Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Abstract

S unrise iii is a stratospheric balloon-borne solar observatory with a 1 m diameter telescope and three postfocus 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. S unrise iii flew successfully for 6.5 days suspended from a zero-pressure stratospheric balloon from northern Sweden to northwestern Canada in 2024 July, gathering around 200 TB of data. The present issue of the Astrophysical Journal Letters focuses on the first scientific results from the data collected during that flight. This Letter 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 Letter ends with an overview of the first set of science results obtained from these data, as presented in the current Focus Issue.

DOI： 10.3847/2041-8213/ae796b

Open Access

Other Link： https://iopscience.iop.org/article/10.3847/2041-8213/ae796b/pdf

Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Abstract

Magnetic reconnection is an important driving mechanism of many chromospheric phenomena, e.g., UV bursts and chromospheric jets. Information about magnetic fields 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 ∼7 kK and the outflow velocity reaches up to ∼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 (∼300 km) and tiny (∼40 km) plasmoids, respectively. We conclude that both linear and circular polarization signals may reveal the distinctive physical mechanisms in reconnections and enhance our understanding of magnetic reconnection in observations.

DOI： 10.3847/1538-4357/ae045e

Open Access

Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/ae045e/pdf

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s11207-025-02485-1

Open Access

Web of Science

Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s11207-025-02487-z

Open Access

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Abstract

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 two-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 (log₁₀ T ≳ 5), although the lower TR (log₁₀ T ≲ 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 O vi 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.

DOI： 10.3847/1538-4357/adac5f

Open Access

Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/adac5f/pdf

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Abstract

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 nonequilibrium ionization (NEI) due to dynamic processes occurring in the vicinity of the transition region. To investigate the impact of these dynamics in the 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 led to an enhancement in the intensity 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 a reduction in intensity 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.

DOI： 10.3847/1538-4357/ad283d

Open Access

Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/ad283d/pdf

Publishing type：Research paper (scientific journal)  

DOI： 10.3847/1538-4357/acf9fc

Open Access

Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Abstract

The physical connection between thermal convection in the solar interior and the solar wind remains unclear due to their significant scale separation. Using an extended version of the three-dimensional radiative magnetohydrodynamic code RAMENS, we perform the first comprehensive simulation of the solar wind formation, starting from the wave excitation and the small-scale dynamo below the photosphere. The simulation satisfies various observational constraints as a slow solar wind emanating from the coronal hole boundary. The magnetic energy is persistently released in the simulated corona, showing a hot upward flow at the interface between open and closed fields. To evaluate the energetic contributions from Alfvén wave and interchange reconnection, we develop a new method to quantify the cross-field energy transport in the simulated atmosphere. The measured energy transport from closed coronal loops to open field accounts for approximately half of the total. These findings suggest a significant role of the supergranular-scale interchange reconnection in solar wind formation.

DOI： 10.3847/2041-8213/acdde0

Open Access

Other Link： https://iopscience.iop.org/article/10.3847/2041-8213/acdde0/pdf

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1093/mnras/stad1509

Open Access

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

Abstract

Chromospheric jets are plausible agents of energy and mass transport in the solar chromosphere, although their driving mechanisms have not yet been elucidated. Magnetic field measurements are key for distinguishing the driving mechanisms of chromospheric jets. We performed a full Stokes synthesis in the infrared range with a realistic radiative magnetohydrodynamics simulation that generated a chromospheric jet to predict spectro-polarimetric observations from the Sunrise Chromospheric Infrared spectro-Polarimeter (SCIP) onboard the SUNRISE III balloon telescope. The jet was launched by the collision between the transition region and an upflow driven by the ascending motion of the twisted magnetic field at the envelope of the flux tube. This motion is consistent with upwardly propagating non-linear Alfvénic waves. The upflow could be detected as continuous Doppler signals in the Ca ii 849.8 nm line at the envelope where the dark line core intensity and strong linear polarisation coexist. The axis of the flux tube was bright in both Fe i 846.8 nm and Ca ii 849.8 nm lines with down- flowing plasma inside it. The structure, time evolution, and Stokes signals predicted in our study will improve the physical interpretation of future spectro-polarimetric observations with SUNRISE III/SCIP.

DOI： 10.1093/mnras/stad1509

Open Access

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media {LLC}  

DOI： 10.1007/s11207-022-01968-9

Scopus

Other Link： https://link.springer.com/article/10.1007/s11207-022-01968-9/fulltext.html

Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Abstract

The Multi-slit Solar Explorer (MUSE) is a proposed mission composed of a multislit extreme ultraviolet (EUV) spectrograph (in three spectral bands around 171 Å, 284 Å, and 108 Å) and an EUV context imager (in two passbands around 195 Å and 304 Å). MUSE will provide unprecedented spectral and imaging diagnostics of the solar corona at high spatial (≤0.″5) and temporal resolution (down to ∼0.5 s for sit-and-stare observations), thanks to its innovative multislit design. By obtaining spectra in four bright EUV lines (Fe ix 171 Å, Fe xv 284 Å, Fe xix–Fe xxi 108 Å) covering a wide range of transition regions and coronal temperatures along 37 slits simultaneously, MUSE will, for the first time, “freeze” (at a cadence as short as 10 s) 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) to the large-scale (∼170″ × 170″) atmospheric response. We use numerical modeling to showcase how MUSE will constrain the properties of the solar atmosphere on spatiotemporal scales (≤0.″5, ≤20 s) and the large field of view on which state-of-the-art models of the physical processes that drive coronal heating, flares, and coronal mass ejections (CMEs) make distinguishing and testable predictions. We describe the synergy between MUSE, the single-slit, high-resolution Solar-C EUVST spectrograph, and ground-based observatories (DKIST and others), and the critical role MUSE plays because of the multiscale nature of the physical processes involved. In this first paper, we focus on coronal heating mechanisms. An accompanying paper focuses on flares and CMEs.

DOI： 10.3847/1538-4357/ac4222

Open Access

Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/ac4222/pdf

Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.2561223

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press ({OUP})  

<jats:title>ABSTRACT</jats:title>
<jats:p>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⊙). 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 &amp;gt; 1.3 R⊙), as suggested by previous solar wind models. In addition, shock formation and phase mixing are important below the lower transition region (s &amp;lt; 1.03 R⊙) as well.</jats:p>

DOI： 10.1093/mnras/staa3533

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1093/mnras/sty490

Language：Japanese   Presentation type：Oral presentation (general)