ABSTRACT. Thirty Meter Telescope (TMT) is a next-generation extremely large telescope with aperture size of 30m under construction by international collaboration involving Japan, U.S., Canada, and India. TMT with Adaptive Optics (AO) will achieve an angular resolution of 0.01 arcseconds and a sensitivity capable of detecting point sources as faint as 30th magnitude. Key sciences of this telescope include exploring the nature of extrasolar planets by direct imaging of Earth-like planets in habitable zones of nearby faint stars, detection of the emission originated from the first massive stars in the universe, and spectroscopic follow-up in multi-messenger astronomy to reveal origins of matter. TMT is a unique extremely large telescope to be constructed in the northern hemisphere, necessary for covering targets in the whole sky with ESO Extremely Large Telescope (E-ELT) and Giant Magellan Telescope (GMT). The optical system of TMT will realize a clean point spread function (PSF), which will be a great advantage over E-ELT and GMT in high-contrast observations for extrasolar planets. High-resolution spectroscopy with high sensitivity is another great advantage of TMT in studying atmospheres of extrasolar planets, precise measurements of radial velocity and redshift variations, and elemental abundances of stars. Toward the completion in the 2030s, Japan is responsible for constructing the telescope structure and the primary mirror segments, as well as developing science instruments. The status of the project will be reported.

ABSTRACT. The Large High Altitude Air Shower Observatory (LHAASO) has delivered transformative results in 2025–2026 that redefine our understanding of cosmic-ray origins. In November 2025, two landmark studies were published. The first provided the first observational evidence that microquasars—black hole binary systems—can accelerate protons to PeV energies. Among five such systems identified, SS-433 was confirmed as a Galactic “PeVatron,” emitting protons beyond 1 PeV. The second result achieved the first precise measurement of the cosmic-ray proton spectrum in the knee region (0.1–10 PeV). Rather than a simple break, the spectrum reveals an unexpected new component, indicating that multiple types of sources contribute to cosmic rays. These findings collectively resolve a seven-decade mystery regarding the origin of the knee and establish black hole systems as major contributors to Galactic cosmic rays.

ABSTRACT. The Trans-Pacific Observatory (TPO) is an international project to design, install, and operate a 2-meter class optical telescope (TP2m) at the Sierra de San Pedro Mártir Observatory (SPM-OAN) in Baja California, México. This initiative brings together the Graduate Institute of Astronomy at National Central University (Taiwan), Universidad Nacional Autónoma de México (UNAM), Aix-Marseille Université (France), and the Shanghai Astronomical Observatory in partnership with the Henan Academy of Science (China). Its primary goal is to strengthen scientific and technological cooperation through shared long-term observing programs and to promote the mobility and training of students and researchers across the Pacific.

TP2m is conceived as a versatile, multi-purpose facility operating in the optical and infrared, capable of conducting both photometric and spectroscopic observations. A central scientific focus is time-domain astronomy, particularly the rapid detection and characterization of transient and variable phenomena such as gamma-ray bursts, supernovae, and eruptive events in stellar and active galactic systems. The facility will also be able to carry out time-critical observations of unpredictable or newly identified targets, including recently discovered near-Earth objects that fall outside standard time-allocation mechanisms. In addition, synergy with the COLIBRI high-cadence transient experiment, also hosted at SPM-OAN, will enhance the scientific output of time-domain studies.

By establishing a modern, flexible ground-based observing platform, TPO significantly expands international capacity in multi-purpose and time-domain astrophysics. It provides a framework for sustained collaborative research across the Pacific, while cultivating the next generation of astronomers and strengthening global partnerships in observational astronomy.

ABSTRACT. The Canada-France-Hawaii Telescope (CFHT) has remained a cornerstone of ground-based astronomy for over 45 years, maintaining a high level of scientific productivity through continuous innovation and a world-class observing site.This presentation provides an overview of the observatory’s current state, beginning with a look at its versatile suite of active instruments, the wide field imagers MegaCam and WIRCam, the spectropolarimeters ESPaDOnS and SPIRou, the Imaging Fourier Transform Spectrometer SITELLE and the upcoming Wenaokeao, a unique instrument that will unite the power of SPIRou and ESPaDOnS into one instrument with a wavelength covereage from 350 nm to 2.3 microns at a resolution of about 75000. I will review recent science highlights that demonstrate CFHT’s ongoing impact, from its critical role in multi-wavelength surveys to its contributions to our understanding of the solar system and stellar astrophysics. These results underscore the telescope's unique niche in the era of 8-meter and 30-meter class facilities.

ABSTRACT. One of the most important signs of exoplanet habitability is the special chemical composition of its atmosphere, which may be a consequence of biological and geological activity on it. According to current concepts, an N2-O2 atmosphere can be a good indicator of life presence on the planet [1,2]. The search for molecules that are signs of such an atmosphere (atmospheric biosignatures) on exoplanets is only possible using modern telescopes. This task will be included in the scientific program of the «Spektr- UF» space telescope (ST) [3] being created in Russia.

A necessary criterion for searching for biosignatures is the possibility of their reliable detection on exoplanets in a time not exceeding the time of the telescope's scientific program. In this work, the overview of potentially observable biosignatures in UV is presented [4]. Particular attention is paid to the indicators of N2-O2 dominant atmosphere (N, O, O2, O3, NO, N2O, NO2). It is shown that the nitric oxide molecule is a promising biosignature for search using ultraviolet space telescopes, including "Spektr-UF". Using the long-slit spectrograph (LSS, R = 1000) on board "Spektr-UF", detection of nitric oxide is possible on typical super-Earths and mini-Neptunes in the habitable zone of G- and K-type stars more active than the Sun [5, 6]. The detection limits of this molecule are up to 30 pc. Similar detection limits can be achieved for oxygen and ozone using a lower resolution spectroscopy mode, R = 200, with a field camera unit of «Spektr-UF». We provide a list of exoplanets – potential candidates for searching for these biosignatures with the «Spektr-UF».

1. Lammer et al. Astrobiology. 2019. Vol. 19, No 7. P. 927–950. 2. Sproß et al. Astronomy Reports. 2021. Vol. 65, No 4. P. 275–296. 3. Sachkov & Kopylov. Proceedings of the SPIE. 2024. Vol. 13093. P. 130933F. 4. Bisikalo et al., FIZMAT. 2024. Vol. 4. P. 1. 5. Tsurikov et al. Astronomy Reports. 2024. Vol. 68. P. 1406–1422. 6. Tsurikov et al. PhD thesis. 2025.

ABSTRACT. DECIGO is a future space mission designed to form a gravitational-wave observatory using three spacecraft. Operating in the 0.1–10 Hz frequency band, DECIGO targets the primordial gravitational-wave background from inflation. B-DECIGO is a precursor mission for DECIGO, which also possesses high astrophysical scientific motivation. It will detect gravitational waves from compact binaries during the pre-merger phase, enabling the prediction of exactly when and where a merger will occur. This allows for the observation of neutron star mergers, kilonovae, and gamma-ray bursts from their very onset using high-resolution electromagnetic telescopes. In this talk, I will present the mission concept, design, and current status of the project.

ABSTRACT. The giant elliptical galaxies at the centers of galaxy clusters are the most massive and largest galaxies in the universe. In cosmological simulations, AGN jets from these galaxies are invoked to mitigate cooling of the surrounding intracluster medium (ICM; comprising hot gas emitting in X-rays), thus regulating the stellar growth of these galaxies. Indeed, in many galaxy clusters, the observed thermodynamics of the ICM indicate that hot gas at cluster cores should cool on relatively short timescales. In a good fraction of the same clusters, the cluster central galaxy displays multiphase (ionized, atomic, and molecular) gas and star formation that sometimes extends well beyond 100 kpc. In addition, these galaxies display powerful AGN (radio) jets, which visibly disturb both their ISM and surrounding ICM. Cluster central galaxies, therefore, provide our most cherished example of how AGN jets mitigate gas cooling onto and hence regulate star formation in galaxies.

Here, we show that present understanding of what dictates gas cooling in cluster cores and hence star formation in cluster central galaxies misses the big picture. Cluster central galaxies that do not display cool gas or recent star formation also generally possess weaker, if any detectable, AGN radio jets; in contradiction with expectations, if such jets regulate gas cooling onto and hence star formation in these galaxies. Instead, we show that there is a close correspondence between the ICM thermodynamics, as well as cool gas, star formation, and AGN radio jets in cluster central galaxies, and the global dynamical state of galaxy clusters: such that only the most dynamically-relaxed clusters, which also possess the coolest ICM cores with the shortest cooling timescales, host cluster central galaxies displaying cool gas, star formation, and powerful AGN jets. Rather than being regulated solely or primarily by AGN feedback, cluster mergers – the only mechanism able to disturb clusters on a global scale – disrupt the ICM from (near) hydrostatic equilibrium, halting gas cooling onto and hence star formation in cluster central galaxies. Only when the cluster becomes sufficiently dynamically relaxed, and the ICM reaches (near) hydrostatic equilibrium, does gas cooling in cluster cores and hence star formation in cluster central galaxies resume; during this time, AGN jets likely play a role in hindering, although in theoretical models are also required to promote, gas cooling.

ABSTRACT. Ultralight dark matter (ULDM) model is a leading dark matter candidate that arises naturally in extensions of the Standard Model. In the Galactic Center, ULDM manifests as dense hydrogen-like boson clouds or self-gravitating soliton cores. We present the first study of the gravitational effects of these ULDM structures on pulsar orbits around Sgr A*, using pulsar timing as a precision dynamical probe, based on a comprehensive and practical framework that includes various kinds of black hole and orbital parameters. Our analysis shows that long-term pulsar monitoring—one of the key objectives of future SKA science—could detect a boson cloud with a total mass as low as one solar mass for boson mass m = 1e−18 eV, and probe a wide range of soliton core masses in the lower-mass regime, assuming a conservative timing precision of σ = 1 ms.

ABSTRACT. The Einstein Probe (EP) is a space X-ray mission dedicated to time-domain astrophysics, aiming to discover high-energy transients and monitor variable objects. As a principal scientific payload onboard EP, the Follow-up X-ray Telescope (FXT) is mainly responsible for prompt and deep follow-up observations of the targets triggered by EP-WXT, and for discovering and characterizing X-ray transients, particularly faint or distant ones. Since these transient signals fade rapidly or evolve dramatically, fast and reliable analysis of FXT data is essential for their discovery and for triggering timely and efficient follow-up observations, which is crucial to identifying the nature of these sources. To address this issue, we have developed a real-time source search toolkit to automatically process EP-FXT observations in real time, detecting all sources within the FXT's field of view, extracting their scientific information, and searching for transients and bursts. The toolkit generates a quick-look database comprising: 1) a suite of high-level scientific products for each observed source, such as position, count rate, flux, variability amplitude, hardness, light curve, an absorbed power-law or blackbody model-fitted spectrum, and power density spectrum; 2) identified transients and bursts; 3) source lists; and 4) sky maps. As the software operates automatically, this quick-look database is continuously updated. Based on this comprehensive quick-look database, we have constructed the EP-FXT source catalog and performed statistical analyses on the physical properties of the cataloged sources, laying a solid foundation for subsequent studies on X-ray transients and variable objects.

ABSTRACT. How neutral hydrogen (HI) galaxies trace dark matter halos remains an open question in galaxy formation. The HI line width, $W_{50}$, traces galaxy rotation and the dark matter (DM) of the host halo. It therefore potentially an observational proxy for tracing the DM halo mass. More massive halos are expected to host galaxies with larger velocity widths and stronger clustering. This work therefore measures HI galaxy clustering from a combined sample of about 39,000 galaxies over 13,700 square degrees at redshift below 0.05 using FASHI DR1 and ALFALFA. The sample is selected using a completeness cut of $C(S_{21}|W_{50}) > 50%$ based on integrated flux and velocity width. A total of 57% of FASHI sources and 92% of ALFALFA sources satisfy this criterion. The selected samples are merged and are used to measure in both monopole and projected two-point correlation functions. We examine how the correlation length, $r_, varies as a function of $W_{50} \approx 150 - km s$^{-1}$. We compare the data with Mock catalogues constructed using a semi-analytic model, SAGE, applied to the MultiDark Planck simulation. The simulations predict stronger $r_ at larger $W_{50}$. The observations show no statistically significant variation with $W_{50}$. This discrepancy may point to limitations in galaxy formation models or to selection effects in the data.

ABSTRACT. Periodic quasi-stellar objects (QSOs) are considered as candidates of supermassive binary black hole (BBH) systems in galactic centers. The periodicity of their light curves can be interpreted as being due to the Doppler boosting caused by the rotation of the two black holes (BHs). Further confirmation of these candidates may require different lines of observational evidence. Assuming the Doopler boosting scenario, in this paper we investigate the (coherent) variations of broad emission lines (BELs) and continuum light curves for active BBH systems surrounded by a circumbinary broad-line region (cBLR) and focus on their dependence on the eccentric orbital configuration. We calculated the variation of continuum light according to the motion of BBHs on elliptical orbits, with simplified orbital orientation for demonstration, the Doppler enhanced or weakened photoionization of each BLR cloud by the central BBH sources and its variation by assuming a shifted Γ-distribution of BLR clouds for a simple BLR geometry, and finally obtain the coherent variation of the continuum and the BELs. The coherent variations of the BEL profiles with the continuum light for those periodic QSOs provide an important way to confirm the existence of BBHs in their center. Future joint analysis of the light curves and multi-epoch observed BEL profiles for periodic QSOs may lead to the identification of a number of BBH systems.

ABSTRACT. relavent papers: arXiv:2603.05287, arXiv:2603.21279 (the second is nominated as RAA highlight)

Galactic bars and spiral arms are primary engines of secular evolution. Measuring their pattern speed, $\Omega_p$, is essential for understanding disk dynamics. We present a novel, unified theoretical framework based on a generalized integral form of the continuity equation over arbitrary closed loops. This "local pattern speed" formalism elegantly recovers the classic Tremaine-Weinberg (TW) method and modern Milky Way formulations as special cases. Our approach accurately maps radially varying pattern speed profiles in simulations, allowing us to disentangle multiple rotating components within a single galaxy. Applied to TNG50 galaxies, the method recovers constant pattern-speed plateaus for coherent bars and reveals a wide diversity of spiral behavior.

Motivated by these diagnostics, we revisit the reported excess of elongated “bar-like” structures in TNG50 early-type galaxies. Using a morphology-agnostic analysis, we show that such structures are ubiquitous in dispersion-dominated systems and are not static triaxial ellipsoids or prolate rotators. Instead, they are genuine slowly tumbling bar-like structures with coherent pattern speeds, typically longer and slower than bars in late-type disks. Tracing their progenitors demonstrates that many originated as ordinary fast bars in gas-richer disks at earlier times, then survived quenching while secularly slowing down and lengthening.

Together, these results establish local pattern speed measurement as a powerful tool to classify non-axisymmetric structures and uncover hidden dynamical features. Furthermore, our findings help reinterpret the apparent tension between simulations and observations regarding barred early-type galaxies, suggesting the discrepancy arises from a complex interplay of secular evolution, observational selection effects, and underlying galaxy formation physics.

ABSTRACT. Whether early-type galaxies (ETGs) have truly ceased evolving is a central question in galaxy formation theory. The traditional view holds that they are "red and dead," but gas accretion may reignite them. In our previous work, we identified a peculiar class of ETGs with interstellar medium metallicities significantly lower than those of star-forming main sequence galaxies—a phenomenon we term "metal dilution"—suggesting that they may be accreting external metal-poor gas and hinting at the possibility of rejuvenation in their late evolutionary stages. However, this finding was based on only 114 galaxies, leaving the universality, origin, and consequences of this phenomenon largely unknown—a blind spot in our understanding of galaxy lifecycles. In this talk, using DESI spectroscopy combined with multi-wavelength and IFU data, we systematically address: the occurrence rate of metal dilution, its distribution as a function of galaxy mass, environment, and redshift, and the possible triggering mechanisms behind it.

ABSTRACT. Resolved star formation histories (SFHs) of galaxies provide valuable insights into galaxy evolution, star formation, and stellar populations. Traditionally, to measure star formation history, one needs to fit simulated color magnitude diagrams (CMD) to the observed data. This includes simulating at least thousands of synthetic CMDs and then finding the one that best fits the observed data. This step will usually require significant computational time and cost. To improve this, astronomers have turned to machine learning to analyze vast amounts of data.In this study, we propose an enhanced deep learning framework to measure star formation histories. We used the Swin Transformer V2 model. By leveraging shifted window self-attention, the model is expected to capture long-range dependencies found in CMD structures. For training, we applied a structural similarity (SSIM) loss for CMD reconstruction and used Kullback-Leibler (KL) divergence to infer age-metallicity distributions. This study will establish a robust, transformer-based baseline for measuring SFHs in future large-scale surveys.

ABSTRACT. SN 2022xxf is an exceptional event: it is the most nearby type Ic-BL supernova known so far (at a distance of ~13 Mpc) and is displaying a second rebrightening episode more than 400 days post-discovery. The supernova displayed its first rebrightening episode at optical wavelengths after ~50 days, due to the interaction of the SN ejecta with a dense shell of CSM material. This optical excess was observed for the following ~50 days, after which the light curve returned to its normal behavior (i.e., powered by Co-56 decay). This supernova was also followed closely at radio frequencies in the first 100 days, showing an initial decay and subsequent rebrightening, mirroring almost simultaneously the increased emission observed at optical wavelengths. The most surprising feature however is the emergence of a second rebrightening episode more than 400 days post-discovery. Our radio observations show that the supernova is undergoing a second, dramatic rebrightening - with an order of magnitude increase in brightness and a clear spectral inversion. I will present the results from our high-cadence multi-wavelength campaign complemented by very-long-baseline interferometry. Our results disfavour an off-axis relativistic jet producing the outflow and instead point to a significant enhancement in the CSM distributed asymmetrically, possibly corresponding to a transition between nuclear burning stages. I will discuss the significance of what we learn from this event on our understanding of stellar life cycle prior to collapse, the diversity in type Ic-BL progenitor systems, and on the required coordination of multi-wavelength and multi-resolution facilities in the LSST/SKA-era of wide-field surveys in understanding the diversity in these systems.

ABSTRACT. Understanding the formation and evolution of protoplanetary disks — from embedded stages to Class II — remains a central challenge in observational and theoretical studies of star and planetary system formation. In this talk, I will synthesize recent results from our group that explore disk physical and chemical processes across a range of evolutionary stages and diagnostics.

We begin by focusing on the earliest stages of disk evolution. Using magnetohydrodynamic simulations of disk formation with varying magnetic field strengths and degrees of misalignment between the magnetic field and the angular momentum axis, we investigate how magnetic configurations regulate outflow morphology, infalling gas kinematics, and the resulting disk structure. From the observational side, we perform a statistical analysis of outflow properties in a sample of young disks using high-resolution ALMA data, revealing systematic trends in outflow morphology and kinematics. These observational results provide independent constraints that can be directly compared with model predictions. I will also discuss ongoing work that examines accretion heating in the inner disk regions at these early stages.

For Class II disks, both high-resolution observations of relatively large disks and statistical studies of large samples, including small disks, are currently being carried out with ALMA. While ALMA primarily probes disk regions beyond several astronomical units in nearby molecular clouds, warmer inner regions are explored with JWST. I will report on some of these ongoing efforts and comparison of disk chemistry models that are used to interpret the data.

ABSTRACT. Hub-filament systems (HFSs) are networks of gaseous and dusty filamentary structures in the interstellar medium that funnel material into common junctions known as hubs. These hubs are widely regarded as the birthplaces of star clusters, including those hosting high-mass stars. Observing these systems in their primordial state, before they are disrupted by newborn stars, is rare but crucial for understanding how high-mass stars accumulate their mass. In our recent work, we studied two such HFSs on small scales (<0.6 pc) that are forming protoclusters at their hubs. JWST near-infrared imaging proved to be a powerful tool for unveiling these systems, and our findings were further confirmed by dense gas tracers such as N2H+ and H13CO+ observed with ALMA. The results reveal gas streams flowing toward the hubs. In the younger of the two HFSs, the velocity gradient aligns with the local gravitational force vectors, while the more evolved system, which hosts an active protocluster, shows no such preferential alignment with gravity. We also find evidence of competitive accretion in action: the most massive cores are located closer to the hub center, supporting the idea that gravitational focusing enhances core growth toward the hub. Additionally, we identified a unique wavy, funnel-shaped structure in position–position–velocity space, highlighting the role of transverse gas flows in channeling mass to the hub. This work introduces new observational proxies for identifying pristine HFSs and sheds light on the early stages of high-mass star formation. In this presentation, I will discuss the detailed results of our recent study.

ABSTRACT. Molecular clouds (MCs) serve as star forming nurseries, birthing stars through intricate processes. Recent observational studies have unveiled a fascinating truth: filamentary structures pervade MCs across a wide range of scales. These elongated threads of interstellar material, spanning from a few parsecs to tens of parsecs in length, play a pivotal role in star formation (e.g., Bergin & Tafalla 2007, Andre et al. 2014, Hacar et al. 2023). High resolution observations reveal rich filamentary substructures at parsec and even sub-parsec scales threading inside MCs. Dense cloud cores are found located along or at the intersections of these filamentary substructures (e.g., Tafalla and Hacar 2015, Hacar et al. 2017). In this study, I use advanced large-scale high-resolution numerical simulations, using multi-physics ORION2 code with adaptive mesh refinement capability (Li et al. 2012, 2021), to explore the formation of dense cores in magnetized and supersonic turbulent MCs. My investigation sheds light on (1) the stability of filamentary substructures and their physical conditions when cores are forming, (2) the consequences of the highly non-uniform gas accretion of dense cores as the result of the connection with filamentary substructure during their formation, (3) the merging of cores due to their proximity along the filament substructures, and (4) the restructuring of magnetic field around dense cores during their formation and evolution. I shall use a few examples in the simulation to discuss the dynamical evolution of some key physical properties, including mass, size, specific angular momentum, kinetic and magnetic energies of the dense cores. The simulation outcomes offer valuable insights into some of the recent observations, such as highly non-uniform separation of dense cores forming along filaments (e.g. Miettinen 2012, Smith et al. 2023), the behavior of core-streamer systems (e.g. Ren et al. 2021, Olguin et al. 2023), and a variety of magnetic field structures around dense cores (e.g. Sanhueza et al. 2021, Pattle et al. 2021).

ABSTRACT. Peculiar orbital clustering of distant Kuiper Belt objects suggest a presence of an additional giant planet in the outer Solar System, commonly referred to as Planet Nine (P9). Numerical simulations suggest that the gravitational influence of such a planet could account for the observed clustering. Despite these predictions, no direct observational evidence for P9 has yet been reported, largely because its hypothesized orbit lies far beyond Neptune, where reflected sunlight is extremely weak and optical detection is challenging.

As a cold, low-temperature body, P9 is instead expected to emit thermal radiation that peaks in the far-infrared. In this work, we search for P9 candidates using two far-infrared all-sky surveys, IRAS and AKARI, whose observing epochs are separated by 23 years. This temporal baseline is sufficient to detect the expected slow apparent motion of P9, approximately ∼3 arcmin yr⁻¹. Our analysis makes use of the AKARI Monthly Unconfirmed Source List, which contains sources detected repeatedly on hour-long timescales but not on month-long timescales, making it well suited for identifying moving Solar System objects.

We identify slowly moving candidates by cross-matching sources between the IRAS and AKARI catalogues. Expected flux densities and orbital motions are first estimated by adopting plausible values for the mass, heliocentric distance, and effective temperature of P9, ensuring detectability in both surveys. These estimates are used to define positional and flux selection criteria, significantly reducing the number of candidate sources. We then construct all possible IRAS–AKARI source pairs with angular separations between 42′ and 69.6′, corresponding to heliocentric distances of 500–700 AU and planet masses of 7–17 M⊕.

After applying all selection criteria, we identify 13 candidate pairs. Visual inspection of the survey images reveals one particularly promising candidate, for which the IRAS source is absent at the corresponding location in the AKARI image obtained 23 years later, and vice versa, consistent with the expected motion of P9. However, two-epoch detections alone are insufficient to constrain a unique orbital solution. Follow-up observations are therefore required to confirm the nature of this candidate and determine its Keplerian orbit. Finally, we discuss the prospects for detecting Planet Nine with our forthcoming CubeSat mission, VERTECS.This result is published in Phan et al. 2025, PASA,42,e064

ABSTRACT. Recently, we have been studying the interactions of supernovae (SN) with asymmetrically or irregularly distributed circumstellar matter (CSM), which has formed into a circumstellar disk, bipolar lobes, or overdensity layers of different morphologies, etc (Kurfürst+ 2026). We investigate the effects of these interactions in terms of hydrodynamic processes and manifestations of observables for different positions of the progenitor star with respect to these CSM formations, up to about 3 to 4 years after the explosion. These events produce overluminous and extremely long-lasting light curves, often with characteristic irregularities. We used the 3D radiative-hydrodynamic code Castro for radiation-hydrodynamic simulations. Using two additional 3D Monte Carlo radiative transfer codes, Sedona and Sirocco, we calculated the time evolution of light curves, continuum, and Lyman-alpha and H-alpha spectral profiles "observed" from different directions at different times, as well as the relative polarization that reflects the morphology of the surrounding CSM. Comparing such models with observations can contribute to the understanding of the CSM morphological and physical structure and the mechanisms of violent outbursts by which this material is ejected into space from stars that approach their death.

ABSTRACT. We present a census of the Compton-thick (CT) active galactic nucleus (AGN) population and the column-density (NH) distribution of AGN in our cosmic backyard using a volume-limited sample within 15 Mpc. This sample is selected via the high-ionisation mid-infrared [NeV] line, an unambiguous tracer of AGN activity that is unaffected by dust obscuration or non-AGN contamination. With intrinsic 2-10 keV luminosities of log L ~ 37-43 erg/s, our sample reaches a parameter space inaccessible to more distant surveys. Column densities were measured through broadband X-ray spectral analysis, primarily using Chandra and NuSTAR. We directly measure a CT AGN fraction of ~32%, significantly higher than that observed by the Swift-BAT survey, but fully consistent with its sensitivity-corrected predictions. Our NH distribution also matches the corrected Swift-BAT results, providing direct observational confirmation of AGN populations expected by Swift-BAT but previously undetected due to its flux limitations. Restricting the sample to the largely unexplored domain of low-luminosity AGN (log L < 42 erg/s), we find a CT fraction of ~19%, comparable to that seen at higher luminosities. Multiwavelength diagnostics generally support our X-ray results, although several intrinsically faint AGN (log L ~ 40 erg/s) deviate in the X-ray-12 µm relation. These cases fall near the empirical limits of the correlation, suggesting that it may break down at very low luminosities or that host-galaxy contamination becomes significant. Most AGN with log L < 40 erg/s are unobscured or only mildly obscured, supporting scenarios in which the torus is weak or absent at low luminosities. Our sample spans a similar range of Eddington ratios to Swift-BAT, though the survey dominates at higher accretion rates. AGN with Eddington ratio of log Edd > -3 in our sample are mainly CT, while those with log Edd < -3 tend to be unobscured. The sample also hosts significantly lower black-hole masses, peaking around log MBH ~ 6 MSun, about 1.5 dex lower than Swift-BAT, indicating that our sample predominantly selects low-mass AGN. In terms of host-galaxy properties, star-formation rates are comparable to Swift-BAT, but our AGN are found in lower-mass galaxies and include many LINER and H II-type nuclei that Swift-BAT largely misses. This indicates that we are identifying weaker or heavily obscured AGN that remain undetected at optical wavelengths.

ABSTRACT. The white dwarf pulsar in the binary system AR Scorpii exhibits strong, periodic optical non-thermal emission, characterised by high linear polarisation and rapid polarisation angle (PA) variations. Observations obtained with the High-speed Photo-Polarimeter (HIPPO) on the South African Astronomical Observatory 1.9 m telescope reveal double peaks in total intensity per spin cycle and systematic phase lags between the total intensity maxima, linear polarisation peaks, and PA inflection points. Such behaviour cannot be fully explained by the classical, centred rotating vector model (RVM), which predicts smooth polarisation variations aligned with the intensity or the linear flux peaks. We propose that an off-centred magnetic dipole anchored in the white dwarf provides a natural explanation. In this configuration, displacement of the dipole axis produces non-uniform emission regions, generating phase lags between intensity peaks, between intensity and linear flux maxima, and between intensity/linear flux and PA inflexion, in agreement with the observed spin-phase lag behaviour.

To characterise the off-centred dipole geometry, we model the optical polarised non-thermal emission of AR Sco using spin-phase–folded polarimetric data. Our aim is to constrain the white dwarf’s emission altitude, magnetic dipole displacement, magnetic moment obliquity, and observer viewing angle. Parameters of the decentred rotating vector model were estimated via Markov Chain Monte Carlo simulations, enabling direct comparison between predicted and observed phase-resolved polarisation behaviour.

We find that the polarised emission originates at altitudes h ≳ 0.3 R, where R is the white dwarf pulsar radius, and that the magnetic moment is significantly displaced from the stellar centre, with offsets ranging from 0.05 R to 0.85 R across the orbital phases of AR Sco. The magnetic field geometry is consistent with an approximately orthogonal rotator, with obliquities between 87° and 94°, and the viewing angle varies between 82° and 114° over one orbital cycle. Employing the off-centred dipole formalism, we reproduce the observed phase lag pattern: the linear polarisation maximum occurs at a distinct rotational phase from the total intensity peak, while the PA exhibits its steepest gradient at an intermediate phase. The model also accounts for the high polarisation fraction and the beat-period modulation arising from interactions between the white dwarf pulsar and its M-dwarf companion.

ABSTRACT. X-ray observations of the tidal disruption event (TDE) candidate AT 2019avd show drastic variabilities in flux and spectral shape over hundreds of days, providing clues on the accretion disc-corona evolution. We utilize a disc-corona model, in which a fraction of the gravitational energy released in the disc is transported into the hot corona above/below. Some soft photons emitted from the disc are upscattered to X-ray photons by the hot electrons in the optically thin corona. By fitting the \textit{NICER} observations of AT 2019avd during epochs when the spectra exhibit significant hardening, we derive the evolution of the mass accretion rate, $\dot{m}$, and the coronal energy fraction, $f$. Our results show that $f$ decreases with increasing $\dot{m}$, which is qualitatively consistent with that observed in active galactic nuclei (AGNs), while the slope of this source, $f\propto \dot{m}^{-0.30}$, is much shallower than that of AGNs. We also find that the non-thermal X-ray spectrum in this source is significantly softer than those typically seen in AGNs {and black-hole X-ray binaries}. We argue that these quantitative differences can be a powerful diagnostic of the underlying magnetic turbulence, which may imply a stronger magnetic field within the TDE accretion disc than that in typical AGNs. It is also found that the evolution of the fitted neutral hydrogen column density follows a similar pattern to that of the accretion rate evolution, which may reflect the accumulation of absorbing material originating from the inflowing streams of stellar debris and/or other related sources.

ABSTRACT. The amount of mass added to the black holes and the energy produced through accretion onto them depend greatly on the physical properties of the accretion flow. The property of simple non-rotating polytropic flow accreting onto compact objects is well known by the classic work of Bondi. We extend the study of polytropic accretion flow in the presence of rotation. We numerically construct the steady-state flow solutions to the rotating polytropic accretion flow. We also consider the rotating Bondi flow with outflow, modelled by self-similar ADIOS. The physical properties and their mass inflow rate at the outer boundary and the final accretion rate into black holes are discussed.

ABSTRACT. SN 2023aew is a peculiar double-peaked supernova discovered at redshift 0.0255. The first peak corresponds to a Type IIb supernova with an absolute magnitude around −17.4 and lasts about 100 days, showing a slow decline and plateau. Later, the supernova transitions to a broad second peak similar to a Type Ic supernova, reaching an absolute magnitude near −18.75 on day 119. Total energy more than 6.5x10^49 erg requires implausibly high 56Ni mass if radioactive-powered. We test delayed fallback accretion scenario using 1D STELLA radiation-hydrodynamics simulations. We adopt well-established Nomoto’s and Bersten's supernova models for the first peak energy. Second peak is modeled with delayed fallback accretion onto a black hole — late fallback can internally heat the ejecta, explaining the temperature rise with a receding photosphere and light curve bumps. The best fit reproduces both peaks. Results demonstrate fallback accretion scenario viability.

ABSTRACT. Isolated stellar-mass black holes traversing dense regions of the interstellar medium, such as molecular clouds, are expected to accrete ambient gas. This accretion process can ionize surrounding gas, carving out a low-density ionized cavity within the cloud. The accreting black holes may also possess accretion discs and jets, producing cosmic rays and triggering hadronic and leptonic interactions. In this work, we consider the accretion process and the effects brought about on the cloud structures, such as the formation of ionization cavities, and on production of energetic particles. We discuss the consequences of the presence of ionization cavities in molecular clouds of different sizes, hence the implications on (i) cloud fragmentation and star formation, and (ii) the inhomogeneity in the cloud environment for cosmic-ray transport in molecular clouds.

ABSTRACT. The ongoing upgrade of ALMA toward wider instantaneous bandwidth and improved sensitivity is expected to significantly enhance molecular line observations in star-forming regions. Expanded spectral coverage will enable the simultaneous detection of a vast number of molecular transitions, providing an unprecedented opportunity to investigate chemical complexity across evolutionary stages, from prestellar cores to planet-forming disks.

However, this anticipated increase in spectral information will also introduce new challenges. The interpretation of rich “line forests” critically depends on the accuracy and completeness of molecular spectroscopic data. In many cases, uncertainties in rest frequencies, line assignments, and excitation properties limit our ability to fully exploit the potential of WSU, particularly for complex organic molecules and their isotopologues. This issue becomes critical when commonly observed transitions are optically thick, forcing us to rely on weaker high-excitation or vibrationally excited lines. In such regimes, the accuracy and completeness of available spectroscopic data are often insufficient, reflecting the historical optimization of spectroscopy databases for low-temperature (∼10 K) conditions.

In this talk, I will highlight how revisiting molecular spectroscopy is becoming essential for advancing astrochemical studies in the ALMA WSU era. I will present recent examples demonstrating how improved laboratory spectroscopy enables more reliable line identification, constrains physical conditions, and provides new insights into chemical evolution along the star and planet formation process.

ABSTRACT. Magnetized turbulence is the dominant process governing the structure, evolution, and star-formation efficiency of the interstellar medium . It develops in a highly inhomogeneous, multiphase environment, where thermal instability and nonlinear MHD dynamics jointly shape the gas morphology. Capturing the full dynamic range of this system, characterized by extremely high Reynolds numbers and large spatial scale separations, has remained numerically challenging.

We present results from a frontier numerical simulation of magnetized, multi-phase interstellar turbulence, achieving an unprecedented resolution of $8192^3$. This "Exascale" calculation allows us to rigorously probe the turbulent cascade across an extended inertial range while simultaneously resolving the sharp density contrasts of the multi-phase medium. We identify the Alfvénic scale and analyze the statistical properties of turbulence in both the cold and warm phases. Furthermore, this resolution reveals the emergence of coherent structures, specifically plasma ropes (Plamsmoid features), which form naturally within the turbulent flow. These structures are critical sites for rapid magnetic reconnection and particle acceleration but remain unresolved in standard astrophysical simulations. Our findings provide a new benchmark for understanding the coupling between thermodynamics and MHD turbulence in the ISM.

ABSTRACT. Polarization of starlight and thermal dust emission due to magnetically aligned non-spherical grains provide a powerful tool to trace the interstellar magnetic field (B-field) morphology and strengths, ranging from the diffused interstellar medium to the dense star-forming regions, and to study grain alignment mechanisms and the grain properties. The mechanism of the alignment of grains is not yet fully clear and stands to be one of the long-standing problems in astrophysics. A clear understanding of the grain alignment mechanisms is important to use dust polarization as a reliable tool to trace interstellar magnetic field. Out of the various theories proposed to explain the grain alignment mechanism, the alignment of grains induced by RAdiative Torques (RATs), known as RAT-A theory, acts as the leading theory which has been well established and could explain various observational results. Also, a very intense radiation field can make the grains rotate very fast and disrupt the grains into smaller fragments instead of alignment, termed as RAT-Disruption or RAT-D. In this work, we perform a comprehensive study and testing of the grain alignment and disruption mechanisms in a massive filamentary and active star-forming infrared dark cloud G34.43+0.24 which harbors multiple protostellar cores using observations of polarized thermal dust emission, with the POL-2 instrument mounted on the James Clerk Maxwell Telescope, at 850 µm. This star-forming filament offers a favourable environment to study the RAT paradigm (RAT-A and RAT-D) since it shows significant variations in the physical parameters like the gas density and dust temperature from the outer to the inner regions and contains massive and luminous protostellar cores inside. We study in three sub-regions as North harboring the bright MM3 core, Center harboring the very bright MM1 and MM2 cores, and South harboring no core. We find decreases in polarization fraction P with increasing total intensity and gas column density, known as polarization hole or depolarization, in each sub-region. To assess for any contribution of magnetic field tangling to cause the observed polarization hole, we estimate the debiased polarization angle dispersion function and our analysis finds that depolarizations in North and Center regions are due to decrease in net alignment efficiency of grains but in South region the effect of magnetic field tangling is significant to cause the depolarization. To test whether the RAT paradigm can reproduce the observational results, we estimate the minimum alignment and disruption sizes of grains using RAT theory, and our study finds that RAT-A mechanism can explain the depolarizations in North and Center regions where B-field tangling effect is less important, except for the core regions. We find hints of RAdiative Torque Disruption in the protostellar core regions of MM3 in North, MM1 and MM2 in Center. We also find that the observed high P value of around 8%-20% in the outer regions of the filament can be explained potentially by magnetically enhanced RAT alignment mechanism. This work has been published in The Astrophysical Journal.

ABSTRACT. The Early Planet Formation in Embedded Disks (eDisk) project of ALMA that has studied 19 young stellar objects (YSOs) at the early evolutionary stages, the so-called Class 0 and I YSOs, in 1 mm continuum and various molecular lines at ~0.04 arcsec resolution, reports that substructures are not detected until the late stage of Class I. This suggests that planet formation may begin relatively late in the Class I phase. However, 1 mm continuum is likely optically thick in dense regions of circumstellar disks, so we further investigate the presence of substructures in a longer 3 mm wavelength at the comparable angular resolution. The spectral index between 1 and 3 mm reveals that many disks exhibit values below 2 in their central regions, which may be primarily attributed to dust self-scattering. Our radiative transfer modeling demonstrates that dust self-scattering can successfully reproduce the observed spectral index and brightness temperature profiles. The inferred maximum grain sizes are typically around 100 micrometers in Class 0 disks and 300-400 micrometers in Class I disks. The estimated dust masses are on the order of several hundred Earth masses, significantly higher than those derived under the optically thin approximation. This discrepancy arises not only from the disks being optically thick, but also from dust scattering, which substantially reduces the observed flux. In addition, residual images from the radiative transfer modeling suggest possible faint substructures in these early embedded disks.

ABSTRACT. Wolf–Rayet (WR) stars, whose hydrogen-rich envelopes have been stripped by strong stellar winds, represent a late evolutionary stage of massive stars with initial masses of >20-25 M_sun. They play a significant role in regulating star formation and driving chemical enrichment through their strong winds, intense radiation, and catastrophic final fate. WR stars are also considered candidates for the progenitors of stripped-envelope supernovae, stellar-mass black holes, and possibly some long gamma-ray bursts. Despite their importance, the Galactic WR population remains significantly incomplete due to the observational difficulties requiring narrow-band photometry or spectroscopy for identification. Moreover, heavy interstellar extinction toward the Galactic plane severely limits the detectability of WR stars at optical wavelengths, leaving many systems undiscovered. The SPHEREx mission, which is actively performing an all-sky near-infrared spectrophotometric survey, provides a unique opportunity to identify these hidden WR stars in heavily obscured regions.

In this work, we develop a systematic framework for WR candidate identification using SPHEREx data. We simulate SPHEREx spectra for various WR subtypes and confirm that their characteristic broad emission lines of He, N, and C can be robustly detected at the low spectral resolution of SPHEREx. These features enable an efficient separation of different WR subtypes, as well as a clear distinction between WR stars and other emission-line objects such as planetary nebulae, cataclysmic variables, and Be stars. Next, we estimate the total Galactic WR population to be about 1,600 based on the currently known sample. We further find that the full SPHEREx mission has the potential to uncover more than ~250–350 previously hidden WR systems, even when accounting for the 6.2" spatial resolution of SPHEREx and the severe interstellar extinction.

We are now testing our framework with ongoing SPHEREx observations, comparing the model predictions with the actual data and refining the method as needed. Early results show that the expected emission and continuum features of WR stars can indeed be recovered in the observations. We are also exploring whether the SPHEREx near-infrared continuum can be used to estimate WR mass-loss rates, and we are preparing machine-learning methods to further improve candidate selection. These efforts highlight the strong potential of SPHEREx to expand the Galactic WR census and to deepen our understanding of massive-star evolution.