On-disk H α light-absorbing plasma structures such as mottles, fibrils, filaments, and H α jets are observable magnetohydrodynamic features in the upper solar chromosphere. We attempt to determine their physical parameters by regarding them as optical clouds scattering the H α -line light incident from below. For this purpose, we developed a new inversion, which we call the three-layer background plus three-component cloud model inversion. This new spectral inversion was found to be applicable to every H α line profile taken from a quiet-Sun region. We used the model parameters inferred from the fitting to determine the temperature and to construct the velocity distribution function at every point in the observed region. This function was used in turn to calculate the column mass, mass flux, kinetic energy, and kinetic energy flux. Our approach yielded three types of Doppler velocities: the mass flux-associated velocity, the kinetic energy-associated velocity, and the kinetic energy flux-associated velocity. We found that the physical parameters of H α -absorbing structures in a quiet-Sun region resolve the long-standing discrepancy between the Doppler velocities of mottles observed on the disk and the rising speeds of spicules observed off the limb. We also found that the kinetic energy budget of the upper chromosphere is large enough for the radiative loss in the upper chromosphere and corona. These results support the hypothesis that magnetohydrodynamic waves heat the upper atmosphere of the quiet Sun.

We investigate an X1.3 flare in active region 13777 on 2024 August 8, which was preceded by precursor brightening associated with small-scale magnetic flux emergence and cancellation at the periphery of the leading polarity. Multi-instrument observations from Solar Dynamics Observatory/Helioseismic and Magnetic Imager, Atmospheric Imaging Assembly, ground-based GONG H alpha, and Goode Solar Telescope/Fast Imaging Solar Spectrograph show that the precursor did not immediately lead to the flare onset, but was followed by a gradual elongation and destabilization of a filament that connected the peripheral pore to the main sunspot. The flare developed first as a two-ribbon flare confined to the low-lying filament and later as a complex-ribbon flare accompanied by the removal of overlying arcades. kappa-scheme analysis proposed by Kusano et al. revealed that the small region of high free-energy at the periphery had already become unstable to the double-arc instability at the time of the precursor brightening, although the large-scale eruption required further coupling with the main sunspot system. These results suggest that even a very small-scale flux emergence at the periphery of an active region can reorganize the magnetic system and eventually lead to a major flare.

This volume defines the exoplanet science program enabled by the dedicated high-contrast coronagraph in the baseline science payload of the 3.5-meter Segmented-Mirror Robotic Space Telescope. The observatory architecture incorporates the optical interfaces, wavefront sensing and control, pointing stability, and operations software required for coronagraphic observations from the outset. The observing strategy gives priority to the nearest stellar systems because they provide the most accessible laboratories for planetary exploration and the most likely destinations of future interstellar missions. The diffraction limit sets a reflected-light horizon of roughly 10–15 pc for planets at 1 AU and roughly 50–80 pc for Jupiter analogs. Within those horizons, the telescope can image nearby giant planets, obtain reflected-light spectra of their atmospheres, survey young systems and circumstellar disks, and support the habitability and biosignature programs that larger future missions will pursue. The wide-field imager complements the coronagraph through transit photometry, occurrence-rate statistics, and long-term monitoring of stellar magnetic activity. A systematic census of the nearest stellar neighbors provides a lasting reference for exoplanet science and future space exploration.

The 3.5-meter Segmented-Mirror Robotic Space Telescope uses an image slicer for all spectroscopic observations. The planning baseline uses R ≃ 1000 for the wide survey and retains selectable R ≃ 5000 bands for precision line measurements. The central science case is a dense emission-line galaxy redshift survey for baryon acoustic oscillations and redshift-space distortions. Supernova and quasar programs exploit the stability, multiplexing, and repeatability of space operations. The supernova tier measures rest-frame U and near-ultraviolet magnitudes that separate optical twins at subgroup precision to z ≃ 0.9–1.1 in standard visits and to z ≃ 1.3–1.5 in ten-hour stacks. Every wide-survey tile receives three spectroscopic orientations, and a joint scene reconstruction uses their different overlap geometries to recover the spectra. The flagship survey covers 100–300 deg^2 and targets 10^6–3 × 10^6 emission-line galaxies. A deep pencil-beam tier and a supernova time-domain tier complement the wide survey. The same observations provide a census of ultra-diffuse and low-surface-brightness galaxies, map intracluster light, and test cold, self-interacting, and fuzzy dark matter through dwarf-galaxy structure and low-mass halo abundance.

On-disk H alpha light-absorbing plasma structures such as mottles, fibrils, filaments, and H alpha jets are observable magnetohydrodynamic features in the upper solar chromosphere. We attempt to determine their physical parameters by regarding them as optical clouds scattering the H alpha-line light incident from below. For this purpose, we developed a new inversion, which we call the three-layer background plus three-component cloud model inversion. This new spectral inversion was found to be applicable to every H alpha line profile taken from a quiet-Sun region. We used the model parameters inferred from the fitting to determine the temperature and to construct the velocity distribution function at every point in the observed region. This function was used in turn to calculate the column mass, mass flux, kinetic energy, and kinetic energy flux. Our approach yielded three types of Doppler velocities: the mass flux-associated velocity, the kinetic energy-associated velocity, and the kinetic energy flux-associated velocity. We found that the physical parameters of H alpha-absorbing structures in a quiet-Sun region resolve the long-standing discrepancy between the Doppler velocities of mottles observed on the disk and the rising speeds of spicules observed off the limb. We also found that the kinetic energy budget of the upper chromosphere is large enough for the radiative loss in the upper chromosphere and corona. These results support the hypothesis that magnetohydrodynamic waves heat the upper atmosphere of the quiet Sun.

Active M dwarfs exhibit frequent and energetic flares that provide a unique laboratory for studying chromospheric heating processes under extreme magnetic activity. To probe the flare process of M-dwarfs, we present a high-resolution (R∼30,000) spectroscopic case study of a superflare on AD Leo, detected on 2023 March 14 using the Bohyunsan Optical Echelle Spectrograph (BOES). Such high-energy events are rarely captured with simultaneous multi-line spectroscopy, allowing us to trace the energy partition and temporal evolution of the chromospheric lines. Based on equivalent width variations, we found that the Hα line radiated 8.8×10^30 erg, implying a total bolometric energy (∼10^33 erg) comparable to the largest solar flares. The Balmer series dominated the energy budget; the individual Ca II H and K lines contributed 47.5

Context. For the analysis of highly resolved solar spectra the simultaneous observation and interpretation (inversion) of only a few (often only one) spectral lines is still the norm. With modern instruments spatially highly resolved spectropolarimetric data covering many lines are available. Aims. For the first time we combine the information from 85 simultaneously observed absorption lines in spatially highly resolved data to test a proposed solar many-line inversion strategy. Methods. We inverted full Stokes spectra recorded with the FISS spectro-polarimeter (FISS-SP) at the 1.6-m Goode Solar Telescope in California, using the SPINOR code. We contrasted two different setups: one following the traditional approach of using a line doublet, and a new method inverting many-lines simultaneously. Results. Compared to results from an inversion using two lines of a line doublet, we discovered more fine-structure and better constrained values using the many-line technique. An average quiet Sun spectrum was successfully reproduced using a model atmosphere, but when inverting spatially resolved data, uncertainties in line parameters and blend configurations did not average out. Thus, a deliberate selection process of lines and line blends was required, in order to make the many-line case converge to a physically expected and coherent atmosphere. We successfully developed and tested such a selection method. Conclusions. Our results highlight that the many-line inversions method delivers more coherent results with superior line of sight (LOS) resolution of the atmospheric structure. Moreover, it effectively detects and utilizes even weak polarimetric signals in noisy data and thereby partly circumvents low noise requirements. It reveals uncertainties in atomic parameters of individual spectral lines and models, as the degree of freedom to compensate for these uncertainties by compromising the inferred atmospheric parameters is considerably reduced. It is thereby pointing to a need for improved atomic data, including log(gf) values, of many lines in the solar spectrum. The many-line method presents significant potential for solar physics and may become the preferred option for future observations with upcoming spectrographs.

Sunspot oscillations consist of multiple wave modes, making it challenging to isolate individual physical processes. To decompose these multi-modal oscillations, we apply empirical mode decomposition (EMD) to Hα Doppler velocity data obtained with the Fast Imaging Solar Spectrograph. By avoiding arbitrary frequency filtering, EMD resolves the oscillations into four distinct modes with unique periodicities and spatial distributions: c1 in the umbra (periods of ∼2 min); c2 in the umbra and penumbra (2.5 − 4 min); c3 in the outer penumbra (4 − 6 min); and c4 in the superpenumbra (∼10 min). We find that all modes, including the high-frequency 1-minute oscillations, coexist in the superpenumbral fibrils and represent potential candidates for transverse waves. Analysis of the c1 and c2 modes reveals the coexistence of umbra-trapped body waves and running penumbral waves within the umbra. Meanwhile, the c3 and c4 modes demonstrate that sunspot waves undergo significant nonlinear evolution as they propagate through the stratified atmosphere. Our results indicate that EMD effectively classifies dispersive oscillations into distinct groups based on their intrinsic timescales and underlying physical natures.

Transverse magnetohydrodynamic (MHD) waves are often observed in the solar chromosphere with two different methods, the imaging method and the spectroscopic method. The velocity amplitudes of line-of-sight (LOS) oscillations inferred from the spectroscopic method, however, are usually found to be much smaller than those of plane-of-sky (POS) oscillations inferred from the imaging method. In order to understand the nature of this discrepancy, we compared these two types of oscillations by applying both methods to the same features. Using the Microlensed Hyperspectral Imager (MiHI) prototype, which provides data with an unprecedentedly high spatial, spectral, and temporal resolution and enables simultaneous acquisition of images and spectra, we detected transverse waves in thread-like structures seen in a quiet-Sun region. To investigate the nature of these oscillations, we analyzed three distinct events. Our analysis revealed that the structures oscillate both in the POS and the LOS directions, with periods of about 2.3 minutes. Notably, the velocity amplitudes measured by the spectroscopic method tend to be smaller than those measured by the imaging method, with differences of up to a factor of 2.3. Moreover, the phase differences between the two types of velocity oscillations vary significantly, with values of 209 degrees, -75 degrees, and 84 degrees for events 1, 2, and 3, respectively. These findings indicate that the transverse MHD waves are elliptically polarized, and that larger amplitude oscillations occur in the POS direction. Our simultaneous detection of transverse MHD waves in two directions suggests the possibility of additional energy transport that may previously have been overlooked.

The Fast Imaging Solar Spectrograph (FISS) is a powerful instrument for studying photospheric and chromospheric events by simultaneously recording high-resolution spectrograms in two spectral bands. Recently, because of a change in the optical setup, unexpected fringes have been noticed on the Ca ii 8542 & Aring; band camera, which persist even after the standard flat-fielding. Here, we develop a new data calibration method for the FISS, including a wavelet-based fringe reduction technique. By applying the wavelet transform independently along each axis of the flat data, we successfully isolate the fringes using a low-pass filter and a Gaussian window in the power spectrum. We implement the phase correction to account for temporal phase shifts in the fringes, enabling their effective removal from object frames without altering spectral profiles. This preprocessing pipeline has been integrated into the Python-based FISSpy package for the FISS data analysis. We anticipate that the proposed calibration method will enhance data quality and be utilized for the next generation of the FISS.

Coronal mass ejections (CMEs) on the early Sun may have profoundly influenced the planetary atmospheres of early Solar System planets. Flaring young solar analogues serve as excellent proxies for probing the plasma environment of the young Sun, yet their CMEs remain poorly understood. Here we report the detection of multi-wavelength Doppler shifts of the far-ultraviolet and optical lines during a flare on the young solar analogue EK Draconis. During and before a Carrington-class (similar to 10(32) erg) flare, warm far-ultraviolet lines (similar to 10(5) K) exhibited blueshifted emission at 300-550 km s(-1), indicative of a warm eruption. Then, 10 min later, the H alpha line showed slow (70 km s(-1)), long-lasting (greater than or similar to 2 h) blueshifted absorptions, indicating a cool (similar to 10(4) K) filament eruption. This provides evidence of the multi-temperature and multi-component nature of a stellar CME. If Carrington-class flares or CMEs occurred frequently on the young Sun, they may have cumulatively impacted the early Earth's magnetosphere and atmosphere.

We report on a flare-driven coronal rain event observed along postflare loops during the decay phase of an X1.6-class solar flare. Although high-resolution studies of flare-driven coronal rain have been conducted, imaging spectroscopic studies are rare due to observational difficulties. Our observation taken with the Fast Imaging Solar Spectrograph, installed at the 1.6 m Goode Solar Telescope of the Big Bear Solar Observatory, provided unprecedented high-resolution spectroscopic imaging data of coronal rain in the H α and Ca ii 854.2 nm lines. We identify two locations along postflare loops with rain displaying distinctly different thermal properties, different Doppler velocities, and different patterns of acceleration and deceleration. We also observed intense brightening at one footpoint of coronal rain, where the spectroscopic analysis reveals an energy conversion process resulting in significant localized chromospheric heating. We thoroughly investigate the footpoint brightening Doppler velocities and compare their spectral line profiles to typical flare-ribbon line profiles. We estimate the spatial scale of the fine structure of the coronal rain and the footpoint brightening. Our results provide important insights into the dynamic and thermal properties of flare-driven coronal rain and the related chromospheric response, which will help validate the flare-driven modeling of coronal rain.

Context. The elemental abundance in the solar corona differs from that in the photosphere, with low first ionization potential (FIP) elements showing enhanced abundances, a phenomenon known as the FIP effect. This effect is considered to be driven by ponderomotive forces associated with magnetohydrodynamic (MHD) waves, particularly incompressible transverse waves. Aims. We aim to investigate the relationship between coronal abundance fractionation and transverse MHD waves in the chromosphere. We focus on analyzing the spatial correlation between the FIP fractionation and these waves, while exploring wave properties to validate the ponderomotive-force-driven fractionation model. Methods. We analyzed the H alpha data from the Fast Imaging Solar Spectrograph of the Goode Solar Telescope to detect chromospheric transverse MHD waves, and Si X (low FIP) and S X (high FIP) spectra from the EUV Imaging Spectrometer on board Hinode to determine the relative abundance in an active region. By extrapolating linear-force-free magnetic fields with Solar Dynamics Observatory/Helioseismic and Magnetic Imager magnetograms, we examine the connection between chromospheric waves and coronal composition. Around 400 wave packets were identified, and their properties, including the period, velocity amplitude, propagation speed, and propagation direction, were studied. Results. These chromospheric transverse MHD waves, mostly incompressible or weakly compressible, are found near loop footpoints, particularly in the sunspot penumbra and superpenumbral fibrils. The highly fractionated coronal region is associated with areas where these waves were detected within closed magnetic fields. Our examination of the statistics of wave properties revealed that downward-propagating low-frequency waves are particularly prominent, comprising about 43% of the detected waves. Conclusions. The correlation between abundance fractionation and transverse MHD waves, along with wave properties, supports the hypothesis that FIP fractionation occurs due to the ponderomotive force from transverse MHD waves in the chromosphere. Additionally, the observed characteristics of these chromospheric waves provide valuable observational constraints for understanding the FIP fractionation process.

Magnetic flux tubes such as sunspots play the role of channels through which magnetohydrodynamic waves carry mechanical energy from the solar interior to the atmosphere. We investigate the spatial distribution of Doppler velocity oscillations in the chromospheric network rosette, a supposed quiet Sun miniature of a sunspot, by analyzing H alpha line spectral data taken with the Fast Imaging Solar Spectrograph of the Goode Solar Telescope. The rosette consists of two regions: a central region displaying H alpha emission and a fibril region displaying H alpha absorption. We have categorized the observed velocity oscillations into three groups depending on location and period. Group I oscillations with periods from 3 to 6 min occur in the central region, group II oscillations with periods from 6 to 20 min in the inner parts of the fibril region, and group III oscillations with periods shorter than 3 min in the outermost parts of the fibril region. We discuss the probable physical origin of oscillations of each group. Our results suggest that the rosette is similar to a sunspot in morphology and oscillation properties, but there exist differences as well.

The investigation of plasma motions in the solar chromosphere is crucial for understanding the transport of mechanical energy from the interior of the Sun to the outer atmosphere and into interplanetary space. We report the finding of large-amplitude oscillatory transverse motions prevailing in the non-spicular Halpha chromosphere of a small quiet region near the solar disk center. The observation was carried out on 2018 August 25 with the Microlensed Hyperspectral Imager (MiHI) installed as an extension to the spectrograph at the Swedish Solar Telescope (SST). MiHi produced high-resolution Stokes spectra of the Halpha line over a two-dimensional array of points (sampled every 0.066 arcsec on the image plane) every 1.33 s for about 17 min. We extracted the Dopple-shift-insensitive intensity data of the line core by applying a bisector fit to Stoke I line profiles. From our time-distance analysis of the intensity data, we find a variety of transverse motions with velocity amplitudes of up to 40 km/s in fan fibrils and tiny filaments. In particular, in the fan fibrils, large-amplitude transverse MHD waves were seen to occur with a mean velocity amplitude of 25 km/s and a mean period of 5.8 min, propagating at a speed of 40 km/s. These waves are nonlinear and display group behavior. We estimate the wave energy flux in the upper chromosphere at 3 x 10^6 erg cm^-2 s^-1. Our results contribute to the advancement of our understanding of the properties of transverse MHD waves in the solar chromosphere.

Recently, complex horizontal patterns of umbral oscillations have been reported, but their physical nature and origin are still not fully understood. Here we show that the two-dimensional patterns of umbral oscillations of slow waves are inherited from the subphotospheric fast-body modes. Using a simple analytic model, we successfully reproduced the temporal evolution of oscillation patterns with a finite number of fast-body modes. In this model, the radial apparent propagation of the pattern is associated with the appropriate combination of the amplitudes in radial modes. We also find that the oscillation patterns are dependent on the oscillation period. This result indicates that there is a cutoff radial mode, which is a unique characteristic of the model of fast-body modes. In principle, both internal and external sources can excite these fast-body modes and produce horizontal patterns of umbral oscillations.

Spiral-shaped wave patterns (SWPs) observed in sunspot umbrae represent the superposition of axisymmetric patterns and nonaxisymmetric patterns of umbral oscillations. These patterns give us physical information about the source of oscillations below the surface. Here we present the statistics of their observational properties determined from the 304 Å line-intensity data obtained with the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory. From the 2013 to 2018 data set, we examined each of the 496 sunspots near the disk center for 2 hr. As a result, we identified 241 SWPs from 140 sunspots, which corresponds to the detection rate of 0.24 per hour in each sunspot. Most of the SWPs had one spiral arm, 48 SWPs had two arms, and only one had three. The oscillation period was estimated at 151 ± 27 s and the lifetime, at 770 ± 250 s, being comparable to those of conventional umbral oscillations. The rotation period of the SWPs was estimated at 190 ± 69 s for the one-armed SWPs and 299 ± 115 s for the two-armed SWPs. We found that the properties of the SWPs have no dependence on hemisphere, latitude, and sunspot size. From the apparent radial speeds of the SWPs and a simple model of wave propagation, we infer that the SWPs may be generated between 2 and 11 Mm below the photosphere with a mean value of about 6 Mm.

Umbral oscillations constitute the most noticeable chromospheric feature of sunspot umbrae—large-amplitude oscillations of intensity (umbral flashes, if very strong) and line-of-sight velocity, with periods of about 3 minutes. These umbral oscillations are usually interpreted as acoustic waves propagating upward under the effect of gravity. However, there have been observational reports that intensity peaks tend to occur in downflowing phases of umbral oscillations, and this appears to be more compatible with downward propagation. We investigate whether this intensity–velocity correlation occurs persistently or not, by determining the vertical flux of the wave energy, based on H α line measurements of the temperature and velocity. As a result, we find that the wave flux is persistently negative in sunspot umbrae, confirming the discrepancy specified above. We attribute this discrepancy to the nonzero fluctuation of net radiative heating. We find that when this effect is taken into account in the energy equation, the pressure is peaked during upflowing phases, being compatible with the notion of upward propagation. We conclude that temperature (and intensity) peaks occur during downflowing phases, not because of downward propagation, but because of radiative heat transport.

Type-IV radio bursts have been studied for over 50 years. However, the specifics of the radio emission mechanisms is still an open question. In order to provide more information about the emission mechanisms, we studied a moving Type-IV radio burst with fine structures (spike group) by using the high-resolution capability of the Low-Frequency Array (LOFAR) on August 25, 2014. We present a comparison of Nançay Radioheliograph (NRH) and the first LOFAR imaging data of the Type-IV radio burst. The degree of circular polarization (DCP) is calculated at frequencies in the range 20 – 180 MHz using LOFAR data, and it was found that the value of DCP gradually increased during the event, with values of 20 – 30%. LOFAR interferometric data were combined with white-light observations in order to track the propagation of this Type-IV burst. The kinematics shows a westward motion of the radio sources, slower than the CME leading edge. The dynamic spectrum of LOFAR shows a large number of fine structures with durations of less than 1 s and high brightness temperatures ( $T_{ \mathrm{B}}$ ), i.e., $10^{12}$  –  $10^{13}$ K. The gradual increase of DCP supports gyrosynchrotron emission as the most plausible mechanism for the Type IV. However, coherent emissions such as Electron Cyclotron Maser (ECM) instability may be responsible for small-scale fine structures. Countless fine structures altogether were responsible for such high $T_{\mathrm{B}}$ .

Recent observations provided evidence that the solar chromosphere of sunspot regions is pervaded by Alfvénic waves—transverse magnetohydrodynamic (MHD) waves (Alfvén waves or kink waves). In order to systematically investigate the physical characteristics of Alfvénic waves over a wide range of periods, we analyzed the time series of line-of-sight velocity maps constructed from the H α spectral data of a small sunspot region taken by the Fast Imaging Solar Spectrograph of the Goode Solar Telescope at Big Bear. We identified each Alfvénic wave packet by examining the cross-correlation of band-filtered velocity between two points that are located a little apart presumably on the same magnetic field line. As result, we detected a total of 279 wave packets in the superpenumbral region around the sunspot and obtained their statistics of period, velocity amplitude, and propagation speed. An important finding of ours is that the detected Alfvénic waves are clearly separated into two groups: 3-minute period (<7 minutes) waves and 10-minute period (>7 minutes) waves. We propose two tales on the origin of Alfvénic waves in the chromosphere; the 3-minute Alfvénic waves are excited by the upward-propagating slow waves in the chromosphere through the slow-to-Alfvénic mode conversion, and the 10-minute Alfvénic waves represent the chromospheric manifestation of the kink waves driven by convective motions in the photosphere.