ASIAA Colloquium is usually held on Wednesdays at 2:20-3:20 pm in Room 1203 of the Astronomy-Mathematics Building, NTU. All scientists are welcome to attend. Seminars on more specialized topics are also held on a regular basis.
The ASIAA-NTU joint colloquium series aims to bring to the physics/astronomy/cosmology community in ASIAA/NTU world renown researchers who will talk about the forefront development of physical sciences.
Galaxies, termed “Cosmic Ecosystems”, consist of stars, gas, and black holes – the interaction among which dictates how a galaxy grows over time as a dynamic entity. Existing theoretical models of feedback offer a basis for how stars and black holes enrich the chemical content of the gas reservoir and/or eject it out of the galaxy through winds. Galactic outflows driven by active supermassive black holes, particularly prevalent in interacting galaxy systems, tend to stop future generations of stars from being formed and drastically alter the fate of the host when star formation is quenched. The details of this active galactic nucleus (AGN) feedback process, which is thought to play a significant role in galaxy evolution across cosmic time, have been difficult to verify observationally. In this talk, I will showcase new JWST and Keck integral-field spectroscopic observations of merging galaxies that trace the movement of the multiphase gas as it traverses the galactic ecosystems, enabling a detailed understanding of this dynamic feedback process. Our early results reveal galactic-scale shocks from starburst-driven superwinds, AGN outflows driven by precessing radio jets, and decelerating winds with signatures of ionization stratification. The power of resolved studies in dissecting how systems dynamically evolve has become indispensable for understanding multiphase gas feedback from nuclear to galactic scales.
Next Seminar:
2024-11-21 Thu 14:20~15:20 [R1203]
Speaker:
Sascha Zeegers (ESA ESTEC and ASIAA)
Topic:
Shining light on the properties of interstellar dust
Abstract:
Interstellar dust plays an important role at every stage in
the life cycle of stars and can be found anywhere in the universe. However,
this dust still raises many questions about its composition and physical
properties. Multiwavelength spectroscopy
provides a powerful tool to study the nature of interstellar dust. By making
use of background stars, we can observe the extinction of stellar light by dust
grains which may reveal grain properties of the dust, such as the chemical
composition, structure and size of the dust grains. Important diagnostic
features of dust fall in the infrared and X-ray band. Observatories such as JWST
in the infrared and X-ray observatories such as Chandra, XRISM and, in the future,
Athena allow us to study these features in unprecedented detail.
In this talk I will show the potential of a multiwavelength
study of interstellar dust. I will show recent results from the WISCI project,
which includes near- and mid-infrared observations with JWST and optical and UV
observations with VLT & HST. I will also discuss recent results obtained
from X-ray spectroscopy and our ongoing interstellar dust laboratory campaign
in Taiwan.
*Seminar* Shining light on the properties of interstellar dust
Shining light on the properties of interstellar dust
Interstellar dust plays an important role at every stage in
the life cycle of stars and can be found anywhere in the universe. However,
this dust still raises many questions about its composition and physical
properties. Multiwavelength spectroscopy
provides a powerful tool to study the nature of interstellar dust. By making
use of background stars, we can observe the extinction of stellar light by dust
grains which may reveal grain properties of the dust, such as the chemical
composition, structure and size of the dust grains. Important diagnostic
features of dust fall in the infrared and X-ray band. Observatories such as JWST
in the infrared and X-ray observatories such as Chandra, XRISM and, in the future,
Athena allow us to study these features in unprecedented detail.
In this talk I will show the potential of a multiwavelength
study of interstellar dust. I will show recent results from the WISCI project,
which includes near- and mid-infrared observations with JWST and optical and UV
observations with VLT & HST. I will also discuss recent results obtained
from X-ray spectroscopy and our ongoing interstellar dust laboratory campaign
in Taiwan.
Hsien Shang
2024-11-27 Wed 14:20~15:20 R1203
Vivian U UC Irvine
*Colloquium* Black Hole Feedback in Galaxy Mergers
Black Hole Feedback in Galaxy Mergers
Galaxies, termed “Cosmic Ecosystems”, consist of stars, gas, and black holes – the interaction among which dictates how a galaxy grows over time as a dynamic entity. Existing theoretical models of feedback offer a basis for how stars and black holes enrich the chemical content of the gas reservoir and/or eject it out of the galaxy through winds. Galactic outflows driven by active supermassive black holes, particularly prevalent in interacting galaxy systems, tend to stop future generations of stars from being formed and drastically alter the fate of the host when star formation is quenched. The details of this active galactic nucleus (AGN) feedback process, which is thought to play a significant role in galaxy evolution across cosmic time, have been difficult to verify observationally. In this talk, I will showcase new JWST and Keck integral-field spectroscopic observations of merging galaxies that trace the movement of the multiphase gas as it traverses the galactic ecosystems, enabling a detailed understanding of this dynamic feedback process. Our early results reveal galactic-scale shocks from starburst-driven superwinds, AGN outflows driven by precessing radio jets, and decelerating winds with signatures of ionization stratification. The power of resolved studies in dissecting how systems dynamically evolve has become indispensable for understanding multiphase gas feedback from nuclear to galactic scales.
Chian-Chou Chen
2024-12-03 Tue 10:00~11:00 R1203
Robert Shelton GMTO
*Colloquium* Giant Magellan Telescope: Current Status and Future Promise
Giant Magellan Telescope: Current Status and Future Promise
This presentation discusses the role of the Founders of the GMT, with reference to their financial, technical, and governance support. The status of the GMT site in Chile will be reviewed including our formal status with the Chilean government. Turning to the telescope itself, the initial suite of instruments will be presented in the context of the scientific capabilities of the GMT. Finally, we will look ahead to key decisions from the US National Science Foundation and future funding of the GMT.
Shiang-Yu Wang
2024-12-04 Wed 14:20~15:20 R1203
Christophe Pichon Institut Astrophysique de Paris
*Colloquium*
Junsup Shim
2024-12-11 Wed 14:20~15:20 R1203
Man Hoi Lee University of Hong Kong
*Colloquium*
Pin-Gao Gu
2024-12-18 Wed 14:20~15:20 R1203
Daniel Wang UMass & ASIAA
*Colloquium*
Yi-Kuan Chiang
2024-12-25 Wed 14:20~15:20 R1203
Yun-Ting Cheng Caltech
*Colloquium*
Yi-Kuan Chiang
Past talks in 2024
2024-01-03 Wed 14:20~15:20 R1203
Cheng Chen University of Leeds
*Colloquium* Dancing with the binary: diverse orbital dynamics and stability around circumbinary systems
Dancing with the binary: diverse orbital dynamics and stability around circumbinary systems
Recent observations have revealed that circumbinary disks misaligned to the binary orbit could be common in the universe. Dissipation in the disc causes it to move either towards coplanar alignment or polar alignment. In the polar configuration, the disc is perpendicular to the binary orbit, with the disc angular momentum vector aligned to the binary eccentricity vector. Since planets form inside disks, circumbinary planets may also form misaligned to the binary orbit. We explore the dynamical evolution and stability of misaligned circumbinary planets. We find that around eccentric binaries, the most stable orbits are those that are close to a polar alignment. Moreover, we find that two circumbinary planets in the same system may result in complicated orbital dynamics and resonances. These interactions could efficiently lead to the formation of free-floating planets because hosting multiple planets around a binary is more challenging than in a single star system.
2024-01-17 Wed 14:20~15:20 R1203
Ming-Tang Chen ASIAA
*Colloquium* The Greenland Telescope, Black Hole Shadow, and Photon Ring
The Greenland Telescope, Black Hole Shadow, and Photon Ring
The Greenland Telescope [i] started scientific observations in 2018. Currently, the Telescope is located at Pituffik Space Base (PSB) in the northwestern corner of Greenland and has participated in the observing campaigns of the Event Horizon Telescope (EHT) and the Global Millimeter-wave VLBI Array(GMVA). The first scientific results featuring the GLT revealed a panoramic picture of the black hole and its jet at a 3 mm wavelength [ii]. The next GLT result will come from the 2018 EHT observations, displaying a sharper black hole image at 1.3 mm. As is expected, many new and exciting research outcomes will be published from the observations after 2018.
The next stage of the GLT project aims to capture the most distinctive signature of general relativity–the photon rings. In their current planning, the EHT and its next-generation follow-up cannot resolve the features of the photon rings because of the lack of the required angular resolution. To achieve such a scientific breakthrough, we will relocate the GLT to Summit Station and conduct observations at 600 GHz and higher. I will present the status of the GLT and its plan for achieving our next goals.
[i] Ming-Tang Chen et al 2023 PASP 135 095001
[ii] Lu, R.-S., Asada, K., Krichbaum, T. P., et al. 2023, Nature, 616, 686
2024-01-22 Mon 14:20~15:20 R1203
Brandon Hensley JPL
*Colloquium* Rethinking the Nature of Interstellar Dust
Rethinking the Nature of Interstellar Dust
Interstellar dust has long been modeled with separate silicate and graphite/amorphous carbon components. In this talk, I will argue that initially distinct populations of stardust get rapidly homogenized in the ISM into a composite material ("astrodust"). I will show that the astrodust+PAH model is compatible with current observational constraints on dust extinction and emission in the diffuse ISM, and that it provides a more natural explanation for the observed polarized emission than do two-component models. I will discuss implications for the lifecycle of dust in galaxies.
2024-01-24 Wed 14:20~15:20 R1203
Chandra Shekhar Saraf KASI
*Seminar* Tomographic cross-correlation of the CMB lensing and galaxy clustering - systematic errors from redshift bin mismatch of galaxies
Tomographic cross-correlation of the CMB lensing and galaxy clustering - systematic errors from redshift bin mismatch of galaxies
The effect of gravitational lensing of the cosmic microwave background (CMB) provides a unique opportunity to obtain a picture of the gravitational potential of the large-scale structure of the Universe at very high redshifts. Tomographic cross-correlation of the gravitational potential with other tracers of the large-scale structure at known redshifts allows tracing the evolution of the structure and testing cosmological models. However, the analysis of upcoming data will require a very good understanding of any systematic errors that may bias cross-correlation measurements. In this talk we will present studies of systematic errors arising from redshift bin mismatch of galaxies with photometric redshift uncertainties. We show their impact on the cross-correlation measurement and cosmological parameter estimates for future data sets. We also present an efficient method for removing the errors.
2024-01-31 Wed 14:00~14:45 R1412
Hiddo Algera Hiroshima University
*Seminar* The Dust and Interstellar Medium Properties of Galaxies in the Epoch of Reionization
The Dust and Interstellar Medium Properties of Galaxies in the Epoch of Reionization
Over the last decade, ALMA has revolutionized our understanding of the interstellar medium (ISM) conditions of distant galaxies. For one, ALMA has now detected (sub-)millimeter continuum emission from dozens of galaxies at z > 6.5, establishing the importance of dust-obscured star formation already within the first 800 Myr after the Big Bang. Moreover, through various bright emission line diagnostics such as [CII]158 and [OIII]88, ALMA can be used to directly study the physical conditions and kinematics of the ISM within the earliest galaxies.
In this talk, I will review what we have learned about the dust and interstellar medium properties of high-redshift galaxies, focusing specifically on the Cycle 7 ALMA Large Program REBELS and its follow-up studies. In addition, I will present recently taken JWST/NIRSpec IFU observations of REBELS sources and discuss how we can use the combined power of ALMA and JWST to learn about early dust build-up in galaxies.
*Seminar* Mapping the cosmic web along FRB sightlines
Mapping the cosmic web along FRB sightlines
Fast radio bursts (FRBs) are among the newest tools in observational astrophysicists’ repertoire to study ionized gas. Their unique, millisecond-duration radio signal is subject to propagation effects in the intervening plasma. One such effect is the plasma dispersion of FRB pulses. FRB dispersion measures (DMs) quantify the net free electron column density through the sightline. FRB DMs can be precisely measured (~0.1%) and thus are sensitive to the most diffuse plasma in the intergalactic medium (IGM) that traditional probes have found challenging to illuminate. This ability to provide novel constraints on plasma has motivated studies of the circumgalactic medium (CGM) of galaxies intersecting FRB sightlines and the cosmic web filaments of the IGM. In my talk, I will highlight some of the work already done leveraging FRBs and introduce the FLIMFLAM survey. The survey is an ongoing endeavor to map foreground matter density along ~20 FRB sightlines. To this end, the survey measures spectroscopic redshifts of the foreground galaxies. Its ultimate aim is to produce statistical constraints on key parameters describing matter distribution in the universe, including the fractions of ionized baryons residing in the diffuse IGM and the virialized gas of halos. We expect our first data release by the end of 2023. Meanwhile, some of our recent work focuses on interesting sightlines that exhibit unusually large DMs. Through foreground mapping, we confirm large host galaxy DMs in some sightlines while others show numerous foreground structures. I will also discuss one sightline where foreground mapping revealed cluster gas that enhanced the DM. I will end with prospects for FRB-based analyses in the near future that I'm excited for.
2024-02-07 Wed 14:00~14:45 R1412
Konstantin Gerbig Yale
*Seminar* Novel insights in planet formation: Formation of dusty filaments & orbital alignment in binary systems
Novel insights in planet formation: Formation of dusty filaments & orbital alignment in binary systems
Planet formation within protoplanetary disks presents an array of unsolved questions, two of which I aim to address in this talk.
First, I'll explore how dust is concentrated to densities sufficiently high for the on-set of planetesimal formation. By drawing a parallel to the formation of underwater sand ripples, I introduce a novel linear, axisymmetric instability capable of transforming turbulent dust regions in a disk's mid-plane into dense, azimuthally stretched filaments. This process hinges on a rapid decrease in diffusivity with heightened dust concentration, a premise supported by our numerical simulations where dust-gas interactions self-generate turbulent diffusion.
Second, I will discuss planet-hosting (wide) binary systems, where recent studies suggest a prevalence of coplanar arrangement of planetary and binary orbits. I propose that this alignment, along with observed obliquity distributions in exoplanetary systems, can be attributed to viscous dissipation in the disk during binary-driven precession. Moreover, our analysis predicts that the alignment tendency should weaken as the binary stellar mass ratio increases, and indeed, I will present new evidence for this trend in TESS data of exoplanet-hosting binaries.
*Seminar* AstroSat UV Deep Field - A unique view of the distant galaxies
AstroSat UV Deep Field - A unique view of the distant galaxies
Observation of deep fields provides a unique scope to explore multiple aspects of extragalactic astronomy by effectively detecting the faintest objects in the distant universe. We utilize the unique angular resolution, sensitivity, and field of view of the Ultra-Violet Imaging Telescope (UVIT) onboard AstroSat to perform deep imaging of the GOODS-north field in the FUV and NUV bands reaching a 3$\sigma$ depth of ~ 27.3 AB mag. Our UV flux measurements of the identified sources complement existing rich multiband data in the GOODS-N field and enable us to probe properties of galaxies between redshift ~ 0 and 1. We study the internal dust extinction of galaxies by constraining their UV continuum slope (bet). Combining with HST F275W, F336W, and KPNO U bands, the UVIT data helped us to estimate beta of 465 galaxies between redshift 0.40 and 0.75. Our beta measurements add new data points to the least-explored redshift regime, further reinforcing the gradual reddening of the galaxy UV continuum with cosmic time. Using a sub-sample of 83 galaxies, we further constrained the beta - IRX law at redshift ~0.5. I Will also discuss how observation of AstroSat UV deep field is unique to constrain the faint end slope of UV Luminosity Function, testing the nature of SFR scaling relation, and finally to search for Lyman Continuum leaking galaxies beyond redshift ~ 1, which are important to understand galaxy evolution and cosmic reionization process.
2024-02-16 Fri 14:20~15:20 R1203
Chun-Hao To OSU
*Seminar* Multi-probe cosmology: challenges and opportunities in the next decade
Multi-probe cosmology: challenges and opportunities in the next decade
In the next decade, large cosmological surveys will map billions of galaxies and measure cosmic structure to unprecedented precision via multiple cosmological probes. Using results from the Dark Energy Survey as an example, this talk will outline the challenges and opportunities of cosmological analyses in the presence of rich astrophysics and observational systematics. In particular, I will describe different cosmological probes measured from the Dark Energy Survey and summarize recent progress on joint analyses of galaxy clustering, weak lensing, and galaxy cluster abundances. I will then highlight the challenges for future, larger experiments such as Rubin Observatory's LSST and describe our progress in tackling these challenges through sophisticated simulations and an AI-enhanced analysis pipeline. I will conclude the talk by identifying a unique opportunity for overlapping imaging surveys and Cosmic Microwave Background surveys that will unlock the constraining power of small-scale weak gravitational lensing measurements.
2024-02-21 Wed 14:20~15:20 R1203
Ya-Lin Wu NTNU
*Colloquium* Monitoring accreting brown dwarfs at Lulin
Monitoring accreting brown dwarfs at Lulin
Variability of mass accretion provides important information about disk evolution and the geometry of the accretion flows. While there are many studies focusing on young stars, accretion monitoring in the substellar regime has been relatively uncommon. At optical wavelengths, the H-alpha emission is a bright accretion tracer, proving an opportunity to observe young brown dwarfs with small telescopes. In this talk, I will introduce our ongoing efforts of monitoring brown dwarfs with the one-meter telescope at Lulin Observatory and present the preliminary results.
2024-02-26 Mon 11:00~12:00 R7S1, Cosmology Hall
Jia Liu IPMU
*Theory Seminar* [Joint LeCosPA-ASIAA Seminar]
Cosmology with Massive Neutrinos
[Joint LeCosPA-ASIAA Seminar]
Cosmology with Massive Neutrinos
Abstract:
Ghostly neutrino particles continue to bring surprises to fundamental physics, from their existence to the phenomenon of neutrino oscillation, which implies their nonzero masses. Their exact masses, among the most curious unknowns beyond the Standard Model of particle physics, can soon be probed by the joint analysis of ongoing and upcoming cosmological surveys including Rubin LSST, Euclid, Roman, DESI, PFS, Simons Observatory, CMB-S4, and LiteBRID. In this talk, I will discuss ongoing works studying the effects of massive neutrinos and will draw a roadmap towards discovering the neutrino mass over the next decade.
Bio:
Jia Liu (https://liuxx479.github.io/) is a computational and observational cosmologist. Liu is an associate professor at Kavli IPMU in the University of Tokyo and the director of the recently established Center for Data-Driven Discovery (CD3) at Kavli IPMU. Liu received her PhD from Columbia University in 2016, was an NSF postdoctoral fellow at Princeton (2016-2019) and a BCCP postdoctoral fellow at UC Berkeley (2019-2021).
2024-02-29 Thu 14:20~15:20 R1203
Seamus Clarke ASIAA
*Seminar* Filaments in a multi-scale framework of star formation
Filaments in a multi-scale framework of star formation
Star formation is a process covering orders of magnitude in spatial and density scales, manifesting as a hierarchy of interacting structures. This necessitates that any complete study of this process must be multi-scale by nature. In this talk I will present my work showcasing the key role that filaments play across spatial scales and how they shape star formation, from >10 pc molecular clouds down to 100 AU protostellar disks. Using a combination of numerical hydrodynamical simulations with molecular line and dust continuum observations, I will focus on addressing a number of open questions surrounding filaments in this multi-scale framework: How do filaments fragment into cores/clumps? How does feedback interact with filaments? How are filaments shaped by their environment? I will conclude by introducing the new ASIAA-SMA key project STREAMS, which will homogeneously calculate the turbulent, magnetic and gravitational energies across multiple scales for 23 massive, star-forming clumps. With its combination of multiple datasets and large sample size, STREAMS will answer the many key, open questions about multi-scale energetics and its link to fragmentation, and high-mass star and cluster formation.
2024-03-05 Tue 14:20~15:20 R1203
Tomomi Sunayama University of Arizona
*Seminar* Precision cosmology with galaxies and galaxy clusters - projects and prospects with ongoing and future galaxy surveys
Precision cosmology with galaxies and galaxy clusters - projects and prospects with ongoing and future galaxy surveys
Over the next decade, large galaxy surveys will map billions of galaxies and probe cosmic structure with high statistical precision. Their ultimate goal is to develop a comprehensive model that describes the Universe from end to end. In this talk, I will introduce two of the most powerful cosmological probes: galaxy clusters and galaxy clustering. These probes offer insights into the growth of cosmic structures spanning back up to 11 billion years. By harnessing ongoing and forthcoming galaxy surveys such as the Dark Energy Spectroscopic Instrument (DESI), the Rubin Observatory's Legacy Survey of Space and Time (LSST), Subaru Prime Focus Spectrograph (PFS), and the Roman Space Telescope, we can measure the growth of structure with unprecedented precision. I will discuss the opportunities and challenges inherent in these galaxy surveys.
2024-03-06 Wed 14:20~15:20 R1203
Liton Majumdar NISER
*Colloquium* Constraining the initial conditions for the formation of extra-solar planets and their atmospheres
Constraining the initial conditions for the formation of extra-solar planets and their atmospheres
Protoplanetary disks serve as the sites where exoplanets are formed. Observations of these sites that give birth to planets reveal a wide range of temperatures, densities, and distribution of various molecules. The Atacama Large Millimeter/submillimeter Array (ALMA) has ushered in a new era in the study of protoplanetary disks, enabling us to explore the physics and chemistry of the outer regions of these disks. With the arrival of the James Webb Space Telescope (JWST), we can now delve much deeper into the inner regions of the disks and also investigate icy volatiles in colder regions. The combined contributions of these two instruments can provide us with greater clarity on the formation of exoplanets and the chemical inventory they inherit from protoplanetary disks. Modeling protoplanetary disks can bridge the gap between our theoretical understanding of exoplanet formation and its connection to atmospheres. Here, we introduce PEGASIS (Protoplanetary Disk and Envelope model for Emissions from GAS and Ice Absorption Simulations), a physicochemical model capable of simulating dust, cold gases, hot gases, and ices in both disks and envelopes.
2024-03-11 Mon 14:20~15:20 R1203
Maciek Wielgus Max Planck Institute for Radio Astronomy
*Seminar* Radio-bright future of studying black holes
Radio-bright future of studying black holes
I will discuss the exciting perspectives related to the near future observations of supermassive black holes at mm/sub-mm wavelengths. Event Horizon Telescope (EHT) is delivering images of subsequent AGN sources, while continuously expanding its capabilities, adding new facilities such as the Greenland Telescope, and testing observations at 345 GHz frequency. These observations correspond to the most central part of AGN sources we were ever able to resolve, opening tantalizing possibilities to study the region of jet formation, collimation, and acceleration and advancing our understanding of the physics of these extreme systems. Some fundamental questions to answer are related to the role of magnetic fields and general relativistic effects around a spinning black hole, location of the jet acceleration zone and its relation to the high energy emission. There is a lot to learn from observations of individual sources such as M87, Centaurus A, 3C 84, or 3C 279, but it is also extremely interesting to study a population of sources imaged at mm wavelength for the first time. In particular, our Galactic Center black hole Sagittarius A* is an uniquely interesting mm/sub-mm source, in which horizon-scale dynamics of a low accretion rate system can be studied. This is very exciting in the context of the source flaring, which we are trying to understand in a theoretical framework of the quasiperiodic flux eruptions expected for magnetically dominated accretion systems. Near future time domain analysis of a collection of mm/sub-mm light curves of Sagittarius A*, along with new coordinated multiwavelength observations, and perhaps even resolved (both in space and in time) observations of the EHT will necessarily shed light on the physical mechanism behind flares and high energy emission, as well as on the importance of magnetic fields in the systems similar to Sagittarius A*.
2024-03-12 Tue 14:20~15:20 R1203
Michael H. Wong UC Berkeley
*Seminar* 10 Years of Annual Hubble Space Telescope Imaging of the Giant Planets
10 Years of Annual Hubble Space Telescope Imaging of the Giant Planets
The Outer Planet Atmospheres Legacy (OPAL) program with Hubble was started in 2014 with the goal of studying time-domain phenomena in Jupiter, Uranus, and Neptune, with Saturn added in 2018 once the Cassini spacecraft was de-orbited. Once a year, the OPAL program images each of our four outer planets, producing pairs of global maps in multiple filters, which are made available at the MAST archive. The OPAL team (Simon, Wong, and Orton) have used the data to discover new dark spots on Neptune, discover a UV-dark oval in Jupiter's southern polar haze cap, measure changes in Jupiter's Great Red Spot over time, detect fine-scale waves, chronicle shifts in haze and cloud layers on all four planets, measure jet streams, and study the structure and evolution of convective storms. The data have also provided a valuable resource enhancing the science return from the Juno and New Horizons spacecraft missions, also supplementing observations from a growing list of observatories including JWST, Kepler, Spitzer, VLA, Keck, ALMA, IRTF, VLT, and Gemini.
2024-03-13 Wed 14:20~15:20 R1203
Jenny Wagner Bahamas Advanced Study Institute & Conferences
*Colloquium* Lensing of '69 -- Free gravitational lensing from its heuristic models
Lensing of '69 -- Free gravitational lensing from its heuristic models
Strong gravitational lenses are massive cosmic objects, like galaxies or galaxy clusters, which can map an extended background source, like a galaxy, into several highly distorted and magnified images. Analysing the properties of those images yields important information about the distribution of the deflecting mass and the background source. Common approaches to reconstruct the source or the deflecting mass distribution model the global properties of the source and the lens. They obtain a consistent description of the entire configuration by refining the model until it matches the observation to a predefined precision.
Here, I introduce a new approach to infer local properties of the gravitational lens and to reconstruct the source only using the properties of the multiple images without assuming a lens or a source model. The approach can be applied to galaxy or galaxy-cluster lenses in the same way and yields the maximum information all lens models agree upon. Showcasing two example lenses, I highlight
1) how to obtain a smoothness scale for dark matter with it from only three multiple images in a newly discovered cluster and
2) how to identify and resolve limits of lens models that may lead to highly unrealistic dark matter properties.
Since data is still sparse at the moment but of increasing level of detail, a model selection to find an appropriate mass density profile is also needed to reduce the increasing amount of computing time when fitting a detailed lens model to the data. Most models are currently based on heuristical fitting functions inferred from simulations. Hence, they lack an explanation for their suitability based on fundamental physical principles. To overcome this issue, I will show how the most common mass density profiles, in particular the famous Navarro-Frenk-White profile found in many simulations, can be derived from symmetry arguments and conservation laws.
References:
- Lens method overview: https://arxiv.org/abs/1906.05285
- Examples: https://arxiv.org/abs/2207.01630 and https://arxiv.org/abs/2306.11779
- Derivation of power-law models: https://arxiv.org/abs/2002.00960
2024-03-19 Tue 14:20~15:20 R104, CCMS-New Phys. building
Anne Dutrey Laboratoire d'Astrophysique de Bordeaux
*ASIAA/NTU Joint Colloquium* From protoplanetary Disks to Planet Formation
From protoplanetary Disks to Planet Formation
Understanding planet formation is a major challenge in modern astrophysics. Planets form in protoplanetary disks orbiting around young stars. These disks are gas and dust residuals inherited from the parent clouds which form stars. It is only recently, with the advent of large mm/submm arrays such as ALMA (Atacama Large Millimeter Array, Chile) and its precursors, in particular the IRAM (Institute of Radio Astronomy Millimetric) array (France), that this field has slowly emerged in the early nineties. In this talk, I will present how our understanding on planet formation has evolved in the last 30 years. For this purpose, after an introduction describing the context, I will focus on the observations and analyses of two emblematic objects: the young low-mass triple system GG Tauri and the young single HAe (2.4 Msun) star AB Auriga. Starting from unresolved images of their protoplanetary disks 30 years ago, I will show how we are now beginning to unveil their nascent planetary systems.
2024-03-20 Wed 14:20~15:20 R1203
Kotaro Kohno University of Tokyo
*Colloquium* ALMA and JWST observations of emission-line galaxies in the early Universe
ALMA and JWST observations of emission-line galaxies in the early Universe
I will present recent observational studies of emission-line galaxies using ALMA and JWST. First, I will discuss the physical and chemical properties of a highly magnified (up to μ~160) and intrinsically faint (sub-L*) galaxy at z = 6.072, known as Cosmic Grapes, located behind the massive cluster RXC J0600-2007. This unique source has been uncovered as a bright 1-mm-wave line emitter by the ALMA Lensing Cluster Survey (ALCS) and subsequent investment of approximately 160 hours of observing time with ALMA, JWST, and MUSE/VLT reveals its highly clumpy nature. I will also demonstrate how the joint analysis of emission lines by ALMA and JWST provides constraints on fundamental parameters, such as electron density, in a metal-poor, low-mass galaxy at z = 8.496, situated behind the lensing cluster SMACS 0723.3-7327. A [OIII]5007 emission line selected galaxy at z = 8.343 behind the lensing cluster MACS J0416-2403, a part of JWST cycle 2 program MAGNIF, will also be reported. A serendipitously uncovered millimeter-wave emission line galaxy reveals the presence of a submillimeter-galaxy-like, dust-enshrouded extreme starburst event hosted by an isolated yet gas-rich grand-design barred spiral galaxy at z = 2.467. Discovery of a CO-bright (i.e., gas-rich) quiescent galaxy at z = 1.146 will also be discussed. Lastly, based on these studies, I will discuss how next-generation submillimeter-wave telescopes, like the LST/AtLAST, equipped with a large-format imaging spectrograph, will revolutionize our understanding of galaxy evolution in the early universe.
2024-03-22 Fri 11:00~13:00 R1412
Susana Lizano UNAM, Morelia
*Theory Seminar* Dust in Transition Protoplanetary Disks
Dust in Transition Protoplanetary Disks
I will discuss transition protoplanetary disks observed by ALMA which
have a large inner dust cavity. They are believed to be in the process
of planet formation although other central clearing mechanisms are
possible. Several of these disks show asymmetric emission that has been
associated with vortices where the dust can be trapped and grow to form
planetesimals. I will discuss the analysis of the dust properties in the
asymmetric transition disks HD142527 and work needed to further
elucidate the properties of this dust trap.
2024-03-27 Wed 11:00~13:00 R1203
James Stone Institute for Advanced Study
*Theory Seminar* Modeling Luminous Accretion Flows Around Black Holes
Modeling Luminous Accretion Flows Around Black Holes
New general relativistic MHD models of black hole accretion flows in luminous systems (such as quasars and X-ray binaries) that include full radiation transport will be described. These models are designed to study the steady-state structure of the accretion disk near the horizon, and the effect of radiation on the launching of relativistic jets from spinning black holes. Moreover, they enable not only the interpretation of the spectra and variability of these sources, but also predictions about the rate of growth of black holes in the early universe, and measurement of the energy and momentum feedback into the surrounding medium, a process likely to be important in galaxy formation. These calculations use a new version of the Athena++ adaptive mesh refinement code based on the Kokkos library that runs on both CPUs and GPUs. A brief description of this new code, as well as other applications and extensions underway, will also be given.
2024-03-27 Wed 14:20~15:20 R1203
Anders Johansen University of Copenhagen
*Colloquium* Rapid accretion of rocky planets and the outgassing of their first atmospheres
Rapid accretion of rocky planets and the outgassing of their first atmospheres
Terrestrial planets have traditionally been thought to form by collisions between protoplanets taking place mostly after the dissipation of the protoplanetary disc, on time-scales of 30-100 million years. I present here a new model where terrestrial planets grow instead by accreting small pebbles in the protoplanetary disc within 3-5 million years. I discuss how the immense pebble accretion heat leads to extensive melting of the growing planets and to the emergence of deep magma oceans. Volatiles such as water, carbon and nitrogen are accreted with the pebbles and partitioned between atmosphere, magma ocean and core. The end of the accretion phase leads to rapid crystallisation of the magma ocean and outgassing of the first atmosphere. I will finally discuss how the atmospheric composition of young planets is key to understanding the origin of life.
*Seminar* ULTIMATE-Subaru and SUPER-IRNET: toward the bright future of the
Subaru Telescope
ULTIMATE-Subaru and SUPER-IRNET: toward the bright future of the
Subaru Telescope
ULTIMATE-Subaru is a next large instrumentation program at Subaru, to develop a wide-field (20-arcmin in diameter) ground-layer adaptive optics (GLAO) system and a wide-field NIR imager (WFI) on Subaru, to strengthen the capability of Subaru Telescope in NIR. ULTIMATE will deliver an improved image quality of FWHM~0.2-arcsec (at K-band) in moderate conditions of Maunakea over the full 20-arcmin FoV. While HSC/PFS are the leading instruments for dark nights, ULTIMATE will be a primary facility instrument for bright nights of Subaru in late 2020s and beyond. In this series of seminar talks, we will introduce science cases of ULTIMATE for (1) galaxy and structure formation, (2) time domain astronomy, (3) Galactic Center observations - for all of which the new capabilities of deep, sharp, wide-field IR observations are critical. Taking this opportunity, we will also introduce the "SUPER-IRNET" program, to promote everyone in the community in Taiwan to join this activity. ULTIMATE-Subaru is a next large instrumentation program at Subaru, to develop a wide-field (20-arcmin in diameter) ground-layer adaptive optics (GLAO) system and a wide-field NIR imager (WFI) on Subaru, to strengthen the capability of Subaru Telescope in NIR. ULTIMATE will deliver an improved image quality of FWHM~0.2-arcsec (at K-band) in moderate conditions of Maunakea over the full 20-arcmin FoV. While HSC/PFS are the leading instruments for dark nights, ULTIMATE will be a primary facility instrument for bright nights of Subaru in late 2020s and beyond. In this series of seminar talks, we will introduce science cases of ULTIMATE for (1) galaxy and structure formation, (2) time domain astronomy, (3) Galactic Center observations - for all of which the new capabilities of deep, sharp, wide-field IR observations are critical. Taking this opportunity, we will also introduce the "SUPER-IRNET" program, to promote everyone in the community in Taiwan to join this activity.
2024-04-03 Wed 14:20~15:20 R1203
Emmanuel Schaan SLAC
*Colloquium* Backlighting the large-scale structure with the cosmic microwave background
Backlighting the large-scale structure with the cosmic microwave background
Upcoming large-scale structure (LSS) and cosmic microwave background (CMB) experiments offer a unique opportunity to turn the Universe into a particle physics laboratory and determine the nature of dark matter, dark energy, and the masses of the neutrinos. I will present innovative methods to jointly analyze these datasets and unleash their full constraining power. My group's research explores two powerful ways of using the CMB as a backlight for the LSS: revealing the invisible dark matter (gravitational lensing) and baryons (Sunyaev-Zel'dovich and patchy screening effects) via their shadows on the CMB. These methods will yield percent-precision maps of the dark and baryonic matter on cosmic scales, from combinations of CMB experiments like the Atacama Cosmology Telescope, Simons Observatory and CMB-S4 with LSS experiments like the Dark Energy Spectroscopic Instrument and the Rubin Observatory. These will not only shed light on dark matter, dark energy and the neutrinos, but they will also constrain models of inflation and transform our understanding or galaxy formation.
2024-04-16 Tue 14:20~15:20 R104, CCMS-New Phys. building
David Schlegel Lawrence Berkeley National Laboratory
*ASIAA/NTU Joint Colloquium* Massive Redshift Surveys and First Results from the Dark Energy Spectroscopic Instrument (DESI)
Massive Redshift Surveys and First Results from the Dark Energy Spectroscopic Instrument (DESI)
The current generation of redshift surveys will provide three-dimensional maps of the Universe with tens of millions of galaxies spanning much of the observable universe. These maps explore physics beyond the standard model, including the physics of dark energy and early universe inflation. I will present new measurements of cosmic expansion and dark energy from the first year of the Dark Energy Spectroscopic Instrument (DESI). DESI is mapping the sky with a 5000-fiber robotic focal plane and 10 optical spectrographs. I will describe the design of the instrument, the survey, and the analysis of the first 5 million galaxies and quasars.
2024-04-17 Wed 14:20~15:20 R1203
David Schlegel LBNL
*Colloquium* First Results from DESI and Future Spectroscopic Surveys
First Results from DESI and Future Spectroscopic Surveys
The Dark Energy Sepctroscopic Instrument (DESI) is mapping 40 million galaxies and quasars to precisely measure the expansion history of the universe. I will present results from the DESI Year 1 data. I will describe the science goals and survey design for the second-generation survey of the Dark Eenergy Spectroscopic Instrument (DESI-2) and the successor Spec-S5. These surveys are designed to improve constraints on dark energy and to probe the inflationary epoch. High-redshift (z>2) galaxies will be selected using a combination of broad-band and medium-band imaging. The more ambitious scope of Spec-S5 relies upon significant upgrades to the telescopes, fiber robots and spectrographs.
2024-04-18 Thu 14:20~15:20 R1203
Toshifumi Futamase Tohoku University
*Seminar* Gravitational Flexion Measurement in Weak Lensing and JWST Applications
Gravitational Flexion Measurement in Weak Lensing and JWST Applications
High-precision data obtained by new-generation observational
instruments such as JWST and EUCLID are expected to bring new
developments to dark energy research. As these datasets surpass
conventional data both in quantity and quality, there arises a need
for more accurate analytical methods. Weak gravitational lensing
stands out as a valuable tool for probing dark matter and dark energy.
Traditionally, gravitational shear, a combination of the second
derivative of the lens potential, has been measured to reconstruct
mass distribution. However high-quality space imaging data are
expected to contain more detailed information of the lensing
potential. We have developed a new method to measure the gravitational
flexion, which corresponds to certain combinations of the third
derivatives of the lens potential. Measuring flexion enables a more
accurate mass reconstruction. In this talk, I will introduce our
method of measuring flexion and present the results of flexion
measurement for the JWST cluster SMACS0723.3-7327.
2024-04-24 Wed 14:20~15:20 R1203
Salvatore Orlando INAF
*Colloquium* Supernova Remnants as Probes of the Life and Death of Massive Stars
Supernova Remnants as Probes of the Life and Death of Massive Stars
The remnants of core-collapse supernovae (SNe) exhibit intricate morphologies and a highly non-uniform distribution of stellar debris. In the case of young remnants (less than 5000 years old), their properties encode valuable insights into the inner processes of the SN engine, including nucleosynthetic yields and large-scale asymmetries originating from the early stages of the explosion. Additional characteristics of the remnants can reflect the nature of the progenitor stars and the interactions between the remnants and the circumstellar medium (CSM), shaped by the progenitor's mass-loss history. Hence, investigating the connection between young SNRs, parent SNe, and progenitor massive stars can be of paramount importance to delve into the physics of SN engines, and to investigate the final stages of massive star evolution and the elusive mechanisms governing their mass loss. In this talk, I will review recent advances in modeling young to middle-aged SNRs, focusing on investigations aimed at linking the observed physical and chemical properties of SNRs to their progenitor stars and SN explosions, thus telling us about life and death of massive stars.
2024-04-26 Fri 12:00~13:20 R1412
Maurice van Putten Sejong University, Korea
*Theory Seminar* Hubble Expansion Beyond ΛCDM in Big Bang Quantum Cosmology
2024-05-14 Tue 14:20~15:20 R1203
Shang-Min Tsai UC Riverside
*Seminar* A Comprehensive Framework for Modeling Photochemistry, Climate, and
Habitability
A Comprehensive Framework for Modeling Photochemistry, Climate, and
Habitability
Exoplanet science has rapidly progressed, not only we have discovered
more than 5000 planets since the first discovery in the 1990s, the
field is transitioning from the stage of detection to atmospheric
characterization. The diversity of exoplanets broadens our
understanding of planetary science and provides a profound perspective
on the evolution of our world. In this talk, I will give an overview
of exoplanet characterization methods and the fundamental processes
governing atmospheric composition. I will highlight recent JWST
findings, including the first detection of photochemistry in an
exoplanet atmosphere and its implications for understanding planet
formation in tandem with disk observations and simulations. I will
address the necessity of moving beyond 1D modeling, to account for
global and temporal properties. By employing a 2D--3D modeling
framework, I reveal distinct spectral features and limb asymmetries
relevant to transit and phase-curve observations. I will discuss the
puzzles surrounding the most common class of planets, known as
sub-Neptunes, which curiously find no analogues in our Solar System. I
will demonstrate how studying their atmospheres can help break the
internal structure degeneracies. Lastly, did JWST detect signs of life
on the sub-Neptune exoplanet K2-18b? I will share our recent insights
into probing microbial life on oceanic sub-Neptune exoplanets. In
closing, I will present my vision for collaborations with the
multidisciplinary expertise at ASIAA.
2024-05-15 Wed 14:20~15:20 R1203
Janet Chen NCU
*Colloquium* Transient Zoo from ePESSTO+
Transient Zoo from ePESSTO+
The current generation of wide-field sky surveys and efficient spectroscopic follow-up observations have led to unexpected discoveries of rare and exotic phenomena among stellar transients. Since 2019, I have co-led the advanced Public ESO Spectroscopic Survey of Transient Objects (ePESSTO+) programme, a collaborative effort involving over 300 experts and early career researchers in supernovae, gamma-ray bursts, and nuclear transients. Our programme contributes crucial data on gravitational wave counterparts, superluminous supernovae, fast-evolving and gap transients, and tidal disruption events through observations with the ESO 3.58-m New Technology Telescope. These efforts substantially expand our observational scope, exploring transient diversities, and enhancing our cosmic understanding. In this talk, I will provide an overview of the current state of optical follow-up of transients and focus on the scientific outcomes from ePESSTO+. Additionally, I will introduce my newly established GREAT lab and discuss our ongoing projects with Lulin Observatory.
2024-05-22 Wed 14:20~15:20 R1203
Harish Vedantham ASTRON
*Colloquium* Radio flashes from plasma storms around exoplanets
Radio flashes from plasma storms around exoplanets
Low frequency (< few hundred MHz) radio observations uniquely probe several processes that determine the habitability of exoplanets such as coronal mass ejections and exoplanet magnetic fields. Radio observations of such phenomena in the solar system are commonplace. I will argue that the extrasolar frontier is now also within reach thanks to powerful new low-frequency telescopes such as LOFAR. I will describe an observational program using LOFAR to systematically survey the low-frequency radio sky for stellar, brown dwarf and exoplanetary emissions with unprecedented sensitivities. I will present some early successes of this campaign including (a) the discovery of evidence for magnetic interaction between a star and its planet (b) the discovery of a cold brown dwarf directly in the radio band using its magnetospheric emissions and (c) solar-type radio bursts on nearby stars possibly associated with coronal mass ejections. I will end with an outlook for harnessing radio astronomy’s unique diagnostic capabilities to advance stellar and exoplanet science.
2024-05-29 Wed 14:20~15:20 R1203
Stephen Appleby APCTP
*Colloquium* Cosmology from the topology of Large Scale Structure
Cosmology from the topology of Large Scale Structure
The distribution of galaxies in the low redshift Universe provides information on the initial conditions, energy content and evolution of the Universe from its almost Gaussian primordial state to the highly non-linear cosmic web that we observe today. In this talk I will introduce a class of statistics that are capable of extracting both Gaussian and non-Gaussian information from the matter distribution. The so-called Minkowski Functionals and their rank-2 tensorial generalisation are a class of topological descriptors of a field which can be used to measure cosmological parameters, test the degree of non-Gaussianity as a function of scale and also provides a mechanism to test statistical isotropy. I will describe these statistics, explain how we extract them from galaxy catalogs and elucidate what they
can tell us about the properties of the Universe.
2024-05-30 Thu 14:00~15:00 R1203
Chao-Chin Yang Department of Physics and Astronomy The University of Alabama, U.S.A.
*Seminar* From pebbles to planets: planetesimal formation and pebble accretion
From pebbles to planets: planetesimal formation and pebble accretion
From pebbles to planets: planetesimal formation and pebble accretion
Abstract: Even though thousands of extrasolar planetary systems have been detected, a comprehensive picture of how planets are formed from their natal protoplanetary disks remains to be drawn. I will review our current understanding of the dust-gas dynamics in protoplanetary disks and its consequences on the formation of planets via the core accretion scenario. Specifically, I will examine how and under what conditions cm-/mm-sized dust pebbles can actively concentrate themselves to high density for km-scale planetesimals to form, the initial mass function of planetesimals, and how pebble accretion assists planet formation, along with some supporting observational evidence.
2024-06-18 Tue 14:20~15:20 R1203
Keiichi Maeda Kyoto U.
*Seminar* Insights into the final evolution of massive stars: studying circumstellar environments around supernovae
Insights into the final evolution of massive stars: studying circumstellar environments around supernovae
It has recently recognized that supernovae showing signatures of strong interaction with the circumstellar media (CSM) are very heterogeneous, with various observational characteristics in the light curve and spectral evolutions. It must reflect diverse natures in the CSM compositions (hydrogen-rich and -free) and distribution (corresponding either to steady-state mass loss or change in the mass-loss rate), ultimately connected to much more diverse stellar evolutionally channels than previously thought. I will provide a biased review on the "interacting" SN populations, covering so-called type IIn, Ibn, Icn, and Ic-CSM supernovae, through optical and radio observations.
2024-06-19 Wed 14:20~15:20 R1203
Jenny Greene Princeton
*Colloquium* Little Red Dots in JWST
Little Red Dots in JWST
I will discuss a fascinating new object we have discovered with
JWST/NIRCam imaging and grism spectroscopy at z>4. With compact sizes
(<100 pc), red rest-frame optical colors, and ubiquitous broad Balmer
lines, these objects have many hallmarks of accreting supermassive
black holes. However, they have x100 the number density of UV-selected
quasars, and appear to have very massive black holes compared to their
hosts. Also, unlike most known accreting black holes, they show no
signs of hot dust or X-ray emission. I discuss our ongoing efforts to
understand the nature of the Little Red Dots, and what they may teach
us about the coevolution of black holes and galaxies.
2024-06-20 Thu 10:30~12:00 R1203
Keiichi Maeda, Janet Chen, Yen-Chen Pan, Ken Chen Kyoto U., NCU, ASIAA
*Seminar* Kyoto-NCU-ASIAA supernovae discussion
2024-06-20 Thu 14:00~15:00 R1203
Tien-Hao Hsieh MPE
*Seminar* PRODIGE - Envelope to Disk with NOEMA - A streamer feeding the SVS13A protobinary and the complexity of the COM emission
PRODIGE - Envelope to Disk with NOEMA - A streamer feeding the SVS13A protobinary and the complexity of the COM emission
We conducted NOrthern Extended Millimeter Array (NOEMA) observations toward the Class 0/I protobinary system SVS13A as part of the PROtostars & DIsks: Global Evolution (PRODIGE) program. SVS13A is composed of two protostars VLA4A and VLA4B with a separation of ∼90 au, for which VLA4A is undergoing an accretion burst that enriches the chemistry of the surrounding gas. This gives us an excellent opportunity to probe the chemical and physical conditions as well as the accretion process. We study the kinematic structures of SVS13A via DCN (3–2) line, and the C18O (2–1) line at about hundred au scale. By combining our observations with previous ALMA high-angular-resolution observations, we find that the binary system (or VLA4A) might be fed by an infalling streamer from envelope scales (∼700 au). If this is the case, this streamer contributes to the accretion of material onto the system with a rate of at least 1.4 × 10−6 Msun yr−1. We further analyzed 12- 11 lines of CH CN and CH 13CN and six selected O-bearing COMs: CH3OH, aGg’-(CH2OH)2, C2H5OH, CH2(OH)CHO, CH3CHO, and CH3OCHO. Although the COM emission is not spatially resolved, we constrained the source sizes to ~0.3 − 0.4 arcsec (90−120 au) by conducting uv-domain Gaussian fitting. Interestingly, the high-spectral-resolution data reveal complex line profiles with multiple peaks; although the line emission is likely dominated by the secondary,VLA4A,at Vlsr = 7.36 kms−1,the numbers of peaks (∼2−5), the velocities, and the linewidths of these six O-bearing COMs are different. The local thermodynamic equilibrium (LTE) fitting unveils differences in excitation temperatures and emitting areas among these COMs. We further conducted multiple-velocity-component LTE fitting to decompose the line emission into different kinematic components. As a result, the emission of these COMs is decomposed into up to six velocity components from the LTE modeling. The physical conditions (temperature, column density, and source size) of these components from each COM are obtained. We conclude that accretion shocks induced by the large-scale infalling streamer likely exist and contribute to the complexity of the COM emission. This underlines the importance of high-spectral-resolution data when analyzing COM emission in protostars and deriving relative COM abundances.
2024-06-26 Wed 14:20~15:20 R1203
Chrystian Luciano Pereira Observatorio Nacional
*Colloquium* Rings Around Small Solar System Objects: Discoveries and Detection Limits
Rings Around Small Solar System Objects: Discoveries and Detection Limits
Until 2013, ring systems were known only around the four giant planets. This perspective shifted when a stellar occultation revealed the presence of two rings around the minor planet (10199) Chariklo (Braga-Ribas et al. 2014), a Centaur object. In January 2017, another occultation revealed the existence of a ring encircling the dwarf planet (136108) Haumea (Ortiz et al. 2017). The third minor body with a confirmed ring system is the big Transneptunian Object (50000) Quaoar. Intriguingly, Quaoar’s ring system is far beyond the classical Roche limit (∼1,780 km). The innermost ring lies about 2,520 km from the Quaoar center (Pereira et al. 2023), and the outermost ring lies about 4,100 km. The latter presents significant longitudinal variations concerning optical depth and width (Morgado et al. 2023). Similarly, observations of flux variations in occultation light curves over two decades of the Centaur (2060) Chiron suggested the presence of material in its surroundings. Published works have interpreted these materials as rings, shells, and jets, but a definitive classification is premature. In this context, stellar occultations by Chiron were conducted in 2018 and 2019 (Braga-Ribas et al. 2023), 2022 (Ortiz et al. 2023), and 2023 to characterize the observed structure, revealing that the material around Chiron presents an evolving structure, which can result from outbursts feeding putative rings. We have also identified objects that presented outbursts and thus could be capable of hosting rings, such as the Centaurs Echeclus (Pereira et al. 2024) and 29P/Schwassmann-Wachmann 1. Stellar occultations by them were observed and used to search for rings or other confined signatures. In cases where detection was not achieved, we obtained upper limits for detecting additional structures. This ongoing work can result in discovering new ring systems, other confined structures, or even small satellites around these small bodies in the solar system. These results and implications will be presented in this talk.
2024-06-28 Fri 12:00~13:30 R1412
Shih-Hsien Yu Institute of Mathematics, Academia Sinica
*Theory Seminar* Heat Equation and Wave Train
Heat Equation and Wave Train
In this talk, we will introduce a way to integrate the heat equation with rough heat conductivity. The solution of heat equation is constructed and one can describe the qualitative and quantitative behavior of the solution. One will also comment the generality of the approach.
2024-07-02 Tue 14:20~15:20 R1203
Eva Lilly Planetary Science Institute
*Colloquium* A Hundred Sleeping Beasts: Dynamical Triggers of Cometary Activity in Centaurs
A Hundred Sleeping Beasts: Dynamical Triggers of Cometary Activity in Centaurs
The Centaur population is comprised of small, likely icy bodies on
dynamically unstable orbits transitioning from the trans-Neptunian
region to the inner Solar system. Centaurs represent an interesting
stage in the dynamical evolution of primordial small bodies scattered
by planetary perturbations from the deep freeze of the TNO reservoir
where they have been stored for billions of years. They enter the
giant planet region as largely primordial objects and carry
information about the composition of their parent populations to our
doorstep.
Here we present a thermodynamical study of Centaurs, complemented with
a visual survey conducted with the Gemini telescopes aimed to search
for cometary activity and to identify possible activity triggers in
the members of the Centaur population. Through the duration of our
survey only one Centaur in our sample - C/2014 OG392 (PANSTARRS)
appeared active. Both results from our survey and the thermodynamical
modeling indicate that the orbital history plays a critical role in
the thermal processing of Centaurs and their potential for onset of
cometary activity. Our in-depth analysis of orbital evolution
revealed that within the past several hundred years every known active
Centaur underwent a rapid orbital change leading to significant
decrease in semi-major axis we call an `a-jump’, which led to a major
increase in the average-per orbit insolation. Such a-jumps typically
occur after close encounters with Jupiter or Saturn and are not
present in recent orbital histories of inactive Centaurs. A single
Centaur can typically undergo several a-jumps throughout its lifetime
leading to the depletion of volatiles and thermal processing of the
nucleus. Our results also show that most of the targets of our survey
dynamically evolved interior to ~14 AU over the past 1000 years, which
is a region where several processes could trigger phase transitions of
volatiles leading to outgassing. However, the apparent inactivity of
inspected Centaurs, including objects with perihelia near Jupiter,
indicates they are either dormant or volatile-depleted, supported by
the fact that apart from C/2014 OG392 their orbital history doesn’t
show significant a-jumps typical for active Centaurs, adding further
evidence that the orbital evolution of Centaurs is the key to
understanding the cometary activity in members of the population.
2024-07-03 Wed 14:20~15:20 R1203
Ruobing Dong University of Victoria
*Colloquium* Observational Planet Formation
Observational Planet Formation
It is hard to see a plane cruising at 10 km, as the plane is tiny and faint in the sky. But, if we can see the contrail trailing behind the plane, we know where the plane is. Now, astronomers are applying the same principle to study how planets form by detecting and characterizing the structures that baby planets produce in their birth cradles — protoplanetary disks. This is a new field largely driven by discoveries made by some of the largest and most advanced telescopes ever built. I will introduce the current status of the field and highlight some of the latest developments as well as unsolved problems.
2024-07-10 Wed 14:20~15:20 R1203
Naomi Hirano ASIAA
*Colloquium* Panchromatic study of the extremely dense prestellar core on the verge of first core formation
Panchromatic study of the extremely dense prestellar core on the verge of first core formation
The prestellar core G208.68-19.02-N2 (G208-N2) in the Orion Molecular Cloud 3 (OMC3) has been studied with the ALMA in Band 4 (2 mm), 6 (1.3 mm and 1.1 mm), 7 (0.83 mm, ACA), 8 (0.75 mm), 9 (0.45 mm), and 10 (0.35 mm). The dust continuum emission revealed a filamentary structure with a length of ~5000 au and an average H2 volume density of ~6 x 10^7 cm^-3. At the tip of this filamentary structure, there is a compact "nucleus" with a radius of ~150--200 au and a mass of ~0.1 M_sun. The nucleus does not have a counterpart at wavelength shorter than 0.35 mm. In addition, there is no sign of CO outflow localized to this nucleus. The spatial distributions of the molecular lines reveal significant chemical segregation in G208-N2. Although N2D+ and H2D+ trace the filamentary structure, they do not exhibit pronounced peak toward the nucleus. Instead, the emission peaks of DCO+, H2CO and CH3OH appear in the vicinity the nucleus. In this talk, we will discuss the possible evolutionary stage, i.e. prestellar of first hydrostatic core, of this enigmatic object.
2024-07-26 Fri 12:00~13:30 R1412
Tai-Peng Tsai University of British Columbia
*Theory Seminar* Boundary gradient estimates and second derivative blow-up for
Stokes equations with Navier boundary condition
Boundary gradient estimates and second derivative blow-up for
Stokes equations with Navier boundary condition
This research is motivated by the boundary effect on the regularity properties of incompressible fluids, noting the recent numerical evidence of boundary singularity of inviscid fluids. For the Stokes system (for linearized viscous fluids), it is well-known that one can improve spatial regularity in the interior, but not near the boundary if it is coupled with the no-slip boundary condition (BC). We show that, under the Navier BC with either infinite or finite slip length, we have Caccioppoli type gradient estimates near a flat boundary, contrary to the no-slip BC case. However, for every finite slip length and q>1, we construct a finite energy solution of Stokes equations with nonhomogeneous Navier BC in the half space with bounded, compactly supported boundary data, bounded velocity and velocity gradient, but unbounded second derivatives in L^q locally near the boundary. To show this, we first derive the explicit Poisson kernel of Stokes equations in the half space with nonhomogeneous Navier BC for both infinite and finite slip length, and derive its estimates. Moreover, we give an alternative proof of the blow-up using a shear flow example, which solves both Stokes and Navier-Stokes equations, but has no spatial decay. This talk is based on joint work with Hui Chen and Su Liang, arXiv:2306.16480 and arXiv:2406.15995
2024-07-30 Tue 15:00~16:00 R1203
Rema Ahmid Technical University of Denmark
*Seminar* 3D printed antennas for space applications
3D printed antennas for space applications
In the rapidly advancing field of space technology, the integration of 3D printing in the manufacturing of antennas offers innovative solutions to existing challenges. This talk will explore the development and application of 3D printed antennas for space missions, drawing on my personal academic journey and research experiences.
I will begin with a brief introduction of myself, Rema Ahmid, detailing my educational background and the pivotal moments that led me to specialize in space antenna technology and why I have arrived to Taiwan. My journey began during my bachelor's studies at the University of Southern Denmark, where I conducted a project on assessing CubeSats as space-based radio antennas. This project involved the use of 3D printed
feed horns and was under the supervision of Roman Gold.
Following this, I pursued a master's thesis at the Technical University of Denmark (DTU) and currently collaborating with IETR, Rennes, focusing on phased arrays for space applications utilizing 3D geometries and additive manufacturing. This work aimed to enhance antenna performance for GEO satellites through the development and testing of modular array architectures made using selective laser melting (SLM), a cutting-edge
metal additive manufacturing technique. The thesis will contribute to the European Space Agency's MOSAIC project, emphasizing the experimental validation of these advanced antennas.
Throughout the talk, I will elaborate on the technical aspects and findings from both my bachelor's and master's theses, highlighting the benefits and challenges of using 3D printing in antenna fabrication.
2024-07-31 Wed 14:20~15:20 R1203
Hyunbae Park University of Tsukuba
*Colloquium* Lyα Opacity of the Intergalactic Medium during Reionization
Lyα Opacity of the Intergalactic Medium during Reionization
Lya emission/absorption features from galaxies beyond redshift 6 offer crucial insights into the epoch of reionization. Recent observation by JWST have unveiled numerous intriguing cases that challenge our theoretical understanding. In this talk, I present how the complexities of the IGM, as reproduced by the Cosmic Dawn (CoDa) simulation, can explain the diverse Lya features from recent observations and leverage them to constrain various properties of the IGM during the reionization era. Specifically, I will discuss stochasticity of Lya line strength, nature of LAE clusters, the Lya damping-wing, and double-peaked Lya emission from galactic spectrum.
2024-08-07 Wed 14:20~15:20 R1203
Hua-Bai Li Chinese University of Hong Kong
*Colloquium* A Unified Interpretation of Magnetic Field and Turbulence Observations
A Unified Interpretation of Magnetic Field and Turbulence Observations
At the onset of the current century, the prevailing belief among astronomers was that solely super-Alfvenic turbulence could rival gravity in the process of star formation. This perspective gradually evolved during the second decade, as polarized thermal dust emission implied a significant level of organization in magnetic fields (B-fields), signifying dynamically strong B-fields and thus anisotropy in both turbulence and gravitational collapse. On the other hand, the relation between the magnetic field (B) and density (n) deduced from Zeeman measurements, expressed as B~n^2/3 , has been interpreted as isotropic gravitational collapse — a consequence of dynamically weak B-fields. The contradiction between the two B-field tracers remains a major mystery (see, e.g., the latest PPVII review chapter). The logic and data behind the above statement will be discussed, followed by my solution to the mystery, which depends on a turbulence-density relation.
2024-08-12 Mon 14:30~15:30 R1203
Ronaldo Laishram Tohoku University
*Seminar* Cosmic Evolution of Star-Forming Activities and Morphologies of Galaxies with Environment
Cosmic Evolution of Star-Forming Activities and Morphologies of Galaxies with Environment
The distribution of galaxies in the universe is inhomogeneous, representing large-scale structures (LSS) that consist of galaxy clusters, groups, and the filaments that connect them. Understanding how galaxy characteristics are influenced by their environments and how they evolve over cosmic time within LSS is crucial. Utilizing narrow-band selected emitters, we investigate the environmental effects on star formation within large-scale structures. Utilizing a novel double narrow-band technique for some case studies, we also explore star-forming activity and the spatial distribution of Hα and continuum emission at z=0.4, probing the cosmic web. We found that star formation in cluster core galaxies is more centrally concentrated and reduced compared to the field sample. We also explore the morphological features and star formation activities of [OII] emitters in the COSMOS UltraDeep field at z ∼ 1.5 using JWST NIRCam data from the COSMOS-Web survey and Subaru Hyper Suprime-Cam. Furthermore, we report the discovery of large filamentary structures traced by [OII] emitters, surrounding an extremely overdense core with a galaxy number density ∼ 11× higher than the field average. Heightened star-forming activity was observed in dense regions, contrary to z=0.4, suggesting an environmental impact on early galaxy evolution. Additionally, we examine the systemic study redshift evolution of star-forming activities with [OII] emitters and morphology. Future studies will explore into the chemical abundance, gas content, and kinematics to comprehend the underlying processes.
2024-08-14 Wed 14:20~15:20 R1203
Martin Bizzarro StarPlan
*Colloquium* Interstellar ices as carriers of nucleosynthetic anomalies in the early Solar System
Interstellar ices as carriers of nucleosynthetic anomalies in the early Solar System
A key cosmochemical discovery is the existence of a disk gradient in abundance of supernovea (SN) nuclides in planetary material with orbital distance. Volatile-poor inner Solar System bodies record SN depletions whereas water-rich outer Solar System objects show enrichments. As this nucleosynthetic variability can be used to trace the source of disk material that accretes to planets, understanding the mechanism responsible for this spatial variability is a major unresolved impediment. Here, we explore the hypothesis that interstellar ices were an important carrier of SN nuclides by conducting a search for the signature of SN nuclides in various types of chondrite meteorites, including carbonaceous and non-carbonaceous chondrites. Chondrites are known to have accreted variable amounts of ices as indicated by the pervasive aqueous alteration experienced by these meteorites while on their parent bodies. Thus, strategically-designed step leaching experiments using mild acids aimed at exclusively dissolving the labile alteration minerals can be used to determine the isotopic signal of the ice component. We focus on the refractory and immobile element zirconium, which owe its nucleosynthesis to both the s– and r–process. In particular, the neutron-rich 96Zr nuclide is overproduced in the explosive He-burning shells of core-collapse supernovae. Thus, 96Zr enrichments preserved in meteoritic components is a hallmark of a supernova signature. The isotopic compositon of the leachates returns highly anomalous signals characterized by variable and extreme enrichments in the neutron-rich 96Zr nuclide. These results are consistent with the ices being the main carrier of anomalous Zr characterized by large 96Zr excesses. By comparing the Zr isotopic composition of the leaches with that of bulk planetary material, we show that the Solar System’s Zr isotopic variability can be ascribed to admixing of variable amounts of interstellar ices to an ice-free rock endmember. These results have important implications for the origin of the Solar System nucleosynthetic variability, the solar ice/rock ratio and planet formation mechanisms. Finally, our data support models suggesting that a significant fraction of the primary reservoir of volatile-rich ices in the early Solar System was direct inherited from the molecular cloud as opposed to formed in the protoplanetary disk.
2024-08-21 Wed 14:20~15:20 R1203
Chian-Chou Chen ASIAA
*Colloquium* Painting a dusty Universe - what have I done in the past five years
Painting a dusty Universe - what have I done in the past five years
Galaxies are essential building blocks of the Universe, and half of their energy is obscured by dust and reemitted in the infrared and submillimeter. Multi-wavelengths observations are therefore essential for painting a complete picture of galaxy formation and evolution. In the past five years, using cutting-edge facilities such as ALMA, VLT, and the JWST, I have led long-term observational programs that aim to tackle a number of fundamental questions related to cosmology and galaxy formation. In particular, what is the origin of the submillimeter background light? What role does dusty galaxy play in galaxy formation? In this talk, I will present our findings on these questions, and introduce the plan for the next five years, including building a large single dish submillimeter observatory that will bring breakthroughs in many fronts of far-infrared and submillimeter astrophysics.
2024-08-30 Fri 14:00~15:00 R1203
Tom Broadhurst University of the Basque Country
*Seminar* Testing the "Taiwan Wave Dark Matter" with high redshift JWST galaxies "going bananas" and asymmetric microlensing in the Dragon arc
Testing the "Taiwan Wave Dark Matter" with high redshift JWST galaxies "going bananas" and asymmetric microlensing in the Dragon arc
We have discovered that lensed galaxies are continuously twinkling when intersected by the Einstein rings, with over 50 microlensing events found in the Dragon and Jupiter arcs. Intriguingly, this occurs mostly along inner edge of the Einstein ring with a broad asymmetric spread. We show this assymetry requires substructure of "negative mass" that is uniquely explained by "Wave" Dark Matter interference as a Bose Einstein Condensate, whereas CDM substructure predicts the opposite behaviour with microlensing events expected mainly along outer rim of the Einstein ring. We can also discriminate between dark matter models using the "banana" effect now recognised in JWST images of high redshift galaxies, which are typically elongated in shape at z>3, in the CEERS, JADES and PEARLS surveys. Our cosmological hydro simulations show this effect can be explained by both Wave and Warm Dark Matter, where galaxies form from smooth filaments as dark matter, gas and stars rains down to the nodes creating prolate shaped galaxies. This is unlike CDM where galaxies initially form fragmented filaments that frequently merge, predicting rounder shaped oblate spheroids. We outline further definitive predictions for JWST.
2024-09-02 Mon 11:00~12:00 LeCosPa R7S1
Maria Dainotti NAOJ
*Seminar* Cosmology with GRBs, QSOs and SNe-Ia
Cosmology with GRBs, QSOs and SNe-Ia
The Hubble tension refers to a persistent discrepancy between measurements of the Hubble constant obtained from supernovae and the cosmic microwave background. To address this issue, we explore alternative cosmological models and combine various data sources, such as gamma-ray bursts (GRBs), quasars (QSOs), baryon acoustic oscillations, and supernovae.
GRBs are among the most explosive phenomena in the Universe, which have been observed up to redshift 9.4 and thus can be used as cosmological probes. For GRBs, we use a relationship involving three factors, the so-called Dainotti fundamental plane: the peak luminosity, the time at the end of an X-ray plateau, and the X-ray luminosity at that time. For QSOs, we use a relationship between UV and X-ray luminosity. We correct these relationships for any biases using a reliable statistical method. We use two types of likelihoods (ways to infer parameters): traditional Gaussian and a new best-fit method. The new method reduces uncertainties in parameters, especially in the Hubble constant, by up to 35%.
2024-09-04 Wed 14:20~15:20 R1203
Chin-Ping Hu National Changhua University of Education
*Colloquium* Unveiling the Connection between Fast Radio Bursts and Magnetars
Unveiling the Connection between Fast Radio Bursts and Magnetars
Fast Radio Bursts (FRBs) remain one of the most enigmatic astrophysical phenomena of this decade, with their origins still largely unknown despite numerous theoretical models being proposed. Magnetars, neutron stars with extremely high magnetic fields and diverse X-ray emissions, stand out as promising sources of part of FRBs. In this talk, I will focus on observational evidence linking FRBs to magnetars, particularly through our recent observations of the FRB-emitting magnetar SGR 1935+2154. Thanks to high-cadence observations carried out by the NICER and NuSTAR, we observed two spin-up glitches within nine hours during an outburst associated with an intermediate flare, a forest of X-ray bursts, rapid spectral changes, and an FRB. These phenomena suggest that rapid changes in rotational frequency might trigger these energetic events, offering valuable insights and directing future observational strategies.
2024-09-11 Wed 14:20~15:20 R1203
Sherry Suyu Technical University of Munich
*Colloquium* Strongly Lensed Supernovae: Past, Present and Future
Strongly Lensed Supernovae: Past, Present and Future
Strongly lensed supernovae (SNe) are emerging as a new probe of cosmology and SN. The time delays between the multiple images of a lensed SN can be used to determine the Hubble constant (H0) that sets the expansion rate of the Universe. An independent determination of H0 is important to ascertain the possible need of new physics beyond the standard cosmological model, given the tension in current H0 measurements. While strongly lensed SNe are rare, the first lensed SN systems are being discovered in the past few years. I will give an overview of these first discoveries and their cosmological results. Future surveys, particularly the Rubin Observatory Legacy Survey of Space and Time, are expected to yield hundreds of such exciting events. I will highlight a new program aimed to find and study lensed SNe for cosmology and stellar physics.
2024-09-18 Wed 14:20~15:20 R1203
Uyama Taichi California State University Northridge / Astrobiology Center
*Colloquium* Direct Imaging of Exoplanets; from investigation of Jovian planet formation/evolution to future explorations for the Second Earth
Direct Imaging of Exoplanets; from investigation of Jovian planet formation/evolution to future explorations for the Second Earth
Since the first detection of an extrasolar planet (exoplanet), thousands of exoplanets have been reported through a variety of detection techniques. Direct imaging is a unique way of proving the presence of exoplanets, providing useful information for their characterizations. I will discuss how direct imaging tackles challenges of controversial planet formation/evolution theories, by presenting current direct imaging observations of young Jovian planets and protoplanetary disks with adaptive optics observation with ground-based telescopes and cycle-1 JWST programs, including our programs with Subaru, Keck, and JWST. I will also introduce prospects for future direct imaging explorations of terrestrial planets and extraterrestrial lives in the next decades.
2024-09-25 Wed 14:20~15:20 R1203
Chris Reynolds University of Maryland
*Colloquium* Probing the extremes with clusters of galaxies
Probing the extremes with clusters of galaxies
Clusters of galaxies provide a wonderful laboratory for studying extreme physics and astrophysics. In this talk, I will conduct a whirlwind tour of some of these investigations, both theoretical and observational. Firstly, I will show that the cores of relaxed galaxy clusters are one of the best environments to study facets of active galactic nucleus (AGN) feedback. Examining the physics at play in these feedback processes necessitates a hard look at the plasma physics of the hot intracluster medium that permeates the cluster, leading us to new understandings of processes as basic as thermal conduction. Secondly, the galaxies at the centers of relaxed clusters, and the supermassive black holes that they host, are amongst the most massive in the Universe. I will discuss these unusual central cluster AGN and present X-ray based spin measurements of the black hole in one remarkable cluster, CL1821+643, which sheds light on the growth mode of the most massive supermassive black holes. Thirdly, I will discuss the use of galaxy clusters for fundamental physics and, in particular, the extraordinary constraints that they set on certain extensions of the standard model of particle physics (namely axion-like particles). I will end with a brief discussion of the future prospects of these studies with next generation X-ray telescopes, especially the proposed Advanced X-ray Imaging Satellite (AXIS).
2024-09-26 Thu 12:00~13:30 R1412
I-Liang Chern Department of Mathematics, National Taiwan University
*Theory Seminar* Variational Principles in Fluid Mechanics
Variational Principles in Fluid Mechanics
I will give an overview talk on the following topics:
• Lagrange and Euler formulations of fluid mechanics
• Variational formulation of fluid mechanics
• Hamiltonian fluid mechanics, symmetry and invariants
If time is allowed, I can also comment on numerical methods and data-driven numerical simulations.
2024-10-09 Wed 14:20~15:20 R1203
Zhi-Yun Li University of Virginia
*Colloquium* Disk Polarization as a Probe of Grain Properties and Kinematics in Protoplanetary Disks
Disk Polarization as a Probe of Grain Properties and Kinematics in Protoplanetary Disks
Spatially resolved disk continuum polarization at (sub)millimeter and centimeter wavelengths was first detected using the SMA, CARMA, and VLA, and has since been revolutionized by ALMA. Initially, the observed disk polarization was attributed to direct emission from magnetically aligned grains. If confirmed, this would provide the long-sought evidence of magnetic fields expected to play a crucial role in disk dynamics and evolution. However, alternative explanations have emerged, including scattering by large grains and grain alignment with respect to the direction of radiative flux. In this talk, I will first explore in detail the scattering-induced disk polarization, emphasizing the effects of disk inclination relative to the line of sight, optical depth, and the potential of polarization observations to probe grain growth and settling in protoplanetary disks. I will then present evidence supporting the co-existence of direct polarized thermal emission from toroidally aligned prolate (TOP) grains alongside scattering by the same grains. Finally, I will discuss a plausible scenario for the inferred toroidal grain alignment, driven by gas aerodynamic drag on grains in Keplerian motion.
2024-10-11 Fri 14:20~15:20 R1203
Melaine Saillenfest Paris Observatory
*Colloquium* Giant planets and their evolving obliquities
Giant planets and their evolving obliquities
The orbits of Solar System planets -- which are approximatively circular
and coplanar -- are well known signatures of the processes at work
during the early stages of the Solar System history. Other key
signatures are the inclinations of the planets' spin axes, or
"obliquities". In this colloquium, I will review the evolution
mechanisms of planetary obliquities. I will show how recent discoveries
about Saturn's moons modify our understanding of the history of giant
planets. The coupled evolution of moons and planetary spin axes may
generically lead to high-obliquity planets surrounded by a ring -- a
configuration that has been proposed to explain the unusual properties
of several exoplanets.
2024-10-23 Wed 14:20~15:20 R1203
Ryosuke Tominaga Tokyo Institute of Technology
*Colloquium* Dust coagulation through hydrodynamic clumping in protoplanetary disks
Dust coagulation through hydrodynamic clumping in protoplanetary disks
Collisional growth of dust grains is the key step in planet formation, especially in the formation of kilometer-sized objects called planetesimals. Since planetesimals are the building blocks of planets, it is important to understand how and how efficiently planetesimals form. There are several obstacles that limit dust growth, which include fragmentation and dust depletion due to radial drift. Streaming instability has been proposed to bridge the gap to planetesimal formation. According to previous studies, the instability drives dust clumping and create massive clumps from which planetesimals form by gravitational collapse. Although it is promising, the massive clump formation is efficient only if the dust grains are sufficiently large. The required dust sizes are larger than the fragmentation-limited size. Thus, there is still a gap between the initial dust growth and planetesimal formation. To bridge this gap, we examine dust coagulation through moderate-level clumping, which should occur prior to the massive clump formation. In this talk, I will discuss how the clumping promotes dust growth and how this process relaxes the condition for planetesimal formation.
2024-10-24 Thu 14:20~15:20 R1203
Yuya Fukuhara Tokyo Institute of Technology
*Seminar* A self-consistent model for dust settling and the vertical shear instability in protoplanetary disks
A self-consistent model for dust settling and the vertical shear instability in protoplanetary disks
The spatial distribution of dust in protoplanetary disks plays a key role in dust evolution and planetesimal formation. The vertical shear instability (VSI) is a potential mechanism for driving turbulence in the outer disk, affecting dust diffusion and settling. Our study presents a semi-analytic model that determines the vertical dust distribution and VSI-driven turbulence strength in a self-consistent manner. Using an empirical formula for the vertical diffusion coefficient based on recent hydrodynamical simulations, we explore equilibrium dust profiles where turbulent diffusion is balanced by settling. We find that for small grains, a stable equilibrium dust distribution exists, allowing VSI-driven turbulence to be sustained at alpha_z ~10^{-3}, where alpha_z is the dimensionless vertical diffusion coefficient. However, for larger grains, this equilibrium solution vanishes, leading to runaway settling, potentially explaining the highly settled dust rings observed in some disks.
2024-10-30 Wed 14:20~15:20 R1203
Yuki Takei Kyoto U.
*Colloquium* CHIPS: an open-source code for modeling supernovae interacting with a massive circumstellar medium
CHIPS: an open-source code for modeling supernovae interacting with a massive circumstellar medium
Supernovae (SNe) are explosive events that occur at the end of the life of massive stars, exhibiting a variety of features in their spectra, primarily depending on their chemical abundances. Some SNe show narrow emission lines in their spectra, which suggests the presence of a dense, slowly-moving circumstellar medium (CSM) around the progenitor. Recent observations indicate that most progenitors of Type II SNe have a confined CSM, making the study of the CSM associated with massive stars crucial for understanding stellar evolution. Although a detailed mechanism that forms the massive CSM is still uncertain, several scenarios have been proposed, including core neutrino emission, burning instability, and pulsational pair-instability.
In this talk, I will explain how the CSM affects the observed light curve of interaction-powered SNe and how we can extract the density profile of the CSM, which may vary depending on its formation process. Specifically, I will introduce a newly developed open-source code, Complete History of Interaction-Powered Supernovae (CHIPS), which is suited to model a wide variety of transients that arise from interaction with a CSM. Contrary to existing modelings, which mostly attach the CSM by hand, CHIPS self-consistently simulates both the creation of the CSM from mass eruption of massive stars prior to core-collapse, and the subsequent SN light curve.
2024-11-06 Wed 14:00~16:00 1st Floor Auditorium
Gender Equality Film Screening Academia Sinica
*Colloquium* 她有話要說 - She Said
她有話要說 - She Said
The movie "她有話要說" (She Said) is a 2022 drama based on real events that led to the exposure of one of the most significant scandals in Hollywood. The film focuses on two New York Times reporters, Jodi Kantor and Megan Twohey, who were instrumental in uncovering the sexual harassment and assault allegations against film producer Harvey Weinstein.
As the reporters investigate, they encounter numerous challenges, from persuading women to share their traumatic experiences to overcoming the intimidation tactics used to keep the truth hidden. Their persistence ultimately helped expose a pattern of abuse and contributed to the rise of the #MeToo movement, which empowered women worldwide to speak out against sexual misconduct.
The movie emphasizes the importance of investigative journalism and the courage of survivors in seeking justice.
2024-11-07 Thu 12:00~13:30 R1412
Sheng-Der Chao IAM, NTU
*Theory Seminar* Adiabatic Approximation and Breakdown in Theoretical Chemistry: Case Studies
2024-11-13 Wed 14:20~15:20 R1203
Ryosuke Hirai RIKEN
*Colloquium* Supernovae and binary interactions
Supernovae and binary interactions
Massive stars, which are the progenitors of core-collapse supernovae, are known to be primarily born in binary or higher order multiple systems. Therefore, binarity is essential for understanding supernova physics and conversely, the supernova physics are essential for understanding binary evolution. In this talk, I will briefly summarize my past work on the interplay between binary interactions and supernova explosions based on 1-3D hydrodynamical modelling and stellar evolution calculations. Specifically, I will focus on three different topics; ejecta-companion interaction, neutron star-star collisions, neutron star rocket mechanism. For the first part, I will highlight how the collision between supernova ejecta and binary companions can alter the appearance of the star and how that can be used to constrain binary evolution physics by monitoring post-supernova companion photometry. In the second part, I demonstrate how new-born neutron stars can sometimes penetrate the companion envelope and possibly lead to various interesting phenomena like forming hypervelocity stars, pulsar planets, peculiar supernovae and Thorne-Zytkow objects. In the last part I will introduce the neutron star rocket mechanism, that has been proposed in the 1970s, and how that can have significant impacts on binary orbits despite the magnitude being rather small.
2024-11-15 Fri 12:00~13:30 R1412
Scott Tremaine Institute of Advance Study
*Theory Seminar* The dynamics of comets, and modified gravity in the solar system
The dynamics of comets, and modified gravity in the solar system
This talk has two (related) parts:
1. Comets have inspired awe since prehistoric times, but even today there are only a few thousand comets with well-determined orbits. Nevertheless, the analysis of this limited sample yields a compelling "standard model" for the formation, evolution and present distribution of comets. This model implies that the primary source of comets is the Oort cloud, containing over 100 billion comets at 5,000 to 100,000 times the Earth-Sun distance. I will review our current understanding of the history and structure of the Oort cloud.
2. The hypothesis that most of the matter in the universe is in some unknown dark form is fundamental to modern cosmology. A speculative alternative is that our understanding of the law of gravity is incomplete. The most influential theory of this kind is modified Newtonian dynamics (MOND), which postulates a breakdown of Newton's law of gravity below some critical acceleration threshold. We explore the predictions of the simplest version of MOND for the formation and evolution of the Oort cloud, and conclude that this is not the correct description of gravity.
2024-11-20 Wed 14:20~15:20 R1203
Jubee Sohn Seoul National University
*Colloquium* Exploring the universe of galaxy clusters through cosmological simulations and dense spectroscopy
Exploring the universe of galaxy clusters through cosmological simulations and dense spectroscopy
Galaxy clusters are important probes for studying galaxy formation and cosmology. Based on the extensive spectroscopic surveys of local clusters and the IllustrisTNG simulations, we explore the various properties of clusters and their member galaxies. In particular, we highlight that the stellar velocity dispersion of galaxies is a unique and useful physical property enabling the investigation of the connection between cluster galaxies and their underlying dark matter halos. We also investigate the coevolution of the brightest cluster galaxies and their host clusters. Finally, we develop the spectroscopic weak lensing tomography which combines the weak lensing analysis with extremely dense spectroscopic survey. I will discuss the synergy between dense spectroscopy and cosmological hydrodynamic simulations in exploring the evolution of galaxy clusters and their member galaxies.
asiaa.sinica.edu.tw)