學術演講及專題研討 (2023)

The James Clerk Maxwell Telescope (JCMT) has been monitoring eight nearby low-mass star-forming regions in the Gould Belt at submillimetre wavelengths for over seven years to search for and quantify the time dependent brightness variability of the resident deeply embedded protostars. Secular variability is common among these protostars; greater than 25% of the sample show measurable long-term brightness changes and 10% show burst behaviour lasting months to years. We interpret this secular variability as reflecting changes in the mass accretion rate from the disk to the protostar, as predicted by theoretical models of (proto)stellar assembly. For a subset of our sample we have contemporaneous mid-IR light-curves which allow additional constraints on the conditions responsible for the brightness variations, confirming that the submillimetre variability is driven by changes in the dust temperature profile of the envelope. Furthermore, we have combined, for one source, single dish and interferometric sub-mm monitoring, which has allowed us to unambiguously recover a time lag in the variability at larger angular scales and use the results to confirm the envelope structure surrounding the embedded protostar.

Planetary explorations have revealed that complex organics are widely present in the Solar System. Infrared spectroscopic observations have discovered that complex organics are synthesized in large quantities in planetary nebulae and distributed throughout the Galaxy. Signatures of organics are found in distant galaxies, as early as 1.5 billion years after the Big Bang. A number of unsolved spectral phenomena such as diffuse interstellar bands, extended red emissions, 220 nm feature, and unidentified infrared emission bands are likely to originate from organics. In this talk, we will discuss what are the possible chemical structures of the carriers of these phenomena, and how these organics are synthesized abiotically in the Universe.

References
Kwok, S. 2022, The Mystery of Unidentified Infrared Emission Bands, Astrophys. Space Science, 367, 16
Kwok, S. 2016, Complex organics in space: from Solar System to distant galaxies, Astr. & Astrophy. Rev., 24, 8
Kwok, S. and Zhang, Y. 2011, Mixed aromatic/aliphatic organic nanoparticles as carriers of unidentified infrared emission features, Nature, 479, 80-83
Kwok, S. 2011, Organic Matter in the Universe, Wiley

I will discuss two topics on exoplanetary systems. The first concerns hot Jupiters, giant planets with orbital periods of a few days. Observations have revealed that many hot Jupiters have orbits that are highly misaligned with the rotation of their host stars. How did such large stellar obliquities come about? What do they inform about the formation of hot Jupiters? The second topic deals with planetary obliquity, which reflects the planet's dynamical history, and can strongly influence the atmosphere condition and climate of the planet. Many Sun-like stars are observed to host close-in super-Earths (or Earth-like planets) as part of a multi-planetary system. Can such super-Earths (or similar habitable planets around M stars) sustain significant obliquities?

Accurate and precise specification and characterization of the ionospheric electron density (N_e) irregularities are important to radio sky-wave communications and satellite navigation. In this scenario, multi-instruction and multi-station systems have been developed and/or organized for ionospheric irregularity and scintillation observations in the Taiwan-Philippines sector. The theoretical simulations show that both scintillation index S4 and S2 values become saturation when a sampling spatial scale is less than the first Fresnel zone (FFZ), and S_4 and S_2 values could be underestimated and be approximately proportional to the logarithm of sampling spatial wave numbers up to the FFZ wave number. We could indicate the existences of plasma bubble and/or sporadic-E (Es) in the Taiwan-Philippines sector using the FS3/COSMIC or FS7/COSMIC2 GPS/GLONASS radio occultation (RO) observations. We verify the latitudinal extent of the tracked plasma bubble or Es using the recorded ionograms from the Vertical Incidence Pulsed Ionospheric Radar (VIPIR) systems located at Hualien and Longquan, Taiwan, etc. We further discuss the spatial and temporal variabilities of two-dimensional vertical scintillation index VS_4 maps based on the simultaneous GPS L1-band signal measurements from more than 130 ground-based receivers located in Taiwan and the surrounding islands. We also operate several high-sampling software-defined GPS receivers and characterize the targeted plasma irregularities by carrying out spectrum analyses of the received signal. Generally, the F-layer scintillation and Es-layer event climatology, namely, its variations with each identified zone, altitude, season, and local time have been documented.

The production mechanism of repeating fast radio bursts (FRBs) is still a mystery, and correlations between burst occurrence times and energies may provide important clues to elucidate it. While time correlation studies of FRBs have been mainly performed using wait time distributions, here we report the results of a correlation function analysis of repeating FRBs in the two-dimensional space of time and energy. We analyze nearly 7,000 bursts reported in the literature for the three most active sources of FRB 20121102A, 20201124A, and 20220912A, and find the following characteristics that are universal in the three sources. A clear power-law signal of the correlation function is seen, extending to the typical burst duration (∼ 10 msec) toward shorter time intervals. The correlation function indicates that every single burst has about a 10-60% chance of producing an aftershock at a rate decaying by a power-law as ~ t^{−p} with p= 1.5-2.5, like the Omori-Utsu law of earthquakes. The correlated aftershock rate is stable regardless of source activity changes, and there is no correlation between emitted energy and time. We demonstrate that all these properties are quantitatively common to earthquakes, but different from solar flares in many aspects, by applying the same analysis method for the data on these phenomena. These results suggest that repeater FRBs are a phenomenon in which energy stored in rigid neutron star crusts is released by seismic activity. This may provide a new opportunity for future studies to explore the physical properties of the neutron star crust.

I will present the physical and statistical properties of dust-obscured AGN as observed through multi-wavelength data. Specifically, my primary focus will be on infrared (IR)-bright dust-obscured galaxies (DOGs) with i - [22] > 7.0 in AB magnitude and a flux density at 22 um > 1.0 mJy. These IR-bright DOGs constitute a subset of optically-faint luminous IR galaxies, typically observed at high redshifts (z~1-3) such as ULIRGs and HyLIRGs. Hydrodynamic simulations suggest that black holes within IR-bright DOGs exhibit their most significant accretion rates during major merger events. This implies that these DOGs likely play a crucial role in understanding the co-evolution of galaxies and supermassive black holes. However, due to their spatial rarity, extensive wide-area surveys employing both optical and IR wavelengths are required for their detection. To date, we have systematically searched for obscured AGN (including DOGs) and examined their statistical and physical characteristics using multi-wavelength data, e.g., the SDSS, Subaru/HSC, WISE, AKARI, ALMA, NuSTAR, and eROSITA. In this talk, I will particularly focus on the following aspects: (i) luminosity function and luminosity density, (ii) clustering properties, (iii) ionized and molecular gas properties, and (iv) AGN and its host properties.

The formation of protostellar disks and the generation of outflows resutls from a complex interaction of magnetic fields, gravity, and angular momentum. The nonideal MHD effects are also crucial to the outcome. Numerical calculations of this phenomenon are challenged by the need to achieve very high resolution near the central protostar, which then imposes strong time step restrictions. I review some recent three-dimensional nonideal MHD simulations that either resolve the central protostar, or use a central sink cell to evolve well into the Class 0 protostellar phase. In the latter case, we find new insights into the driving of the low-velocity outflow that emerges from near the disk edge. The launch region is identified as primarily the interface between the inwardly advected magnetic field of the pseudodisk and the outwardly diffusing magnetic field of the disk. I present some details of the structure and dynamics of the outflow zone.

JWST's unmatched sensitivity across the full range of infrared wavelengths, with unprecedented spatial resolution, is revolutionizing every area of astronomy in its first year--as we expected. I will present a personally biased list of several JWST surprises in extragalactic astronomy that most of us did NOT predict. I'll start with unexpected results on galaxies JWST is finding at very high redshifts, including how and where they rapidly formed stars, metals and dust, and re-ionized the Universe. Then I'll discuss JWST observations of nearby active galactic nuclei. We may have missed a lot of them previously due to their amazingly heavy dust obscuration. Close-up views are suggesting that the high-speed gas outflows they launch may not always be simple two-sided jets. And some of our ideas about how their outflows might have shut down star formation--known as "AGN feedback"--may also need revision. In fact, we may have to re-think some of our ideas about what a 'galaxy' and an 'AGN' actually are. While trying to answer these questions, we should look at the incredible new data with open minds about what we thought we knew previously.

Ultra-High Energy Cosmic Rays (UHECRs) consist of protons and nuclei that possess energies exceeding about 10 exaelectronvolt (10^19 eV) and interact with Earth’s atmosphere. With the establishment of the Pierre Auger Observatory (covering about 3600 sq. km) in the Southern hemisphere and the Telescope Array Project (800 -> 3200 sq. km) in the North, the research community aimed to pioneer "charged-particle astronomy" to probe sources capable of accelerating particles to such extreme energies. However, prevailing evidence suggests a dominance of nuclei over protons at these energy levels, which implies greater deflections away from the source direction by galactic and extragalactic magnetic fields at a given energy. Subsequently, there has been remarkable advancement in modeling the transport of UHECR nuclei through the intergalactic medium and within potential sources like Gamma-Ray Bursts, AGN, or kpc-scale jets. This has led to sophisticated models linking source and propagation, affirming that populations of “similar” sources align with the observed, spatially averaged UHECR spectrum and mass composition. These models also bridge the gap to high-energy neutrino observations by IceCube, utilizing the advantages of multimessenger studies. The current challenge lies in pinpointing individual UHECR sources from the data accumulated over more than a decade. To achieve this, advanced models and inference techniques are required to disentangle the effects of UHECR propagation from present and future the spatial and spectral observations, utilizing all available modeling insights.

The chirp masses of the 90 blackhole binaries detected by LIGO are visibly bimodal which we demonstrate means that 80% of these events are highly magnified, with redshifts spanning z=1-4, whereas 20% are unlensed at low redshift z<0.3, with black hole masses of 8-12 M_sun, like stellar black hole remnants in our Galaxy. We have uncovered a similar surprising population of massive black hole progenitor stars at high redshift in deep Hubble & JWST imaging that lie on the Einstein rings of lensing clusters. The relative motions of the lens-source-observer frames allows the detection and recognition of luminous stars that transit a critical curve, so that individual lensed stars are visible at high redshift z=1-7, with high magnifications of typically 1000. Both of these massive star related populations seen by LIGO and JWST are surprisingly abundant, straining conventional lensing calculations and furthermore many of the lensed stars are found offset from the critical curves of standard smooth dark matter predictions. We argue that the highly corrugated pattern of lensing we predict for Wave Dark Matter is enhancing the lensing rate of stars and black holes and also accounts for the positional offsets at a level of ~20pc corresponding to coherent bosonic dark matter of mass 10^{-22}eV.

Supermassive black holes are an integral component of most simulations of galaxy formation. Well-established observed relations in the local universe between black holes and their host galaxies provide important constraints on the models. Even so, the physical connection between the two remains elusive. I will review observational results, using Hubble, and Subaru’s Hyper Suprime-Cam, which establish the evolution in these relations with cosmic time and present insights on the coupling between supermassive black holes and massive galaxies. Finally, new results from a JWST program will be presented which aims to extend these studies out to the first billion year of our Universe using NIRCam and NIRSpec.

Our new, rare JWST discoveries of the most distant lensed galaxies are all compact dwarfs, with spectroscopic redshifts of z=9-10.5, and magnifications of 10-20. Over an order of magnitude more dwarfs should have been found for standard CDM than for WaveDM or WarmDM, corresponding to m_AB~31, well beyond the reported deep field data of typically m~28 so that only high luminosity galaxies are detected by JWST where DM predictions hardly differ. This absence of low luminosity galaxies at z>9 favours a suppressed mass function characteristic of Wave or Warm DM. In contrast, we are uncovering a surprising abundance of individual lensed stars with JWST, within giant arcs, at cosmological distances (1 < z < 5) that are highly magnified (hundreds to thousands of times) on the Einstein rings of lensing clusters. In detail we notice many of these stars lie just off the Einstein ring indicative of local lensing perturbations that we show point to WaveDM perturbations that cause the Einstein Ring to become corrugated on the de Broglie scale (~10pc). Finally I will show direct evidence for WaveDM within a deep JWST image of a local dwarf galaxy serendipitously discovered with JWST, where the dense core is offset and asymmetric, confirming directly the essential soliton random walk prediction of Wave Dark Matter made by the leading experts here in Taiwan!

The mass of a star is its most important property because it determines its evolution and defines its temperature, internal structure, and size throughout its life. Robust mass measurements are, therefore, essential for our understanding of stellar evolution and are crucial to studies of disk and planet formation, stellar populations, and more. Measuring a star's temperature from optical observations is often the easiest way to determine its mass. However, this traditional approach ignores the strong magnetism of young stars, which produces dark and bright spots on their surfaces. Recently, infrared studies have revealed that starspots can significantly affect the surface temperature of stars, raising concerns about the reliability of previous mass measurements. In this talk, I present the results of an infrared spectroscopic survey focused on the impact of magnetism on T Tauri stars. Specifically, I will describe how magnetic-induced starspots produce a systematic change in the temperature measurement of low-mass young stars. Additionally, using observations from ALMA, I will discuss whether optical or infrared observations are more reliable when deriving stellar masses from stellar evolutionary models.

In space, charged particles follow magnetic field lines, which can become twisted and distorted due to the motion of the plasma. When the magnetic field lines become tightly twisted, they can break and rejoin in a different configuration. This process is called magnetic reconnection, and it can rapidly release a tremendous amount of energy. During such a "magnetic explosion”, the magnetic energy is converted into kinetic energy of the plasma particles, which are accelerated to high speeds, and thermal energy, which heats up the plasma. This process can occur in various astrophysical environments, leading to solar flares, coronal mass ejections, geomagnetic substorms in Earth's magnetosphere, and potentially the bright, short-duration radiations from magnetospheres of neutron stars.

Understanding the rate at which reconnection processes magnetic flux is critical to estimating the energy conversion rate in these natural phenomena. In this talk, I will discuss the milestones in modeling the reconnection rate, which has finally led us to a significant breakthrough with the help of first-principles computer simulations and in-situ spacecraft observations. I will explain the essence of the up-to-date theory, and show how we can extend it to relativistic reconnection in extremely magnetized astrophysical plasmas.

Core-collapse supernovae are the spectacular deaths of massive stars, critical in various branches of astronomy, from galaxy to planet formation. In the lead up to these cosmic explosions, massive stars generically experience mass loss. In the last few years, transient surveys such as ZTF and the high resolution ALMA have been able to probe mass loss in the final months - days before core-collapse. This corresponds to the violent, decisive oxygen shell burning phase, where either convection-generated internal waves or unstable explosive burning are predicted to eject mass at rates up to ~1 solar mass / year. However, current mass loss theory based on 1D simulations is not consistent with observations of these final months. In this talk I will present results from 3D hydrodynamics simulations of massive stars during oxygen shell burning (~10 minutes before core-collapse). I will focus specifically on lessons related to nuclear burning and internal gravity waves which these mass loss estimates are based on, and then discuss these differences in the context of recent observations.

In order to investigate the structure formation and evolution in the distant Universe, emission line galaxies (ELGs) are suitable targets for upcoming spectroscopic surveys (e.g., PFS, Euclid, DESI). Since massive OB-type stars source the strong emission line, ELGs generally are young star-forming galaxies. Thus, the clustering nature of ELGs is expected to be quite different from that of luminous red galaxies, which are widely studied in past spectroscopic observations. In order to address the clustering properties of ELGs, we utilise galaxy formation hydrodynamical simulations: IllustrisTNG. We have developed the method to simulate emission line intensity with stellar population synthesis code PEGASE-3. In simulations, we can directly investigate the relationship between the properties of ELGs and host halos and measure the cosmological statistics, e.g., projected correlation function. With these high-fidelity mock ELG catalogues, we measure the halo occupation distribution (HOD) and find the signature of infalling distinct halo contribution as suggested by semi-analytic simulations. Next, we measure the projected correlation function and infer HOD parameters with the correlation function. Then, we discuss whether the true HOD can be reproduced from the projected correlation function measurement. Finally, we present the ongoing analysis of the three-dimensional anisotropic power spectra of simulated ELGs. We infer cosmological parameters from the power spectra and directly compare them with the input values used in simulations. This ``cosmology challenge'' analysis examines which theoretical template can correctly reproduce the correct cosmological parameters.

Although dark matter (DM) is an essential component for describing the observed structure of the universe, its origin and nature remain unknown. Nevertheless, theoretical studies based on numerical simulations suggest that DM halos, self-gravitating bound objects composed of DM, exhibit several distinct features, which could offer clues to discriminate between different DM models. In this talk, focusing particularly on halos in cold and fuzzy DM models, I will discuss the (non-)universal features in the inner structure of halos and present two results: (i) a newly discovered universal feature in the radial phase-space structure of CDM halos and (ii) cosmological dependence of the core structure in fuzzy DM halos that leads to a non power-law behavior in the core-halo relations.

Feedback from supernovae (SNe) plays a fundamental role in galaxy formation. However, current cosmological simulations adopt empirical sub-grid prescriptions to model SN feedback due to limited resolutions, reducing their predictive power. Recently, galaxy-scale simulations have started to reach parsec-scale resolution to follow the small-scale physics in the interstellar medium, providing a promising way forward. In this talk, I will present a suite of resolved galaxy simulations using four different hydrodynamical codes, including Gizmo, Arepo, Gadget, and Ramses, as part of the SMAUG collaboration project. I will demonstrate the striking difference between Lagrangian and Eulerian codes in terms of the star formation bustiness, gas morphology, and galactic outflow rates in the simulations. This is caused by the behavior in the dense, collapsing gas clouds, which controls the clustering of star formation and the subsequent SN events, where highly clustered SNe have a more substantial dynamical impact on the interstellar medium. I will also discuss the key factors that control SN clustering, such as star formation efficiency and stellar lifetime.

Magnetic fields are ubiquitous in universe, space, and laboratory plasmas. Especially, self-generated magnetic fields are important to know the mind of nature. The formation of Weibel-mediated collisionless shock is studied as theory, simulation, and experiments with huge lasers. Following a series of computer simulations and experimental studies of the physics, a simple model equation is found to describe the time evolution of magnetic turbulence.

The magnetic instability is saturated by magnetic pressure, and thicker filaments continue to be generated by current coalescence (magnetic reconnection) mechanism. The model equation concludes the fact that the filament spacing increases linearly in time, and the magnetic energy power spectrum is given as |B_k|^2 \propto k^{-2}. The time evolution of the turbulence is characterized with the cascade toward smaller k.

With use of Alfvén current limit condition, the criteria of collisionless shock formation are evaluated. The present theory is compared to corresponding experiments done with NIF laser (https://lasers.llnl.gov/ ) and a variety of PIC simulations.

The theory is also applied to evaluate the strength of magnetic field near the shock front of the supernova remnant SN1006. The enhancement of magnetic field of about 25 μG is concluded in the present theory.

I will talk about laboratory astrophysicsactivities in the world [1] and talk about the titled topics along with the tutorial paper [2].

References: [1] H. Takabe and Y. Kuramitsu, “Recent progress of laboratory astrophysics with intense lasers,” High Power Laser Sci. Eng. 9, E49 (2021) [2] Hideaki Takabe. "Theory of magnetic turbulence and shock formation induced by a collisionless plasma instability." Physics of Plasmas 30.3 (2023): 030901.

The circumgalactic medium (CGM) contains the fuel for future star formation and the record of past feedback, making it uniquely sensitive to the physics of baryonic flows. Characterizing the diffuse multiphase CGM across cosmic time holds a key to unveiling the drivers of galaxy growth, the priority area of the Cosmic Ecosystems theme highlighted by the 2020 Decadal Survey. The Cosmic Ultraviolet Baryon Survey (CUBS) is designed to map intergalactic and circumgalactic gas at intermediate redshifts, bridging the gap between previous efforts at z < 0.4 and at z ~ 2. The program utilizes high-quality quasar absorption spectra and matching deep galaxy survey data. It exploits the synergy between space-based UV spectroscopy and ground-based wide-field surveys to advance our understanding of the cosmic evolution of baryonic structures. In this talk, I will highlight a few examples that illustrate how combined space-based UV and ground-based optical echelle absorption spectroscopy of distant QSOs provides a powerful tool for resolving distinct ionization and thermodynamic states, as well as chemical enrichment histories, within the blended multiphase medium over a broad range of gas densities. The accompanying deep and wide galaxy survey data further provide a sensitive record of the environment on both large and small scales, revealing a diverse range of galaxy properties. I will present empirical evidence showing that diffuse CGM is turbulent. For the first time, a clear distinction is found in the significance of turbulent energy between passive and star-forming haloes. I will also review other key findings from the CUBS program and briefly discuss the future outlook for CGM studies.

Supermassive black holes have been discovered dynamically at the centers of more than 100 local galaxies, but the local census is highly incomplete, particularly in the high mass regime. A robust determination of a black hole’s mass requires both superb datasets and extensive theoretical modeling. I will describe recent progress in studying black holes in M87 and other massive galaxies enabled by integral-field spectroscopy on 10-meter-class telescopes and by triaxial stellar dynamical modeling. I will also discuss the implications of these results for gravitational wave signals from merging black hole binaries targeted by ongoing pulsar timing array experiments.

The mechanism by which stars explode as supernovae is still a subject of great interest because there are still many unknowns. Detailed observations will be made if a supernova occurs in the Milky Way in the near future, and our understanding of the explosion mechanism of supernovae will be significantly improved. However, the event rate of supernovae is low. The youngest Type Ia supernova remnant found in the Milky Way is about 100 years old, and the youngest core-collapse supernova remnant in the Milky Way is about 350 years old. Under these conditions, we are taking a unique approach to understanding the explosion mechanism of supernovae. We run 3D numerical simulations of the process from supernovae to supernova remnants and compare them with young supernova remnants to find hints of the explosion mechanism of supernovae in young supernova remnants. To our knowledge, we did the first 3D numerical simulations from a supernova to a supernova remnant in the world. In this seminar, we will present some exciting comparisons between our numerical simulations and some young supernova remnants.

IXPE is a joint NASA and Italian scientific mission launched into low-earth equatorial orbit on December 9, 2021. IXPE uses new technology---developed in Italy---for measuring the degree of polarization and the position angle--- and advances of X-ray optics technology---developed in the United States at the Marshall Space Flight Center---to provide 1-arc minute scale imaging polarimetry in the energy range 2-8 keV. I will present some of the often surprising and unexpected results from the first year of the mission on accreting supermassive and stellar mass black holes, neutron stars, magnetars, and supernova remnants.

Rapidly growing black holes (BHs) are surrounded by accretion discs that make quasars the brightest objects in the Universe. Their brightness is known to be variable, but the causes of this are not implied by simple disc models and still debated. Due to the small size of accretion discs and their great distance, there are no resolved images addressing the puzzle. In this work, we study the dependence of their variability on luminosity, wavelength and orbital/thermal timescale (torb, or tth). We use over 5,000 of the most luminous quasars with light curves (LCs) of almost nightly cadence from > 5 years of observations by the NASA/ATLAS project, which provides ∼2 billion magnitude pairs for a structure function (SF) analysis. When time is expressed in units of orbital or thermal timescale in thin-disc models in the random walk (RW) regime, we find a universal structure function, independent of luminosity and wavelength, supporting the model of magneto-rotational instabilities as a main cause. In other words, we find evidence showing the variability is caused by the turbulence in the disc. Over a > 1 dex range in time, the fractional variability amplitude follows log(A/A0) ≃ 1/2 × log(∆t/tth). Any offset from the universal relation can be caused by incorrect orbital timescales and thus incorrect luminosities. Quasar luminosities are affected by the viewing angle of the disc, appearing overluminous when viewed pole-on and underluminous when viewed at high inclination. The angle is essential in BH mass estimation but usually unknown for radio-quiet quasars. We correlate these offsets with suggested inclination spectroscopic indicators, using a subsample of 753 luminous quasars with C IV and Mg II lines. We expect quasars with more blueshifted C IV lines to be viewed more pole-on and thus appear overluminous. In contrast, our SF analysis finds that presumed pole-on discs appear underluminous. We discuss possible explanations but reach no satisfying conclusion.

Magnetic reconnection is a fundamental process of converting magnetic energy into plasma energy. We will review the experimental results of plasma merging and magnetic reconnection and explain the basic concept of magnetic reconnection from the early MHD models, to particle-in-cell simulation results, and to the analytic kinetic theory [1-8]. In particular, the recent experimental results show that the magnetic energy is converted mostly to ions with ion energy gain proportional to(Brec^2 /n_in), where n_in is the plasma density and Brec is the reconnecting magnetic field component in the upstream. To understand the key magnetic reconnection results, we will show the particle-in-cell (PIC) simulation results and an analytic theory to explain the mechanisms of ion and electron heating/acceleration by understanding the reconnection layer structure of electrostatic potential, magnetic field, current, and electron and ion densities and flow velocities. In particular, the electrostatic potential is produced due to charge separation resulting from different electron and ion meandering orbit widths in magnetic field reversed geometry, and ions gain energy mainly from the electrostatic potential drop in the current sheet and downstream region. Electrons gain energy mainly due to acceleration by the inductive reconnection electric field in the current sheet. The ion energy gain scales with (Brec^2/n_in) and the electron energy gain is proportional to(Brec^2/n_in)Se where Se (> 1) depends on how long electrons are accelerated by the reconnection electric field in the current sheet. [1] C. Z. Cheng et al., Phys. Plasmas 28, 072101 (2021) [2] C. Z. Cheng et al., Phys. Plasmas 22, 101205 (2015) [3] C. Z. Cheng et al., Plasma Fusion Res. 11, 1401081 (2016) [4] S. Inoue et al., Nuclear Fusion 55, 083014 (2015) [5] Y. Ono et al., Phys. Rev. Lett. 107, 185001 (2011). [6] Y. Ono et al., Nuclear Fusion 59, 076025 (2019). [7] H. Tanabe et al., Phys. Rev. Lett. 115, 215004 (2015). [8] H. Tanabe et al., Nuclear Fusion 61, 106027 (2021).

Our Solar System has kept a record of the earliest phases of its evolution, at the time when all current ingredients were dispersed in a dense molecular cloud, the pre-stellar cloud core. This is testified by the similarities between the chemical composition of primitive material, such as comets and carbonaceous chondrites, and that of young protostars, where the pre-stellar ices have just evaporated. Of particular interest are the D and 15N fractionation processes in H- and N-bearing molecules present at the various phases of star- and planet-formation, as they provide information on the chemical journey from clouds to planets, thus our astrochemical origins. Here, I will summarize our current understanding of D- and 15N-fractionation in molecular material from clouds to protoplanetary disks and highlight puzzles.

Making use of exponential increases in computing power and memory per dollar, radio astronomers have been able to search larger areas of sky with ever higher bandwidth at high time and frequency resolution. In 2007, a mysterious millisecond-duration burst was found around the cellphone band. This kind of signal is now known as fast radio burst (FRB), energetic bursts visible at a cosmological distance. Hundreds of more FRBs have been detected in the past 5 years with dedicated radio surveys. FRBs are a new probe of cosmological matter, since each burst carries information on the number of electrons it encounters before reaching the earth. In this talk, I will review the current understanding of the origin of FRBs, as well as the many remaining mysteries, including the location of the FRBs, the magneto-environment and the long-term periodicity I found with one source. I will also introduce current and upcoming instruments which will detect more FRBs with orders of magnitude better spatial resolution. The result will be an explosion of opportunity for understanding burst origin and probing cosmic matter distribution at various spatial scales.

Over 200 quasars have now been discovered at z > 6, with nine at z > 7, just 690 Myr after the Big Bang. The leading contenders for the seeds of these supermassive black holes are direct-collapse black holes (DCBHs) due to the collapse of 10^4 - 10^5 solar-mass primordial stars at z ~ 20. It has long been thought that these supermassive stars required unusual, exotic environments to form that were difficult to pair up with the rare, massive halos required to ensure the growth of these seeds to 10^9 solar masses by z ~ 7. However, we have performed new, state of the art numerical simulations that the rare halos capable of hosting SMBHs by this redshift formed their own seeds without any need for unusually strong Lyman-Werner UV backgrounds, supersonic baryon streaming motions, or even atomic cooling. Besides overturning nearly 20 years of thought on the origin of the first quasars, our simulations show that z > 6 SMBHs were a natural consequence of structure formation in cold dark matter cosmologies. They also account for the demographics of these objects, about 1 Gpc^-3 at z ~ 6.

The formation of stars remains a fundamental question in astrophysics. In this talk, I will be discussing our ongoing research into the physical and chemical conditions that govern the early stages of star formation. Specifically, I will cover four projects: 1. Estimating the age of prestellar cores (Lin et al. 2020). 2. Investigating mass accretion towards protostellar disks (Thieme et al. 2022, Hsieh et al. 2020). 3. Analyzing magnetic fields in star-forming regions (Ko et al. 2020, Wang et al. 2020, and various BISTRO papers). 4. Applying machine learning techniques to identify young stellar objects (Chiu et al. 2021). While our understanding of star formation is far from complete, these projects have allowed us to make some progress in unraveling the complexities of this intriguing process.

The Extragalactic Database for Galaxy Evolution (EDGE) is an ongoing effort to join resolved CO imaging with optical IFU spectroscopy to advance our understanding of star formation in galaxies. In this talk I will review some scientific highlights of the project, primarily based on CO observations with CARMA & APEX and IFU observations from CALIFA. I will also discuss the design of the database and how interested researchers can access it. Future extensions of EDGE will enable us to more sensitively probe the depletion of gas reservoirs and the limits of star formation regulation, which remain key unsolved problems in the study of galaxy evolution.

Astronomy's current model of galaxy evolution is built on a foundation of hierarchical growth, in which small galaxies merge together to form larger ones. In addition to the simple accrual of mass, this merging process is predicted to fundamentally change the galaxies' properties, such as dramatic morphological transformations, the triggering of bursts of star formation and high rates of accretion onto the central supermassive black hole. In this talk I will explain the physical processes behind these predictions, and present the observations that we are performing in order to test the theory. Although many of the predictions are indeed borne out by experiment, there have been some surprising conflicts as well, that demand revisions to our models of how mergers shape galaxy evolution.

I describe new tools and techniques I've built to solve different problems in gravitational dynamics. First, I describe our popular Rebound code, MERCURIUS, designed to solve for the evolution, including formation and long-term dynamics, of planetary systems. Unlike its predecessor, MERCURY, it is numerically symplectic and time-reversible. I also describe current work on a code, TRACE, which significantly improves on the accuracy and speed of MERCURIUS.

I then tackle the problem of the stability of the Solar System. Although great progress has been made in the last decades towards an understanding of chaos and stability of the Solar System due to the development of modern computers, I show that all studies I found are affected by numerical chaos, which causes artificial Solar System chaos and instability. The physical mechanism behind Mercury's orbital instability has been traditionally described by a diffusive process in a secular frequency, but our current work shows a subdiffusive process fits simulated data far better.

I describe new tools for the potential discovery of interstellar objects (IOs). The tools solve the linking problem, in which independent observations are linked together as a potential object of interest, using crude approximations. These objects are then validated using state of the art orbit fitters. I describe the validation tests I've done with this pipeline, which promises to be able to exploit the vast Solar System data expected from Rubin/LSST.

I next describe a suite of tools, including powerful new Kepler solvers and new symplectic integrators and their tangent equations, called NBODYGRADIENT. Unlike other popular methods, we can solve planetary systems with arbitrary geometries and orbits including moons. We have implemented these tools to solve the transit timing variation problem, and derive the properties and possible compositions of TRAPPIST-1 planets.

The outflow launched by the accretion disk formed after a neutron star merger is an important contributor to the total ejecta from the merger, and hence to the kilonova emission and heavy element yield. The amount of mass ejected and the kinematic, thermodynamic, and compositional properties of the ejecta have many dependencies, making up for a rich landscape of possibilities. I will provide an overview of the problem, and discuss progress in our understanding of this landscape on 3 of its dependencies: the gravitational compactness of the disk, the post-merger magnetic field configuration, and the extent of neutrino flavor transformation by the fast flavor instability.

Radio emission from supernovae (SNe) is believed to attribute to synchrotron emission from electrons accelerated by an SN shock propagating circumstellar medium (CSM). Since the lengthscale and density of CSM reflect the lookback timescale and the magnitude of mass-loss activities of SN progenitors, respectively, radio emission can be used as an indicator of the stellar evolution of massive stars in the viewpoint of mass-loss activities. Recent transient survey facilities and rapid optical follow-up observations have indicated that at least a fraction of SN progenitors experiences enhanced mass-loss activities just prior to the explosion. Here we suggest millimeter emission (~100GHz) from SNe immediately after the shock breakout as an independent tracer of the nature of the circumstellar environment in the vicinity of SN progenitors. This enables us to examine the final moment of massive stars prior to the core collapse, highlighting the importance of target of opportunity observations by Atacama Large Millimeter/submillimeter Array. In this talk we introduce our recent works related to the modeling of radio emission from infant SNe, including future prospects and application of our method to the examination of properties of supernova remnants.

The sudy of proto-planetary disks has so far focussed on the largest, brightest objects that extends over 100s of au. However, like planetary systems, protoplanetary disks exhibit a large diversity in size, and many protoplanetary disks are much smaller than the one studied so far. Previous studies in continuum revealed very compact dusty disks, with radii of only 10 to 20 au. Taking advantage of the new capabilities of NOEMA, the NOrthern Extended Millimeter Array, we have started to explore such disks, in particular their molecular content to characterize the gaseous counterpart. After presenting the capabilities of the recently completed NOEMA, I will discuss some preliminary results of these studies that reveals a striking diversity.

Source count --- the number density of sources as a function of flux density --- is one of the most fundamental statistics of imaging observations. One of the advantages is its simplicity, i.e., compared with more complicated and advanced analyses such as luminosity/mass functions, there is little room for analysis errors to distort results, yet the source counts still carry important information on galaxy evolution. We present these fundamental statistics for the newly advent James Webb Space Telescope (JWST) MIRI instrument in the six mid-infrared bands, i.e., 7.7, 10, 12.8, 15, 18 and 21 ~m. The resulting IR populations of galaxy source counts are up to ~100 times deeper than previous works, reflecting the superb sensitivity of the JWST.

Furthermore, we physically interpret these JWST number counts to constrain cosmic star-formation history (CSFH), and black hole accretion history (BHAH). Following Gruppioni et al. (2011), we parameterize IR luminosity functions (LFs) and their evolutions for five different populations of galaxies (star-forming galaxies, starbursts, composite, Seyfert 1 and 2). By simultaneously fitting the model to the six mid-infrared number counts, together with the previous results, we determine the best-fit evolutions of MIR LFs for each of the five types of galaxies, and thereby, CSFH and BHAH. The obtained CSFH and BHAH are consistent with the previous estimates, but thanks to JWST, our estimates are based on tens to hundreds of times fainter MIR sources, whose existence was merely an extrapolation in previous studies.

Bio: Daniel Jaffe is Vice President for Research and Professor of Astronomy at the University of Texas at Austin. As Vice President for Research, Jaffe oversees sponsored projects, major research cores, and research compliance. He oversees several major interdisciplinary research institutes, including the Texas Advanced Computing Center, and the University’s Bridging Barriers grand challenge research initiative. His unit plays a major role in developing large center grant proposals. Jaffe leads a research group in astronomical spectroscopy, astronomical instrumentation, and development of dispersive optics using precision nanolithography. His team studies the formation of stars and planetary systems and the effects of stellar radiation on the dense interstellar medium using infrared spectroscopy. They also study the physics of protoplanetary disks and use radial velocity techniques to search for planets around very young stars. He is PI for a Korea-Texas collaboration to build high-resolution near-IR spectrometers including IGRINS, which has been a productive instrument on the McDonald Observatory 2.7m, the 4.2m Lowell Discovery and the 8m Gemini South telescopes. The team is constructing a revolutionary 1-5 micron high-resolution spectrometer for the Giant Magellan Telescope. Jaffe's group develops novel diffractive devices for infrared spectroscopy using Si nanolithography. They have built the mid-IR grisms for the NIRCam instrument on the James Webb Space telescope and have fabricated near-IR immersion gratings for IGRINS and for the ISHELL spectrograph on the NASA IRTF while developing new production techniques for space astronomy and earth science applications.

Jets and outflows are integral parts of the physical processes that form the protostellar systems. We review the characteristics of these enigmatic powerful phenomena that constitute telltale signs of the underlying fundamental physics revealed by generations of radio and optical telescopes. We highlight the breakthrough advances in theoretical understanding of the formation, thanks to the unprecedented revelation of the fine delicate structures. Kinematic and morphological theoretically predicted features of jets, winds, and outflows are extracted and favorably compatible with observational data down to sub-arcsec resolutions. The systematics of coupled nested velocity and emission components spans from Class 0 to II jet–outflow systems in molecular and atomic lines, whose ubiquitousness is naturally explained.

Several ongoing surveys, notably by TESS and Gaia missions, are likely to discover star-black hole binaries in our Galaxy in the near future. A fraction of them may be triple systems comprising an inner binary, instead of a single black hole. They may be progenitors of the BBHs discovered from the gravitational wave. If such a star-binary black-hole system exists in our Galaxy, its outer tertiary star should exhibit a radial velocity modulation reflecting the nature of the inner binary. Combining an analytic approximation based the quadruple perturbation theory and N-body simulations of such triples, we examined the detectability of wide-separation inner BBHs in the Galaxy from the characteristic signals of the radial velocity of the tertiary star. The resulting radial velocities consist of two different types of modulations, short-term radial-velocity variations of roughly twice the orbital frequency of the inner BBH, and long-term modulations in significantly inclined triples. The latter is due to the precession of the inner and outer orbits over roughly the von Zeipel-Kozai-Lidov oscillation timescale. We conclude that it is quite feasible to detect such radial velocity modulations if those triples exist in our Galaxy.

A significant fraction of exoplanetary systems is known to exhibit spin-orbit misalignments. This surprising fact has been mainly revealed by a spectroscopic method, known as the Rossiter-McLaughlin effect for transiting planetary systems. This method measures the projected angle between the stellar spin and the planetary orbital axes, but is insensitive to the obliquity of the stellar spin with respect to the observer. Asteroseismology offers a unique method to infer the stellar obliquity in a complementary fashion. In this talk, I will first review the current statistics of the observed spin-orbit angles and proposed models for the origin of the misalignment. Then I will show our recent work on the spin-orbit architecture of transiting planetary systems using asteroseismology, and discuss its implications.

I will present our our new state-of-the-art Messenger Monte Carlo MAPPINGS V code (M³). The turbulent ISM causes inhomogeneity of electron temperature and density within the nebula, which is most effectively modeled through Monte Carlo ray tracing methods. We analyze the dependence of different optical emission lines on the complexity of nebular geometry, finding that the emission lines residing on the nebular boundary are highly sensitive to the complexity of nebular geometry, while the emission lines produced throughout the nebula are sensitive to the density distribution of the ISM within the nebula. Our fractal photoionizationmodel demonstrates that a complex nebular geometry is required for the accurate modeling of H II regions and emission-line galaxies. Finally, I will discuss the opportunities for these types of models for understanding galaxy formation and evolution with the current and next generation telescopes including JWST and the GMT.

Pulsars and Fast Radio Bursts (FRB) are some of the most energetic and "fast" astronomical objects. They are both possibly from "neutron stars". In this talk, I will introduce some of my group and collaborators' pulsars and FRB research using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). I will talk about the discovery and timing of new pulsars, testing theories of gravitation using pulsar timing, and measuring pulsar emission and geometry. I will also talk about some of the FAST FRB key science project results, including the large sample repeating FRB studies and the radio follow-up of the Galactic FRB source -- SGR J1935+2154.

AGN feedback plays an important role in regulating star formation activity and nearby interstellar medium (ISM) through outflowing winds and ionizing radiation. However, in the past, the lack of high spatial resolution in the infrared has limited our ability to closely examine the star-forming ISM in the vicinity of an AGN. The advent of integral-field observations through the James Webb Space Telescope (JWST) has opened up a tremendous opportunity to study the starburst-AGN connection in the sub-kpc scale. In this presentation, I will present the MIRI IFU observation of a type 1 Seyfert galaxy NGC7469, which hosts both a rapidly accreting black hole and a circumnuclear starburst ring with a radius of 500 pc. The high spatial and spectral resolution of MIRI has enabled us to isolate the starbursting event surrounding the AGN and study the dust and warm molecular gas on a ~100 pc scale. Our findings show that the starburst ring exhibits prominent Polycyclic Aromatic Hydrocarbon (PAH) emission, with grain sizes and ionization states varying by only ∼30%. A suite of H2 pure rotational lines is also detected throughout the ring, enabling us to estimate the warm molecular gas mass and temperature. Our study demonstrates that with JWST, we can finally study the resolved properties of the near nuclear ISM in great detail, even in the dustiest galaxies, on the scales of individual star-forming regions.

Dwarf galaxies are little fuzzy galaxies that contain much fewer stars than Milky Way-mass galaxies. The observation of these little galaxies can provide constraints on the physical properties of dark matter, and enhance our understanding of the galaxy formation and quenching mechanism. Finding these dwarf galaxies is, however, not an easy task as they are faint and dim from our perspective. I will describe our recent efforts on the search for nearby dwarf galaxies. I will start with the Satellites Around Galactic Analogs (SAGA) Survey, a spectroscopic survey that identifies satellite galaxies around more than 100 Milky Way-like analogs at 25-40 Mpc, putting our Milky Way in a cosmological context. I will highlight some new SAGA results and then discuss how SAGA data can be applied to other dwarf galaxy searches, which include an ongoing secondary target program with the Dark Energy Spectroscopic Instrument (DESI) and a plan for the Rubin Observatory Legacy Survey of Space and Time (LSST). Both programs will make a much larger population of dwarf galaxies available for the study of dark matter in coming years. Finally, I will turn to our searches for much closer and much fainter dwarf galaxies with resolved stars in the Milky Way’s backyard (within 1 Mpc), and discuss how these ultra-faint dwarf galaxies push our understanding of the galaxy-halo connection to a much lower mass regime.

Decades ago, astronomers viewed the warm ionized interstellar medium (WIM) as a turbulent, space-filling plasma with a mean density of about 0.03 electrons/cm^3 in the Galactic plane. How accurate is this picture? In particular, is there evidence for a more bubble-like (porous) distribution of the WIM? Techniques developed over the last twenty years, broadly referred to as scintillometry, allow us to make new progress on this question. By giving us the ability to locate scattering centers along the line of sight to pulsars, evidence is emerging that a bubble-like topology is appropriate for the WIM. I will present results of a survey of 22 relatively nearby pulsars, observed with the Green Bank Telescope and the Arecibo Telescope. Most show one dominant scattering screen along the line of sight, but higher sensitivity observations reveal larger numbers of scattering screens. What view of WIM topology is implied by these observations?

The Universe evolves as it expands. It was once generally smooth and filled with neutral gas, as revealed by the cosmic microwave background observations. Today’s Universe is predominantly filled with ionised plasmas threaded by magnetic fields. How did the transition happen? How do we probe the cosmic evolutionary history from the Earth? In this colloquium, I will discuss how astrophysicists explore the evolving Universe, with foci on two research frontiers: large-scale cosmic magnetic fields and gas reionisation. These two science themes have formed several key science projects for the forthcoming unprecedentedly powerful radio telescopes, the Square Kilometre Array (SKA), its precursors (e.g. ASKAP, MeerKAT, MWA) and pathfinders (e.g. LOFAR), among many other experiments. I will highlight, with demonstrations, the essential ingredients to optimise the scientific gains from these observational experiments by studying how information is encoded into the radiation we receive (i.e., cosmological radiative transfer). Finally, I will conclude this talk with a summary of the key findings from my theoretical calculations and an outlook on the exciting developments in our understanding of the ever-changing cosmos.

Cosmological large-scale structures are shaped by nonlinear processes mainly driven by gravity. Previous methods of analyzing this rely on theoretical templates that are based on perturbative expansion about the linear solution, restricting the extraction of information to large, mildly nonlinear, scales. On the other hand, N-body simulations can uncover structures on smaller scales, until non-gravitational effects such as gas cooling and feedback eventually become a factor. However, their high computational cost hinders their direct use in statistical inference. In this talk, I will discuss the emulator approach as a potential solution. In particular, I will present our Dark Quest simulation project and its applications to the SDSS and HSC datasets. I will briefly touch on the future direction of the whole analysis framework, which involves coupling simulators and observations for automated knowledge acquisition.

Neutrinos are massless in the standard model, but neutrino oscillation experiments have confirmed that at least two out of the three active neutrino species have mass. Cosmological data can be an important probe for neutrino properties, like mass, energy density, and non-standard interactions. In this talk, I shall first discuss the bounds on the neutrino mass sum and the mass hierarchy from cosmological data, and how cosmological data cannot differentiate between the normal and inverted hierarchy well. Next, using Bayesian evidence and KL Divergence calculations, we shall see that there is no conclusive evidence for normal neutrino mass hierarchy from the combined power of the latest neutrino oscillations, neutrinoless double beta decay, and cosmological data, when we consider mass hierarchy agnostic priors. Finally, we shall look at constraints from cosmological data, on the possible neutrino non-standard self-interactions mediated by a heavy scalar, its role as a potential solution to the Hubble tension, and how this self-interaction model can help reconcile two inflationary models: Natural Inflation and Coleman-Weinberg Inflation, with cosmological data, even though these inflationary models are ruled out at more than 2-sigma in the Lambda-CDM model.

Ice plays a critical role in chemical evolution during star formation. Complex organic molecules, which have become frequently detected in Class 0/I protostars, form on ice mantles and desorb into gas-phase when the temperature increases. However, the formation pathways of COMs and whether most protostars undergo similar chemical evolution remain open questions with little observational constraints. Most COMs form in the ice mantles covering dust grains. While ALMA provides sub-100 au resolution for studying gaseous COMs in nearby embedded protostars, measurements of the chemical composition in ices had been limited by low-resolution and limited sensitivity until JWST, which can probe ices at a spatial scale comparable to that by ALMA with unprecedented sensitivity. In this talk, I will overview the role of ice in the chemical evolution of star formation as well as the formation pathways of COMs. I will discuss the recent JWST results on ice in protostellar environments, especially focusing on the latest results of the CORINOS and IceAge program. I will also discuss the prospects of ice chemistry in the era of JWST.

The astronomers started to explore the universe with the multi-messenger since the 21st century. Studies of the gravitational wave (GW) play an important role and became popular in multi-messenger astronomy. In this talk, I will simply introduce the role of GW in multi-messenger astronomy and then introduce the basic contents of GW including the design to detect it, the projects of the ground-based observatories, the Taiwanese team involved in these projects and my cooperative studies related to these projects. The novel timing algorithm is the key to resolve the GW signal from the noisy data so I will also introduce these timing methods. In addition, searches of GW do not only depend on a good timing algorithm but also on an efficient pipeline, which is based on the artificial intelligence/deep learning. I will also demonstrate some preliminary results obtained from my cooperative studies. Now the open science center also provides lots of archival data obtained from LIGO-Virgo and as well as the KAGRA, and more manpower and computing resources are required to update our understanding of the universe to the next stage. Please join us!

In this talk I will describe recent results on modeling plasmas accreting onto supermassive black holes SgrA* and M87*, the prime targets of the Event Horizon Telescope. Specifically, I will present recent results from largest-to-date 3D GRMHD simulation and 2D kinetic simulations of pair production discharges, magnetic reconnection and global accretion flows. I will argue that flares from SMBHs are powered by relativistic magnetic reconnection during flux eruption events in magnetically arrested disks. Additionally, I will show that collisionless physics of accreting plasmas can produce significant changes in the large-scale flow dynamics, via the enhanced rate of magnetic reconnection and dynamically important heat flux, compared to commonly employed GRMHD models.

Over the past two decades, the realm of dusty, star-forming galaxies (DSFGs) has changed our understanding of the cosmic star formation embedded in the dust, thanks to the combination of space and ground-based IR and millimetre telescopes. Meanwhile, with the new advance of JWST, we have come to another new era to study statistical properties and internal structures of DSFGs. During my talk, I will go through the observations of different scales of DSFGs and discuss the new opportunities to explore the early Universe with DSFGs. I will start with the large sky surveys for DSFGs, particularly focused on the ALMACAL sky survey, which has turned ALMA into a survey machine by utilising all the calibration observations. I will present our recent efforts on the multi-band survey for DSFGs and ongoing projects. After that, I will introduce several new opportunities to understand the interstellar medium of the DSFGs, especially on the initial mass function and the magnetic fields. In the last part, I will discuss the clustering properties of DSFGs and their connections to the cosmic web and present-day galaxy clusters. I will also discuss possible collaborations with local experts from ASIAA.

I will give a summary of my recent works on the dynamics of well-coupled dust grains in protoplanetary disks under radiation pressure and planet-disk interactions. In the pre-planet-formation study, I will show that the stellar radiation on the dust grains could trigger an instability, leading to the formation of dust clumps at the inner disk edge that breaks the commonly assumed axisymmetry. The clumps effectively reduce the extinction level in the disk, sustaining the disk edge recession due to radiation pressure, and shedding light on the formation of large dust cavities in the observed transitional disks. Moreover, the dust clumps may be the seed of planetesimal formation. In the post-planet-formation study, I will show that the planet-disk interactions will produce morphological features on the dust ring trapped at the pressure maximum outside the planet-opened gap. Vertically, the dust on the gap edges will be carried to high disk elevations by the planet-induced meridional gas flows. And radially, the dust trapped at the planet-induced pressure bump will be additionally perturbed by the planetary wakes in the gas, resulting in a widened dust ring. These findings may help to explain the radially extended dust rings in the planet-hosting disk PDS 70 and AB Aur, and the nontrivial pattern of the deprojected dust ring in the GM Aur disk.

Time-resolved infrared spectroscopy, offering both temporal and spectral resolution in the experimental measurements, plays an important role in atmospheric, biological, and chemical physics studies. Dual-comb spectroscopy, a multi-heterodyne Fourier transform spectroscopy based on two frequency combs at slightly different repetition frequencies, enables broadband molecular fingerprinting with high-resolution and fast spectral acquisition. Here, a new approach for high-resolution time-resolved spectroscopy using mid-infrared dual-comb spectrometers will be reported. The time-resolved dual-comb spectra under different experimental conditions can be measured with Doppler-limited resolution at microsecond time resolution. Moreover, employing the dual-comb spectrometers coupled with a flash photolysis cell, multiple species, including the free radicals and reaction intermediates can be simultaneously and quantitatively detected, thus enabling to explore complex reaction processes and mechanisms. Our recent works on the study of the yields and formation mechanisms of OH and HO2 radicals in the reactions involving the Criegee intermediates, short-lived species involved in many key atmospheric reactions, will be presented in this talk. The approach with time-resolved dual-comb spectroscopy holds promise not only in exploring the issues of chemical physics but also in discovering transient processes of light-matter interactions in different fields.