A5058524930- Solar and Space Plasma Dynamics
- Stellar, planetary, and galactic studies
- Astro and Planetary Science
- Astrophysics and Star Formation Studies
- Ionosphere and magnetosphere dynamics
- Astrophysical Phenomena and Observations
- Gamma-ray bursts and supernovae
- Astrophysics and Cosmic Phenomena
- Geomagnetism and Paleomagnetism Studies
- Solar Radiation and Photovoltaics
- Pulsars and Gravitational Waves Research
- Galaxies: Formation, Evolution, Phenomena
- Magnetic confinement fusion research
- Astronomy and Astrophysical Research
- High-pressure geophysics and materials
- Astronomical Observations and Instrumentation
- Neutrino Physics Research
- Adaptive optics and wavefront sensing
- Spacecraft and Cryogenic Technologies
- Space Exploration and Technology
- Oil, Gas, and Environmental Issues
- Gas Dynamics and Kinetic Theory
- Photocathodes and Microchannel Plates
- Planetary Science and Exploration
- Earthquake Detection and Analysis
Osaka University
2020-2025
Osaka Health Science University
2021-2023
National Astronomical Observatory of Japan
2019-2020
Nagoya University
2016-2019
Kyoto University
2011-2017
Understanding the processes of planet formation and accretion in young systems is essential to unraveling initial conditions planetary systems. The PDS 70 system, which hosts two directly imaged protoplanets, provides a unique laboratory for studying these phenomena, particularly through H-alpha emission commonly used tracer. We present multi-epoch observations examine variability signatures within this focusing on b c. Using Hubble Space Telescope narrowband imaging from 2020 2024, we...
We report the simultaneous extreme-ultraviolet observation of magnetic reconnection inflow and outflow in a flare on 2010 August 18 observed by Atmospheric Imaging Assembly board Solar Dynamics Observatory. found that during rise phase flare, some plasma blobs appeared sheet structure above hot loops. The were ejected bidirectionally along (outflow), at same time as threads visible images moved toward (inflow). upward downward ejection velocities are 220–460 km s−1 250–280 s−1, respectively....
Observations revealed that various kinds of oscillations are excited in solar flare regions. Quasi-periodic pulsations (QPPs) the emissions commonly observed a wide range wavelengths. Recent observations have found fast-mode magnetohydrodynamic (MHD) waves quasi-periodically emitted from some flaring sites (quasi-periodic propagating magnetoacoustic waves; QPFs). Both QPPs and QPFs imply cyclic disturbance originating sites. However, physical mechanisms remain puzzling. By performing set...
Abstract Current state-of-the-art spectrographs cannot resolve the fundamental spatial (subarcseconds) and temporal (less than a few tens of seconds) scales coronal dynamics solar flares eruptive phenomena. The highest-resolution data to date are based on imaging, which is blind many processes that drive energetics dynamics. As shown by Interface Region Imaging Spectrograph for low atmosphere, we need high-resolution spectroscopic measurements with simultaneous imaging understand dominant...
Solar flare emission is detected in all EM bands and variations flux density of solar energetic particles. Often the radiation generated stellar flares shows a pronounced oscillatory pattern, with characteristic periods ranging from fraction second to several minutes. These oscillations are referred as quasi-periodic pulsations (QPPs), emphasise that they often contain apparent amplitude period modulation. We review current understanding flares. In particular, we focus on possible physical...
Abstract Solar active regions (ARs) that produce strong flares and coronal mass ejections (CMEs) are known to have a relatively high non-potentiality characterized by δ -sunspots sheared magnetic structures. In this study, we conduct series of flux emergence simulations from the convection zone corona model four types been observationally suggested cause flares, namely spot–spot, spot–satellite, quadrupole, inter-AR cases. As result, confirm -spot formation is due complex geometry...
We report a new evaluation of the accretion properties PDS~70b obtained with VLT/MUSE. The main difference from previous studies in Haffert et al. (2019) and Aoyama & Ikoma is mass rate. Simultaneous multiple line observations, such as H$\alpha$ H$\beta$, can better constrain physical an accreting planet. While we clearly detected emissions PDS~70b, no H$\beta$ were detected. estimate flux 3-$\sigma$ upper limit to be 2.3~$\times$~10$^{-16}$~erg~s$^{-1}$~cm$^{-2}$. ratio $F_{\rm...
We carried out a magnetohydrodynamics simulation where subsurface twisted kink-unstable flux tube emerges from the solar interior to corona. Unlike previous expectations based on bodily emergence of knotted tube, we found that kinked can spontaneously form complex quadrupole structure at photosphere. Due development kink instability before emergence, magnetic twist apex is greatly reduced, although other parts still strongly twisted. This leads formation structure: pair coherent, spots and...
The role of slow-mode MHD shocks in magnetic reconnection is one great importance for energy conversion and transport, but many astrophysical plasmas the plasma not fully ionised. In this paper, we investigate, using numerical simulations, collisional coupling between a proton-electron charge-neutral fluid neutral hydrogen 1D Riemann problem initiated constant pressure density background state by discontinuity field. This system, limit, characterised two waves: fast-mode rarefaction wave...
We perform three-dimensional magnetohydrodynamic simulations of magnetospheric accretion in a T Tauri star to study the and wind structures close vicinity star. The gas accreting onto consists from boundary failed disk winds. is commonly found as multi-column accretion, which consistent with observations. A significant fraction angular momentum flows removed by magnetic fields conical winds turbulent inside near magnetosphere. As result, torque significantly reduced compared simple...
Abstract Accretion plays a central role in the physics that governs evolution and dispersal of protoplanetary disks. The primary goal this paper is to analyze stability over time mass accretion rate onto TW Hya, nearest accreting solar-mass young star. We measure veiling across optical spectrum 1169 archival high-resolution spectra obtained from 1998–2022. then converted using 26 flux-calibrated cover Balmer jump. measured excess continuum has an average 2.51 × 10 −9 M ⊙ yr −1 Gaussian...
Extreme ultraviolet imaging spectroscopic observations often show an increase in line width around the loop-top or above-loop-top (ALT) region of solar flares, suggestive turbulence. In addition, recent found oscillation Doppler velocity ALT region. We performed three-dimensional magnetohydrodynamic (MHD) simulations to investigate dynamics region, with a particular focus on generation turbulence and excitation oscillatory motion. rapid growth MHD instabilities upper parts (arms magnetic...
We studied the acceleration mechanisms of chromospheric jets associated with emerging flux using a two dimensional magnetohydrodynamic (MHD) simulation. found that slow mode shock waves generated by magnetic reconnection in chromosphere and photosphere play key roles jets. An important parameter is height reconnection. When takes place near photosphere, out- flow collides region where plasma beta much larger than unity. Then moves along field. This motion generates wave. The wave develops to...
For a better understanding of magnetic field in the solar corona and dynamic activities such as flares coronal mass ejections, it is crucial to measure time-evolving accurately estimate energy. Recently, new modeling technique called data-driven model, which time evolution driven by sequence photospheric velocity maps, has been developed revealed dynamics flare-productive active regions. Here we report on first qualitative quantitative assessment different models using flux emergence...
A search of the hard X-ray archive data NuSTAR found a transient source, J230059+5857.4, during an observation 1E 2259+586 on 2013 April 25. multi-wavelength analysis using X-ray, optical, and IR data, mostly taken in its quiescent phase, was conducted to identify origin J230059+5857.4 elucidate phenomena associated with flare activity. The results indicated that stellar occurred single M-dwarf, M-dwarf binary, or pre-main-sequence star. exhibited higher emission measure temperature,...
Abstract Stellar spin is one of the fundamental quantities that characterize a star itself and its planetary system. Nevertheless, stellar spin-down mechanisms in protostellar pre-main-sequence phases have been long-standing problem formation theory. To realize spin-down, previous axisymmetric models based on conventional magnetospheric paradigm had to assume massive winds or produce highly time-variable ejections. However, this picture has challenged by both numerical simulations...
Photoevaporation caused by X-ray and UV radiation from the central star has attracted attention as a key process driving dispersal of protoplanetary discs. Although numerous models have been used to investigate photoevaporation process, their conclusions vary, which is partly due differences in adopted spectra host star, particular, extreme-UV (EUV) soft bands. This study aims construct EUV (soft) emission spectrum pre-main-sequence stars using physics-based model that focuses on...
ABSTRACT We report a strong association between the particle acceleration and plasma motions found in 2010 August 18 solar flare. The are tracked extreme ultraviolet (EUV) images taken by Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory Extreme UltraViolet Imager (EUVI) Terrestrial Relations spacecraft Ahead , signature of was investigated using Nobeyama Radioheliograph data. In our previous paper, we reported that EUV many blobs appeared current sheet above flare...
Abstract We perform three-dimensional global non-ideal magnetohydrodynamic simulations of a protoplanetary disk containing the inner dead-zone edge. take into account realistic diffusion coefficients Ohmic resistivity and ambipolar based on detailed chemical reactions with single-size dust grains. found that conventional dead zone identified by Elsässer numbers is divided two regions: “the transition zone” coherent zone.” The has same properties as zone, extends outside in radial direction....
Abstract The IceCube Collaboration has reported possible detections of high-energy neutrinos from nearby Seyfert galaxies. While central hot coronae are proposed as the primary neutrino production site, exact coronal cosmic ray energy budget been loosely constrained. In this study, we propose a new stringent upper bound on galaxies, considering both accretion dynamics and observed properties radio-quiet Notably, even under calorimetric condition where rays lose all their energy, our limit...
Solar flares are an explosive phenomenon where super-sonic flows and shocks expected in above the post-flare loops. To understand dynamics of loops, a two-dimensional magnetohydrodynamic (2D MHD) simulation solar flare has been carried out. We found new shock structures which were not resolved previous work by Yokoyama & Shibata. study along reconnected magnetic field, kinematics energetics plasma investigated selected field lines. It is that crucial to determine thermal flow On basis 2D MHD...
The X-ray and extreme-ultraviolet (EUV) emissions from the low-mass stars significantly affect evolution of planetary atmosphere. However, it is, observationally difficult to constrain stellar high-energy emission because strong interstellar extinction EUV photons. In this study, we simulate XUV (X-ray+EUV) Sun-like by extending solar coronal heating model that self-consistently solves, with sufficiently high resolution, surface-to-coronal energy transport, turbulent heating, thermal...
We present the results of a global, three-dimensional magnetohydrodynamics simulation an accretion disk with rotating, weakly magnetized central star. The is threaded by weak, large-scale poloidal magnetic field, and star has no strong stellar magnetosphere initially. Our investigates structure flows from turbulent onto reveals that fast at high latitudes occurs even without magnetosphere. find failed wind becomes fast, high-latitude as result angular momentum exchange mediated fields well...
Abstract We investigate how magnetically driven outflows are powered by a rotating, weakly magnetized accretion flow onto supermassive black hole using axisymmetric magnetohydrodynamic simulations. Our proposed model focuses on the dynamics an intermediate scale between Schwarzschild radius and galactic scale, which is ∼1–100 pc. demonstrate that rotating disk formed parsec-scale acquires poloidal magnetic fields via accretion, this produces asymmetric bipolar outflow at some point. The...