arXiv subjects

Takuma Matsumoto

Publications and source records attributed to Takuma Matsumoto.

At least 37 records · Page 2Linked to original sources

arXiv2026

Solar flare ribbons structured by uncombed chromospheric loops

A part of the magnetic energy released during a flare is transported to the lower atmosphere. High-resolution observations show that flare ribbons, sites of energy deposition at the footpoints of flaring loops which appear bright in the chromosphere and transition region, are structured on small spatial scales on the order of 100 km. Based on idealized numerical models of flares it is suggested that the ribbon fine-structures could originate from a tearing instability and the development of plasmoids in current sheets. Here we report on Fe I 5250.6 Å and Mg I b2 5173 Å spectral observations of a solar flare from the Tunable Magnetograph onboard the SUNRISE III balloon-borne mission that reveal an intricate link between the flare ribbon structure and the ambient chromosphere. We identified uncombed chromospheric loops and non-flaring fine-structures that are interspersed among brighter flare ribbon threads. These loops remain stable on timescales of minutes. Spectral lines from these regions show reduced emission or self-reversal in the line core compared with the immediately adjacent flare ribbons. We discuss the potential role of these structures in the onset of a flare. Furthermore, we suggest that irrespective of the complexities in the flaring current sheet, uncombed chromospheric loops and nonflaring fine-structure might play a role in spatially modulating the flare energy deposition in the lower atmosphere.

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arXiv2026

Sunrise III: Instrument, mission, data, and first results

Sunrise III is a stratospheric balloon-borne solar observatory with a 1-m diameter telescope and three post-focus instruments, along with an image stabilisation system, all within a protective gondola. It samples the lower solar atmosphere, from the solar surface to the middle chromosphere, at a resolution approaching 50~km on the Sun. Sunrise III flew successfully for 6.5 days suspended from a zero-pressure stratospheric balloon from northern Sweden to north-western Canada in July 2024, gathering around 200 TB of data. The present issue of ApJL focuses on the first scientific results from the data collected during that flight. This paper introduces this Focus Issue, providing a very brief overview of the capabilities of the instrumentation, the flight and of the gathered data. Challenges for the measurements, data reduction and interpretation are also briefly touched upon. The paper ends with an overview of the first set of science results obtained from these data, as presented in the current Focus Issue.

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arXiv2026

Quantifying the effect of passband on observations in the Ca II K line

Full-disk observations of the Sun in the Ca II K line have been carried out since the late 19th century at various observatories worldwide. These long-term records of solar activity are crucial for reducing discrepancies among solar irradiance reconstructions and for advancing our understanding of the solar dynamo. To construct a consistent composite record, data from different observatories must be cross-calibrated to account for variations in spectral passband and spatial resolution, which are the primary sources of discrepancies between archives. In this study, we use high spectral and spatial resolution observations in the Ca II K line from the state-of-the-art Sunrise III mission to emulate different passbands and derive empirical contrast-contrast relationships between them. We find that these relationships are well described by a power law and provide coefficients for different combinations of passband widths in the range 0.1--9 Angstroms and spatial resolutions between 1 arcsec and 6 arcsec. Applying such a relationship to observations from two major Ca II K archives demonstrates its potential to improve their cross-calibration. The results provide a foundation for the construction of a consistent, century-long time series of solar activity from historical and modern Ca II K observations.

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arXiv2025

Synthetic Ca II 8542 Å Stokes Profile Associated with Chromospheric Magnetic Reconnection in a Simulated Active Region

Magnetic reconnection is an important driving mechanism of many chromospheric phenomena, e.g., UV bursts and chromospheric jets. Information about magnetic field is indispensable for analyzing chromospheric magnetic reconnection, which is mainly encoded in polarization signals. The purpose of this work is to predict possible Stokes features related to chromospheric reconnection events, from realistic two-dimensional magnetohydrodynamic simulation and Stokes profile synthesis. An emerging magnetic flux sheet is imposed at the bottom boundary of a well-relaxed unipolar atmosphere that spans from the upper convection zone to the corona. The reconnection region is heated to $\sim$7 kK and the outflow velocity reaches up to $\sim$35 km s$^{-1}$. Through Stokes profile synthesis, several Stokes features related to reconnections and plasmoids are reproduced. We found sign reversal features on circular polarization and amplitude reduction features on linear polarization at reconnection sites. Also, we report strong linear and circular polarization signals corresponding to huge ($\sim$300 km) and tiny ($\sim$40 km) plasmoids, respectively. We conclude that both linear and circular polarization signals may reveal the distinctive physical mechanisms in reconnections, and enhance the understanding of magnetic reconnection in observations.

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arXiv2025

Sunrise III: Overview of Observatory and Instruments

In July 2024, Sunrise completed its third successful science flight. The Sunrise III observatory had been upgraded significantly after the two previous successful flights in 2009 and 2013. Three completely new instruments focus on the small-scale physical processes and their complex interaction from the deepest observable layers in the photosphere up to chromospheric heights. Previously poorly explored spectral regions and lines are exploited to paint a three-dimensional picture of the solar atmosphere with unprecedented completeness and level of detail. The full polarimetric information is captured by all three instruments to reveal the interaction between the magnetic fields and the hydrodynamic processes. Two slit-based spectropolarimeters, the Sunrise UV Spectropolarimeter and Imager (SUSI) and the Sunrise Chromospheric Infrared spectro-Polarimeter (SCIP), focus on the near-ultraviolet and the near-infrared regions respectively, and the imaging spectropolarimeter Tunable Magnetograph (TuMag) simultaneously obtains maps of the full field-of-view of $46 \times 46$ Mm$^2$ in the photosphere and the chromosphere in the visible. The instruments are operated in an orchestrated mode, benefiting from a new Image Stabilization and Light Distribution unit (ISLiD), with the Correlating Wavefront Sensor (CWS) providing the autofocus control and an image stability with a root-mean-square value smaller than 0.005''. A new gondola was constructed to significantly improve the telescope pointing stability, required to achieve uninterrupted observations over many hours. Sunrise III was launched successfully on July 10, 2024, from the Esrange Space Center near Kiruna (Sweden). It reached the landing site between the Mackenzie River and the Great Bear Lake in Canada after a flight duration of 6.5 days. In this paper, we give an overview of the Sunrise III observatory and its instruments.

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arXiv2025

Comparison of Polar Magnetic Fields Derived from MILOS and MERLIN Inversions with Hinode/SOT-SP Data

The detailed investigation of the polar magnetic field and its time evolution is one of the major achievements of Hinode. Precise measurements of the polar magnetic field are essential for understanding the solar cycle, as they provide important constraints for identifying the source regions of the solar wind. The Spectropolarimeter (SP) of the Solar Optical Telescope (SOT) on board Hinode has been the instrument best suited to make such measurements. In this study, we compare the SOT-SP data for the polar regions, processed using two representative Milne-Eddington inversion codes, MILOS and MERLIN. These codes are applied to the same level-1 SOT-SP data, and the same disambiguation algorithm is used on the maps that go through the two inversions. We find that the radial magnetic-flux density (the magnetic-flux density with respect to the local vertical) provided by the MERLIN inversion tends to be approximately 7%-10% larger than that obtained from the MILOS inversion. The slightly higher radial magnetic-flux density from MERLIN appears to be common to the polar magnetic fields observed at different phases of the solar cycle. When MILOS is run with the same scattered-light profile and the same magnetic filling factor that are derived with the MERLIN inversion, the radial magnetic-flux density derived from the two inversions is almost the same. We attribute the difference in the radial magnetic-flux density to different filling factors adopted by the two inversions, based on whether the scattered-light profiles are assumed to be the Stokes I profiles averaged over the neighboring pixels or over the entire field of view. The relationship between the radial magnetic-flux density and magnetic filling factor could be more complex in the polar (limb) observations due to the possible contributions of the transverse magnetic-field component to the estimation of the radial magnetic-flux density.

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arXiv2025

Modeling the Solar Transition Region: Effects of Spatial Resolution on the Atmospheric Structure, Emission and Non-Equilibrium Ionization

The solar transition region (TR) is a narrow interface between the chromosphere and corona, where emitted radiation contains critical information pertinent to coronal heating processes. We conducted 2-dimensional radiation magnetohydrodynamics simulations using adaptive mesh refinement to spatially resolve the fine structure of the TR while simultaneously capturing the larger-scale dynamics originating from surface convection. The time evolution of ionization fractions for oxygen ions is computed alongside the simulations. A minimum grid size of 1.25 km is achieved in the TR, enabling adequate resolution of the upper TR (log$_{10}T \gtrsim$ 5), although the lower TR (log$_{10}T \lesssim$ 5) remains under-resolved. Doppler shifts and nonthermal widths synthesized from TR lines exhibit convergence with grid sizes as coarse as 40 km, though some discrepancies persist between our results and observed TR line properties. A notable enhancement in emission from \ion{O}{6} lines, converging at a grid size of 2.5 km, shows an intensity 1.2 times that expected under ionization equilibrium, attributable to shock interactions with the TR. While model refinements are still required, our ability to resolve the TR offers critical insights into TR line characteristics arising from non-equilibrium ionization states, advancing our understanding of the coronal heating problem.

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arXiv2024

Anomalous emission from Li- and Na-like ions in the Corona heated via Alfvén wave

The solar ultraviolet intensities of spectral lines originating from Li- and Na-like ions have been observed to surpass the expectations derived from plasmas with coronal approximation. The violation of the coronal approximation can be partially attributed to non-equilibrium ionization (NEI) due to dynamic processes occurring in the vicinity of the transition region. To investigate the impact of these dynamics in Alfvén-wave-heated coronal loop, a set of equations governing NEI for multiple ion species was solved numerically in conjunction with 1.5-dimensional magnetohydrodynamic equations. Following the injection of Alfvén waves from the photosphere, the system undergoes a time evolution characterized by phases of evaporation, condensation, and quasi-steady states. During the evaporation phase, the ionization fractions of Li- and Na-like ions were observed to increase when compared to the fractions in ionization equilibrium, which lead to the intensity enhancement of up to 1.6. This over-fractionation of Li- and Na-like ions was found to be induced by the evaporation process. While collisions between shocks and the transition region temporarily led to deviations from ionization equilibrium, on average over time, these deviations were negligible. Conversely, under-fractions of the ionization fraction led to intensity reduction of down to 0.9 during the condensation phase and the quasi-steady state. Given the dependency of the over/under-fractionation on mass circulations between the chromosphere and the corona, these observations will serve as valuable benchmarks to validate not only Alfvén wave models but also other existing mechanisms on coronal heating.

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arXiv2023

Systematic analysis of $t$ and $^3$He breakup reactions

Systematic measurement of $t$ and $^3$He knockout processes is planned. The weakly-bound nature of these nuclei may affect the interpretation of forthcoming knockout reaction data. Purpose: We aim at clarifying breakup properties of $t$ and $^3$He by investigating their elastic and breakup cross sections. We employ the four-body continuum-discretized coupled-channels method with the eikonal approximation to describe the $t$ and $^3$He reactions. The breakup cross section of $t$ is found to be almost the same as that of $^3$He and is about one-third of that of $d$. Coulomb breakup plays negligible role in the breakup of $t$ and $^3$He, in contrast to in the deuteron breakup reaction. It is found that $t$ and $^3$He tend to breakup into three nucleons rather than $d$ and a nucleon. It is shown that the breakup cross sections of $t$ and $^3$He are not as large as those of d but non-negligible. Because about 80% of them corresponds to the three-nucleon breakup process, a four-body breakup reaction model is necessary to quantitatively describe the breakup of $t$ and $^3$He.

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arXiv2022

Dineutron in the $2^+_1$ state of $^6$He

We investigate the dineutron in the $2^+_1$ state of $^6$He via analysis of its decay mode by using the complex scaling method. In this letter, we propose the cross section for the resonant state to distinguish the resonant contributions from the nonresonant ones. As the results, it is found that the shoulder peak appears in the cross section for the resonant state as a function of $\varepsilon_{n\text{-}n}$. Furthermore, we show that the $S$ = 0 component of the cross section, where $S$ is the total spin of the valence two neutrons, has a peak around the shoulder peak, which comes from the dineutron configuration in the $2^+_1$ state. Thus we conclude that the shoulder peak is expected to indicate the existence of the dineutron in the $2^+_1$ state.

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arXiv2021

Investigation of multi-step effects for proton inelastic scattering to the $2^{+}_{1}$ state in $^6$He

Multi-step effects between bound, resonant, and non-resonant states have been investigated by the continuum-discretized coupled-channels method (CDCC). In the CDCC, a resonant state is treated as multiple states fragmented in a resonance energy region, although it is described as a single state in usual coupled-channel calculations. For such the fragmented resonant states, one-step and multi-step contributions to the cross sections should be carefully discussed because the cross sections obtained by the one-step calculation depend on the number of those states, which corresponds to the size of the model space. To clarify the role of the multi-step effects, we propose the one-step calculation without model-space dependence for the fragmented resonant states. Furthermore, we also discuss the multi-step effects between the ground, $2^{+}_{1}$ resonant, and non-resonant states in $^6$He for proton inelastic scattering.

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arXiv2021

Three-body description of $^9$C: Role of low-lying resonances in breakup reactions

The $^9$C nucleus and related capture reaction, ${^8\mathrm{B}}(p,γ){^9\mathrm{C}}$, have been intensively studied with an astrophysical interest. Due to the weakly-bound nature of $^9$C, its structure is likely to be described as the three-body (${^7\mathrm{Be}}+p+p$). Its continuum structure is also important to describe reaction processes of $^9$C, with which the reaction rate of the ${^8\mathrm{B}}(p,γ){^9\mathrm{C}}$ process have been extracted indirectly. We perform three-body calculations on $^9$C and discuss properties of its ground and low-lying states via breakup reactions. We employ the three-body model of $^9$C using the Gaussian-expansion method combined with the complex-scaling method. This model is implemented in the four-body version of the continuum-discretized coupled-channels method, by which breakup reactions of $^9$C are studied. The intrinsic spin of $^7$Be is disregarded. By tuning a three-body interaction in the Hamiltonian of $^9$C, we obtain the low-lying $2^+$ state with the resonant energy 0.781 MeV and the decay width 0.137 MeV, which is consistent with the available experimental information and a relatively high-lying second $2^+$ wider resonant state. Our calculation predicts also sole $0^+$ and three $1^-$ resonant states. We discuss the role of these resonances in the elastic breakup cross section of $^9$C on $^{208}$Pb at 65 and 160 MeV/A. The low-lying 2$^+$ state is probed as a sharp peak of the breakup cross section, while the 1$^-$ states enhance the cross section around 3 MeV. Our calculations will further support the future and ongoing experimental campaigns for extracting astrophysical information and evaluating the two-proton removal cross-sections.

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arXiv2021

Probing the physics of the solar atmosphere with the Multi-slit Solar Explorer (MUSE): I. Coronal Heating

The Multi-slit Solar Explorer (MUSE) is a proposed NASA MIDEX mission, currently in Phase A, composed of a multi-slit EUV spectrograph (in three narrow spectral bands centered around 171A, 284A, and 108A) and an EUV context imager (in two narrow passbands around 195A and 304A). MUSE will provide unprecedented spectral and imaging diagnostics of the solar corona at high spatial (<0.5 arcsec), and temporal resolution (down to ~0.5s) thanks to its innovative multi-slit design. By obtaining spectra in 4 bright EUV lines (Fe IX 171A , Fe XV 284A, Fe XIX-Fe XXI 108A) covering a wide range of transition region and coronal temperatures along 37 slits simultaneously, MUSE will for the first time be able to "freeze" (at a cadence as short as 10 seconds) with a spectroscopic raster the evolution of the dynamic coronal plasma over a wide range of scales: from the spatial scales on which energy is released (~0.5 arcsec) to the large-scale often active-region size (170 arcsec x 170 arcsec) atmospheric response. We use advanced numerical modeling to showcase how MUSE will constrain the properties of the solar atmosphere on the spatio-temporal scales (~0.5 arcsec, ~20 seconds) and large field-of-view on which various state-of-the-art models of the physical processes that drive coronal heating, solar flares and coronal mass ejections (CMEs) make distinguishing and testable predictions. We describe how the synergy between MUSE, the single-slit, high-resolution Solar-C EUVST spectrograph, and ground-based observatories (DKIST and others) can address how the solar atmosphere is energized, and the critical role MUSE plays because of the multi-scale nature of the physical processes involved. In this first paper, we focus on how comparisons between MUSE observations and theoretical models will significantly further our understanding of coronal heating mechanisms.

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arXiv2021

Systematic study on the role of various higher-order processes in the breakup of weakly-bound projectiles

The virtual photon theory (VPT), which is based on first-order Coulomb dissociation restricted to the electric dipole ($E1$), has been successfully used to explain the breakup data for several cases. Our aim is to study the role of various higher-order processes that are ignored in the VPT, such as the nuclear breakup, interference between nuclear and Coulomb amplitudes, and multistep breakup processes mainly due to strong continuum-continuum couplings in the breakup of two-body projectiles on a heavy target at both intermediate and higher incident energies. For the purpose of numerical calculations, we employed eikonal version of three-body continuum-discretized coupled-channels (CDCC) reaction model. Our results for the breakup of $^{11}$Be and $^{17}$F on $^{208}$Pb target at 100, 250, and 520 MeV/A, show the importance of nuclear breakup contribution, and its significant role in the multistep processes. The multistep effect on Coulomb breakup for core-neutron projectile was found to be negligible, whereas it was important for core-proton projectile. Coulomb-nuclear interference (CNI) effect was also found to be non-negligible. Quantitatively, the multistep effects due to the nuclear breakup was found to depend on the incident energy through the energy dependence of the core-target and nucleon-target nuclear potentials. The nuclear breakup component, the CNI effect, and the multistep breakup processes are all found to be non-negligible; hence, the assumptions adopted in the VPT for the accurate description of breakup cross sections are not valid.

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arXiv2021

Investigation of contributions of the $2_2^+$ resonance in $^6$He via analysis of $^6$He($p$, $p'$)

We investigate the contribution of the $2^{+}_{2}$ resonance in $^6$He to observables via analysis of the $^6$He($p,p'$) reaction by using the continuum-discretized coupled channels method combined with the complex-scaling method. In this study, we obtain the $2^{+}_{2}$ state with the resonant energy 2.25 MeV and the decay width 3.75 MeV and analyse contributions of resonances and nonresonant continuum states to the cross section separately. It is found that the $2^{+}_{2}$ state plays an important role in the energy spectrum. Furthermore, contributions of nonresonant continuum states are also important to clarify the properties of the $2^{+}_{2}$ state.

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arXiv2021

Practical method for decomposing discretized breakup cross sections into components of each channel

Background: In the continuum-discretized coupled-channel method, a breakup cross section (BUX) is obtained as an admixture of several components of different channels in multi-channel scattering. Purpose: Our goal is to propose an approximate way of decomposing the discretized BUX into components of each channel. This approximation is referred to as the "probability separation (P-separation)". Method: As an example, we consider $^{11}$Be scattering by using the three-body model with core excitation ($^{10}\mathrm{Be}+n+\mathrm{T}$, where T is a target). The structural part is constructed by the particle-rotor model and the reaction part is described by the distorted wave Born approximation (DWBA). Results: The validity of the P-separation is tested by comparing with the exact calculation. The approximate way reproduces the exact BUXs well regardless of the configurations and/or the resonance positions of $^{11}$Be. Conclusion: The method proposed here can be an alternative approach for decomposing discretized BUXs into components in four- or five-body scattering where the strict decomposition is hard to perform.

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arXiv2020

Full compressible 3D magnetohydrodynamic simulation of solar wind

Identifying the heating mechanisms of the solar corona and the driving mechanisms of solar wind are key challenges in understanding solar physics. A full three-dimensional compressible magnetohydrodynamic (MHD) simulation was conducted to distinguish between the heating mechanisms in the fast solar wind above the open field region. Our simulation describes the evolution of the Alfvénic waves, which includes the compressible effects from the photosphere to the heliospheric distance $s$ of 27 solar radii ($R_\odot$). The hot corona and fast solar wind were reproduced simultaneously due to the dissipation of the Alfvén waves. The inclusion of the transition region and lower atmosphere enabled us to derive the solar mass loss rate for the first time by performing a full three-dimensional compressible MHD simulation. The Alfvén turbulence was determined to be the dominant heating mechanism in the solar wind acceleration region ($s>1.3 R_\odot$), as suggested by previous solar wind models. In addition, shock formation and phase mixing are important below the lower transition region ($s<1.03R_\odot$) as well.

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arXiv2019

Borromean Feshbach resonance in 11Li studied via 11Li(p,p')

A dipole resonance of 11Li is newly found by a 9Li + n + n three-body model analysis with the complex-scaling method. The resonance can be interpreted as a bound state in the 10Li + n system, that is, a Feshbach resonance in the 9Li + n + n system. As a characteristic feature of the Feshbach resonance of 11Li, the 10Li + n threshold is open above the 9Li + n + n one, which reflects a distinctive property of the Borromean system. A microscopic four-body reaction calculation for the 11Li(p,p') reaction at 6 MeV/nucleon is performed by taking into account the resonance and nonresonant continuum states of the three-body system. The angular distribution of the elastic and inelastic scattering as well as the breakup energy spectrum recently observed are reproduced well.

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