；Astronomical Institute of the Czech Academy of Sciences（捷克科学院天文研究所）
We analyze a grid of radiative hydrodynamic simulations of solar flares to study the energy balance and response of the atmosphere to nonthermal electron beam heating. The appearance of chromospheric bubbles is one of the most notable features that we find in the simulations. These pockets of chromospheric plasma get trapped between the transition region and the lower atmosphere as it is superheated by the particle beam. The chromospheric bubbles are seen in the synthetic spectra, appearing as an additional component to Balmer line profiles with high Doppler velocities as high as 200 km/s. The…
The Atmospheric Response to High Nonthermal Electron Beam Fluxes in Solar Flares I: Modeling the Brightest NUV Footpoints in the X1 Solar Flare of 2014 March 29
We model the Neupert effect that relates flare heating energy with the observed SXR emission. The traditional form of the Neupert effect refers to the correlation between the time-integrated HXR or microwave light curve and the SXR light curve. In this paper, instead, we use as the proxy for heating energy the ultraviolet (UV) emission at the foot-points of flare loops, and modify the model of the Neupert effect by taking into account the discrete nature of flare heating as well as cooling. In the modified empirical model, spatially resolved UV lightcurves from the transition region or upper c…
Suppression of Hydrogen Emission in an X-class White-light Solar Flare
我们提出了独特的NUV观测的一个良好的观测X级耀斑从NOAA 12087在Ondjuejov天文台获得。耀斑显示出强烈的白光连续谱，但在较高的巴耳末线和莱曼线中没有可检测到的发射。RHESSI和费米的观测表明它有极硬的X射线谱和伽马射线辐射。我们使用的RADYN辐射流体动力学代码进行两种类型的模拟。第一种是用光谱指数约为3的电子束沉积3 x 10^11 erg/cm^2/s的能量，第二种是将同样的能量直接施加到光球层。观测和模拟的结合使我们能够得出结论，白光发射和氢发射线的抑制或完全缺乏最好地解释了一个模型，其中占主导地位的能量沉积层位于太阳大气层的较低层，而不是色球层。
The metastable Helium (He*) lines near $10830~{\rm A}$ are ideal probes of atmospheric erosion--a common phenomenon of close-in exoplanet evolution. A handful of exoplanet observations yielded well-resolved He* absorption features in transits, yet they were mostly analyzed with 1D isothermal models prescribing mass-loss rates. This work devises 3D hydrodynamics co-evolved with ray-tracing radiative transfer and non-equilibrium thermochemsitry. Starting from the observed stellar/planetary properties with reasonable assumptions about the host's high energy irradiation, we predict from first prin…
Lower atmospheric lines show peculiar profiles at the leading edge of ribbons during solar flares. In particular, increased absorption of the BBSO/GST \hei~10830~Å line \citep[e.g.][]{Xu2016}, as well as broad and centrally reversed profiles in the spectra of the \mgii~and \cii~lines observed by the \iris~satellite \citep[e.g.][]{Panos2018,Panos2021a} have been reported. In this work, we aim to understand the physical origin of the \iris\ ribbon front line profiles, which seem to be common of many, if not all, flares. To achieve this, we quantify the spectral properties of the \iris~\mgii~ribb…
Red-shifted components of chromospheric emission lines in the hard X-ray impulsive phase of solar flares have recently been studied through their 30 s evolution with the high resolution of IRIS. Radiative-hydrodynamic flare models show that these redshifts are generally reproduced by electron-beam generated chromospheric condensations. The models produce large ambient electron densities, and the pressure broadening of hydrogen Balmer series should be readily detected in observations. To accurately interpret upcoming spectral data of flares with the DKIST, we incorporate non-ideal, non-adiabati…
While solar flares are predominantly characterised by an intense broadband enhancement to the solar radiative output, certain spectral lines and continua will, in theory, exhibit flare-induced dimmings. Observations of transitions of orthohelium He I $λλ10830$Å and the He I D3 lines have shown evidence of such dimming, usually followed by enhanced emission. It has been suggested that non-thermal collisional ionisation of helium by an electron beam, followed by recombinations to orthohelium, is responsible for overpopulating the those levels, leading to stronger absorption. However it has not b…
On the nature of off-limb flare continuum sources detected by SDO/HMI
太阳动力学观测站上的日震和磁成像仪提供了对离临边耀斑发射的独特观测。白光（WL）的连续增强被检测到的Fe 6173 A线的“连续”通道在所观察到的耀斑的脉冲阶段。在本文中，我们的目标是确定辐射机制是负责这种增强被视为以上的肢体，在色球高度约1000公里或以下。使用一个简单的分析方法，我们比较了两个候选机制，氢复合连续（Paschen）和汤姆逊连续由于散射的磁盘辐射耀斑电子。这两种机制都依赖于电子密度，而电子密度通常在耀斑的脉冲阶段由于碰撞电离（由于电子束的热电离和非热电离）而增强。我们的结论是，电子密度高于$10^{12}$ cm $^{-3}$，Paschen复合连续显着占主导地位的汤姆逊散射连续，有一些贡献，从氢自由的发射。这进一步支持了详细的辐射流体动力学（RHD）模拟耀斑色球加热的电子束。我们使用RHD程序FLARIX计算了半圆环中耀斑加热的时间演化。临边上方的合成连续体结构类似于HMI检测到的临边外耀斑结构，即它们在临边上方的高度以及辐射强度。这些结果是一致的，最近的研究结果有关的氢巴耳末连续增强，这是清楚地检测到在磁盘耀斑的IRIS近紫外光谱仪。
